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<HAL>
16-06-2011, 10:28 PM
Some images of measurements made on loudspeakers that greatly outsell Harbeth and are found in some pro studios. Therefore they must be right! They tell the sound engineer mixing the CD you are willing to buy everything he/she needs to know .....

Points to note = = generally elevated presence band to punch image forward like picture 3 here (http://www.harbeth.co.uk/uk/index.php?section=products&page=designersnotebookdetail&id=6). A big peak at 4kHz, where the ear is maximally sensitive. Extremely fatiguing to listen to. Apparently endorsed by professionals.

Don Leman
16-06-2011, 11:07 PM
If the pro studio's use monitor speakers that have peaks in the frequency response, how will that affect the recordings that come out of their studios? One might assume the recordings would have a dip in response where the peaks were when the project was mastered.

A.S.
17-06-2011, 08:18 AM
This is an interesting one. I've looked a bit further into this and for your interest attach a picture of three "pro" monitors (A, B, C) and one "domestic" monitor (D) measured under controlled conditions. D was measured using a different audio test set, but I've made sure the vertical/horizontal scales are directly comparable with the others. (I could possibly have exported D and imported into the later A-B-C measuring system but that needs some time).

What do you make of these? These were measured three years ago and as far as I know, A and B are current models. A is what I'll call a 'Euromonitor'. B is the manifestation of a particular approach to speaker system design. C .... any thoughts? And D? Which one would be expected to give the 'most natural' sound? And if you were a professional sound engineer, based on these curves alone, which one would you have most confidence in as telling you what is really going on in your mix? And which would be likely to give you most or least listening fatigue?

As you can see there are, even now 2011 some eighty or so years after recognisable loudspeakers appeared, very big measurable differences between speakers. Let alone sonic differences.

No competitive brand names will be revealed.

NOTE: Ignore the exact dB markings on the left scale. dBs can be usefully relative (as well as absolute) measurements, like percentages and speaker designers tend not to need to know what a sensitivity figure is, for example, 85.5dB at some frequency. We need to know by how much it varies across the audio band. So, although the left dB scale axis is exactly comparable, you cannot deduce anything from reading the absolute numbers: we've just laid these four speakers out on the page neatly, not in sensitivity ranking.

>

Labarum
17-06-2011, 02:12 PM
D has the flattest response by a big margin.

Is the notch at about 180Hz in B down to poor crossover design and the 80 Hz hump in C a booming port?

A is flat enough in the mid bass till the driver begins to roll off but the treble response looks rocky.

A and B have a rising response over 10kHz - could they scream a bit?

Please tell us which of these four designs is active and which passive?

HUG-1
17-06-2011, 03:25 PM
Please tell us which of these four designs is active and which passive?All are passive. C is the largest, probably B the smallest?

Interesting observation ..... 'A's treble response looks rocky'. With some basic tools and no more than five minutes free time could you investigate that issue on A? Before you reach for the tool kit what would your method of attack be to expose the peakiness?

BTW; A, B, D are two way models. C is a three way.

Labarum
17-06-2011, 03:44 PM
All are passive.

Then we are not talking about mainstream products of choice used by Audio Professionals, where a passive speaker is today the exception.

In what price bracket is each of the speakers referenced?

{Moderator's comment: can't say for sure. Two examples are heavily marketed to pro users/very serious audiophiles. Don't think the performance would be any better/worse even if an amp was built into/onto the cabinet.}

EricW
17-06-2011, 05:34 PM
D would clearly be the most accurate (I think); but it looks as though C would be unfatiguing to listen to because of the rolled-off treble.

I think Don's point above is an interesting one. I would think that a mix made on either A or B, if it sounds right on those speakers, would inevitably sound a bit "dull" on a truly flat loudspeaker, e.g. D.

Don Leman
17-06-2011, 05:45 PM
Although it was mentioned only C is a three way, D looks suspiciously like the Monitor 40.1 so that would be my choice.

Of the others I would say that peaks in response are more disturbing that dips. B would be my choice as the rising response above 10k is largely outside the fundamentals of most music so might be noticible as added sparkle. It does have a few dips in in the midrange but I don't think they would bother me as much as the peaks in the other graphs.

{Moderators comment: no! D is not M40! Far cheaper\smaller.}

DSRANCE
18-06-2011, 12:04 PM
My own tuppence worth...

Most small "pro" monitors (and I suspect, many larger ones too :) ), have the presence and treble region peaked up a little so that the engineer can hear distortions and so on in the mixes "under a magnifying glass." These speakers are NOT for comfortable music listening enjoyment and neither are they designed for "total" and "clinical" full-range neutrality - neither are Harbeths IMHO, but I digress and shall need to address this comment later ;) By the way, many European studios and mastering suites use B&W 800 series speakers, which have more of a presence-recessed balance if anything.

I also feel that engineers can get atuned to the character of the monitors they're using, so speakers which measure the way shown above can be got used to and heard "through.".

I was very recently chatting by email to a chap who does video production for a living and is a keen music and vintage audio enthusiast. His preferred little monitor is a UK/far eastern active model with built-in preamp and DAC, which measures very well and apparently sounds extremely good. However, he has extensive experience of the smaller modern monitors that are freely available on the pro market at very attractive prices (and also a few "designer" ones as well for a good few thousand quid), and finds that although they're great studio tools, he couldn't relax with them at home and some, active or not, aren't very clear in sound either (there's a rather popular little active "Euro-box" which turns up time after time in pictures, apparently with this characteristic).

Back to my possibly controvertial comment above regarding Harbeths, and hopefully to bring this post full circle. These days, after many years of listening to all kinds of speakers, good and bad, all I want to do is to kick back and lose myself in the music I choose to play at home. I DON'T want the speaker to throw it at me "warts and all" and neither do I want a pretty false sense of "space" and "depth" which some carefully tailored domestic speakers do (vinyl has often done this all by itself when compared to the master recording in my experience). I want a realistic balance with great and natural reproduction of acoustic instruments from a speaker perfectly able to "rock it" at reasonable levels on occasion, but with great subtlety at lower levels. I find the various "BBC Legacy" speaker types far more able to do this and, of course, Harbeth do seem to me to be leading the field by a country mile at present (the other UK maker with roots in this thinking does well in the UK dealer-chains with their less expensive models which nod to their past, but don't really follow it IMO and their classic series isn't promoted here at all).

I appreciate Harbeth make "pro" based models in their range too, but maybe a "proper" speaker isn't what's wanted in a busy studio where everything has to be done quickly and LOUD!!!!!. I love the 40.1 deeply and had the pleasure of some Monitor 30's a few weeks ago. For me though, the return to the SHL5's brought a sigh of relief, although I fully appreciate the "extra warmth" of the latter may not be ideal in some rooms, but the sound was so much more "comfortable," and wanting me to listen to more and more tracks (I was only there for a day, so much different music to listen to). Having said this, I shortly have some good working LS5/9's coming my way for nowt that spent their lives in a video-editing suite and I eagerly look forward to hearing what the "different" bass alignment will do in my little sitting-room.

I suppose that what the jottings above mean, is that I'd like the clarity of a good pro-monitor, but presented in a gentler, saner and more music and ear-friendly way. This is why Alan spends hours and HOURS listening and fine tuning his designs for long term listening enjoyment, rather than the clinical, magnified analysis of the signal fed them. You CAN heve the best of both worlds :)

I hope you all take the sentiments above with the sincerity I wish to convey and that I haven't gone off on a tangent with them. Words can be so difficult to describe feelings I find...

cornelius
18-06-2011, 03:03 PM
OK - had a quick look, I'll give it a try:

A: the dip between 1-4k will make the monitors sound smooth - home theatre boom and sizzle sound - bass and treble is accentuated - but where are the mids ("compressed" sound?). The peak at 4k will give the illusion of detail and be effective as our ears will still hear that high frequency well.

B: the dip around 200Hz - hmm... "cleans" up the bass so they're easy to place and make one think that they're getting "tight, defined" bass that's "accurate"? Can't understand a dip, most monitors are small and bass is the first thing to go - If anything I'd expect a bit of a bump up, so they don't sound too thin.

C: at first I thought C was a combo of A and B - big dip around 200Hz but instead of a sharp rise at 4kHz, there's a dip - hi end not exaggerated here. 2 interesting things between 200 and 500Hz - not sure what that would sound like. Looks like these speakers go deeper than A and B, these will feel bass heavy (dip at 200Hz and the rise between 50 and 100Hz).

D: obviously the flattest response - does this mean they're the best?

{Mod comment: Edited all to Hz, by convention.}

A.S.
18-06-2011, 08:11 PM
....(snip) C: at first I thought C was a combo of A and B - big dip around 200Hz but instead of a sharp rise at 4kHz, there's a dip - hi end not exaggerated here. 2 interesting things between 200 and 500Hz - not sure what that would sound like. Looks like these speakers go deeper than A and B, these will feel bass heavy (dip at 200Hz and the rise between 50 and 100Hz).

D: obviously the flattest response - does this mean they're the best?A valiant effort to attribute various subjective sonic effects to excesses or shortages of energy in various audio bands. It theory, you're right: we know since 1938 (table attached again from our original thread) that, as you say, even before WW2, a common subjective language was being applied to loudspeaker evaluation. But that's only part of the story. The real devil is what we call coloration and this wretched coloration matter seems to have a dimension to it which is simultaneously intangible and highly significant. That's just the sort of problems engineers shy away from if life and limb are not under threat. I'd like to treat coloration as an entirely separate post because it defines how we judge speakers once we've explained away - as you've started to do - the lumps and bumps in the frequency response. So back to the solely measurable, objective evaluation for now.

In post #5 it was asked ...


With some basic tools and no more than five minutes free time could you investigate [the peakiness in the treble] that issue on A? Before you reach for the tool kit what would your method of attack be to expose the peakiness? That was a good question because without much effort we can dig around in the speaker system and at least identify how that peak comes about. Since the peak (or indeed any other features of the frequency response) were definitely picked-up by the measuring microphone in the chamber (see picture of Derek accurately positioning the microphone with a large T-square) and they are 100% repeatable, we must be able to determine their real physical source. I'd really like to let you think about this. Remember, just with a few tools and a few minutes, what can we glean about the peak. Or indeed any other curiosity of the measured response. And outside the chamber, two audio measurement systems being compared side by side, fed from the same precision microphone (picture).

BTW, let's assume that we just borrowed these speakers and destroying them in the interests of scientific curiosity isn't an option. And certainly not the 'deep probe' investigation you see in the other picture - although that may ultimately be necessary!

>

DSRANCE
18-06-2011, 08:50 PM
That narrow-band peak hints at a metal cone taking off, as most do around 4 to 6kHz as I remember. To tame this, very steep filters set too low for many tweeters (back then) would be needed and a cone peak would be replaced with a rather stressed tweeter harshness..

A.S.
19-06-2011, 09:40 AM
That narrow-band peak hints at a metal cone taking off, as most do around 4 to 6kHz as I remember...Ah ha! Astute answer, but the wrong one! You fell into my trap David!

Can't move ahead on this one until someone tackles this one:


With some basic tools and no more than five minutes free time could you investigate [the peakiness in the treble] that issue on A? Before you reach for the tool kit what would your method of attack be to expose the peakiness?

If you work this through for yourself the result will be very interesting I'm sure and directly relates to your otherwise normally apt comment, but wrong in this case.

Clue. You need a screwdriver if you are unlucky.

DSRANCE
19-06-2011, 10:32 AM
Ah ha! Astute answer, but the wrong one! You fell into my trap David!



Just remembering a long-ago chat and comparison of two crossover points on prototype 7's Alan :)

Screwdriver? Can't be loose drivers/crossover bits can it????? I know that some cheaper tweeters could spit and fizzle more if the fixing screws (not just the mounting ones) weren't reasonably and firmly tight.

A.S.
19-06-2011, 11:24 AM
... Screwdriver? Can't be loose drivers/crossover bits can it????? I know that some cheaper tweeters could spit and fizzle more...Ho ho! You've done it again! You're still in the trap! Tweeter? Bit of lateral thinking please!

A.S.
20-06-2011, 02:30 PM
I admit to being disappointed. Let's step back ...

Back in post #3, we showed the frequency responses on axis of four so called monitor loudspeakers. A, B and C are or have been heavily marketed into the professional studio/broadcast markets. D is sold as a 'domestic monitor' and as someone noted, D has the flattest frequency response but is not marketed to the pro market. That's strange don't you think?

Then attention was turned to the peak in the frequency response of speaker A. Contributors suggested that as this was in the 4kHz region (i.e. above the normal crossover frequency for a two way speaker) that the source of the peak was the tweeter itself. I anticipated that would be the observation and asked how that could be verified with simple tools and five minutes. So here is the answer which is obvious (to a speaker designer) ...

1) The peak is real. It is not a measurement artefact. It appears not only on axis, but laterally (and probably above, below too) and will exist today as it did in 2008. In fact it may even have grown in magnitude over time.
2) Where can this peak come from? It's not a subtle notch or bump: it's thin and prominent. It can only be from ...
- i) the tweeter
- ii) the cabinet or grille
- iii) the woofer (?)
- iv) the crossover

or some combination of these perhaps. And it is at a very critical frequency and is most likely to be highly audible because of its magnitude and frequency. (More on that later when we've worked this through).

And the tools we need are - initially our fingers. If the speaker is bi-wired, our luck is in: we can just remove both of the links plug the red/black signal wires into the lower terminals, and without repositioning the speaker or disturbing it in any way, we run a frequency response measurement driving only the woofer via its internal crossover, then save the data. Then pull out the wires and plug then into the upper, tweeter-only terminals. Then we can measure the tweeter via its crossover and save the data. By now we have three on axis measurements with the speaker and microphone is exactly the same positions in space:

- System response, the complete as-sold speaker
- Response of woofer via its crossover alone
- Response of tweeter via its crossover alone

And if we are not so lucky and the speaker isn't biwired, what do we do then?

EricW
20-06-2011, 06:26 PM
And if we are not so lucky and the speaker isn't biwired, what do we do then?

I'm guessing that by comparing on axis and off axis measurements at the peak frequency of the resonance, and comparing the measurements with those of adjacent frequency bands, would help isolate the source of the resonance. That is, you'd likely have one type of roll-off if it were the tweeter, another if it were the woofer, and yet another if it were the cabinet. I'm not sure you could isolate a crossover problem this way, though.

A.S.
20-06-2011, 11:15 PM
Perhaps. But first we need to capture some acoustic measurements.

So, no biwire connections then. What to do? We unscrew the bass unit, pull off one wire, refit woofer and measure the tweeter + crossover freq. response. Then replace wire to woofer, pull off one tweeter wire, refit tweeter. measure bass unit + xover alone.

Now and only now do we have some frequency plots to even begin to analyse where this prominent peak is coming from.

Phew.

EricW
21-06-2011, 12:01 AM
Phew.

I feel a bit dense.

On the other hand, perhaps we've all now been so thoroughly conditioned not to open our Harbeths, we unthinkingly apply the same to other speakers as well!

A.S.
21-06-2011, 07:19 AM
Right, let's move onward. Finally - and I'm sure of this - if you're interested in the finer points of why speaker may measure and sound different the ultimate point is likely to be an eye-opener! You won't read this sort of stuff anywhere else!

Let's assume that by now we have some frequency response measurements of the speaker complete, bass unit (via crossover) and tweeter (via crossover). I said we had five minutes and some basic tools. We've fully used the five minutes (and maybe a little more) and I'm hopeful that the measurements we made in haste just by unlinking the biwire links or pulling off the drive unit wire (assuming they are not soldered on) will tell enough of a story. But if we were really doing a serious 'forensic' investigation of a bought speaker we'd have to bypass the crossover completely, and measure the frequency response of the raw drive units when driven directly from the amplifier, still in the enclosure. If the speaker is ported, that will be a big help because we can run the amp cables through the port hole and attach them directly to the woofer and tweeter in turn, having disconnected the normal wires from the crossover that feed them. The wires may prevent the grille from being fitted, which will means that we won't be able to directly compare measurements because all grilles have some influence on the frequency response to a greater or less degree. But it will give us the big picture.

Alternatively, if we actually own the speakers under examination and are willing to permanently modify them, we can drill some holes on the back of the cabinet and run cables from the drive units out through the back to a connector arrangement, and also from the crossover output through the back. Then we have complete flexibility. With no effort and without disturbing the position of the speaker at all, we can just route the amp drive signal to the drivers directly*, through the crossover to the drivers individually or as working pairs. That's really the best way, but it will prevent us from selling-on the speaker later due to the holes in the back panel. We could of course, just remove the drive units from the enclosure and measure them in space, but that will tell us something different and we're trying to dig into this purchased speaker as it is not redesign it. So, whether or not we have the raw drive unit (driven directly) frequency responses or not depends upon how curious we are about deconstructing the system.

We know from this TeckTalk that the crossover has several functions, and just dividing the audio spectrum between the bass/mid driver and the tweeter is only one. Level adjustment and baffle-step compensation are as vital. But what an analogue (conventional, passive) crossover can't easily do - and perhaps shouldn't even be asked to attempt - is to try to cancel-out sharp peaks that may occur in a drive unit. Those sharp peaks are indications that for mechanical reasons that drive unit finds it easier - hence is more efficient at - producing certain frequencies than others. We expect a natural rise in sensitivity (sound pressure output, dBs with frequency) across the working band of a drive unit (then a fall-off) and a crossover/equaliser can restore the sound output to flat over a wide audio range, but cancelling sharp, narrow, tall (high efficiency) peaks is much more difficult. And my well leave a tell-tale sonic signature that sounds as bad or worse than the unattended peak.

So then, what is the drive unit designer's nightmare? If he's designing a bass/midrange unit, he's expecting the device to operate well from, say, 20Hz to 5kHz or more. 20Hz to 200Hz is one octave. 200Hz to 400Hz another. 400Hz to 800Hz, another. 800Hz to 1600Hz another. 1600-3200Hz another and finally 3.2kHz to 6.4kHz another. So that drive unit is being asked to perform perfectly over six octaves. That's a really, really tough technical challenge. That's like designing a car engine to perform in a perfectly predictable linear way from idling to 10,000 rpm without rattles, vibrations, lag or buzzes.

At the bottom end of the audio range the drive unit just has to pump air and virtually any old driver with any old cone material/surround will do. But as we enter the hundreds of Hz and even more critically, up near the top end of the bass/mid driver's range very very strange and complex interrelationships between the electro-mechanical parts become noticeable in the frequency response. The seemingly humble, uninteresting surround (surely that's just a rubber ring that hold the cone to the chassis?) and the cone itself - even the humble, boring dust cap - starts to behave not as one glued-together whole system literally playing the same tune, but each starts to generate sound independently. So the dust cap, for example, can 'sing' at some frequencies even though its made of soft cloth and securely glued to the cone. And taming these various independently vibrating parts is the same problem as trying to trace a rattle in your car which is manifest only at a certain speed - where you think it's coming from and where it's actually coming from are often different places.

OK so far?

garmtz
21-06-2011, 10:28 AM
Yep, I'm with you. Interesting stuff, please do continue... ;)

A.S.
21-06-2011, 11:20 AM
Next step.

As mentioned in post #20, with a passive loudspeaker the crossover (or rather, crossover-equaliser) has limited and rather broad-sweep capabilities. We can't use it as a magic cure-all. We are going to be seriously disappointed if we grab a couple of cheap sweat shop drive units and bung them in a cabinet and expect the crossover-equaliser to miraculously smooth-out all the lumps and bumps in their frequency response. It can't be done with a passive analogue crossover; it theoretically may be possible to use a digital crossover-equaliser to cancel every little ripple in the drive unit's raw response but that may introduces other perhaps even more audible side effects.

So what? Well, the sonic quality of the complete speaker system that you buy cannot ever be better that the latent mechanical abilities - good and bad - of the drive units. Read that again: think about it. Absorb it deep into your soul. It is uber important.

Labarum
21-06-2011, 08:01 PM
Alan, do loudspeakers suffer from unpredictable Wolf Notes as do stringed instruments?

http://en.wikipedia.org/wiki/Wolf_tone

A master violin maker can turn out many instruments all to the same high standard and specification, but they can show quite different and quite unpredictable resonances.

A mass produced speaker might be made to very close engineering tolerances, but the rogue resonances might show themselves.

Are Harbeth drivers individually adjusted to minimise such resonances?

A.S.
21-06-2011, 09:41 PM
In previous posts we were discussing the engineering difficulties of designing a bass/midrange drive unit that would span six octaves or so, neither artificially boosting nor suppressing frequency bands. Such a drive unit doesn't exist. The real problems of imperfect (even unpredictable behaviour) become apparent in the last octave or two - from say 1.5kHz to 6kHz or thereabouts. And that's the general picture across the entire speaker industry.

In a previous example we showed that speaker A (not one we are to analyse in this post) exhibited a marked peak in the response at around 5kHz. Contributors suggested that this was a characteristic of the lower end of the tweeter. I disputed that, because using the method described, the real source of the peak had been discovered and it wasn't the tweeter. Nor was it the crossover. It was a characteristic of the bass/midrange unit 'bleeding through' the crossover and manifesting itself in the final summed woofer + tweeter response on axis. And you could hear it very clearly, even from outside the room in which the speaker was playing. Wherever you placed the measuring mic, wherever you stood, the peak pumped high energy right through the room. Exceedingly fatiguing, but not, very surprisingly it seems, to the customers of that model.

Sometimes a peak can be intentionally engineered into a drive unit to tailor the sound. An example of this may be the LS3/5as bass unit*. All Harbeth LS3/5as were of the second generation so called 11 ohm version, and I have plenty of frequency response measurements of the bass/midrange drive unit measured via the crossover-equaliser and directly connected, bypassing the crossover-equaliser. Attached is a measurement I made in 2008 during the development of what became the P3ESR. It tells a very interesting story.

I reported as far back as 1990 that I was inspired to design the original HL-P3 after listening to my daughter's voice on the 3/5a, which by that time we'd produced for a couple of years. There was a subtle but nevertheless additional brightening of tone to her reproduced voice which was most definitely not there in the real voice. It wasn't unpleasant; in fact, I've noticed that many pianists love the extra sparkle, and rather than describe it as a defect, its surely fair to say that it's a mild and sometimes attractive coloration, lifting the sound 'out of' the box. But it is truly not present in the original voice.

It took a few more years to really understand the source of this benign character since the system response (for a full assembled, as sold speaker) on axis didn't really show anything terribly elevated in the low treble. So whatever the source of this sonic feature, it was subtle. And in the sonic world, subtle audibility means 'at a reduced loudness'; another way of saying partially or fully masked.

But, once the crossover is bypassed and the drive units are driven individually, we can get an insight into this lower treble brightness. The grey background anechoic graph shows that the frequency response is smooth and rising to about 1kHz (that's easy to equalise to a nice flat response providing you have enough components in the crossover). Then there is a sharp transition between 1kHz and 2kHz, and then from about 3kHz the start of a gradual roll-off, exactly as you would expect for a bass/midrange unit working at the very upper edge of it's capabilities. And then something very strange happens: at about 4kHz, the gradual decline remarkably reverses direction and become a gain in loudness, and at 5kHz [Peak 1] there is a prominent peak which is nearly as loud as the maximum efficiency of this driver at 1kHz. And that boost around 5kHz is very characteristic indeed.

Thoughts on this buried resonance issue?

* We will never know for sure whether the frequency response we show was an intentional design feature or an unavoidable consequence of other more pressing engineering or cost decisions.

>

P.S. Just going through the archive I found another annotated image of the same issue from a year earlier (2007) - white background. Slightly different (non-anechoic) set-up, but the same outcome.

EricW
22-06-2011, 01:24 AM
Thoughts on this buried resonance issue?



My guess: I notice you say that the resonance occurred when the driver was driven directly. I presume then that it's possible to tame or control the resonance by means of the crossover design, not by equalization but by adjusting the low-pass slope so that the frequencies that would otherwise trigger the resonance in the woofer/midrange are sufficiently attenuated so that resonance doesn't become a problem.

I imagine there are a number of complex variables of driver and crossover characteristics that must be adjusted to and balanced off against each other for this to work properly.

kittykat
22-06-2011, 03:01 AM
Ill have a go at this…

Observations: 1. Driver by itself has peak. 2. Peak is reduced once attached to cabinet

Hypothesis:

1. system interaction with tweeter masks peak (eliminated)
2. interaction as a system with cabinet and or damping material masks peak?
3. system interaction with crossover masks peak (eliminated)
4. permutations of some or all of the above?

Along the path of No. 2, attaching the driver to the cabinet is doing something, and if its not electrical, it can only be mechanical? Which means the cone, parts, frame, material or combinations are resonating? Apart from the cone itself, can there be an audible resonance from the driver frame etc., however subtle it may be?

Labarum
22-06-2011, 03:33 AM
Thoughts on this buried resonance issue?

* We will never know for sure whether the frequency response we show was an intentional design feature or an unavoidable consequence of other more pressing engineering or cost decisions.



The wavelength of the resonance matches the diameter of the cone. A standing wave develops across the cone. Could this be the "Wolf Note" of the instrument?

Such a resonance would be more effectively buried by a high order filter with a steep slope. That would be more easily achieved with an active crossover.

A.S.
22-06-2011, 10:50 AM
Good analysis. To look at your responses...


... I notice you say that the resonance occurred when the driver was driven directly. I presume then that it's possible to tame or control the resonance by means of the crossover design... by adjusting the low-pass slope so that the frequencies that would otherwise trigger the resonance in the woofer/midrange are sufficiently attenuated so that resonance doesn't become a problem.


... system interaction with crossover masks peak (eliminated) ... Which means the cone, parts, frame, material or combinations are resonating?


Such a resonance would be more effectively buried by a high order filter with a steep slope That's three comments which show a common thread. You've suggested that we can 'cut off' the peaky contribution of the woofer at its upper limit by somehow manipulating the crossover to more sharply roll-off the woofer's output.

Now that sounds do-able on the face of it. Before we consider solving the issue electrically let's have a look at some commercially available and bass/midrange units. Maybe that'll give us a feel for how much of an issue this upper end of the bass/mid working range is. And could this performance area be Factor X that defines the sonic abilities of a loudspeaker, good or bad?

An example of a very beautifully made 8" unit with a magnesium cone, here (http://www.seas.no/index.php?option=com_content&task=view&id=71&Itemid=95). And a 6" version here (http://www.seas.no/index.php?option=com_content&task=view&id=69&Itemid=93). And the 4.5" version here (http://www.seas.no/index.php?option=com_content&task=view&id=60&Itemid=84). The manufacturer says of these modern, respected drive units "... Magnesium cone drivers are world renowned for their high definition, low distortion and sound reproduction."

What do they all feature in common?

derekhughes
22-06-2011, 12:21 PM
An experience I had some years ago may be interesting.

I was experimenting with metal cone bass units, & had similar response peak to the ones Alan linked to, so designed a crossover with a sharp cut-off.

Although reduced, the resonance was still clearly audible, so the next step was to add a 'suck' circuit which reduced the electrical input to the woofer at the peak frequency by around 30dB (i.e. 97% reduced). However the peak was still audible (at 3%), though reduced but not as much as should have been the case with the reduced input drive to the unit - very strange. Then a piece of lateral thinking occurred, & I disconnected the TWEETER - resulting in a much reduced resonance.

The conclusion was that the ACOUSTIC output from the tweeter was driving the resonance via the air, independent of any electrical input to the bass driver!

So no metal coned Bass drivers for me!

Derek

EricW
22-06-2011, 04:53 PM
What do they all feature in common?

The cone material?

Derek's story about the tweeter suggests to me that it does not require much energy to excite a resonance in a metal-coned woofer.

Hence, I am starting to rethink whether EQ'ing via the crossover can ever fully fix the problem.

[EDIT TO ADD ADDITIONAL MATERIAL]

Thinking about this further, I went to Wikipedia and looked up the article on "Resonance". These are the first sentences:


In physics, resonance is the tendency of a system to oscillate with larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy.

Resonances occur when a system is able to store and easily transfer energy between two or more different storage modes ...

The comment about "small ... driving forces produc[ing] large amplitude oscillations" seems to reinforce the tweeter example given above, and to my mind anyway suggests why EQ as a curative approach may not work, because unless you EQ amplitude to zero at a particular frequency (probably impossible) you will still, or may still, have a resonance problem.

DSRANCE
22-06-2011, 07:06 PM
[Edit] - Alan, many thanks for your posts before this one which were placed after I'd typed the comments below but actually posted before this one.

Alan, if you remember why I posted suggestions of the tweeter being set too low in crossover (5 kHz is not too low), it was because the metal-cone bass unit (in the design we discussed at the time) took off at 5kHz or so, needing very steep crossover slopes (4th order in total - driver plus electrical) and too low a turnover frequency - in my opinion. You showed me what this (or something very similar) would do to a Compact 7 prototype and it was pretty horrible I remember.

Anyway, I also remember some vintage JBL's (L26 Decades) being reviewed a couple of times in the UK nearly forty years ago and the fact that they were two way with a 10" bass driver caused no end of problems. Unlike the L100 driver, which has an apparently smooth response over practically all it's range, the L26 varient had a massive peak or peaks at 3kHz or so. The little cone tweeter could work well from around 5khz or so, but getting the two to work together, let alone disperse properly at the crossover point, was almost impossible I understand. To see the measurements and subjective impressions, the HiFi Choice review from 1976 was quite telling. The L100 featured in a web-blog where someone took the reasonably good and solidly made drivers and designed a new crossover for them, placing the whole shebang in a more substantial box, getting much better integration and a better sound (in the author's opinion) for his trouble. To be fair to JBL, their later speakers did similar things and responded well because of it.

Before I totally bury myself in the mud, I ought to say that modern drive units do seem to have wider passbands and possibly lower distortion than many made forty years or so ago, so the problems in the peaky speaker discussed in earlier posts probably wouldn't happen in a well designed mid-priced speaker these days, would it?

{Moderator's comment: you have seen the curves provided in the link showing modern metal drivers and their peaks haven't you? By the way it is k not K by convention.}

Then I shall stay with small-case k :)

A.S.
22-06-2011, 09:39 PM
Derek's story about the tweeter suggests to me that it does not require much energy to excite a resonance in a metal-coned woofer.

Hence, I am starting to rethink whether EQ'ing via the crossover can ever fully fix the problem.

Thinking about this further, I went to Wikipedia and looked up the article on "Resonance". These are the first sentences:

... At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy. Resonances occur when a system is able to store and easily transfer energy between two or more different storage modes ... Exactly so. It's the same experience when your car wheels are very slightly out of balance by even a few grammes - at the all critical rotational speed (i.e. frequency) the smallest variation in the road surface will perturb the wheel/suspension sub-system and violent vibration will result. As you say, the amount of energy input is minute - the corresponding outcome is great.

The relevance to a drive unit is highly apt. A bass/midrange unit is exactly analogous to the wheel/suspension system, and music is the road. The wheel/suspension system even if imperfectly balanced (the shock absorbers are weak) can cope with the big, long, slow undulations in the road as it winds its way through the countryside up and down hill. But when the road surface has lots of tiny imperfections each one sends a little low energy shock wave (i.e. an impulse) into wheels/suspension and if the frequency of those seemingly innocuous 'tickles' coincides with the car's undamped natural resonance, you have a serious instability problem. The lower registers in the music are like that long, slow cross-desert highway: any old truck with knackered suspension can cope with that. And the tiny gaps between the globules of tarmac that generate the micro shock waves are akin to the harmonics and micro tones of the music. They don't have to be loud to have a huge impact. All they have to be is omnipresent - and in music that's exactly what we find.

Derek is probably the most experienced drive unit designer in the country and as he has said, if you strip out the damping from a cone (i.e. you make it of a brittle, ringy material like metal), you've removed its natural shock absorber. And it will inevitably ring. The issue is solely and depressingly - at what frequency and by how much. And there is absolutely no escape from that trap.

So yes, as I've said many times before, the material from which the bass/midrange cone is formed defines the ultimate dynamic performance of the system, its coloration and its resolution. Everything else is of far lesser importance.

So let's look at some more examples of speaker cones, this time those not using metal cones.

(To follow)

A.S.
23-06-2011, 12:19 PM
With the idea firmly in our mind that the cone material (or more accurately, the complete 'software'* of the speaker) has a great influence over the resulting measurable frequency and transient response we can compare different loudspeaker drive unit design approaches side by side. What we're looking for is the overall smoothness or response - and although a few lumps and bumps in the response are inevitable, what we're most interested in is big peaks.

Here are some 8" units that are basically the same magnet/chassis but with different cones. A hard coated paper driver here (http://www.seas.no/index.php?option=com_content&task=view&id=72&Itemid=96) and a metal cone here (http://www.seas.no/index.php?option=com_content&task=view&id=71&Itemid=95). Remember: these two very nicely engineered drivers fulfil different customer's requests (otherwise SEAS wouldn't make them) and they are fundamentally the same motor but driving two different cones. See how differently they behave in the upper frequency ranges on axis? And see how radically different they are off axis, meaning sideways to the driver. So if you toe-in your speakers you are listening on-axis; if you don't then you are listening off-axis. This on/off axis drive unit performance will influence what you hear.

It must be obvious that two cones exhibiting such grossly different measurable electro-acoustic behaviour must have significantly different sonic personalities - and of course they very definitely do have. Which you prefer depends upon many personal factors.

*Speaker designers talk of drive unit 'software' and 'hardware'. The hardware is the non-moving parts such as the (ferrite) magnet and the chassis and connection panel. The software is all the parts that are moving and glued together - the cone, the voice coil, the corrugated suspension (hidden under the cone), the dust cap and the all-important cone surround. It is glue that keeps these parts together during the working life of the drive unit. If any glue joint becomes weak or fails then that part will be free to resonate at its natural frequency and will buzz along with the music.

A.S.
24-06-2011, 10:02 AM
Someone asked a question about glues which seems to have vanished. Sorry but can you ask it again please?

Pluto
24-06-2011, 10:58 AM
Someone asked a question about glues which seems to have vanished. Sorry but can you ask it again please?
Alan - it's here (http://www.harbeth.co.uk/usergroup/showthread.php?1317-Low-wattage-tube-amplifier-combine-with-high-sensitivity-speakers&p=14994#post14994)

Please delete this post when it has served its purpose.

GregD
24-06-2011, 07:14 PM
Looking at those metal cone driver's frequency response graphs on the SEAS website, shows that all three have that gradual dip followed by a big peak like you were explaining Alan. So that's what you have to deal with if you make a speaker with a metal cone drive unit? Even the paper cone has a slight high-frequency peak (although not as prominent as the metal cones.

In view of you repeatedly drawing our attention towards thinking about the paramount importance of the cone material; along with knowing that Harbeth put a huge effort into developing RADIAL cone material, not to mention your speakers' performance, I am seriously curious about how a RADIAL drive unit would measure-up against these more common materials. From what I've read here, RADIAL is a very unusual material specifically designed for making drive units, whereas paper and metal are not. Is it too much to expect that RADIAL is essentially free from the sort of problems encountered with paper/metal because it is engineered at the molecular level to be "right".

Could it be said: Get the cone material right in the first instance and the rest is a (relative) doddle? (as long as you're a loudspeaker design genius like you or Derek ;P)

Labarum
25-06-2011, 07:18 AM
Yes, "perfect" is a big word; but maybe the "Radial" material offers a significant improvement over doped paper, polypropylene or metal.

Perhaps we could see the graphs for Radial?

But see also here

http://www.harbeth.co.uk/usergroup/showthread.php?349-Harbeth-RADIAL-v.-other-cone-materials-...

Labarum
25-06-2011, 10:25 AM
Two more questions:

1. What are the advantages of using a metal cone or dome for the mid-range unit in a three way? It would have clarity and, provided the resonance could be managed, might be excellent. The resonance would of course be much higher than that of the 5" drivers we have been looking at.

2. What about Kevlar as a cone material - B and W use it.

Interesting interview and text here

http://www.bowers-wilkins.com/Discover/Discover/Technologies/Kevlar.html

{Moderator's comment: are not many midrange driver about 5"}

Labarum
25-06-2011, 12:41 PM
{Moderator's comment: are not many midrange driver about 5"}

Maybe you're right. But do they need to be so big? The midrange drivers on my Quarts are 5cm (half of 5") aluminium domes. I have always thought those drivers to be the strength of the speakers. The ATC soft dome is 7.5cm.

GregD
25-06-2011, 11:42 PM
It has already been shown that the metal and paper cones have fundamental resonance problems. The metal cone high-frequency resonance peak is a real problem, Derek Hughes rejected the idea too, which he mentioned in an earlier post on this thread. Alan has also discussed the short-comings of the dome midrange unit you mention, elsewhere on the HUG.

If these materials could give the required results, I would suggest Harbeth would use them now rather than investing in the RADIAL research project, because it would be much cheaper and less time consuming than developing their own cone material.

DSRANCE
26-06-2011, 12:17 PM
It has already been shown that the metal and paper cones have fundamental resonance problems. The metal cone high-frequency resonance peak is a real problem, Derek Hughes rejected the idea too, which he mentioned in an earlier post on this thread. Alan has also discussed the short-comings of the dome midrange unit you mention, elsewhere on the HUG.

If these materials could give the required results, I would suggest Harbeth would use them now rather than investing in the RADIAL research project, because it would be much cheaper and less time consuming than developing their own cone material.

Greg, I think that the proof of the pudding is there for all to hear, if they get the chance, as it's the very fact of the smoothness and sweetness, with no loss of treble "details," that separate current Harbeths from the "HiFi" competition.

I know I mentioned that I thought modern drive units to be better than most commercial models of a few decades ago, but designers of inexpensive speakers today have a huge problem in designing something that has to look good yet still have a "boppy" bass and a sparkly treble. I fully appreciate that this is nothing to do with the likes of Harbeth, but many commentators I respect have said that the smaller "meter-bridge" pro models do tend to boom and screech a little and I suspect that what is in this thread may have more than a little to do with it, not just under-damping the bass to make it "port-bound" and setting the tweeter too high in level.

Do ALL conventional drive units have resonance issues, or is it more a fact of consistency in manufacture?

Gan CK
26-06-2011, 04:29 PM
I guess if one is not or has not been exposed to Harbeth's RADIAL, then i reckon conventional drive units aren't so bad after all. Since my exposure to Harbeth, even the old HL-mk4 with the TPX cone was able to let me immediately discern cone colorations from other spks. With RADIAL, i feel that this is even more pronounced today despite the fact that material science has supposedly improved considerably. Look at all the boutique spks that we have today. Alot of these spks use so called 'ultra high tech drivers' made of Ceramic, Aluminium, Magnesium, Diamond, Beryllium & whatever sandwich material but ironically, these spks often derail the listener away from the reality of music.

With Radial, i feel that Harbeth has really set the benchmark in what a hifi loudspeaker can achieve with regards to tonal accuracy/purity & musicality, whilst at the same time not sacrificing transparency, definition & musical involvement.

A.S.
26-06-2011, 08:10 PM
... I reckon conventional drive units aren't so bad after all. Since my exposure to Harbeth, even the old HL-mk4 with the TPX cone was able to let me immediately discern cone colorations from other spks...TPX plastic is by no means a conventional cone material. Why Audax couldn't promote it - or more accurately, why the speak industry showed total disinterest in changing from the status quo (polypropylene, paper and later kevlar) is, I believe, the greatest oversight the audio industry has ever made. TPX has (or had, when we looked at it's technicalities some twenty years ago) the lowest mass of any polymer, and hearing familiar music on a pair of Mk4s that I borrowed from Harbeth's founder Dudley Harwood changed my life. The shock of partially lifting the coloration veil had such a profound effect on me (I can easily recall the experience in about 1986) that I quit a very well paid job in the semiconductor industry to pursue the subject of speaker cone development via owning this company.

The conclusion must be that apathy is very much alive and well (in audio manufacturing and consumerism) and why bother tackling real engineering issues such as cone development, when you can tart up and flog the conventional as the new.

Gan CK
27-06-2011, 02:44 AM
Yes Alan, the MK4 also had a very deep impact on me when i heard it the first time. I had a couple of references at that time from KEF 105, Gale 402, Rogers Studio 1 & probably Spendor SP-1 but the MK 4 at that time was to me a revelation in terms of tonal neutrality & musicality.

However, i discovered another revelation when i switched from the old HL-5 (with TPX) to SHL-5. That's the Radial revelation!

EricW
27-06-2011, 06:38 PM
The conclusion must be that apathy is very much alive and well (in audio manufacturing and consumerism) and why bother tackling real engineering issues such as cone development, when you can tart up and flog the conventional as the new.

And yet presumably most manufacturers realize that cone material is not irrelevant (to say the least): I see all kind of reference to cone materials in marketing literature - composites, metals of all types, doped paper, mica-filled polypropylene, kevlar, doped kevlar, and on and on. It can't all be marketing, surely? Presumably manufacturers are chasing some kind of performance advantage, but apparently without - as you say - doing the fundamental work of developing the best possible material. Very curious indeed.

Can I ask what may be a hard question? Within the limits of (known) materials science, how much room is there for a "better" material than RADIAL? Put differently, if you were to conceptualize the ideal cone material (capable of existing in the universe as we know it, i.e. must have mass etc.), what is the gap between RADIAL and the ideal?

{Moderator's comment: Interesting question. What would you think was the primary requirement or two?}

EricW
27-06-2011, 10:56 PM
What would you think was the primary requirement or two?}

You will reach the limits of my knowledge very quickly, but I would guess (not necessarily in order):

1. Relatively low mass
2. High rigidity
3. High internal damping

I would image other materials might give you two out of three (e.g. 1 and 2 in the case of metal), but getting the right combination of all three would be extremely tough. And maybe there are others I haven't thought of.

A.S.
27-06-2011, 11:24 PM
The real killer problem is 1), low mass. As this tread is about efficiency, you can imagine that every gram of mass you can shave raises the sonic sensitivity by about 1dB or so (for a typical 5-8 inch unit). So, to get from say 85dB to a nice marketable 90dB, if you lose 5g or weight, you've achieved that. Conversely, add a gram or two and that tolerable 85dB drops to 83 or so. A noticeable reduction.

Furthermore, your 2) and 3) imply rubbery-like damped materials which are, by definition .... heavy. So you see we are in a real engineering trap here. We want it all, we want it now, but it must be a light as a feather! The only way around this is some lateral thinking.

Labarum
28-06-2011, 08:21 AM
Furthermore, your 2) and 3) imply rubbery-like damped materials which are, by definition .... heavy. So you see we are in a real engineering trap here. We want it all, we want it now, but it must be a light as a feather! The only way around this is some lateral thinking.

In 1957 Peter Walker of Quad offered his lateral thinking in the Quad full range electrostatic loudspeaker - a thin plastic membrane (clingfilm) stretched tight in an electrostatic field. That original electrostatic will still give the best modern speakers a run for their money.

There is also the Magneplanar loudspeaker with a membrane stretched in a magnetic field maintained my a distribution of many small permanent magnets. The membrane has a conductor running through it which reacts with the magnetic field to displace the membrane. This is in effect a full range ribbon speaker.

Both these systems reduce the mass of the radiator, but there are other engineering trade-offs.

{Moderator's comment: Low mass, yes, but also low damping. See the problem?}

A.S.
28-06-2011, 08:34 AM
I would much like to develop the discussion of the RADIAL technology but it really is far more complex than just peering at a few graphs. It's a sort of 3D engineering problem which (here) can only be viewed in 2D.

I'm still not finished PDFing the RADIAL project. I've tickled this documentation for over 18 months but the sheer volume of it and the fear of accidentally discarding some vital pages (which I've done several times and managed to Undelete from the server) means it needs full concentration, and certainly can't be subcontracted.

Over the next months I'll try and find a way of exposing more without - and I'm very aware of this - giving away anything that could advantage others in this field. It's always far easier (and cheaper) to take-on someone else's brainchild and develop it than do some genuine blue-sky research yourself!

Only last week I rediscovered the meeting minutes from the Govt. committee overseeing the RADIAL project (because it was part funded by a Govt. grant) at which I expressed my "disgust" at the slow technical progress. Fortunately, the senior member agreed with me. The path to RADIAL was not direct - there were many almost insurmountable technical hurdles.

HUG-1
28-06-2011, 10:35 PM
And here is something from the archive. Announced in 1993, just as we were in the final run of the RADIAL cone research project.

EricW
29-06-2011, 02:03 AM
...we are in a real engineering trap here. We want it all, we want it now, but it must be a light as a feather! The only way around this is some lateral thinking.

I have one thought - possibly lateral, possibly not - though it doesn't relate to cone material as such.

But when it comes to mass, I imagine the significance of mass is not absolute, but that what counts is the amount of mass that needs to be driven in relation to the amount of power available to drive it. So, for example, a top of the line Mercedes Benz will be relatively fast despite being relatively heavy, because of the amount of power available from the engine.

Would not the same be true of a speaker drive unit?

Right track or dead end?

Gan CK
29-06-2011, 04:24 AM
Despite the widespread appearance of so many 'exotic' materials on loudspeakers over the past few decades, i feel that only Harbeth's Radial is a genuine technological breakthrough & a major milestone in pushing the boundaries of loudspeaker design. Its really very very difficult to pin down the sonic characteristic of Radial because it really doesn't seem to have one. Maybe its still not perfect but at this moment, i feel that its head & shoulders above all others.

Paul G Smith
04-07-2011, 08:12 AM
I have one thought - possibly lateral, possibly not - though it doesn't relate to cone material as such.

But when it comes to mass, I imagine the significance of mass is not absolute, but that what counts is the amount of mass that needs to be driven in relation to the amount of power available to drive it. So, for example, a top of the line Mercedes Benz will be relatively fast despite being relatively heavy, because of the amount of power available from the engine.

Would not the same be true of a speaker drive unit?

Right track or dead end?

What about the brakes and shock absorbers and the tyre wear :) A powerful engine needs equally powerful brakes.

Imagine then, a speaker cone which had an extremely low mass, approaching the mass of the air itself, needing therefore very little power to accelerate, but equally importantly requiring very little braking power to stop it. The air surrounding it would absorb the kinetic energy of it's movement and so it would therefore be more likely to follow the instructions given it by the driving force, taking very little time to accelerate and decelerate.

Colouration would be near zero and we would all buy one!


This was the theory behind Quad's electrostatics and the Fane Ionophone but these solutions have their own problems and limitations.

honmanm
06-07-2011, 11:04 PM
But when it comes to mass, I imagine the significance of mass is not absolute, but that what counts is the amount of mass that needs to be driven in relation to the amount of power available to drive it. Would not the same be true of a speaker drive unit?

Probably not the car analogy because at its heart a speaker drive unit is a transducer or servo motor - converting one form of power to another. Maybe tyres would be the automotive analogy? An amplifier that is able to source or sink infinite current should be able to hold a driver in precisely the right position at all times (that is a bit of an oversimplification for other reasons).

Real world amplifiers will fall short of that ideal, and real-world speakers too. That's where the fun begins - finding those combinations where the components do not interact to the detriment of the sound quality.

On a different note, there has been some mention of panel speakers - Maggies and Quads - on this thread. I suspect that the Quad membrane is light enough that the air itself provides sufficient damping - though I do wonder how the surface wave in the membrane is damped at the boundaries where it is bonded to the frame... I'd love to understand the physics.

In the case of the Maggies although the membrane is light and stiff the "midbass" wires are comparatively heavy and if you tap the back of a Magneplanar speaker you'll probably hear the panel resonate. But if you look at a "naked" Maggie there is a carefully positioned rivet that pins the membrane to the magnet assembly, towards the middle of the membrane but clearly not centralised. At a guess it breaks the resonance of the panel into a number of lesser & less objectionable modes (analogous to different sized panels on a box speaker?). One of the black arts at the Magneplanar factory is the tensioning of the panels, I've heard...

I'm pretty sure the designers of dipole-radiating speakers have a relatively easy job of controlling resonances in the structure of their products, maybe this outweighs the imperfections of the panel itself.

A.S.
26-09-2011, 12:21 PM
...I'm pretty sure the designers of dipole-radiating speakers have a relatively easy job of controlling resonances in the structure of their products, maybe this outweighs the imperfections of the panel itself.By which you mean, I think, that as the supporting structure of frame of a panel speaker is unlike a box (the box traps sound inside, the frame is completely open) the contribution of the box to the overall sound can be bypassed.

Interestingly, a few years ago a highly respected speaker manufacturer with excellent technical resources invented a box cabinet damping system which substantially reduced the contribution of the cabinet to the overall sound. Test measurements confirmed this remarkable achievement. But to my ear, the overall sound was consequently rather bass shy and devoid of any warmth - uninvolving is a word. Carefully tuned, the cabinet can make a very useful contribution to enriching the sound and pulling the listener into the music as a Stradivarius does and a cheap mass produced violin rigidly glued doesn't. Don't underestimate the importance of a well tuned box!

Gan CK
26-09-2011, 01:28 PM
Yes the contribution of the enclosure must not be overlooked.

I've heard not so subtle differences between poorly made & well made acoustic guitars & violins. The better ones always sound richer in tone just like Harbeths always sound richer than many lesser but much more expensive spks. However, to a lot of ignorant audiophiles, they think that the BBC thin wall cabinet is simply a marketing ploy to cut corners & manufacturing cost. What a joke!

A.S.
26-09-2011, 05:30 PM
...However, to a lot of ignorant audiophiles, they think that the BBC thin wall cabinet is simply a marketing ploy to cut corners & manufacturing cost. What a joke!Surely you are pulling our legs?!

I can tell you from bitter experience that not one cabinet maker in ten would be remotely interested in tackling the complexity of a 'BBC thin wall cabinet'. I know this because production here has a constant brief to cover the eventuality that our cabinet suppliers suddenly cease and leave us high and dry. That leaves me with the task of explaining to a prospective supplier what the thin-wall concept is, what the likely skill-set and precision tooling the cabinet maker will need and an indication of the hidden difficulties and complexities. Most walk away at that point as an impossible specification with ridiculous tolerances at an unprofitable price. The occasional one will go so far as to make a sample of two and then, fully appreciating the magnitude of the task and our QC requirements, intentionally price themselves out of contention.

The issue is that the Harbeth front and/or back panels are removable, and are made at a different time on a different machine to the main top/side/bottom/side wrap; they are not naturally tongue-and-grooved into the cabinet as it trundles along the production line as all 'modern' cabinets are. Hence, assembled without the front/back as an open shell, great skill is required by humans to make sure the cabinet dries truly square etc. etc. etc.. There are so many internal and constructional factors that have to be carefully controlled piece by piece, let alone the parts you see - the veneer. Bringing on a new cabinet supplier and having them up to speed at the right QC level, all issues tied down, needs a minimum of about two years. That's been our experiece.

I admire and respect anyone able to take on the challenges of the 'BBC thin-wall cabinet' and to deliver in bulk to a great technical and cosmetic standard at a price we and you can afford. It is nothing short of a woodworking nightmare. But is does sound great.

Gan CK
26-09-2011, 06:34 PM
No i am not kidding Alan. I have received comments via emails & personal messages from people with regards to the BBC or rather Harbeth thin wall cabinet. In today's context where many solid, fanciful looking & supposedly inert loudspeaker cabinets exist, many simply fail to see the merits of the thin wall cabinet. The worst was when a guy said it was a marketing ploy. Thank god we the Harbeth users who frequent the HUG here know better. Some time ago I posed this question to you on why a Harbeth thin wall cabinet can sound so unboxy & uncoloured in the critical midband. And i recall you used a cracked bell as an illustration on how the BBC lossy cabinet works & that has been deeply rooted in my mind since then. So much so that i have also used the same illustration to enlighten others. I've always been fascinated with the BBC thin wall lossy box & how it works to deliver a thoroughly musical, warm & involving sound, whilst not forgetting the role of the excellent Harbeth Radial driver & the complex crossover to seamlessly integrate the drivers.

Labarum
26-09-2011, 09:51 PM
A lot of furniture made in the austerity years following World War 2 used "thin wall" construction. I have some of it and am amazed at the carpentry skill displayed in this furniture. A thin plywood skin was used with hidden bracing - all to construct strong and durable products using the minimum amount of wood which was in very short supply. Once particle boards became available the style of construction changed and the skill used in its construction diminished.

I guess the Harbeth thin wall cabinets use some of the techniques then common in any furniture factory.

Gan CK
27-09-2011, 06:20 AM
I came across a French loudspeaker that also use thin wall cabinets but quite different from those that Harbeth uses. Their cabinets are larger, front & back panels are not removable & i suppose the internal walls are not damped with bitumen. A tap on the cabinet told me so. And it uses high efficiency full range drivers made from paper.

The resulting sound? Yes it was quite dynamic with tight bass but the midband is extremely peaky & coloured. Unbearable for me honestly. A far cry from Harbeth's tonally accurate & sweet midband.

hifi_dave
27-09-2011, 11:48 AM
Were these the Audio Affair speakers which use PHY drivers ?

A.S.
27-09-2011, 03:22 PM
... I have some of it and am amazed at the carpentry skill displayed in this furniture. A thin plywood skin was used with hidden bracing - all to construct strong and durable products using the minimum amount of wood ...Thin-wall v. brute-force MDF is like comparing origami (http://origami.org.uk/) to Meccano (http://www.meccano.com/models/easy-box.html/). Both have their appeal. But the skill level is very different as is the investment in time to achieve a perfect result.

Gan CK
27-09-2011, 04:18 PM
Were these the Audio Affair speakers which use PHY drivers ?

No those were not Audio Affair spks but they also happen to use PHY full range drivers. Its HQ is in France but actual manufacturing is done in Montreal, Canada.

witwald
03-02-2013, 09:13 AM
The conclusion was that the ACOUSTIC output from the tweeter was driving the resonance via the air, independent of any electrical input to the bass driver!

So no metal coned Bass drivers for me!

Now that is truly interesting! It's easy to forget that the speaker cone itself is just a panel of sorts, and as such, its resonances can be excited by other sound sources, and it is only the internal damping in the cone material that will cause this resonance to decay away once the stimulus is removed. A big sharp peak will ring for quite a while, unfortunately.

Thank you, Derek, for sharing your observation. It is very instructive.

witwald
03-02-2013, 09:30 AM
And yet presumably most manufacturers realize that cone material is not irrelevant (to say the least): I see all kind of reference to cone materials in marketing literature - composites, metals of all types, doped paper, mica-filled polypropylene, kevlar, doped kevlar, and on and on. It can't all be marketing, surely? Presumably manufacturers are chasing some kind of performance advantage, but apparently without - as you say - doing the fundamental work of developing the best possible material.

It would seem to me that, more often than not, choosing any particular "new" cone material is done more for product differentiation purposes than for performance gains. If a good cone material like TPX can fall by the wayside, then I'd hazard a guess that there must be other things at work in the business of selling loudspeakers to consumers in the mass market, and even to "audiophiles".