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Thread: Harbeth Monitor 40.1 specific

  1. #161
    Jeff Day Guest

    Default Re: Rate your own room ...

    Quote Originally Posted by A.S. View Post
    Umm. I'm not so sure about that. I think that half way between a cave and an anechoic chamber with a score of about 5 would be a well designed, sweet sounding concert hall. Such a room would have an excellently well controlled decay across the entire band, no 'hot' frequencies which seem to hang-on after the note and would never draw attention to itself.
    So, I think we have to be realistic and say that the beautiful room you listen-in must be somewhat less damped than a '5' rating would honestly justify. Almost all domestic rooms have far, far less absorption than ideal for listening to hi-fi minus the room's overarching contribution. And that really is the nub of the problem. There are three ways forward ....

    1. Increase the damping and hence absorption in the room, perhaps significantly and accept that the acoustic treatment is going to impact on the cosmetics - which just may not be acceptable and/or

    2. Change or somehow modify the speakers themselves to pump less bass into the room and/or

    3. Introduce some electronic adjustment in the signal path (of the amp) to reduce the amount of drive to the speakers in regions where the room's absorption is lower than ideal.
    Alan, you've inspired me to play around a bit more.

    I used my real time analyzer with pink noise to evaluate what was happening from 22Hz to 21.6KHz and found a peak around 51Hz with things somewhat elevated starting about 200Hz and down to 36Hz

    Using a Mac with Amarra software (replaces the sonic software engine of iTunes, made by the studio folks Sonic Solutions) I was able to EQ it out with the Amarra equalizer (the same thing can be done with the iTunes equalizer, but it's not as sophisticated, but priced right). That makes it nice when playing Redbook files stored in my iTunes music library on my Mac through iTunes to a USB DAC.

    Now if it only worked in the analog domain that easily. It's almost enough to make me go all digital. Almost. ;-)

    Thanks for your suggestions.

    Best,

    Jeff

  2. #162
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    Default Room tuning

    Quote Originally Posted by Jeff Day View Post
    ...but rather an RT60 anyalyzer and measured reverb decay time for each octave band, 31Hz - 16kHz, by pulsing pink noise on and off through the M40.1s, filtering the incoming signal by octave band...
    I'm glad to see some useful feedback on this overnight. I too have done some research, which is in general agreement with others contributions. My knowledge of acoustics is negligible, but using a little common sense and practical experience maybe I can contribute something.

    First, about your measurement method. I'm not sure who advised you, but the standard way for measuring room acoustics is to use one-third octave analysis across the audio band, not full octave. Obviously, 1/3 octave would give you three times the resolution and give you a much more interesting understanding of 'hot frequencies' in the room which could be buried in the crude full-octave averaged measurement. So, I strongly recommend that in future, at least 1/3 octave, or better is used for analysis if your equipment is capable of resolving that detail. When I am designing speakers, and I've got to the point where the basic 'anechoic' response is as I want it, I then switch between 1/12th, 1/6th and 1/3 octave displays measuring in my listening room to see how the room screws up my nice flat response. Full-octave display just wouldn't tell me anything useful.

    Second - and this has been touched on by others - having read late last night the BBC's internal papers about studio construction and measurement, I concur with other comments that even with the walls loaded-up with thick, properly designed absorber panels protruding a foot into the studio control room, the BBC could not achieve the 0.3s revereb specification you claim in your normal, untreated domestic room down to those low frequencies. Something is wrong: either your measurement system is deceiving you, and somewhat underestimating the LF reverb (full ocatve resolution?) or your listening room by some good luck is miraculously absorptive at low frequencies. That just might be so, but is it likely?

    Once again, we can find much useful information in the BBC archives if you know where to look and have a vaguely photographic memory! Back at the BBC in the 70s, they were becoming aware that the acoustic specification they'd set for the whole corporation was not really achievable for tight-budget divisions, such as the then new BBC local radio. So, the question was asked, by how much can the reverberation spec be relaxed especially in the low frequencies without (too much) or even noticeable degradation of perceived quality in the low frequencies. The middle and upper frequencies had to still meet the approved specification, and could be made to do so with relatively inexpensive (i.e. thin, stick-on) surface treatment. The problem was that bass treatment costs money, is heavy and shrinks rooms.

    Attached is data from the BBC report which describes an experimental studio, fully lined with 1 foot thick, floor to ceiling bass absorbers (see radio studio picture) covering much of the surface, and the same studio with the absorbers removed. As you can see, the bass reverberation time increased from an astonishingly good 0.4-0.5s (approx.) to about 1.2 secs. without the absorbers - just what I'd expect. The BBC went about the evaluation by using real voices in the room, recorded them and played them back outside to see how changes in the room's treatment influenced perceived quality. Note - I suspect that one voice (highlighted comment) was Derek Hughes' father.

    The conclusion of all this was Fig. 3 a 'recommended maximum permissible bass rise for a talks studio'. Above all, please note that (on a third-octave basis) the reverb-frequency curve is smooth, no 'hot' lingering frequencies, and that a doubling or so is acceptable at the very lowest frequencies. How this translates to music listening I cannot say but this is a good working rule. Personally, I don't believe that bass can be usefully absorbed unless a) the walls are significantly covered to a depth of about 3 feet (1m) in something absorbent or b) are covered in bass-traps (see picture) to a depth of a foot or so. Speaker cones, spikes, cables etc. etc. cannot absorb bass or they would be defeating known physics and they would have been used by the BBC in lieu of millions of pounds of old-fashioned, physical, room treatment.

    Full BBC report here

    >
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    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  3. #163
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    Default Re: Harbeth Monitor 40.1 specific

    I'm still waiting for my 40.1's to arrive but from experience with the 7's and 5's I would suggest you take a look at some lightweight open frame type stands.

    I use the Something Solid stands which are tailor made for the speaker and your requirements, so I have ordered different heights for each of my demo Harbeths.. The ideal (for me) being with the main tweeter at my ear level when seated.

    The open frames in comparison to the heavier, solid constructions are much cleaner, airier and more nimble. The heavier stands invariably sounding the way they look - fat and heavy.

    It's worth trying.

  4. #164
    Jeff Day Guest

    Default Re: Room tuning

    Alan,

    I did the RTA analysis using 1/3 octaves and it does show rising frequencies in the room below about 200 Hz - I believe I said that in one of my messages, but maybe I left it out. It's just the RT60 measurement that uses octaves and then averages to get room's reverb. You'll see the reason for this below in a moment, but in general RT60 is useful from 200Hz up to get average room reverb measurements (the majority of musical information falls within this region), and RTA analysis is most helpful for characterizing the region below 300 Hz to analyze what?s going on in the bass (and where most issues for loudspeaker setup occur).

    Now let's talk about the BBC article you attached for a moment: the purpose of the article is to describe how rising low frequencies in rooms degrade speech intelligibility, it?s not about music, and it?s not about how low frequency performance of a loudspeaker is affected by room acoustics - an important point, and one which could mislead you if you weren?t reading carefully and thinking about the implications. In fact, you might note that the article states in the first paragraph of section 6.2 that their studies with voice intelligibility ?cannot have practical significance? for ?bassy? loudspeakers, which is of course what the M40.1s are.

    The article does make a few points that are relevant to our discussion however: The article says reverb time (RT60) in rooms works ok 200Hz and above (first paragraph), but isn't useful below that (which means it works fine for most musical content except the bass region below 200Hz). So while my room may measure in the 350 ms range as an average, that doesn?t have a lot to do what?s going on in the bass, which is the point I?m trying to get across. So I think you may be confusing what kind of useful information RT60 provides and what it means, compared to what information RTA provides and what it means, which is getting us off track with addressing my immediate problem of sorting out the bass issues of the M40.1 in my room.

    I am astonished by your comment: ?Personally, I don't believe that bass can be usefully absorbed unless a) the walls are significantly covered to a depth of about 3 feet (1m) in something absorbent or b) are covered in bass-traps (see picture) to a depth of a foot or so.? Surely you don?t expect your customers (I?m one of those, not the enemy, in case you forgot) to cover their walls with 3 feet of sound absorbing material in order to make your speakers work in the bass? No offense intended, but surely that?s ridiculous.

    Here?s the deal: I have had lots of speakers in this room, as well as my own SHL5s and M40.1s. Some of my speakers, like the Avantgarde Duos, go deeper in the bass than the M40.1, and none of them have had issues with the bass in the room that require heroic measures like the M40.1 apparently does to resolve. If you?ll notice a fair number of the other posts talked about how they have difficulties with the bass on their Harbeth M40.1s too, and the Stereophile review of the M40.1 also pointed that both Dudley and Atkinson had trouble with bass performance in their rooms as well.

    So what you?re not picking up on is that for most people the M40.1s have trouble with the bass in most rooms, and many of those people are experienced in audio, as I am, and while you seem to always want to blame people?s rooms or their measurement techniques for the issues, you are sidestepping the actual issue of bass problems with the M40.1. Many of these people, like me, are your customers, and you do us a disservice by cavalierly dismissing the issues we are having with our M40.1s in most rooms. You need to ask yourself what it is about the M40.1 that is causing so many of your customers to have problems that they don?t have with other speakers.

    Frankly, as a customer, that attitude, and the apparent need to have to go to heroic measures to solve bass problems in the M40.1, pisses me off. As a responsible manufacturer you need to offer your customers a fix for the M40.1 that resolves the overblown bass issue, and get out of the denial stage that it exists ? that would be a responsible way to treat customers who have put enough faith in you to buy your products.

    Best,

    Jeff

  5. #165
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    Default Re: Room tuning

    It seems obvious to me that there really is no substitute for taming low frequencies in a room* than to use some mechanical method - such as bass traps of one design or another - or driving the speaker electrically with less bass to counterbalance the room's lift at those low frequencies. The essence of the BBC article was to indicate that, as you say, a broad and relatively dry room in the middle frequencies does not necessarily imply much absorption at low frequencies. The (skimpy) acoustic treatment that works well in the middle frequencies is actually useless at treating significantly lower frequencies. Furthermore, they showed that a room can be more lively (undamped) in the bass and yet still sound acceptable. As all listening rooms destroy the bass quality to one degree or another, humans are very forgiving of that and tend to hear through the lumps and bumps in the bass. Just as well or the hi-fi experience would be impossible!.

    I have no intention to 'blame you' (your words) and I have been considering constructive ways of helping you. The facts are these: I have no issues with the bass in my listening room so I cannot synthesise your issue. But as I showed here I have large rockwool batts behind my speakers because I want the room to be as neutral as possible.**

    There are no issues with the bass in properly designed BBC control rooms where the low frequency absorption is controlled and adequate. The M40.1 is a large box, with lots of bass potential and works at its best in an environment sympathetic to the low-end characteristics. That means, inevitably, that to get the very best sound at home, the room needs to be as absorptive as possible in the bass or as some have found, external signal EQ can be applied very effectively if needed. That's how it's always been with these big BBC boxes.

    *You misunderstood my intention. I was making a general point about bass absorption - I did not direct that comment to any particular make or model of speaker - I was commenting on bass in rooms, not speakers in rooms.

    ** It took me ages to track-down a bass issue. I noticed one day when accidentally slamming shutting a kitchen cupboard door in the adjacent kitchen, the characteristic 'boom' of a bass note. It transpired that the volume of air in every cupboard and the compliance of their doors created a row of efficient resonators at one particular bass note. For super-critical listening, you have to remember to open the cupboards a little. You certainly can't blame loudspeakers for that coincidence.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  6. #166
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    Default Re: Harbeth Monitor 40.1 specific

    I presume Alan is referring to the BBC studio when stressing on bass absorption with walls that are significantly covered with absorbent material. That wouldn't be ideal in domestic applications and moreover it would render the whole room to be more dead than it is right now. Being the least experienced here I suppose Jeff would have known everything I was going to suggest. Since I do not have any experience with the M40.1 I don't have any constructive views to offer but was surprised by the overblown bass issue that was brought up here. As far as things are concerned, I have a friend who owns the M40.1 in a less than ideal living room who didn't mention about any "serious" bass problems except for the fact that he acknowledges the constraints of his room that according to him may have limited the performance of the speakers. There is another M40.1 user in Audiogon who seems to be pretty happy with the sound he is getting from the speakers after upgrading from a pair of Dynaudio C4.

    I have just checked out the Stereophile review of Art Dudley for the first time an hour ago after reading claims that he was having trouble with the bass performance of the M40.1. In a short paragraph it was stated that although Dudley had 1)expected some challenges in getting a huge speaker like the M40.1 far enough from the side walls in his small listening space and 2)encountered a less than perfect smooth response throughout the bottom octaves in his small room, he still found the smoothness of the M40.1's bass response to be acceptably good in his small 12'x19' room(footnote 2). It was further mentioned that bass response improved when room boundaries became more distant. The overall conclusion of the review was more than positive.

    With the above assessment I am little intrigued to hear about overblown bass problems of the M40.1 in a larger 20'x29' space. This, however can happen as every room is different. To quote a case, I have another friend who had his Compact 7ES-3 in a dedicated room of about 15'x21' in size, a relatively small speaker in a huge listening space, and the bass was literally out of control and boomy. Up till today he has not successfully resolved the bass problems in his room and still finding ways to overcome it despite some advice of sticking some bass traps at the corners of the room. He is currently doing some research on Franck TChang's acoustic resonance products.

    In providing effective bass absorption in the form of traps at strategic locations, I guess Jeff must have known about this, that is to place them at the corners of the room where most bass energies will tend to collect. I presume the Acoustic Revive panels currently at the front corners of the room act as diffusors without any bass-trapping. This is one alternative solution that may or may not resolve bass problems in the room.

    Just to clear any doubts, I am being neutral with my comments and do not wish to interfere with any direct discussion or confrontation between Jeff and Alan. My intention is the same with most here, that is to help although I am fully aware most folks here are more experienced than I am. There may be more areas that need to be looked into apart from the room or speakers -can *possibly* be due to amp matching(a few tube amps tend to exhibit bloated bass) or some other setting-up issues, although I do know the Leben is a great amp.

  7. #167
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    Default Re: Harbeth Monitor 40.1 specific

    Quote Originally Posted by ryder View Post
    I presume Alan is referring to the BBC studio when stressing on bass absorption with walls that are significantly covered with absorbent material. That wouldn't be ideal in domestic applications and moreover it would render the ...effective bass absorption in the form of traps at strategic locations, ... that is to place them at the corners of the room where most bass energies will tend to collect. ...
    Useful feedback.

    I absolutely agree that in any practical domestic general-purpose living/listening environment it is most unlikely that there will (ever) be really enough mechanical (wall) absorption, especially at low frequencies because of cosmetic issues. So, in the real world we have to accept that there will probably be a degradation in the bass quality of any speaker used in almost any room, other than an anechoic chamber.

    When I mentioned in the other post that to really absorb those low frequencies deep absorption would be necessary - protruding a meter or two into the room, a serious challenge for the decor of a domestic room, I didn't just pluck that from thin air. To be effective, wall treatment must be about 1/3 of a wavelength deep. So, we know that 100Hz has a wavelength of 3m, so to soak that up (unless we use a BBC-style bass-trap) there's our 1m of rockwool lagging. At 50Hz, we'd need to double that up to 2m! Gulp!

    You mentioned bass traps only in the corners. Frankly, I'm not sure about the worthwhile efficacy of the corner-only traps. Surely, the BBC experience - indeed the experience of anyone treating studios and concert halls is that the treatment has to be all over the walls, floor ceiling. It's a matter of smothering the bass by absorption so no matter which route the sound waves take as they bounce around the room, they are losing energy into the extensive absorber lining.

    Bass in rooms will always be a challenge. We touched on this issue back in 2006 here.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  8. #168
    Jeff Day Guest

    Default Re: Room tuning

    I appreciate your response, Alan, and that you are trying to help, so let's continue to discuss this a little bit more and see if we can't make some meaningful headway on the M40.1 bass integration topic.

    Even though quite a number of your customers are having issues with M40.1 bass integration in a normal domestic listening room (even treated ones like mine), you are not, and nor are your BBC installations (we'll set aside that BBC control rooms are not representative of a home listening environment for the moment). I was under the impression that you designed the M40.1 to be optimized for home use, rather than BBC control rooms - am I mistaken?

    Perhaps you can show us how you succeeded on that front with integrating your M40.1s into your home listening room.

    If you wouldn't mind doing the same thing I did and describe the size of your home listening room, the positioning of your M40.1s, and post some photos of your room showing the speakers, associated equipment, and the location of room treatments, I think it might be helpful in getting started.

    And for a reference point for me to understand where you are coming from, where do you rate your room on the 1 to 10 scale you proposed? If you could couple that to measurement by posting a jpg of the RTA analysis of your room that would help immensely (it took me less than 5 minutes to do mine).

    This would go a long way towards explaining what you consider to be good in-room bass performance from the M40.1. It may be that you prefer or are used to more abundant bass than is typical, which is ok, but it will help sort out the difference in subjectivity towards bass response between us.

    I'll did the same with 1/3 octave RTA for my room, and have attached the RTAs for 1) my M40.1s positioned in the best placement for the most balance response (not all that balanced) without equalization, and 2) the same thing after digital equalization to give a more typical in room response of the room. There are a couple of peaks that I haven't EQ'd out yet, but you get the idea.

    Best,

    Jeff
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  9. #169
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    Default Re: Room tuning

    Jeff,

    In 2006 I made a post here of my room and I described the room treatment. The M40.1 and the P3ESR were entirely designed in that room.

    Looking at your untreated curve, I cannot recognise what I believe the M40.1 measures in my listening room (described above). You didn't mention how far away you put the microphone etc. etc.. In my room there is a smooth lift in output from about 80Hz -200Hz, (plus a few dBs, just adds richness) and no obvious problems below 80Hz - to my ears.

    I'd rate my room as about 2/10 in the bass and in the middle and upper frequencies about 4/10.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  10. #170
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    Default Re: Harbeth Monitor 40.1 specific

    In contrast to studios and BBC, domestic listening environments especially living rooms need to have high WAF hence the usage of acoustic treatment products have to be toned down. Most often large acoustic panels or bass traps are only feasible to be placed in dedicated listening rooms as most folks(especially the wives) cannot tolerate these unsightly tweaks. The most basic setup of having two traps at the front two corners of the room will suffice for most cases. Of course if one has the intention to go a step further there is always the ultimate bass trapping solution at the expense of aesthetics . The picture below is taken from the ASC website that illustrates on a basic to an advanced setup. There are many useful links and information on acoustical solutions on the web and my favourites were the ones from ASC and Real Traps.



    Due to the impracticality of these huge and bulky room treatment products in most domestic applications, some manufacturers have come up with small little tweaks that are less intrusive in the form of small little bells and cups of some sort. These resonance-control products were claimed to be equally effective compared to conventional room treatment products(if not better) although I have yet to experience them. Not cheap though.

  11. #171
    Jeff Day Guest

    Default Re: Room tuning

    Alan, the description is nice, but it would be nice to know the room dimensions, your position for placement of the loudspeakers, and see photos of the room along with the RTA response of the room. Without that the description isn't of much use.

    I showed mine, now it's time for you to show yours. :-)

    Best,

    Jeff

  12. #172
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    Default Re: Harbeth Monitor 40.1 specific

    As I explained, every textbook on acoustics this past hundred years or so correlates the thickness, area, compliance, density and absorption coefficient (quality) of treatment with sonic absorption. If a product becomes available for room damping in this universe which ignores thickness, size and softness and is proven to do the job of expensive, heavy conventional treatments then basic physics will have to be re-written and acousticians thoroughly and expensively re-trained.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  13. #173
    Jeff Day Guest

    Default Re: Room tuning

    Oops, forgot to say the the microphone was located at the listening position which is approximately 13 feet away from the loudspeakers.

    Best,

    Jeff

  14. #174
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    Default Re: Room tuning

    One or both speakers playing simultaneously?
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  15. #175
    Jeff Day Guest

    Default Re: Harbeth Monitor 40.1 specific

    I have been using them spiked, but I take the spikes out when moving them around to try different positions so they are easier to move, then when done the spikes go back in.

  16. #176
    Jeff Day Guest

    Default Re: Harbeth Monitor 40.1 specific

    Quote Originally Posted by hifi_dave View Post
    I'm still waiting for my 40.1's to arrive but from experience with the 7's and 5's I would suggest you take a look at some lightweight open frame type stands.

    I use the Something Solid stands which are tailor made for the speaker and your requirements, so I have ordered different heights for each of my demo Harbeths.. The ideal (for me) being with the main tweeter at my ear level when seated.

    The open frames in comparison to the heavier, solid constructions are much cleaner, airier and more nimble. The heavier stands invariably sounding the way they look - fat and heavy.

    It's worth trying.
    Hi Dave, I do indeed have several pairs of open-frame stands coming my way to try, so we'll see how that works out. Thanks for your suggestion, appreciated.

    Jeff

  17. #177
    Jeff Day Guest

    Default Re: Room tuning

    Quote Originally Posted by A.S. View Post
    One or both speakers playing simultaneously?
    Both, to get an idea what is going on in the room at the listening position when the M40.1s are playing.

    In asking you what you are hearing at home, I'd like to see an RTA of your room from the listening position, so I can better understand what you are hearing at the listening position. I'm not really interested in anechoic measurements as they don't directly relate in a useful way.

    I think with your thread about setting up a listening room, detailed information about your own room and how you optimized it for the M40.1s would be an excellent topic, and really help Harbeth customers like myself who are working through improving their listening experience.

    Best,

    Jeff

  18. #178
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    Default Re: Room tuning

    I bet that you'd say that you were driving both speaker simultaneously. Jeff - there are two aspects of your measurement strategy which are, as far as I'm aware unique to you, and not widely used in the speaker industry - and certainly not by Harbeth.

    1. You drive both speakers simultaneously with a test signal even though they are in different physical places in the room radiating sound along different pathways to the microphone and via all reflective surfaces.

    2. You are measuring a long, long way away from the speakers (13 feet, about 4m) at your listening position.

    I would never attempt such a test setup because (in my opinion) although it will draw some sort of response curve on your analyser screen that curve cannot be interpreted adequately. Or at all. It is as good as meaningless. Why? First, if you drive both speakers, and they are in different places so (obviously) at some frequencies there will be constructive and at others destructive interference. The mic hasn't the intelligence of the human ear to resolve that - and you've already said that you are doing averaging in your analyser - so most likely, at the low frequencies where the wavelengths are long, the dissimilar path lengths from the speaker to mic will effectively add the L + R sounds together, whereas the different path lengths will cancel in the middle and especially upper frequencies. That explains to me the left-to-right downward slope of your curve.

    Second, measuring so far from the speakers just isn't going to tell you what you want to know about the speakers (which you are criticising) at all. I fully appreciate why you want to measure at your hot spot; because that's where you listen but you will not get a useful result with your method. Or any method across a useful frequency band without an anechoic chamber for a room. Or at least, I couldn't if I replicated your setup. I think you mentioned Atkinson/Stereophile, so I had a look at how he measures 'in room'. Typical example here: note also bass lift. As he says, he measures the speaker at a number of points in an arc, about three feet (not thirteen feet) to about 4 feet from ONE driven speaker then averages the measurements together over the arc. That will yield a useful response of how the speaker drives the room, but of course, in the speaker's nearfield. I use a similar method. That's the standard way of measuring a speakers 'in-room' response. Yes, it's most probably not the situation at the hot spot, but that point is extensively polluted by the room's contribution.

    Finally, we can again refer to the BBC's work in this area. Bob Walker - brilliant engineer, last audio boffin and acoustician recently retired from Research Dept. wrote in his AES paper about the realities of speakers in rooms and the resulting distribution of their sound in the room:

    -----------------------------------------
    "In any partially or fully enclosed space that uniform spreading (of sound from a speaker) proceeds for only a short time until part of the sound wave strikes some acoustically significant object. What then happens is always complicated. Sound propagates as a wave function and demonstrate all the properties usually associated with the interaction of waves and objects -- reflection, refraction and absorption. What happens when a sound wave meets a discontinuity in the medium depends on the acoustic properties of the boundary materials and the size of the discontinuity in relation to the wavelength of the sound wave. Over the normal audio frequency span, wavelengths range from about 15mm to 7m. That nicely encompasses most sizes of objects within rooms, and even the room itself. Plus, the interactions between sound waves and the room and its contents cover the whole gamut of reflections and refraction effects, as well as absorption. It is that complexity which renders a real sound field impractical to treat analytically.

    In a typical room there is usually at least the floor surface within about 2m of the source. Therefore, from a maximum of about 6ms onwards, the sound field (even outdoors) contains components which have interacted with some surfaces or objects. After 30 ms in a small room with a sound wave front will have travelled in every direction to the boundaries of the room and will have interacted at least once with every object contained therein."
    ----------------------------------------

    So, putting a microphone far away from any speaker in a non-anechoic room will swamp the microphone with initially the direct sound and then in just a few millseconds, reflections from all and every object in the room, and the room walls. What the mic sees will be the (small) contribution direct from the speaker plus a vast amount of reflected sounds, all added together. You will not be able to tease the speaker from the room because your averaging analyser is not intelligent; what you have is a composite measurement of speaker + room. I would be extremely cautious indeed about trying to equalise the response at your hot spot by slavish attention to the graph - I just wouldn't do it myself. By all means apply a little EQ to taste and by ear, but I strongly recommend that you do not frighten yourself with the graph and certainly do not use it as a guide to eq: use your ears for that only. I suspect that if you EQ for a flat graphed response at 13' the result will be bass-light and too bright i.e. lean and thin.

    I have a very busy week ahead with X-Factor TV this week but I think this is plenty coverage of this topic for now from my side - over to others.


    Source: R. W . Walker, BBC. 'A simple acoustic room model for Virtual Production'. 106th AES Convention, Munich, May 1999. Reprint #4937
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  19. #179
    Jeff Day Guest

    Default Re: Room tuning

    Actually, Alan, I think you are confused about what I'm talking about with RTA, and why I asked to see an RTA of your room at the listening position. As a result you ended up comparing apples to oranges and unfortunately missed what I was trying to convey.

    Here's why: I'm talking about using RTA to optimize speaker performance at the listening position in a room as listening & speaker positioning is adjusted, not to measure loudspeaker as in the example you used. Do you see the difference?

    John Atkinson was attempting to duplicate an anechoic response by using a near-field method to measure speaker performance, which is different than what I'm talking about. But still John maintains that bass boost occurs with the 40.1:

    "In his "Manufacturer's Comment" (October, p.203), Harbeth's Alan Shaw took exception to this measurement technique, feeling the 2pi midbass boost misleading. He had sent me a true anechoic frequency-response measurement for the Harbeth M40.1, this taken in the BBC's anechoic chamber, which is large enough to allow a reflection-free time window of 300 milliseconds for the measurement. His and my measurements were broadly similar in the midrange and treble, allowing for differences in mike distance and measuring axis, etc., and the shapes of the two curves were broadly consistent at low frequencies. However, compared to his anechoic curve, my nearfield curve was elevated by +5dB or so with respect to the reference level at 1kHz. "What is the real frequency response?" Alan asked in his comment. "Easy answer: Trust the anechoic measurements above all others!"

    But no one listens in an anechoic chamber. They listen in rooms of varying sizes. If you think about it, a measurement taken in an anechoic chamber and a nearfield, 2pi measurement are at opposite ends of a continuum of measurement conditions. The first assumes the room boundaries are, in effect, infinitely far away; the second that one of the room boundaries is infinitely close. A speaker that measures flat in the low bass, such as the Harbeth M40.1, will sound as if it has a bass boost in a real room, the amount of that boost depending on the room size ... At the other end of the spectrum, Art's smaller room boosts the midbass more than mine does, but then, his lighter wall construction?my room is solid-walled for the first 4' above the floor?doesn't support the bottom octave quite as much. But the speaker still has a little more upper and midbass in my room than I have found to sound natural. While I thought the Harbeths scored highly in vocal reproduction and imaging in Art's room, with smooth, clean highs, the lumpy, excessive bass did eventually irritate me. As is almost always the case with a large speaker that measures anechoically flat down to a low frequency, the Harbeth measures and sounds a touch midbass-heavy in a smallish room. Therefore, the larger the room, the better, especially as the smoothness of the speaker's midrange requires it to be well away from room boundaries. As Art found, the M40.1's treble balance can be fine-tuned by experimenting with toe-in. However, with the listener sitting straight on the tweeter axis and using solid-state amps, the treble does become fatiguing, I felt. While solid-state amps will better control the Harbeth's excessive in-room bass, a tube amp will probably work better with the highs."

    You might notice that John's published RTAs show the same sort of bass heavy response, published in his response to your criticism of his measurement techniques.

    But back to what I'm talking about with RTA: Almost every pro installer uses RTA analysis in just the way I described to determine the best location of the listening position and location of the loudspeakers to get the most even in-room response. It's the quickest way to set up a system. Now do the earlier RTAs make more sense for you? For reference to this common technique for room setup I refer you to Jim Smith's excellent book Get Better Sound.

    I'd still like to see an RTA plot of your room measured at the listening position please, for the reasoned described above.

    Best,

    Jeff

  20. #180
    Ron Herbster Guest

    Default Room treatment for bass

    Hi Jeff.

    Great looking room and from all appearances you have ample room to find the optimal speaker placement. I have a smaller room which is the den and my speaker placement options are minimal. I am fortunate to have floor to ceiling book cases behind both speakers and on one side wall. There is a large overstuffed couch along another wall with decorative pillows sitting on top of the couch propped against the wall, also 2 large chairs with ottomans and heavy curtains on all windows. We are at a point now where nothing else will fit in this room. I guess it is what one calls cosy. When I owned the 40s I had a Rives PARC to solve the bass issues. I found with the 40.1s the Rives was not needed but I did have to add the Cathedral panels to the 4 corners which solved the bass issues.

    If you plan to keep your 40.1s it sounds like you will have to address your bass problem head on and add room treatment. I would start with the 4 Cathedral panels and if that is not sufficient start adding bass busters starting with 2 in corners behind each speaker.
    I have also heard small incremental improvements in bass performance with different electronics, cables, power conditioner, etc. but the big leap in performance is through room treatment or eq if that is the route you choose.

    I know what you battling is very frustrating and wish you all the best in finding the right solution.

    Kind regards,
    Ron

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