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HUG - here for all audio enthusiasts

Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
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What the 'professionals' think makes a great speaker ~~~

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  • #31
    Modern drivers?

    [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

    Comment


    • #32
      Damping, cars, cones and shock absorbers

      Originally posted by EricW View Post
      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)
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • #33
        Side by side comparisons of cones, and speaker hardware and software

        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 and a metal cone here. 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.
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #34
          Someone asked a question about glues which seems to have vanished. Sorry but can you ask it again please?
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • #35
            Glues ...

            Originally posted by A.S. View Post
            Someone asked a question about glues which seems to have vanished. Sorry but can you ask it again please?
            Alan - it's here

            Please delete this post when it has served its purpose.

            Comment


            • #36
              Is RADIAL the perfect cone material?

              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)

              Comment


              • #37
                Perfect is a big word

                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/s...one-materials-...

                Comment


                • #38
                  Midrange in three-way? Material choices?

                  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/Discov...es/Kevlar.html

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

                  Comment


                  • #39
                    Midrange driver size?

                    Originally posted by Labarum View Post
                    {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.

                    Comment


                    • #40
                      RADIAL cone - the optimim solution

                      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.

                      Comment


                      • #41
                        Are all convtional drive units bad?

                        Originally posted by GregD View Post
                        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?

                        Comment


                        • #42
                          Exposure to Harbeth's RADIAL v. 'boutique speakers'

                          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.

                          Comment


                          • #43
                            Originally posted by Gan CK View Post
                            ... 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.
                            Alan A. Shaw
                            Designer, owner
                            Harbeth Audio UK

                            Comment


                            • #44
                              The RADIAL-cone revalation

                              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!

                              Comment


                              • #45
                                The ideal cone material?

                                Originally posted by A.S. View Post
                                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?}

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