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Speaker stands for Harbeth speakers at public exhibitions

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  • Speaker stands for Harbeth speakers at public exhibitions

    In discussing our Bristol appearance for next month, I have brought up an issue that colleagues had never thought about: the height of the speaker stands at a show compared to the listening room at home. In my humble opinion, the material and construction of the stands can be a matter of personal taste, but the height is really important, down to the last cm. or two.

    Why?

    The speaker designer has to make a decision before he starts work on the crossover where to direct his measurement microphone, the one tool that will tell him about the technical performance of the loudspeaker - the frequency response. As most loudspeaker boxes have the drive units mounted vertically along the centre line (as all Harbeth speakers do) the position of the microphone horizontally left/right of the speaker (for a fixed vertical point off the floor) would give the same measured response. However, vertically, the frequency response that the microphone measures radically alters as the microphone is raised and lowered along that cabinet centre line, vertically.

    The sound waves from the bass/mid driver and tweeter arriving at the microphone take an path through the air from their respective voice coils. As the tweeter's voice coil is far in front of the woofer's*, and far closer to the microphone when the microphones is directed towards the upper quartile of the cabinet (approximately), it's wave leads the woofer's. Conversely, when the microphone is lowered to be directed to the lower half of the cabinet, the tweeter's sound wave lags that woofer's. That lead/lag is another way of saying that the tweeter's phase relationship with the woofer depends upon where the microphone is placed relative to the woofer and tweeter vertically. All professional speaker designers must decide for themselves where to clamp the microphone vertically relative to the drive units, and to mark that vertical point onto the prototype cabinet with a marker pen as the Reference Measurement Axis (RMA).

    Then the bun fight with the marketing department begins.

    Speaker designers generally opt for two reference measurement axis; both are equally valid and in the great scheme of things only give subtly different technical results. One designer might habitually consider his RMA to be when his measuring microphone is pointed precisely at the apex of the tweeter dome. Another designer, again following his personal preferences, might measure with a ruler the vertical separation between the centre of the tweeter and centre of the bass/midrange unit, divide that in half, and mark that point on the baffle as his RMA. That would be where he would point his measuring microphone.

    Once the designer has settled in his mind where his RMA is, he can start work on the design of the crossover. One thing is sadly inevitable: when designing, he can only adjust the system crossover/equaliser/time delayer to perfectly integrate the bass/mid and tweeter sound waves as they hit the microphone diaphragm (or listener's ears) at that one fixed, vertical RMA. Not 2cms above RMA, 13cms below RMA or at any other point in space vertically. Every multi-way can only behave at its best with the measuring microphone or listener's ears exactly at that correct vertical point and nowhere else. The RMA was fixed at the design of the speaker, and the network was conceived and adjusted to compensate for the fact that the tweeter is physically (and sonically) in front of the woofer. That compensation is not universal: it is only for one point in space above the floor, wherever the RMA was set.

    And? This is where the real world and the idealistic designer clash.

    The designer sticks to his guns that the RMA is at a certain identifiable point on the baffle: 'level with the tweeter', '3cms below the tweeter' or whatever. He knows that at that point and no other vertical position that the drive units integrate as he wishes. The marketing boys are made aware of that, and make some sketches of suitable stands, and they feed back some market survey results to the designer. They say 'sorry, but that RMA you told us about for model XYZ: it's far too low down in the cabinet. We've played around with some matching stands, and gee wizz, considering that the average listener has ears that are about 1.2m above the floor when seated, listening, we're going to have to make some really, scarily, domestically unacceptably high stands to lift those speakers up high enough for your RMA to match the listener's ears ..... can't you move your RMA upwards until it's level with the top of the cabinet, or even higher!, so that we can sell short, domestically acceptable stands..?'. The answer is no, he can't 'steer' the sound upwards. The drive units are where they are relative to each other.

    What does this all mean?

    It means that almost no domestic listening is undertaken at the correct listening height relative to the designer's RMA. Speaker stands for home use are, generally, far too short. That means that almost all domestic listening is undertaken far from the optimal (RMA) height, and the resulting sound is far from at its best, perhaps significantly so. There is likely to be a significant mis-match between the energy output from the bass/mid and the energy output from the tweeter in the crossover region, with a veiling of sound and loss of detail. The one single biggest investment that any hifi system can make, far eclipsing changing any other element in the home audio system is to raise the speakers or conversely, sit lower.

    You can see the idea here in this video I made some time ago.

    So what? Well, to showcase loudspeakers to the very maximum of their potential, regardless of all other factors of stability, cosmetics and so on, there has to be an optimal match to the loudspeaker's RMA to the ear height of a seated listener. In a small hotel bedroom, with the speakers rather close to the audience, that means the stands really must be significantly taller (50-100% or so) than consumers are accustomed to use at home. Other factors which suggest tall stands at a show are that as available seats become occupied, listeners in all but the front row are sitting in the acoustic shadow of others. In addition, with all seats taken, many/most listeners are standing, and what they hear far above RMA and what a seated listener hears a little above RMA are radically different, and very much to the disadvantage of the standing visitor.

    The problem the is not a technical one of fabricating taller stands especially for a public exhibition, it is the suggestion that it may convey that the good sound is only achievable with what may prove to be excessively tall stands for normal domestic use.


    * View the speaker cabinet from the side and you can see that the tweeter is screwed onto the baffle, the voice coil just behind the diaphragm. Conversely, the bass/mid voice coil is deep inside the cabinet, at the apex of the bass/mid cone.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  • #2
    How are you expecting the audience to listen?

    I am not quite sure what the question is, but I also do not know what happens at these shows. In your documentation you recommend placing the tweeters at ear height (I presume because that is what they were designed for), which, given the dimensions of particular models, then leads to specific recommendations for stands. However, these can never be listener specific: some people are taller than others, and some people sit on taller chairs than others.

    For use at home, people can get stands at the exact height required, but for a demo you have to go for a common denominator. So are you expecting people to sit on tall upright chairs, or even to be standing up? If so, are you planning for the average male, or average female? And even more specifically, for which age group, given that your average 60 year old male will be about 2 inches shorter than his 30 year old son (indeed).

    If indeed they will be standing up, I think you would do well to have taller stands, and even more so since there may be a lot of damping from these warm bodies. Is that the dilemma, with your marketing people arguing that speakers on taller stands will be harder to sell?

    Comment


    • #3
      Made to fit

      I always supply stands for Harbeth speakers at a height to suit the listener's ears. They measure their ear height when seated and I calculate the height of the stand, though for domestic harmony they are sometimes a little lower than optimum.

      For a show it is tricky, as the majority of listeners will be too far left or right of centre, too far back or standing. Impossible to get it correct for all.

      Comment


      • #4
        Adjustable height stands

        I bought some Chinese made stands that are easily adjustable in the height and also found some Canadian made stands that are height adjustable. I find that is the optimal sort of speaker stands.

        Ideally there should be changeable top covers to adjust for various speaker models. If you find a woodworker he could do some for you.

        Comment


        • #5
          The room sound

          Apologies for being a spoilsport in a passionate scientific discourse but being an engineer I cannot help pointing out the reality.

          And that reality is this - regardless of how accurately the speakers are positioned relative to the height of the listener's ears or conversely how accurately the listener aligns his/her ears to the level of the speakers - the soundwaves that reach the ears do not, in fact cannot (in most practical real life situations) come from ONLY directly from the speakers.

          What reaches the listener's ears are a mix of direct and reflected (heavens forbid) soundwaves. Unless all the other surfaces in the room are completely "neutral" - i.e. they neither absorb nor reflect sound-waves, that WILL be the reality.

          Therefore, most listeners / consumers (such a shame that most people using the speakers are not scientists) do not care too much about using laser beams to align their speakers - they enjoy the music ( hopefully) based on what reaches their non-accurate ears. And the speaker that sounds good, wins their heart.

          Comment


          • #6
            Listening on-axis still best

            Originally posted by SChat View Post
            What reaches the listener's ears are a mix of direct and reflected (heavens forbid) soundwaves. Unless all the other surfaces in the room are completely "neutral" - i.e. they neither absorb nor reflect sound-waves, that WILL be the reality.
            That is undoubtedly the reality, since no one listens in an anechoic chamber, but does it negate the point that the flattest frequency response will be obtained with the ear level with the tweeter (assuming that's how the speaker's been designed)? I wouldn't have thought so.

            Comment


            • #7
              Loudspeakers arrangement at the showcase.

              Originally posted by A.S. View Post
              So what? Well, to showcase loudspeakers to the very maximum of their potential, regardless of all other factors of stability, cosmetics and so on, there has to be an optimal match to the loudspeaker's RMA to the ear height of a seated listener. In a small hotel bedroom, with the speakers rather close to the audience, that means the stands really must be significantly taller (50-100% or so) than consumers are accustomed to use at home. Other factors which suggest tall stands at a show are that as available seats become occupied, listeners in all but the front row are sitting in the acoustic shadow of others. In addition, with all seats taken, many/most listeners are standing, and what they hear far above RMA and what a seated listener hears a little above RMA are radically different, and very much to the disadvantage of the standing visitor.

              The problem the is not a technical one of fabricating taller stands especially for a public exhibition, it is the suggestion that it may convey that the good sound is only achievable with what may prove to be excessively tall stands for normal domestic use.

              * View the speaker cabinet from the side and you can see that the tweeter is screwed onto the baffle, the voice coil just behind the diaphragm. Conversely, the bass/mid voice coil is deep inside the cabinet, at the apex of the bass/mid cone.
              Very rational and convincing remark.

              When I sit in swivel-chair in my studio I can easily change my sitting height which is very comfortable while working with computer or at the desk. Rear monitors are mounted for practical reasons on high 100 cm stands serving either as cd bookshelves thus the tweeters are fair 130cm from the ground. Sometimes I have a break and listen to newly bought recordings via these monitors only for their more "analytical" and less "offensive" (less bass) sound. With ears at the height between tweeter and midwoofer the sound seems to be very plastic with very well organized soundstage. I think less soundwaves too early reflected from floor plane change the character of overall sonic impression in plus.

              For similar reasons monitors in radio, recording and post-production studios are arranged much higher than at home where music lover seats in his/her beloved comfortable armchair in repose position.

              ATB

              Comment


              • #8
                'The point'

                No, it certainly does not negate THE point.

                However, it does make the point a little less critical than it may seem reading some of the discussions. In fact in real life situations with real people (who do not normally sit still) THE point, some may dare suggest, is irrelevant.

                Comment


                • #9
                  Correct speaker height

                  Originally posted by SChat View Post
                  No, it certainly does not negate THE point.

                  However, it does make the point a little less critical than it may seem reading some of the discussions. In fact in real life situations with real people (who do not normally sit still) THE point, some may dare suggest, is irrelevant.
                  Irrelevant? Perhaps. Speaking for myself, it's not something I worry about much. But that doesn't mean it's entirely unimportant. To me, one of the great things about this forum is that it provides the informational and factual basis for distinguishing between things that are entirely a matter of fantasy or audiophile OCD, and things that are actually real and measurable and do make a certain amount of difference. Correct speaker height does appear to fall into the latter category, as far as I can tell.

                  How important or "relevant" that is to a specific listener is probably a matter that's individual and subjective, and a matter of personal taste and preference. The point I take, though, is that it's something real, not something made up.

                  Comment


                  • #10
                    A real issue to be taken seriously

                    Originally posted by EricW View Post
                    Irrelevant? Perhaps. Speaking for myself, it's not something I worry about much. But that doesn't mean it's entirely unimportant. To me, one of the great things about this forum is that it provides the informational and factual basis for distinguishing between things that are entirely a matter of fantasy or audiophile OCD, and things that are actually real and measurable and do make a certain amount of difference. Correct speaker height does appear to fall into the latter category, as far as I can tell.

                    How important or "relevant" that is to a specific listener is probably a matter that's individual and subjective, and a matter of personal taste and preference. The point I take, though, is that it's something real, not something made up.
                    The response to this issue has been most interesting.

                    If I was to give you a list of my top five recommendations for how to get the best possible sound from your system, No.1 would be to put your ear somewhere about level with the tweeter. That's not just with Harbeth speakers - it's likely to be true of most/all multi-way speakers.

                    I'm ashamed to show you the effect on the frequency response of listening vertically off axis. It's not pretty. Huge energy suck-out. But there again, if a hole of, say, 3dB or more (much more) at crossover between the bass/mid and tweeter is not deemed to be audible, then that surely suggests that the fabled differences between electronics and accessories are complete and utter self delusion..... how else can one explain away a halving or more of power?
                    Alan A. Shaw
                    Designer, owner
                    Harbeth Audio UK

                    Comment


                    • #11
                      Improvising for optimum height

                      I think many people confuse the necessary effect - good integration of the tweeter and woofer for best sound, with the ancillary requirements - a nice looking stand; often blending the prerequisite rational problem with the irrational problem - of looks.

                      I'd add my two cents to say that you can get the first effect {best integration} right by any means. telephone books, bits of 2 by 4 from the homewares shops, or any number of cheap but relatively flimsy looking stands from flat pack manufacturers, or universal stands.

                      However. A cheap car, that gets you from a to b is not the same experience the same journey in a bespoke luxury marque. Even at the same speed.

                      For my mind, find a stand that is the same height as recommended, then look for a design which matches your unconscious sensibilities and aspirations. That is a good recipe for satisfaction. Pay what you can. But not more.

                      Originally posted by A.S. View Post
                      The response to this issue has been most interesting.

                      If I was to give you a list of my top five recommendations for how to get the best possible sound from your system, No.1 would be to put your ear somewhere about level with the tweeter. That's not just with Harbeth speakers - it's likely to be true of most/all multi-way speakers.

                      I'm ashamed to show you the effect on the frequency response of listening vertically off axis. It's not pretty. Huge energy suck-out. But there again, if a hole of, say, 3dB or more (much more) at crossover between the bass/mid and tweeter is not deemed to be audible, then that surely suggests that the fabled differences between electronics and accessories are complete and utter self delusion..... how else can one explain away a halving or more of power?

                      Comment


                      • #12
                        Audio example of listening above tweeter (generalised)

                        Originally posted by gabsiechan View Post
                        I think many people confuse the necessary effect - good integration of the tweeter and woofer for best sound, with the ancillary requirements - a nice looking stand; often blending the prerequisite rational problem with the irrational problem - of looks...
                        Here is a piece of music modified to illustrate the sonic effect of sitting above tweeter axis, as most people do: their stands are sub-optimal.

                        0-12 seconds: correct sound, listening on axis
                        12-22 seconds: simulated effect of listening slightly above axis (perhaps 10cms or so)
                        22- end: revert to correct

                        Loading the player ...


                        Listening even further above axis makes the effect even more dramatic.
                        Alan A. Shaw
                        Designer, owner
                        Harbeth Audio UK

                        Comment


                        • #13
                          Other solutions?

                          Is this an argument in favour of a stepped baffle or dual concentric cones?

                          Comment


                          • #14
                            One step forward... two back

                            Originally posted by willem View Post
                            Is this an argument in favour of a stepped baffle or dual concentric cones?
                            Stepped baffle: doesn't make the slightest difference - the issue is that when there is a half wavelength difference in arrival time from the tweeter to the ear and bass/mid to the ear, there is total cancellation of sound in the crossover region. Stepping the baffle just moves that point of cancellation somewhere along a vertical arc.

                            Dual concentric: imagine that you are the tweeter element mounted deep in the neck of the bass/midrange cone. Now from that perspective, look out into the room. What do you see? You see that you are firing into the room through what is, in effect, a horn: the bass/midrange cone constriction. That introduces serious peaks and troughs into the tweeter response.
                            Alan A. Shaw
                            Designer, owner
                            Harbeth Audio UK

                            Comment


                            • #15
                              Desk top speakers

                              In the end, this is pretty bad news, although in a normal listening room one could at least try to get pretty close. It is also something users of desk top audio should be concerned with.

                              I have a set of LS3/5a's as my desktop speakers, and I raised them from the desk to get rid of bass boom. Now I know I had another good reason to do so. Yet I guess many people do not raise their desktop speakers. At least I found it very hard to find some stands to do that (the only suitably sized ones I could find were from Isoacoustics).

                              Comment

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