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Real bass response?

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  • Real bass response?

    I was reading the Devialet SAM web when I found something shocking. They say that their SAM system can take the bass response of any speaker to a lower level. But if you select any Harbeth speaker in their web, the SHL5* for instance ( https://www.devialet.com/en-eu/exper...uper-hl5-plus/ ), you will see that the bass response WITHOUT SAM is 27 Hz, much lower than the 40 Hz bass response claimed in the Harbeth specs sheet. And with SAM, it goes to 19 Hz.

    The rest of speakers also show lower bass responses without SAM than the specs sheets. I donīt know if they have a different measurement system. I also donīt know if a software can get a speaker work to a lower bass response. But if the measurement system is different, the lower bass response with SAM that they promise is not real, they should measure it with the same system so we can know exactly how SAM can improve it from the official Harbeth data that we owners know. Because 19 Hz is only 8 Hz lower than 27, while it is 21 Hz lower than 40.

  • #2
    First of all can I clarify that we have never been approached by Devialet, so we have no idea about where they obtained any Harbeth speaker, its condition, age, whether it had been user modified or any other detail. So your opinion about how the test process operates and the sort of equipment used and the environmental conditions (indoors? outdoors? in anechoic chamber?) is as good as ours.

    One thing that really should be specificed, but I see no mention anywhere, is to know if the measurements were made with the grilles off or on. This is not so trivial a question, because at LF the grille cloth (of any speaker) will damp the air flow through the port, which is generally a good thing, especially in the subsonic bass region which bedevils turntables.

    As for the drawing on the link above, without axes, it cannot be evaluated in any techical way: it is graphic art and that must be firmly kept in mind. Why it doesn't have axes one can only guess.

    Surely what we all strive for in our domestic rooms with their low acoustic absorption - especially as frequency lowers - is not quantity of bass but quantity of bass? Sure, bass quantity can be beefed-up, but the consequent and inescapable additional cone movement will dramatically drive-up distortion. Simple choice: in round numbers, choose 3% distortion and 40Hz extension or 60% distortion and 20Hz extension with the corresponding and dramatic reduction in power handling (hence lower spl potential as the bass range is extended for any given loudspeaker system).

    There is nothing for free in acoustics. Make your choice. And ask about distortion.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    • #3
      I use SAM calibrated for SHL5+ 40th LE. The process is done at various dealers around the world. One guy with a box of tricks. See https://m.youtube.com/watch?v=DWFDPCKS3XM
      However it works I like the result, especially on jazz. Gives it real snap. I also sometimes use a REL S2, filling in from 25 to 40hz that I turn on or off from the Devialet remote.

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      • #4
        Since lasers cannot penetrate the grille, the measurement has to be made with the grille off.

        That completely messes-up my designed bass response. The grille is not just a cosmetic enhancement and drive unit protector from little fingers, it's a critical part of the bass damping arrangement and will be so for every vented loudspeaker regardless of brand. Just try blowing through the grille cloth yourself and you'll see that it offers considerable resistance to air flow - which I've taken into account during the design.

        This laser measurement strategy is not appropriate to vented systems with a grille. Again, not a mention of the resulting increase in distortion which must logically result from more movement of the bass cone in a narrow magnetic field.

        Of course, the modified sound may appeal to the listener, more base usually does, but I have spent a long time optimising extension, power handling and distortion - all with the grille on as we recommend. During development I have designed, listened and tuned SHL5plus/Anniversary with the grilles fitted except when swapping over drive units and quick casual listening.

        If the system is applied to the speaker then the grille must not be fitted again, and that in itself will slightly alter the mid/top balance. So, expect a different bass/mid and mid/top nature to the one I designed.
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

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        • #5
          One point is that Davialet do not specify the response at the frequency they quote. The Harbeth spec is +/-3dB to 40 Hz, but they could be specifying at -6 or -10dB, as is often the case.
          Also they state that the software will prevent overload at the lower frequencies that they boost at, this implies compression of some sort, which can hardly be musically good.
          I had a listen to a pair of their speakers a couple of weeks ago, they were 'OK' but certainly not up to Harbeth standards, so one doubts their assessment of good sound quality.

          Comment


          • #6
            Originally posted by derekhughes View Post
            One point is that Davialet do not specify the response at the frequency they quote. The Harbeth spec is +/-3dB to 40 Hz, but they could be specifying at -6 or -10dB, as is often the case.
            Also they state that the software will prevent overload at the lower frequencies that they boost at, this implies compression of some sort, which can hardly be musically good.
            My understanding is that the measurements are intended to determine the drive level at which there is significant non-linearity in the output of the driver or when it reaches its maximum excursion.
            The maximum output of the amplifier is then limited to avoid reaching that point.
            Would this not be preferable to the usual situation where the amplifier's output is not limited and the listener can potentially increase the volume until the speaker is damaged?

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            • #7
              To try and boost a speaker's output BELOW the port resonant frequency is something I would expect loudspeakers designers to avoid.

              There is an 6th order alignment which tunes the port lower and then boosts AT the port frequency, thus using the fact that minimum cone movement is at that frequency, but below that the cone and port output are out of phase. This is widely used in active speakers, which the Devialet system is in effect, but they are trying to do it without making the necessary adjustments to the port (which Alan is right to resist, as it is an integral part of the design).

              Comment


              • #8
                Originally posted by derekhughes View Post
                There is an 6th order alignment which tunes the port lower and then boosts AT the port frequency, thus using the fact that minimum cone movement is at that frequency, but below that the cone and port output are out of phase.
                The low-frequency alignment referred to above was published by D. B. Keele Jr., in a paper in the Journal of the Audio Engineering Society: A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments. June 1975, Volume 23, Number 5.

                A PDF copy of this paper, and many others, can be obtained from Keele's web site here.

                Figure 3 in that paper shows the low-frequency response of an unequalised 380-mm vented-box 113-litre system with the box tuned to Fb = 28 Hz. It also shows the response of the second-order high-pass-filter equaliser that supplies 6 dB peak boost at 30 Hz.

                As shown in Figure 5, the resulting sixth-order vented-box 113-litre system has a -3 dB cut-off frequency F3 = 26 Hz (Fb = 26 Hz). This is compared to the fourth-order QB3 vented-box 113-litre system whose F3 frequency is higher, with F3 = 39 Hz (Fb = 33 Hz). The frequency response of a second-order C2 closed-box 39.4-litre system with F3 = 63 Hz is also provided, and serves to illustrate why vented-box systems are a popular choice with designers of loudspeaker systems.

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                • #9
                  I turned the SAM off the other day. The bass is filled in to 25hz by a subwoofer. Iíll stick with that. Plenty of people apply limited SAM, typically 30% to 60%. Iíve not bothered experimenting. The sound quality and convenience is such that for the last year, besides changing from SHL5+ to SHL5+ LE for the walnut veneer, Iíve not given audio much thought. Iíve been listening more at home and going to fewer concerts, probably not a good thing. Whether itís the quality of the Devialet electronics, that most music I stream tends to be high definition, the added subwoofer or the LE changes to the speakers, the end result is a good one.

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