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Real speakers in real rooms - what to expect especially in the lower frequencies

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  • #16
    [6] Acoustic damping - vital to tame room resonances

    In the video in my post #11, I used a beer bottle as a handy resonator. I showed how this bottle had its own natural resonant frequency and with just a little energy input from me (lightly blowing across the open neck) it was set into vigorous resonance. And that's exactly how the seemingly solid surfaces in your room behave when they are excited by a little energy radiating from the loudspeakers.

    As I mentioned in post #7 ...

    ... the best, cheapest, easiest and quickest way to reduce bass problems is .....TURN DOWN THE VOLUME. Pump less acoustic energy into the room! Then there is less to bounce around! Sit closer! ...
    and that must be true because with both the air in the bottle and the walls in the listening room, there is a certain minimum 'huff' that's needed to overcome their inertia and set them into motion. And motion is an essential prerequisite to them generating sound, even though it may not be apparent to the human eye or even to the touch. But a vibration detector would readily measure their sonic contribution.

    In the current version of the Harbeth User Guide here we mention the efficacy of (thick) curtains and drapes in the listening room. They need not be permanently drawn across walls - they could be drawn for listening and then withdrawn - and they should be spaced away from the wall as this magnifies their acoustic benefits. Alternatively, although more visually intrusively, the wall/door/surfaces could have acoustic tiles permanently attached. Or the existing panels could be removed and re-hung on energy absorbing joists. Whatever method we chose, the end game is to increase the amount of acoustic damping in the room because that is sure to eliminate or at least ameliorate resonances. And resonances in the listening room can never bring us closer to the music; they will always color the recorded sound by introducing tonality that just wasn't present at the recording venue. The more minimalist, bare and unfurnished the room the less the absorption, and inevitably the more the walls/ceiling/floor/door/windows will contribute to the sound.

    So, back to the beer bottle and its simplistic analogy with a room surface in resonance. How can we damp its propensity to sing-out at its natural frequency? Can we apply damping to tame it and how much do we need? Do we need sophisticated materials or techniques? Will damping the air in this bottle demonstrate the importance of damping in the listening room as a general concept?

    Watch my demonstration video .... here. I was surprised myself.

    We have to accept that in the real world, few if any of use can build a $$$ listening room engaging world-class acousticians. But if we can get the idea of acoustic damping firmly in our mind then we just may be able to turn even the most challenging lively room into one that is good enough to enjoy great sound in without spending a fortune. As I've shown with the bottle, we need only the minimum amount of damping optimally positioned. We need no more than that.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    • #17
      Summary of videos about room resonances thus far

      Pulling together Alan's videos in this thread concerning resonances in the listening room >>>>>>. You can read the full posts by referring back to his subject [No.] previously.

      Note: the video will play after adequete buffering (hopefuly).

      ================================================== ================================================

      [4] Here is the video of the spectral analysis of the door bang testing.

      [5] Video of using a beer bottle as a tuned resonator to simulate a panel's natural resonant frequency

      [6] The meaning of damping when applied to resonances

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      • #18
        Some people like coloration

        Originally posted by A.S. View Post
        ?.... And resonances in the listening room can never bring us closer to the music; they will always color the recorded sound by introducing tonality that just wasn't present at the recording venue. ......
        But I know there are many people who cannot bring themselves closer to music in a damped room (need not necessarily be over damped).*

        Recently, I attended a live performance and had a chance to talk about the venue's acoustics to the pianist *who happens to be an accomplished musician. In his opinion the acoustics was excellent. However, to my ears, even though the music was good but it was not without coloration and smearing.*

        The room itself wasn't big. Maybe, about 20ft x 60ft. The ceiling was at least 20 ft high.* A single mic for the piano and one for the pianist (both mics were on all the time) the double bass came with its own amplifier and speaker and the drums with two mics. *The piano and the drum sound were played thru a pair of Bose Speakers hung about 10 ft above them. Even without the speakers, you could hear the unamplified sound clearly at where I was sitting . So imagine how much smearing that we were hearing from the sound directly from the speakers and from the instruments and from the room itself which wasn't treated at all!

        To my friends that's *how their system should sound like. They call it "the sound got the energy". *IMO, most of us experienced music with reverberations. *We were exposed to guitar or piano sound played in our living room or in our classroom which adds much colouration to the original sound. And that, we have accepted as natural to us.*


        ST*

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        • #19
          Can't play

          For some reason on my iPad i can only get the image of Alan looking like an air traffic controller, however cannot get it to play, the timer shows, but has 0:00. Will try it later on my computer...

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          • #20
            All play on Mac

            All three play fine on Mac with Flash v 11.1.102.55 plugin.

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            • #21
              Homebrew acoustic measurements of your Room Characteristics.

              This thread is totally spot-on regarding the problems of room resonances and how they wreak havoc on faithful sound reproduction (especially the bass regions).

              Perhaps i would share some home-brew methods on how to measure the severity of room colouration in one's listening space. Keep in mind that this is not a professional rig, but purely an enthusiast's attempt into further demystifying the boundaries between black-arts and acoustic sciences.

              The rig is as follows:
              1) A good condenser measurement mike. These usually require phantom power (48VDC) from a powered mike preamp. Good example would be a Behringer ECM8000 or Dayton EMM-6. If one's really nitpicky, one may buy a calibrated version from 3rd party companies such as Cross-Spectrum Labs (with calibration file & all).

              2) Mike preamp that supplies phantom power to the condenser mikes. (Example, Behringer MIC200) (Would recommend to feed the mike preamp's line level output into the computer for lower noise floor signals).

              3) Mike stand. (or a generic camera tripod stand would do fine)

              4) a SPL meter. ( for input-level referencing, typical Radioshack is fine)

              5) Mac or PC computer with line level input. (don't use the mic-inputs , coz they're terribly noisy)

              6) If on MacOS, get (buy) this software called FuzzMeasure. If on PC, get Room EQ Wizard (available Freeware from HomeTheaterShack website). Familiarise oneself with these software.

              7) Misc. cabling and connectors to hook everything up nicely.

              Once the above rig is put up and the mike position as the listening position, one can then proceed to execute some interesting measurements:

              A) Overall room response (dB vs. Freq). This would give an overall response at the listener's position. Typically most people stop at this graph but it is not even revealing close to the true picture of the room colourations. Avoid 1/3 Octave resolution as its too coarse. Use at least 1/12 Octave to really see the problem spots.

              B) Waterfall Plot. Now we're getting somewhere.... this would be a 3D "aka waterfall" plot of how the frequencies DECAY in the room. x-axis: Freq, Y-axis: dB, Z-axis:time(ms)



              (Those "mountains" that lunge forward are bad news.... best to keep them pushed back.)

              C) Decay times. Depending on what software, you might be able to generate a RT-60 Spectrum graph. Very useful in revealing overly long bass decay notes especially in small room setups.


              Once this has been comfortably achieved, one can then proceed to experiment with speaker placement, listening spot location, and hanging temporary drapes and whatnots to get the best compromise in sound reproduction.

              One last note, since' we're only concerned with how its going to sound at where we're seated at, we would just focus on taking measurements at our listening positions in the room unlike a THX engineer who is trying to get the best sonic experience for a wide audience in a THX certified Cineplex hall.

              Anyone trying this out over the Xmas holidays ? Do share your findings!

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              • #22
                "Losing half the music": why musicians hate hi-fi

                In an intriguing guest editorial in the April 2012 issue of The Absolute Sound, Robert E. Greene claims that most real musicians hate hi-fi because of a massive hole in the frequency below middle C in reproduced music. That hole, somewhere between 100 and 300 Hz, he suggests, is caused by the fact that most speakers have not been designed to interact with floors correctly, leading to a loss of response that is "massively destructive to music".

                I seem to recall that Alan has already written about floor reflections, but I can't find the thread. I don't want to waste anyone's time by repeating a discussion that might already have been covered extensively. If this is as destructive to one's enjoyment of music as Greene suggests, then I'm surprised that all loudspeaker manufacturers don't bear it in mind as one of their primary design issues. Greene doesn't say how one might correct for this. Can anyone (Alan, if you have the time?) comment on this.

                David

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                • #23
                  Link

                  here's a link to the editoralhttp://www.enjoythemusic.com/tas/ in question.

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                  • #24
                    Site about sound

                    Hi David,

                    It would be very worthwhile also to visit Robert's site at http://www.regonaudio.com/ as there are lots of great articles relating to Audio there.

                    Cheers,
                    Noel.

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