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Thread: Room Acoustics - Understanding the Measurements - Next Steps

  1. #11
    Quote Originally Posted by microstrip View Post
    IMHO the 1/3 octave smoothing hides the useful information in the bass - 1/12 or 1/24 is needed bellow 200 Hz before debating peaks. Perhaps it is a good time to remember we had an excellent WBF thread written by Amir some years ago, Acoustic-Measurements-Understanding-Time-and-Frequencyhttp://www.whatsbestforum.com/showth...-and-Frequency.

    In my longer room (31') the second eigenvalue was around 35 Hz with corresponding very long decays at this frequency and I managed to improve it significantly, both in subjective listening and measurements, building very large bass tuned traps - see http://www.whatsbestforum.com/showth...l=1#post133862. As I had plenty of space behind the speakers, they are hidden by curtains. I am in the process of building a second one covering the whole back wall.
    Thanks! How did you tune the membrane to said frequency? I would be interested in building a Helmholtz Resonator at 29.2Hz. I will read the other posts, information is always good.

  2. #12
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    Quote Originally Posted by Florian View Post
    Thanks! How did you tune the membrane to said frequency? I would be interested in building a Helmholtz Resonator at 29.2Hz. I will read the other posts, information is always good.
    I have used mainly the excellent calculators from mh-audio http://www.mh-audio.nl/ACalculators.asp#showcalc. I choose to use a limp membrane (6,38 kg/ square meter) as I have read that it has a much broadband tuning than solid panels. I calculated it to a frequency about 20% higher as in this site it is stated that
    "Filling the cavity with fibreglass or mineral wool tends to lower the resonant frequency by up to 50 per cent as well as doubling the effectiveness of the trap. It also lowers the Q of the trap so that it is effective over a wider frequency range. A typical panel-type trap is effective for frequencies around one octave either side of the centre frequency, which at least has the advantage that you don't have to be absolutely accurate to get results. "
    Under construction!

  3. #13
    I am exclusively a listener to digital sources. So, Dirac EQ does a wonderful job of controlling room modal issues in the bass for me. Some other EQ tools might be just as effective.

    I do no passive treatments. Helmholz resonators might be effective at a single frequency, though difficult to fabricate and calibrate exactly. And, of course, they are forever fixed at that single frequency. So, your room, speaker and furniture configuration must stay forever unchanged.

    Have you investigated active bass treatments? These are essentially "negative" subwoofers, with active amps and circuitry to counter modal peaks with out of phase cancellation signal. And, they are not directly connected to your system, other than through the ebb and flow of sound in your room, which they "hear" via a built in mike. They are not dirt cheap, and not outrageous either. But, they seem to be effective at low frequencies, unlike passive bass traps. Bob Katz did a review earlier this year of one brand in Stereophile. There may be a few others, but I do not have the links offhand.

    Some subs with mike calibratable internal digital circuitry, JL Audio for example, can also provide EQ for a limited number of modal issues within their range. That, of course, requires the built in a-d and d-a in the sub channel, but it does not require a digital xover and need not affect the rest of the frequency range. However, I am not a fan of using a subwoofer without a high pass and low pass xover, but that could be an analog xover. But, xovers might open their own can of worms, and good ones, especially in the analog domain, are not cheap.

    And, multiple subs can also provide smoother bass evening out room modes, but that requires much experimentation and measurement, with final effectiveness unpredictable for your specific situation at specific frequencies.

    Personally, I am quite happy with a single sub, a digital xover in my PC via JRiver library/player software and PC Dirac providing full range EQ. Room modes are pretty much gone, and I love the sound.

  4. #14
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    Quote Originally Posted by Florian View Post
    Hello everyone,

    i thought id share some of my measurements and gather some Feedback. Also i would like know what Options i can take to lower the 29.2Hz resonance as the "off the shelf" Absorbers dont do anything down there. I use 8 GIK Soffit Traps and some other devices (ceiling, curtain etc...)

    Attachment 29327
    Smoothing 1/3

    Attachment 29328
    Time (I still have to find a way to fix the reflection)

    Attachment 29329
    The very deep bass rises cause the most challanges

    The room is 5.97m in length, 4.25m width and 2.4m in height.

    Attachment 29330

    Cheers

    Florian
    god i wish i knew how to use dsp. i recently heard a pair of older monitor audio's with parasound amps and front end with 4 m&k subs and all kinds of tweaking and cool dsp and it was one of the most musical sounding systems i have ever heard. he then switched to a old dynaco amps and images were almost holographic 3d and **** was floating in space and i was shocked. i think the total system was about $15K. i went home and listened to my system (same material) and it sounded lifeless and boring. it is amazing what a well thought out and planned system can do with modern technology. i just dont understand any of this. but i can tell you it works and works well.

  5. #15
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    i am just barely understanding this dsp stuff. does anyone have a step process or guide on how to learn more about dsp and how to use it in your system. i know there is ton of software out there. is there a like a top 5 list? and what about room acoustics ... does one use dsp in conjunction with room acoustics? thanks in advance for the input.

  6. #16
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    Quote Originally Posted by Fitzcaraldo215 View Post
    Helmholz resonators might be effective at a single frequency, though difficult to fabricate and calibrate exactly. And, of course, they are forever fixed at that single frequency. So, your room, speaker and furniture configuration must stay forever unchanged.
    I am very much in favor of the Helmholtz resonators. The issue posted here is solely due to the measurements of his room. This means that furniture and speakers do not have any (or hardly any) effect on those standing wave. You might tweak the problem a bit but not eliminate it: moving speakers, listening position, speakers that don't go that low, ...
    Yes, HH resonators are single frequency, and if you use them without absorber inside then their band width is really narrow, but also really impactful which is what is needed here. And mind you, the impact is not on the resonator frequency alone but also on the harmonics of that frequency!!

    On the other hand, the +/- 5 dB bump in the low end is everything but worrisome! I do am surprised to see the decay at that frequency to be that long while this seems to cause only a few dB extra. I would expect the peak to be closer to at least 10 dB, but well acoustics is not an exact science or rather, we do not always have the exact data at hand to be fully informed on effective conditions.

    SMT does make and commercialize very effective HH resonators.
    Aries Cerat, SMT and Entreq distributor for Belgium & The Netherlands - Tenor Audio Audition Center
    New website under construction, till then check www.audiorefinement.eu

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