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. "
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.
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.
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