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I have a nasty room resonance which I will be correcting by adding a notch filter to my Bassis Unit (Marchand). I am also in the process of assembling a Borbely amp which will be used to power my woofers.An engineer friend has advised me to wait until the Borbely amp is operational before testing the room to identify the room resonance because all amps sound different.
While I agree that all amps sound different, the resonance is primarily dictated by room dimensions, and speaker placement. I wouldn't think the sound the amp would change the resonant frequency, though there are probably amps which make the resonance sound better or worse. Should I wait?
Technically, it is impossible for an EQ to correct room modes. In practice, you can gain some relief by using such EQ in the very lowest frequencies, however, realizw that this will not actually eliminate the room mode, just partially counter it with another deviation from linear response. One thing to be aware of, is to NOT try and use a notch filter of the same depth as the measured resonance peak. Go for only about half or less of the amount it seems it would take. Otherwise transient bass information will be adversely affected.As for letting the amp burn-in, this is SOP, and while it might tighten up the bass some, probably not enough to make you want to not try and address the bass problems.
Jon Risch
> Technically, it is impossible for an EQ to correct room modes.Jon, what makes you think this is the case? While I agree that EQ cannot help any dips caused by room modes, it can certainly work on any peaks in the frequency response.
For clarity's sake, if we look at the upper bass on up, then the room modes are an acoustical phenomena, which occure with a steady state input that extends beyond one cycle of excitation. This defines most common bass notes, as even decaying drum notes hang on in time long enough to excite modes.We hear the direct sound, and then hear the room modes build-up, and for most of the frequency range, we perceive the direct sound as the sound of the music/instrument. Trying to EQ one of the peaks will reduce the direct sound level, and the room mode still exists, and is just as strong as ever. Reduced excitation of the mode does result in less overall level using averaging and a sound level meter, but the direct sound is weaker, while the mode build-up is still there full strength. In essence, you have actually reduced the direct sound, and relative to that level, increased the room build-up level. In other words, the room modes will actually stick out more!
As could be surmised, the cancellation modes can not even be fudged like the peaks seem to be fixed, as no matter how much energy you pump into that frequency, it will still want to cancel. The direct sound will have a huge bump at that frequency, while the room mode cancellation will still tend to kill it steady state.
The same goes for diffraction dips, refelction dips/peaks, etc.
The best way to deal with room modes, refelctions, diffractions, is to absorb them, acoustically damp them, then not only is the SPL meter satisfied, so are your ears.
In the very deep bass, below about 100 hz, the difference between steady state and transient signals becomes blurred, and your ear is more forgiving in the time domain, so some judicious EQ can actually help some here, but you are essentially 'getting away with it', not bending the laws of physics.
DIY acoustic treatment of a room is not that expensive or that hard to do, see:
http://members.xoom.com/Jon_Risch/a1.htmJon Risch
But in the bass, since the wave lengths are so large, the direct vs reflected are practically in phase and are one and the same (also depending on how far you have the speakers from the walls).
From the bass up the frequency response when compensated in the time domain can be EQ'd to correlate to what we hear (of course a plain jane EQ can't do this, but it can help bass resonances).(Oh, and Jon, please look at my "symposium" post, you probably have some good insight on the topic)
I agree with you and "Harleyd", not the engineer. Amps do sound different, but they would have to sound grossly different (with an aberration of some sort) to remove a problem which is basically a room/speaker interaction problem.
Im no expert.....but I cant see how any amp can change standing waves in any room....at least if the amp is running properly;IE rolled off below 500hz for example. What you said make sense to me, anyway
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