This was passed on to me. (See below)

I agree with it (and always have).

The BFD is a low end piece to begin with. I think that believing the 1ms spec is akin to believing speaker response specs.

I've heard that it could be as much as 20 times that spec as far as the total delay after EQ.
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quote:Tom Ascher wrote:
> It appears that the primary use of equalizers is to get rid
> of room resonances that result from systems being in spaces
> considerably smaller than auditoriums or theaters where music
> is generally heard.

That might well be the most popular use, but it's the wrong use.
It's a waste of an equalizer and it is garaunteed NOT to do the
job.

> But, the broader issue is that any room can be considered an
> extension of the speaker enclosure and will introduce
> resonances at various frequencies throughout the audible range
> and that it really is necessary to have some way of "voicing"
> a system to a given room.

No, any room CANNOT be considered an extension of the speaker
enclosure. This is because of the inherent delays due to room
resonances put these effects well outside of the realm
associated with enclosure issues.

> Of course, speaker selection and placement, mounting, use of
> room treatment materials are all part of adjusting a sound
> system so it sounds good in a given room. But, there remain
> some problems that really cannot be dealt with short of some
> form of equalization.

Let's look at the falacy of this overall approach. Let's assume,
for the purpose of discussion, that the axial frequency response
and the power response of the speaker is perfect: it is dead
flat from 20 to 20 kHz anechoically. Let's further assume that
we want to maintain that response at the listener's ears. (We
can geeralize the assumptions to say that whatever the response
of the speaker is, flat or otherwise, we want to preserve it
by the time it reaches the listners ears.)

Now, let's play the loudspeaker in the room. Sit 3 meters away
from it. The first thing to reach your ears is the direct sound
from the speaker, completely unaltered by the room. Whetever the
response of the speaker is anechoically, THIS is what reaches
your ears first.

Now, let's say your room has a nasty resonance at some
frequency. In order for that resonance to affect what you hear,
the energy from the loudspeaker has to travel to where that
resonance is formed, it has to excite that resonance and that
resonance has the effect of dramatically extending the
reverberation time at that frequency, and the delayed,
reverberated result now has to travel the remaining distance to
your ear in order for you to perceive it.

And it arrives at your ear, AFTER the unaffected direct sound
made it and stimulated your ears.

Now, put an equalizer in and try to correct that resonance.
Let's say that the resonance cause a 15 dB peak in the response
at 300 Hz (not likely, but let's pretend). So you take your
equalizer and dial in a -15 dB hole in the electrical signal
going to the speaker at 315 Hz (because you went out and bought
a fancy 1/3 octave equalizer, none of which have a 300 Hz band,
by the way).

Now, let's play the loudspeaker in the room. Sit 3 meters away
from it. The first thing to reach your ears is the direct sound
from the speaker, with its new 15 dB hole in the response,
COMPLETELY UNALTERED BY THE ROOM. Whatever the response of the
speaker is anechoically, NOW modified by a 15 dB hole in the
response, THIS is what reaches your ears first.

And at the same time, the energy from the speaker travels about
the room, and STILL excites the room resonance (but at a lower
level) and STILL gets delayed and reverberated (sorry, but the
reverberation time at the resonance is not changed by the amount
of energy you put in it).

So, instead of a perfect speaker affected by a room, you now
have a speaker with a big whopper 15 dB hole in the response
that's somewhat less affected by the room.

A room's acoustical problems are fixed by dealing with the
causes of the room's acoustical problems, not by screwing up the
signal fed into it.

The problem is that MOST of the instrumentation available to
most people for "measuring" room response are completely
inadequate to the task. 1/3 octave real-time analyzers, pink
noise generators and sound level meters, warble tones and all of
it simply lose ALL the important time information that describes
WHY the room behaves the way it does. It hides much f the
information altogether.

You have a room with a nasty side-wall reflection? Propose how
an equalizer eliminates that reflection and it's effects? Bad
floor-ceiling slap echo? How and why would an equalizer fix it?
(Hint: it won't). Reverb time of the room about 1/4 second
EXCEPT at 200 Hz, where it's 1 second? How does something which
operates in the electrical frequency domain correct for energy
stirage and delay in the time domain, especially when that agent
is no longer causally connected to the stimulus?

Yes, you're absolutely right:

"It appears that the primary use of equalizers is to get rid
of room resonances that result from systems being in spaces
considerably smaller than auditoriums or theaters where music
is generally heard."

But they are ineffective at doing so.

--
| Dick Pierce
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...Whaddayathink?