[Arny Krueger]

"Soundhaspriority" wrote in message

"Ethan Winer" ethanw at ethanwiner dot com wrote in
message
...


First you should measure, with oscillator or a
Stereophile Test CD, and a lowly Radio Shack SPL meter.
If the room is pressurizing below a certain frequency,
the measured SPL at or below that frequency will be
independent of position.

So far so good.

As you go up in frequency, you should see
the modes. Chart them out in 1/3 octave steps.

The train seems to be headed off the tracks.

Small rooms do have this situation where they start tipping up the bass
below a certain frequency. Ideally, you match that up with the roll-offs of
the woofers, and it really works. There are two problematical situations,
one where the woofer starts rolling off out before the room starts picking
up, and the other where the room starts picking up before the woofer starts
rolling up. The first situation gives you a hole, while the second gives
you a peak. The peak is more troublesome, but neither is ideal.

This is independent of modes, but your measurements will probably show both.
The only useful information about modes would relate to how you use your
knowlege of them to more precisely identify any mismatches between your
woofers and the room.

One approach to backing modes out of room measurements is to take
measurements at diverse locations. The modes are location-dependent so they
will eventually average out. Unfortunately, you might grow old taking
enough data to get reliable results.

I've seen arrays of like a dozen mics and complex averaging hardware used to
get reliable high resolution results in a reasonble amount of time.
Thinkable for developing small rooms with audio systems that are produced in
volume, but otherwise not. IOW, the automotive guys have been here, and
left.

Third octave tests are not useful in small rooms. I've
seen peaks and adjacent nulls closer than a musical
whole step. This is not only common, but typical. So
third-octave is mostly a "spot check" here and there,
and completely misses the true response and the mode
frequencies.

Agreed.

I'm giving him a methodology for which the tools are
cheap and simple. If I were doing the job, I would use a
spectrum analyzer.

Won't help. A detailed view of mud is still mud.

But you're wrong about the traps. His room is too
small, and the problem too severe.

What small rooms do is either a problem or an opportunity, depending on how
you manage it. In the end, you might end up with both traps and some eq.
The traps are going to help you make any remaining problems more clear, and
easier to manage.