[Powell]

Looking for a methodology to measure the acoustic response
of new video production studio. I'm not interested in software
modeling whatsoever. There is 80' drape which covers most
of three walls except when using the green screen. I've notices
significant slap echo when shooting in this mode.

My thinking at this point is to place one speaker in three test
locations across the practical width of the room about 1/3 of
the way out from the backdrop wall. When we measure a
speakers frequency response the measurement microphone is
usually placed 3' from the speaker face. Where do you place
a microphone when the subject is the room itself, besides
avoiding null points?

[Don Pearce]

Powell wrote:
Looking for a methodology to measure the acoustic response
of new video production studio. I'm not interested in software
modeling whatsoever. There is 80' drape which covers most
of three walls except when using the green screen. I've notices
significant slap echo when shooting in this mode.

My thinking at this point is to place one speaker in three test
locations across the practical width of the room about 1/3 of
the way out from the backdrop wall. When we measure a
speakers frequency response the measurement microphone is
usually placed 3' from the speaker face. Where do you place
a microphone when the subject is the room itself, besides
avoiding null points?


Don't avoid the null points - those are the big errors you are trying to
correct. You will be wasting your time trying to measure a bad room,
though; you have already identified the major errors. Get those fixed to
your audible satisfaction, then think about measuring what is left. And
remember it is the errors you want to measure, not the good stuff. Seek
them out by playing sine waves and walking around with a finger in one
ear, seeking null points.

You won't get rid of the nulls, but if you can reduce their depth from a
probable 30-odd dB right now to perhaps less than 10dB (an ambitious
target), you will have done your job.

There are two ways to do this - diffusion and absorption. Diffuse with
clutter that covers flat walls. If once this is done you feel you need
to reduce the reverberation a bit, put in absorption. See Ethan Winer's
web site for some good stuff.

d

[Powell]

"Don Pearce" wrote

Powell wrote:
Looking for a methodology to measure the acoustic response
of new video production studio. I'm not interested in software
modeling whatsoever. There is 80' drape which covers most
of three walls except when using the green screen. I've notices
significant slap echo when shooting in this mode.

My thinking at this point is to place one speaker in three test
locations across the practical width of the room about 1/3 of
the way out from the backdrop wall. When we measure a
speakers frequency response the measurement microphone is
usually placed 3' from the speaker face. Where do you place
a microphone when the subject is the room itself, besides
avoiding null points?

Don't avoid the null points - those are the big errors you are trying to
correct. You will be wasting your time trying to measure a bad room,
though; you have already identified the major errors. Get those fixed to
your audible satisfaction, then think about measuring what is left. And
remember it is the errors you want to measure, not the good stuff. Seek
them out by playing sine waves and walking around with a finger in one
ear, seeking null points.

You won't get rid of the nulls, but if you can reduce their depth from a
probable 30-odd dB right now to perhaps less than 10dB (an ambitious
target), you will have done your job.

There are two ways to do this - diffusion and absorption. Diffuse with
clutter that covers flat walls. If once this is done you feel you need to
reduce the reverberation a bit, put in absorption. See Ethan Winer's web
site for some good stuff.

Thank you.

In the field where there is room I use portable 3' x 7' sound
absorption panels. And these would greatly help but there's no
room. A spectrogram of the room should identify interferences
masking the spoken word frequency. As I recall slap-echo has
a unique waveform. Music recording to some lesser extent
needs considered. In which case diffusion will not be as
important as absorption to in order to minimize individual
interference and room reverberation.

Placement of the speaker and recording microphone seems
critical to interpreting the frequency sweep data... the source
of my question. How do you accurately record a room's true
sonic signature?

[Don Pearce]

Powell wrote:
"Don Pearce" wrote

Powell wrote:
Looking for a methodology to measure the acoustic response
of new video production studio. I'm not interested in software
modeling whatsoever. There is 80' drape which covers most
of three walls except when using the green screen. I've notices
significant slap echo when shooting in this mode.

My thinking at this point is to place one speaker in three test
locations across the practical width of the room about 1/3 of
the way out from the backdrop wall. When we measure a
speakers frequency response the measurement microphone is
usually placed 3' from the speaker face. Where do you place
a microphone when the subject is the room itself, besides
avoiding null points?

Don't avoid the null points - those are the big errors you are trying to
correct. You will be wasting your time trying to measure a bad room,
though; you have already identified the major errors. Get those fixed to
your audible satisfaction, then think about measuring what is left. And
remember it is the errors you want to measure, not the good stuff. Seek
them out by playing sine waves and walking around with a finger in one
ear, seeking null points.

You won't get rid of the nulls, but if you can reduce their depth from a
probable 30-odd dB right now to perhaps less than 10dB (an ambitious
target), you will have done your job.

There are two ways to do this - diffusion and absorption. Diffuse with
clutter that covers flat walls. If once this is done you feel you need to
reduce the reverberation a bit, put in absorption. See Ethan Winer's web
site for some good stuff.

Thank you.

In the field where there is room I use portable 3' x 7' sound
absorption panels. And these would greatly help but there's no
room. A spectrogram of the room should identify interferences
masking the spoken word frequency. As I recall slap-echo has
a unique waveform. Music recording to some lesser extent
needs considered. In which case diffusion will not be as
important as absorption to in order to minimize individual
interference and room reverberation.

Placement of the speaker and recording microphone seems
critical to interpreting the frequency sweep data... the source
of my question. How do you accurately record a room's true
sonic signature?




A room doesn't have a sonic signature. Every possible path between any
two points in the room has its own signature. What you are trying to do
is get all of those paths as similar as possible.

Slap echo is a good place to start. Find a place that sounds
particularly bad and put an omni mic there. Record a sharp sound like a
hand clap, and look on your computer screen. You will see the spike of
the clap, followed rapidly by a trail of others. By measuring the time
delay between them and relating that to the speed of sound (345m/sec)you
can judge which walls are causing the problem and get working on them.
Absorptive panels can be a good idea. Space them along the wall, then on
the wall opposite put more, but staggered from those on the first wall,
so that at no point do you have blank wall facing blank wall.

What you should be aiming for is complexity, so that echoes and
reverberations are nicely jumbled. If your room is simple to analyuse
you can be sure that it will not sound good.

d