Re: Question on sound booths

["Alain de Cheveigne'" <Alain.de.Cheveigne@xxxxxx>]

Leonid,

In summary: (1) Define your needs.  (2) Identify issues specific to 
your setting.  (3) Get the manufacturer to commit to measurable 
specs. (4) Oversee the assembly.  (5) Don't pay until your 
requirements are met.

Requirements may differ according to whether you'll be doing human 
psychophysics, human electrophysiology, or animal physiology.  They 
depend also on whether you'll be running near-threshold tasks or 
suprathreshold.

If you'll be running tasks near threshold, threshold of hearing 
defines the objective to attain.  If working with animals keep in 
mind that they might have lower thresholds.  This determines your 
requirements with respect to ventilation & light noise, and together 
with external ambient noise levels, your isolation requirements.

Ambient noise is highly variable from setting to setting, and over 
time.  Peak levels are usually what count (door slamming, loud 
speech, etc.) rather than a long-term average.  Is the booth to be 
installed in a room full of lively students?  Air conditioning is a 
concern because the low frequency noise it produces is hard to 
isolate against.  It may make sense to acoustically treat the room 
that the booth is installed in (reducing reverberation reduces sound 
level as well as voice levels).

Structure-borne vibration may be a issue (footsteps, machinery, 
subway, etc.).  If so the booth may need to be installed on vibration 
isolators.

Sound absorbing inner walls and a carpet may be useful to limit 
subject-produced noise.

Ventilation is a tricky issue.  You need ventilation during an 
experiment, and in addition there may be official health 
requirements.  Make sure that the manufacturer's specs apply with 
ventilation on (and be prepared to fight on this issue).  Booth 
ventilation inlets/outlets should not be connected to the building 
air conditioning.

It's a good idea to have a window.  This allows to check if an 
experiment is running (and the subject is still alive) and it allows 
the option to install a screen outside to avoid acoustic and/or 
electric noise.

Holes for cables.  These should be large enough for all the cables 
you might need, including connectors unless you rewire them. 
Plugging the space around the cables with putty should give adequate 
isolation.  You can also install a box over the opening and fill with 
acoustic foam.  Make sure that the tube that lines the hole does not 
constitute an acoustic bridge.   A hole is more flexible than a patch 
panel.

Fire alarm. Check the requirements.

Power outlet(s) inside the booth.  Power cables should be shielded.

Light.  Be aware that lights may produce sound, heat, and electrical 
interference.

If you're doing electrophysiology (human or animal) it may be worth 
having lights fed with filtered DC.   You may also want a faraday 
cage.

It's a good idea to be present during assembly to check for obvious 
mistakes such as damaged seals, acoustic bridges between walls, 
missing calking, etc.

Define measurable requirements and make sure that you can force the 
manufacturer to meet them.  For example make sure that they won't 
charge you for testing.  Isolation is very hard to measure because it 
requires extremely high sound levels outside the booth to reach a 
measurable level inside.

Good luck!

Alain


> Dear List,
>
> We are considering two different sound booth manufacturers available 
> in the California area. Both are offering the booths of comparable 
> size and nominally same specs, but with very different prices 
> attached to them. Does anyone have experience in ordering booths? 
> How do we choose? Anything in particular to watch for besides the 
> specs?
>
> Thanks a lot!
>
> Leo