Date: Thu Mar 8, 2001 1:46 pm
Subject: Re: [acoustics] Re: studio design
In a message dated 3/8/01 3:06:05 AM Eastern Standard Time,
> Please tell me what the different coloumns mean and do.
> What am I supposed to paste in the sorted column.
> What does the critical absorption zone and critical diffusion zone signify?
> we can seethem as only percentages.
At the top you enter the reverb time of the room (calculate this using a
Sabine worksheet ... so much concrete, so much carpet, so much acoustic
ceiling tile, etc.) there is a second sheet on Doug's page. You can link the
pages so when you change one the RT60 or reverb time automagicly updates
(RT60 is the time it takes sound to drop off 60 dB in loudness ... a
pragmatic measurement standard of the rooms reverb energy or the decay rate
of sound energy 0.6 to 0.75 seconds is a reasonable range for a , the louder
the music the shorter the time you should target)
Down below in the first column enter the room's dimensions (this can also be
linked to the Sabine sheet) and room volume is calculated above. To the
right of room dimensions, the rooms fundamental modes are generated ... and
to the right the critcal zones are calculated ... the zones are rules of
thumb that tell you where to focus your efforts as to absorbtive treatment
vs. diffusive treatment.
Below is a string of columns ... the 1st is just each mode run through
doubling to the 6th octave. Copy this column (which is a list of formulae)
and then "paste special" it in the next column as "values" ... this gives you
a list of numbers to sort vs. a list of formulae. To the right are two
columns, the 1st shows you the difference in Hz between each successively
higher room mode, the 2nd shows the relative change as a percentage. To the
right of that are markers that you must move around to match the zones
calculated above ... the markers are helpful when measuring the real room
later as they point to parts of the sound spectrum where you should look for
problems and solutions (through either diffusion or absorbtion).
If you enter 26' and 13.5 as two of the room's dimensions the second harmonic
of the 13.5 lines up very close to the fundamental of 26 (42 Hz and 43 Hz
respectively). This difference is less than 5% which is pretty much a
gurantee that these modes will interact to cause problems. By changing the
26' dimension to 25' you increase this difference to 42 and 45. If you
want to zoom in then format the 1st column to show a couple of numbers to the
right of the decimal.
This change doesn't make the problem go away ... it just spreads the pain
around a bit .. I understand you are constrained by the shop's bay width, but
gettin the main room depth off the doublied value of the width by at least 5%
should help enormously. Might also be a good idea to put a couch with a few
absorbtive panels on the wall above on one of the two walls 25' apart ...
maybe a diffusion array on the opposite wall. You will want to focus on
diffusing sounds from about 140 Hz to about 600 Hz ... polycylindrcals would
be a cheap way to get something happening in this range, and they would help
keep the LF energy down.
Scott R. Foster