Which type of Loudspeaker when measuring impulse response (normal LS - OMNI LS)?
sergioTOOL
measurements with a sweep sinusoidal signal (in my case I will carry
out measurements in classrooms -9m x 7m x 3m- with the final aim of
obtianing their RT60)?
I´ve read Omni sources are recommended placed at representative
positions were the sound source will be (say front of the classroom
were the lecturer will be, or the stage at a theater). Or with white
noise and traditional loudspeakers locating these facing a corner in
the room, aiming to spread the sound by means of reflecting it.
In my case I only have a large and powerful enough loudspeaker (of the
PA type) and a free software (EQWizard, seems very good) which carries
out the measurement using sweep sinusoidal signals as sound source.
What do you reckon.
Cheers
Sergio
Savant
Sergio,
It all depends on what you're trying to measure. If you want the room
RTs - and that's all - then an omni source would be best; a dodec, or
something similar.
If you're also wanting to get information about the loudspeaker system
- measures of speech intelligibility, clarity, etc. - then a signal
through the room system might be best.
For the most accurate measure of speech intelligibility, I would
suggest a "talker" loudspeaker playing the test signal into a system
microphone.
Depending on what you are tasked with measuring, you may need to
conduct one, some, or all of the above.
BTW, if you don't have a dodec, a normal, wide-range loudspeaker will
work fine. You'll just want to make sure you take various measurements
in the room with the loudspeaker pointed in different directions and
with microphones located around the room at different positions. This
is not unlike the ISO methods I believe you and I have discussed
before. ;)
All the best,
Savant
sergioTOOL
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ONCE AGAIN. MANY THANKS!
I´m only after the RT to improve to ´acoustics´ of the classrooms as
the lecturers have been complaining of the ´acoustics´. From what
I´ve read and studied, reducing the RT of a classroom down to around
0.6-0.8s will suffice. I guess that at the moment is near 3s as its
walls are concrete and brick!! and plasterboard ceiling.
Since we´re on it. How do you suggest I distribute the absorbers in
the classroom. Dropped ceiling systems are very popular but can´t use
them here since there are already plasterboard dropped ceilings to
sound isolate the classrooms from rain noise (noise was unbearable
for
lectures due to the rain falling on the roof´s tiles).
Should I aim to distribute it evenly around the classroom (including
the roof)?
How effective is it to only install abosrbents only on the ceiling
(as
it´s done with dropped ceilings)? Are we not disregarding wall
reflections? Or is wall treatment only important in cases were first
reflections are important?
Cheers!
Sergio
Savant
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Some distribution of absorption on the walls and ceiling will be
necessary, but avoid overabsorbing. A good guide is the free Classroom
Acoustics booklet available from ASA:
http://www.nonoise.org/quietnet/qc/booklet.htm
A PDF can also be downloaded from the above link. Check out Figure 10
in particular; dimensions are almost the same as the room you're
working on!
Also, the target RT might be a bit low. Again, avoid overdoing it.
Targeting between 0.8 and 1.0 seconds at mid frequencies should work
well, IMO.
Savant