room responses etc.

[Martin Czech]

I'm taking up the room responses thread which was laying down so long
due to excessive cycling. The correlation technique is now clear to me
and first computer experiments were successfull.

Further on I plan:

-a set of portable battery driven devices for recording of such responses
anywhere I like and I'm allowed to. Battery driven things might be
psychological better for getting a permission for churches etc. as well.

-I want to use a pseudo random noise source, this gives a pulse
train which should directly drive a loudspeaker via MOSFET push-pull
tansistors and capacitive coupling. I need only a unipolar supply then
and the "amplifier" will consume a minimum of power, cause it is really
switching. The speakers and crossover network should filter out most of
the hf garbage...

-I want to use my portable DAT for recording. Professional equipment seems
to do severall recordings for averaging.  This leads to synchronisation
problems with the noise source. One idea to get arround is to use the
optical out as clock source via pll for the pseudo noise gen. This
locking would also reduce possible alias problems.

-All this (speaker, battery, microphone, DAT, cables...) should fit into
a medium size suitcase.

Problems: 

-nonlinear characteristic of "power amp". How does it change with
battery life? 
-hf artefacts? alias ?
-how stable will the pll be?
-every now and then the system has to be calibrated, i.e. a recording
has to be made in an anechoic chamber. Needless to say I have none.
would it suffice to go outdoors and do a free air recording?
What about ground reflexions?
-microphone characteristic, I don't know which char. is best


m.c.