From: daw@cray.com (Dave Wright)
Subject: Acoustic Measurement was Re: Designing Crossovers
Summary: MLSSA, TEF, Hyperception, TDS
Organization: Cray Research, Inc.
Date: 1 Oct 92 10:20:43 CDT

In article <1992Sep30.230858.6934@cbfsb.cb.att.com> rprice@cbnewsg.cb.att.com (rodney.price) writes:
>
>>(Patrick W Lauson) writes:
>>
>>>perfected one without the use of an anechoic chamber...
>>
>>Thank you, But if I gave you that impression about 
>>Anechoic chambers then I was wrong. There is test 
>>equipment available that can reduce or eliminate the need 
>>for the A Chamber. Respectable resulit can be optained 
>
A >real room is going to give you all kinds of reflections.  How do you 
>fix this sort of problem? 
>


There are several software packages available that I can recommend that
can sort out the direct sound from the reflections. I don't mean to
endorse any particular package. I wish I could have all of them.
Loudspeaker designers and Acoustical consultants, Sound system designers,
studio designers depend on these tools to correlate what they hear with
what they measure. The publishing list can start with Heyser in AES circa
1967 with TDS using a HP3580. A frequency sweep is sent out and the HP3580
could be tuned (or offset) to look at the speaker direct sound or the room
reflections. This measurement does not need anechoic but has limits for
the resolution based on sweep rate and bandwidth of filtering. ALso the
low frequency measurements would still require reflection free or open
field measurements. I've seen people make outside measurements. TDS then
lead to TEF which Crown/Techron put on a micro DOS platform and now the
MAC. Further examples of this can be found in Audio magazine starting in
1974. 

Later MLSSA came out in 89. Instead of using a sweep tone and a filter, a
Maximum Length Sequence signal generated by software is pulsed into the
room. MLSSA have several advantages like measurement properties can be
handled in postprocessing later, not at the time of measurement. What this
means is you make your measurement at several locations and then can go
back to those same samples later and slice and dice the data different ways
to look for different things like reflection problems or room resonances.

There is also a DSP package called Hypersignal that can seperate out the
direct and reflected sound. I believe this package had some of its roots
from AT&T.

For those interested in acoustic design/measure software you can't leave
out LMS for speaker enclosure design, SPICE for crossover design, and
EASE or ACOUSTICADD for room acoustic design and sound system coverage
design. With EASE or ACOUSTICADD you can auralize what the sound system
will sound like in a yet unbuilt room that is still in CADD or AUTOCAD
design stages.

I do endorse the best classes to get exposure to these technologies if you
are in the buisness. That is Don Davis and SYN-AUD-CON. They offer 4 day
workshops and are sponsered by companies like
Altec/JBL/EV/Crown/Klipsch/SHURE/Community to name a few. These workshops
run about $600 and are well worth it for the Audio professional. Davis was
one of the first professionals to use early Spectrum analyzers to tune
hand wired equalizers and then graphic EQs since their availability.

Syn Aud Con, 12370 W Co Rd 100 N, Norman IN 47264     #812-995-8212

I know that several readers of this newsgroup have been to these classes.
What do you think of them.

Distributer:    DRA Laboratories
Name:           MLSSA
Address:        Sterling VA
Contact:        703-430-2761
Price:          $3500 (software)

Distributer:    Crown/Techron
Name:           TEF 20 Sound Lab
Address:        1718 W Mishawaka Rd, Elkhart IN 46517
Contact:        219-294-8000
Price:          $5000  (hardware and software)


Distributer:    Signalogic/Hyperception
Name:           Hypersignal Workstation/Acoustic
Address:        9704 Skillman #111 Dallas TX 75243
Contact:        214-343-0069
Price:          $1500(Hypersignal)/ $1000(hyperstation)

Distributer:    Renkus-Heinz Inc.
Name:           EASE
Address:        17191 Armstrong Ave. Irvine Ca 92714-5717
Contact:        714-250-0166
Price:          $1700

Distributer:    Altec-Lansing / ElectroVoice
Name:           ACOUSTICADD / Mark4
Address:        PO 26105 Oklahoma City, OK 73126
contact:        405-324-5311
Price:          $1000  (presently Altec dealers only)

Distributer:    Audio Technology
Name:           LEAP/LMS
contact:        503-624-0405
Price:          $


Dave Wright
Newsgroups: rec.audio