sound decade ?
"Mike Rivers" wrote in message
ups.com...
On Feb 24, 10:36 am, "Henry Kolesnik"
wrote:
I just got the book Sound System Engineering by Don Davis and Carolyn
Davis and it has 2 short sections on sound decades.
I've been able to make absolutely no sense of the replies (relevant to
your question) here, so I got out my copy of Sound System Engineering,
checked the index for "decade" and found nothing. In what section or
chapter (by title, please, not page number or chapter number) did you
find this? My edition is very old (the hand calculator pictured is an
HP-35) so it may not be in mine, but I'm willing to look for it if I
knew where to look. Your question, and the answers, may make more
sense in context than just looking at a formula.
Mike
My book is the Second Edition FIRST PRINTING 1987 and decades are in
the index. In The Contents at the first of the book we see Section 2
Mathematics for Audio Systems, Decade Calibration page 26 and Section 3
Using the Decibel, Calculating the Number of Decades in a Frequency Span
page 57..
I accept and agree that it is easier and much more convenient to plot on
log-log paper any values that have a wide range and log base 10 is fine.
I also find it very practical to say some pitch or frequency depending
on whether we're talking about sound or electrical signals that the
range is 2 or 3 octaves. If we're discussing audio and I say starting
at 20Hz every one knows 2 octaves is 80Hz. Or if I say 880Hz but one
octave lower you go to 440Hz or 0.3010 decade in either case. So
decades aren't of much practical use as far as I can see. Or take the
span 20 to 20Khz is 3 decades is easy to do mentally and easy to
understand whereas that same span is not quite 10 octaves, not too
practical, but failrly easy to calculate on HP 11C.
RDJones mentioned; "Crossovers, ie: the woofer is the first decade, mids
are the second
and the tweeter is the third." For speakers that puts woofers producing
20 to 200Hz, midrange producing 200 to 2000Hz and tweeters 2000 to
20,000Hz. This is my example to be used only for illustration because
you never want any crossover in the 2000Hz neighborhood because it can
degrade the human voice.
From another book, Audio Cyclopedia by Tremaine it shows crossovers at
450hz and 5000Hz for a 3 way and 200, 1000, 3500, & 10KHz for a 5 way.
It should be noted that the plots are on semilog paper but the filter
rolloff is specd at 6dB per octave.
In the Audio Engineering Handbook by Benson plots are on semilog paper
and rolloff in dB per octave.
Neither of the above books cover decades. I'm starting to think that
decades are only used because we plot on log rule graph paper and that's
because we don't have octave ruled graph paper. Their practical use is
limited.
Out of curiosity and because I've been shook up by sub woofers in
theaters and now some cars can vibrate mine, what is the frequwncy range
for these sub woofers and what is the rolloff, octaves or decades,
however they are specd.
tnx
--
73
Hank WD5JFR
|