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Re: 2 source interference



The information below is in response to a couple of Leigh Palmer's
comments/questions... plus a bit more because I feel like writing about
this.

First of all, in dealing with all the audio hype about how to put "high
fidelity" in my home or office, my ear and my billfold have to be the final
judges. Sometimes small or modest investment of money makes a large audible
difference. Sometimes large investments make zero audible difference (to
me). Sometimes the lack of audible difference makes sense because the hype
doesn't make physics sense. Other times the lack of audible difference is
surprising because the hype seems to make some scientifically credible
claims.

I think my ear is a fairly good judge because (a) I am a musician, (b) I
attend a lot of live concerts of all types (large orchestra, small ensemble,
classical music, jazz music, even rock and roll, marching band, etc.) in a
variety of performance halls, (c) in the 1950's when I was growing up and my
dad was having difficulty making financial ends meet, he started a part-time
business selling hi-fi equipment (mostly binaural tape recorder systems
which gave a pretty realistic sound back then) so I have been comparing
"hi-fi" to live performances for roughly 45 years.

(1) On one hand I agree with Leigh that worrying too much about speaker
phasing is "a bit of a joke." On the other hand, playing around with
phasing is one of several audio variables that can make a very significant
audible difference. The difference is stereo imaging. When I am listening
to the "hi-fi," can I close my eyes and pretend I am at the live concert?
Is the violin sound coming from the correct position? The trumpets? The
percussion?

I have some demonstration tapes and records in which the engineers have
deliberately played games with the phasing. Aside from switching the
location from which you think the sound is coming, they can also make it so
you can't you can't place the sound. They can also make it sound like the
source of the sound wanders around as the instrument plays different notes,
even though they aren't changing anything after the initial set-up.

I have also played around with speaker placement in my living room including
combinations of direct and reflected sound, center speakers, rear speakers,
sub woofers, simulated surround sound using the Dynaco wiring scheme with 6
db blended stereo, etc.

A major problem I have encountered is that recordings today are engineered
with many microphones compared to the early binaural recordings with just
two microphones. Therefore the audio engineers partly "create" the imaging
you hear in addition to your hi-fi system and your living room. Therefore,
the number of speakers turned on, and the speaker arrangement that provides
the most real stereo imaging for one recording might not be the best for a
different recording.

In the end, I don't worry about this much even though I find it interesting
and it's fun to play with. If I want to experience a realistic sound, I go
to a real concert. The times I sit down in my living room and just listen
are not often enough that it makes any sense for me to worry about all this
(other than for fun). Most of the time I listen to recorded music these
days, it's background music. And if I'm in my office, or if I'm home and my
kids are doing homework, I typically have to listen through headphones
anyway.

Anyway... phasing does make an audible difference. But aside from making
sure my main stereo speakers are phased correctly with respect to each
other, I don't worry about this too much. If I did... if I always wanted
the best... I would have to alter the speaker arrangement as well as several
other parameters every time I switch to a different recording. I went
through a "phase" in my life in which I did that. But I discovered I was
listening to the stereo instead of listening to the music. Today I just
listen to the music.

(2) The Bose waveguide radio does deliver fantastic sound. But I don't have
one and probably never will. It's too expensive. It might be good for my
office, except there I need headphones so I don't bother other people. At
home, a small component system with bookshelf speakers in my study gives
just as good of sound and is more flexible, although it takes up more space,
has wires, and isn't as portable. And if I want to listen to loud music, I
either have to use headphones, or go to the living room where my main hi-fi
system has big speakers. (And I also need to be the only person home.)

(3) I agree with Leigh about "monster cables" and similar gimmicks.
Gimmicks are sometimes expensive, sometimes not, but there is no audible
difference and therefore gimmicks are a bad investment at any price.

(4) I can hear a slight difference between solid state amplifiers and vacuum
tube amplifiers. However, I seem a bit odd in the sense that I prefer the
solid state amplifiers. The people who think the harmonic distortion of the
tube amplifiers makes the sound more realistic are wrong according to my
ears.

(5) I remember being impressed several times by speaker systems.

(a) I was first impressed by AR (Acoustic Research). These guys really got
the air-suspension speakers going. Their little AR-4x speakers delivered
incredible sound for the size and money. For larger/louder sound their AR-3
speakers were the standard for many years. (I'm talking late 1960's early
1970's).

(b) I was impressed by Bose when they first came out with a speaker box with
9 small speakers, 8 facing backwards and one facing frontward. How could
those small speakers deliver all that sound?

(c) I have been impressed by a number of small air suspension bookshelf
speakers in the past 10 years.

(d) I was impressed with the Bose waveguide radio.

(e) Many years ago my sister spent the money (and space) to install the full
size Klipsch folded horn speakers in her living room. Now these were
impressive, and still are impressive. She probably will never replace them.
Of course, I haven't replaced my AR-3a speakers.

(f) My dad built his own giant speakers with double 15-inch base speakers
and horn midrange and horn tweeters. Even though this is 20 years old, it
sounds great.

But... I still say the bottom line is... listen to the music. Probably
75-85 % of the time I listen to music, I am using a portable CD player with
a good set of Koss over the ear or Sennheiser on the ear headphones. That
way I can listen to what I want, as loud or soft as I want, without
bothering or being bothered by other people. Incidentally, high quality
headphones do not seem very popular today. However, many recordings are
mixed and/or engineered by audio engineers wearing headphones. Therefore,
good headphones, with a recording engineered by good engineers using
headphones, sound very nice.

(6) For sound demonstrations in the classroom I use bookshelf air suspension
speakers that cost me about $100 (the pair) 10 years ago, and they're only
12" by 6" by 8". For experiments in the lab involving interference, and
echoes and sonar, I use a horn tweeter at 500 to 3000 Hz, or sometimes
"clicks" from a square wave generator with short duty cycle. Major
problem... it drives everyone else crazy. Note: John Denker recommended
using horn tweeters for experiments... I think this is pretty good advice.



Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817