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From: Douglas Tate <100576.32~ompuserve.com>
Date: 03 Jan 96 05:22:46 EST
Subject: Dr Dolittle

Vern and Bobbie have been discussing resonating together recently. There are a
lot of ramifications in what has been said but one thing seems not to have been
mentioned (although I might have missed it)

When you are being chased by a police car ... you know! ... the sound of the
siren is at a certain pitch. You can tell if they are gaining as the pitch goes
up, and the sense of relief as they overtake and disappear into the distance is
added to by the calming effect of the pitch going down. ie Doppler effect,
sound source coming towards you foreshortens the waveform, (pitch up), going
away waveform lengthened, pitch down.

Talk has been of resonators. Empty containers (politicians?) making a sound
when you energise them (blow across top for example) When the harmonica is
played it appears to me that there are a couple of different mechanisms. Both of
which have been mentioned but not had their differences noted.

1) When a harp is 'blown' the mouth cavity, lungs, sinus and anything else down
the food processing factory acts as a resonator. The fact that the resonator is
causing resonation by forcing a little reed to excite its frequency doesnt
matter. The reed could be artificially wiggled. (people who have had the 'voice
box' removed surgically use an electric vibrator on the side of the throat to
excite the vocal tract into resonance.

2) When a harp is blown and the hands are used to effect a chamber of sorts we
have a resonating dumbell. ie, two resonating chambers with the sound exciter
stuffed in the middle. I haven't seen any scientific treatise on unbalanced /
compensatory / complementory resonators. (Doesn't appear in any of the books I
could find) This situation certainly works for me soundwise!!!

Into all this comes a possible red herring. Doppler. Does the flow of air into
the mouthorgan alter our perception of what the true resonant system is
producing by introducing a Doppler lowering of apparent pitch? (Converse with
blowing) For example, the 'pinged' pitch of a reed is different to the blown
pitch. (OK, I know there are other things at work here as well).

Does all this matter?? Well yes, I think it does. I am happily in disagreement
with Vern on a number of points, not on the scientific 'exactitudes' which he
correctly points out (no, that is not a statement of my own superior knowledge
of all things scientific, but that he keeps on getting me scurrying to my books
to verify what he is saying!!) but on the possible interpretation of what we
hear and the possibility that what we hear has other factors than the ones
mentioned.

I have a great regard for the EAR/BRAIN combination. It is a very sensitive
device. It has been said that 'if the eye had the sensitivity of the ear we
would be able to see a torch bulb on the moon' (no, I can't quote source) Think
of the tremendously complex task you do when listening to a full blooded
symphony orchestra. You can follow individual lines, hear two or three strands
of melody as distinct entities in a whole msihmash of other things going on.(and
hear that irritating kid five rows away chatting to its Mum. In a party,(old
fashioned cocktail party) you can hear and follow three or four conversations
going on at once. You can hear the wiggles on a vinyl recordwhich are only a
few millionths of an inch high in amongst other things going on. I say that you
can hear the differences caused by the materials used in a harmonica, you may
not be able to quantify it exactly, which makes scientists curl up at the edges,
but it is a factor in the overall sound production.
One gross effect of altering a system in an 'insignificant' way. (OK I know
that this instrument is meant to resonate.) I have a very good guitar. I did
some work on the machine heads (the twiddly bits at the end) and, whilst the
glue was drying I left a clamp, (about 4 ounces, 100Grams) attached. The guitar
sound was different. Took the clamp off and the sound brightened up again. Yes
I do know why it happened and is not a harp discussion, it does illustrate that
the unexpected can upset an obvious argument. Of COURSE the machine head area
doesn't influence the sound of a guitar .... Whoops.

Vern mentions blind testing of 'an old Italian violin' and a modern violin and a
set of listeners not being able to hear the difference. Was that a GOOD old
italian violin, or one of the rubbishy ones which have survived. Age does not
necessarily improve quality (except in Vern's and my cases). Point minus one
to Vern.
Vern also mentions that you cannot, blind tell the difference between a blow and
draw note. Rubbish, I say. So I tried it to prove my point ... and couldn't. I
had been confusing in my own mind the difference between getting a pupil to play
the thing so that there appeared to be no difference in the way the note was
attacked and the actual sound the harp makes. The harp I did this on was a
S-50. I think there is a little difference in the high frequency content, but
I wouldn't be able to say which was which individually just by hearing an
isolated note played out of context. Point one to Vern.

Douglas T