Re: [Harp-L] Cover Material and shape

["Vern Smith" <jevern@xxxxxxx>]

----- Original Message ----- 
From: "Joseph Bernard" <bjosephmex@xxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Sunday, July 13, 2008 10:46 AM
Subject: [Harp-L] Cover Material and shape


> I just took the carpet out of my son´s room and put in a marble floor. 
> I´m rather certain that the sound is different, even if he is playing the 
> same Hertz.

Of course it is.  The carpet is more absorbent than the marble.  You are 
hearing much more reflected sound from the floor that arrives, maybe via the 
walls or ceiling, at your ear a few milliseconds later than the sound 
directly from the harp.  Before electronic reverb was readily available, 
some of the old harmonica trios recorded in hotel bathrooms with tile and 
marble floors and walls.  We all enjoy singing in the shower.

I recently listened to a DVD of our band performance that was played in a 
rehearsal room that had mirrors (for dance practice) on the end walls.  The 
sound had a terrible "boomey" distortion on certain notes.  When I listened 
to the DVD at home, the problem disappeared.  The "live" room was resonating 
at certain frequencies and the TV just happencd to be placed at a node of 
the standing wave.  I went back and sang to the room at the location of the 
TV and it boomed for me too.  When I moved a few feet to either side, the 
effect was greatly reduced. This also explains why we have trouble with 
feedback when we use mics and speakers in that room.

Your floor dimensions are also much longer than the wavelengths of the sound 
waves.  Objects that are small with respect to the wavelengths, such as 
harmonicas, do not affect sound the same way.   The frequency of C4 (middle 
C, hole 1 blow on a C harp)  is about 262 hz.  The speed of sound in air at 
68 degF is 1129 feet/sec.   Thus the wavelength of middle C is 1129/262 or 
about 4.3 feet.  Every higher octave reduces that length by half.  Even the 
wavelength of C7, the highest note on a C harp is about 6.5 inches, longer 
than any dimension of a diatonic.

Except for the reeds, the parts of a harmonica are small, stiff, filligreed, 
and in contact with materials of different densities and damping 
factors...including hands.  If you tried to design a structure that would 
not respond to sound, you could hardly do better than the harmonica.

Vern
Visit my harmonica website www.Hands-Free-Chromatic.7p.com