Re: [Harp-L] Speaking of amp stands...



Vern writes:
It is easy to over-estimate the directionality of an amp. The mental image of a beam of sound emanating from the front of the amp like a beam of light is unrealistic. Because the speakers are small with respect to the the wavelengths of sound being produced, diffraction* causes the sound waves to disperse almost equally in the hemisphere to the front of the amp. A better mental image would be to think of throwing the amp into a calm lake and watching the resulting waves.

Turning the amp at various angles to a sound level meter and plotting the readings would show the directionality of the amp. A cruder experiment would be to determine the minimum angle that could be detected by a blindfolded listener.

* diffraction: seehttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/diffrac.html

Vern

Amazing! Along with his usual flair at describing how physical and acoustic science principles apply to the real world of harmonica players, Vern has just issued the very first ~footnoted~ Harp-L post I can recall. In fact, perhaps the first footnoted email list post I can recall ever! Gotta love 'im! :-)


What is it, 83 years young? And still pushing envelopes. Heck, I'll be delighted to even be able to ~say~ "harmonica" at that age.

Thanks again, Vern!

Michelle

PS: Another slightly less crude way to demonstrate an amp's angular sonic directivity might be to use a standard stage mic' as a sound level meter placed at equidistant angular increments in front of the speaker as Vern suggests. Plot the amplitude of the PA's sound level meter as a function of the angle in front of the speaker.




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