Re: [Harp-L] Speaking of amp stands...
- To: harp-l@xxxxxxxxxx
- Subject: Re: [Harp-L] Speaking of amp stands...
- From: Michelle LeFree <mlefree@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 31 Jan 2011 11:27:46 -0700
- In-reply-to: <201101311406.p0VE5njH029753@harp-l.com>
- References: <201101311406.p0VE5njH029753@harp-l.com>
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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
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!
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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