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

[Michelle LeFree <mlefree@xxxxxxxxxxxxxxxxxxxxxx>]

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.