Re: OT-fundamentals in sound (was singing bowls)

[kevin <hideaway53@home.com>]

Hi Bret:

Just wanted to let you know, that was a great reply!  Clear,
straightforward...what can we say?  Your explanation of the link between
sound and air moved us!

Best,
Roctologists
aka LoOpdOctOrs


on 10/18/00 9:13 PM, Bret at echoplex@yahoo.com wrote:

> Lindsay,
> Sound is not 'moving air'.
> Sound is compression and rarefaction of air.  The difficulty with
> creating low frequency sound in air is not that you have to 'move' the
> air, but that you have to 'compress' and 'decompress (rarefact)' the
> air, at a given frequency.
> 
> This is difficult because of the impedance mismatch between a vibrating
> object (say a raw unmounted speaker cone) and the air.  That is, they
> do not couple well (it is an inefficient transfer of mechanical
> movement to compression of air).  Speaker box design helps to 'couple'
> the speaker to the air so that the speaker cone movement 'compresses'
> the air.  
> Horn speakers are the highest efficiency because they assist in
> coupling the air to the driver movement.  The horn diaphragm can be
> small, but if the horn couples the diaphragm to the air well it can
> create high spl at low frequencies (with small movement of the cone,
> ala Klipsch).  This conversion is more efficient in a horn speaker than
> a raw speaker.
> 
> These pressure waves in air (we call sound) radiate like the waves
> created in a pond when a rock is dropped into still water.  In water
> the waves radiate as a widening circle around the point of origin
> (until disturbed by objects in the water, or until they dissipate all
> their energy).  In air, sound pressure waves radiate and expand
> outwardly in spheres of compression and rarefaction radiating from the
> point of origin (until disturbed by objects, or until they dissipate
> all their energy).
> 
> A bowl 20" wide has a circumference of about 62.8".  I don't know how
> high your bowl is, but let's say it is 4" high, and let's say it is a
> cylinder shape.  So, the surface area of this bowl is about 251 square
> inches.  A 15" Loudspeaker has less than 176 square inches.
> 
> So, the surface area of a 20" bowl is greater than that of a 15"
> Loudspeaker.  
> 
> I can feel the intense, low freq vibration of these bowls in my hands,
> much like I feel the intense vibration of my 15" bass speaker, and like
> I feel the intense low freq vibration in gongs that I have.  These
> gongs are only about 12" in diameter (about 113 square inches of area).
> These small gongs generate a VERY LARGE, LOUD, LOW Freq sound that I
> both hear and FEEL with my skin.
> 
> The singing bowls radiating surface is shaped in a cylinder, or in
> rounded bowls somewhat spherical (excluding the top and bottom of the
> bowl).  This would assist the bowl in efficiently radiating the spheres
> of compression and rarefaction we call sound.
> 
> With an oscilloscope I will measure the low frequency generated by my
> small bowl (~6" diameter) to see if my assertion is correct (that the
> bowls truly do generate these low fundamentals that we hear).
> bret
> 
> --- lindsay@pavestone.com wrote:
>> 
>>> I just dont understand why bowls should not vibrate them?
>> 
>> Yes, the tones are too low for the bowl to physically produce them.
>> If you
>> think about it, bass notes are pretty darn large airwaves and
>> therefore
>> require pretty darn large instruments to produce them.  At 20Hz, the
>> wavelength is 56 feet long.  There's just no way a bowl 20" wide
>> weighing
>> eight pounds can move that much air with enough energy to produce the
>> tone.
>> Imagine how much more difficult it is to move 56 feet of air than,
>> say, a
>> mere 2.47 feet for a 440Hz A note.
>> 
> 
> 
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Messenger - Talk while you surf!  It's FREE.
> http://im.yahoo.com/
>