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Date: Wed, 18 Apr 2001 16:51:34 -0700
From: Grant Green
Subject: Re: [CB] Contrabass cats and cars

>The question for the list is, was the car behaving like:
>a.) An octo-contrabass ocarina, or
>b.) A stopped 32+ foot organ pipe? (A stopped 32-foot pipe
>blows about 8 Hz).
>The car in question is a VW Passat wagon, which is not anywhere
>near 32 feet long. Only the two rear door windows were open,
>each about 1/3, and the heater was on fan speed 2,
>non-recirculating. Needless to say, the windows were open just
>long enough to clear the air.

a.)  You're driving a self-propelled subcontrabass aeolian ocarina.
The interior of the car is too wide to form an acoustic "air column"
like an organ pipe, so it behaves more like a wine jug ;-)  Air
volumes that aren't "column shaped" typically act more like Helmholtz
resonators, where the resulting frequency is a function of the
enclosed volume and the area of the opening(s):
f = ( c * a^.25 ) / ( pi^1.2 * sqr( 2 * v) )

f = frequency in herz, cycles per second
c = velocity of sound = 1130 feet/second at 72 degrees F.
a = area of circular hole in square feet
v = volume of the vessel in cubic feet.

If we guess at a few numbers (and assume that the formula applies to
something the shape of a VW interior):  for area, let's assume the
windows are about 20" long, and that they were down 6".  This makes
the area (a) 240 in^2, or about 1.67 ft^2.  If we guess an interior
volume of about 200 cu ft, and plug everything into the equation, we
get a frequency of about 16 Hz.  I suspect that the interior shape
makes a difference, and possibly the hole shape...

>By the way, Grant, I visited the Contrabass page recently and
>noticed some pictures seem to have been added to the gallery.
>I checked out the bass harp - awesome! I'm not surprised that it
>doesn't draw - those reeds must be huge! Who would think E1
>would come from something that compact. What are the
>overall dimensions, anyway?

Yep, the reeds are pretty large, as harmonicas go.  I'll see if I can
remember to measure it tonight...


Grant Green        
Professional Fool  ->

From: "Bret Newton"
Date: Wed, 18 Apr 2001 20:49:32 -0500
Subject: [CB] Sarrusophone Help

I am having a problem with my sarrusophone.  I can't seem to figure out how
exactly to hold it.  There are 3 neck strap (4 with the one thats lying in
the case) and I can't make heads or tails out of any of them.  So if anyone
has any knowledge of this please help.  Also, if anyone is in the Dallas/Ft.
Worth area I will be playing the sarrus on Monday at UTA in the Beethoven 5.
  E-mail my privatly for more info.
Bret Newton

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Date: Thu, 19 Apr 2001 08:47:38 -0400
From: Lawrence de Martin
Subject: Re: [CB] Contrabass cats and cars

Craig wrote:

> From: bitwise
> ...I partially lowered the rear windows. Upon doing this, I immediately experienced a DEEP rumble
> - .... I estimate this was about
> 4-8 Hz, based on my being almost able to count individual cycles.
> The question for the list is, was the car behaving like:
> a.) An octo-contrabass ocarina, or
> b.) A stopped 32+ foot organ pipe?

Neither.  An Ocarina is a Helmholtz resonator where the air mass of the hole resonates with the
volume of the cavity.  The air mass of the area enclosed by the window edge is too small to produce
this low note.  An organ pipe resonance is based on the length in relation to the speed of sound
(as all orchestral wind instruments) and as you pointed out the car is less than 32'.

The car is an Aeolian resonator, which is based on vortex turbulence.  The  pressure on the outside
of the car is lowered by the Bernoulli principle, so it sucks air out.  This movement continues
until the pressure equalizes, but by then the air around the hole has momentum so it overshoots,
further reducing the internal pressure.  At some point, the "air knife" moving past the window cuts
off a piece of the internal air mass, and it snaps back.

> From: "Dave Spiegelthal"
> Subject: Re: [CB] Bass saxes and cat purrs
> I remember reading once that scientists still haven't figured out how such a small animal can
> produce such low frequencies.

Vocal chords are also Aeolian resonators, unlike cars they have a defined frequency from the
tightness of the chord and regulated air flow.  There is no limit to the bass frequency produced by
a small source, just a limit on the power.  Throttled air sources - sirens, wind and organ are
among the most efficient sound generators.

Humans can train to put out a lot of low frequency, like the monks of the Drepung Loseling
Monestery.  They have several recordings replete with dongchen (tibetan long horns) that document
that power.  Perhaps they learned this vocal technique from the sacred snow lions.

Larry de Martin

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