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Re: OT:Singing bowl measurements

Hi Bowling Freaks,

Unfortunately I have no bowl in my Setup and so I only can guess about
this phenomen,discussed so strong in this Forum ! Really interesting.

I still belive-as summary of all bowling entries-that this mysterious
low tone is a psychoacoustic effects.Our ear/brain recognizes the
real existing overtones.The fundamental is missing.So our brain adds
to the real existing harmonics the fundamental/not really hearable
Prime-tone of the harmonic sectrum.This phenomen is well known and used
in several signal processors,to make a sound more rich and fat.
Exciters simply said.
The question is,in wich relation the real appearing harmonics exist.
Harmonics are the multiple of the fundamental tone.
                1:2:3:4:5 .....etc.
So if overtones from 2 to infinity will be heard,our brain will add
the 1-fundamental to this spectrum.
This is the simple harmonic scale-Fourier transformation.

The problem appears,when the relation is odd.Best traces in a bell
sound.This bell sound has usually a harmonic spectrum of :
                1:1,1:2,2:3,3:4,4:5,5 and so on
So our brain gets tricked again.It will "calculate" this harmonic
spectrum until it is back to the simple relation:
                1:2:3:4 and so on.....
But it will not be the same as the real harmonic spectrum.If the 
fundamental tone of the bell (1) is still in listenable frequency-
more then 20Hz,it will spoil a little bit the harmonic spectrum of
a simple Fourier-series.A kind of odd tone will appear,but it sounds
still harmonic.Because the fundamental tone is nearly eliminated in 

Another thing is,how close we are to the instrument when we play it.
When I play the bowl-so I am seated beside it,I recognize more
frequencies as the audient who is a little far away.

I had once had the chance to play a Sitar-like instrument.Not really a 
Sitar-but also an indian instrument.Sorry-I forgot the correct name ! 
              (Have to do some research in my books)
The drastic moment was,when I listened to the play of this instrument
as audient,with a distance of 2 meters to the play.The sound was
incredible thin and went on like "pling pling pling" or a non amplified
electric guitar.
The extreme happened,when I did hold this instrument in my own hands
and tried to play on it.The sound of it was fat and extraordinary.
How could this appear ? First thin and then fat sounding.

It could be described,that this instrument is only created for 
the player only and not for audients.This instrument has a Sitar look,
with two resonance bodies(bowls?).One Pumpkinsized resonator near to 
the headstock and one near the bridge.
Usually this instrument is made according to the body sizes of the
player.A body instrument relation.

What happens ? This instrument-simply said- is resonating through the
whole body of the player.So he has the experience of a full fat sound.
If you are only audient,then only "Pling Pling" comes to your ear and 
you donīt understand why the player is so fascinated about the sound.

So the secret of this instrument could be the not only the ear-instrument
interaction.It is also an interaction with the resonating capacity
of the body.Vibrations can be also recognized by the body.

Maybe this low tone experience could be similar to the this body-
instrument resonance.

If this mystery low of tone of the bowl also appears when we are audients
and have a distance to the event,then this theory is not valid and I 
have to come back to the psycoacoustic phenomen,where the brain adds
the missing funadamental.

The resonance factor of the venue could also be an explanation,but not
as strong as the other two theories.

I think-donīt know-that the bowl has not the "Volume" capacity to make
a big church Hall resonate.
A church Hall(Room) is also part of the acoustic.It has its own
resonating capacity with fixed frequencies and delay interactions.
But if the amount of the source(bowl) is not strong enough  this 
resonance  can not "start in" and so the typical resonance frequencies
will not appear.
Before an "acousitc Model" will resonate,there must be enough source-
energy to start the resonating process.
In this case of physical modelling,a hollow body of a guitar is
similar to a big cathreadal room.Both will resonate(differently) when 
a source starts the acoustic process.
In a guitar the strings are the(selfoscilating sources) the hollow
body is the resonator.Each guitarist knows,that the size of the 
body of a guitar can change the sound extremley,besides other factors.

So I think,that the surrounding surface is not the reason,that this
fundamental harmonic will appear in real.It can has an effect,but is
not the reason for the fundamentals appearing.

So it can be only the psychoacoustic effect or the "body-instrument-
vibration index",maybe also an interaction of both,wich prepares us 
this fundamental,mystery tone.

But this is only a guess from my side.The scientific about the way
we hear,or our hearing can be tricked is still not yet discovered
totally.There are still more questions outside as answers.
This needs at least further research.


Matthias Grob schrieb:
> >My son Eli and I studied the output of his singing bowl with a
> >spectrogram.
> great! Thank you Bret and Eli!
> >I overstated the bowls size in my earlier post.  It is 117 mm outside
> >diameter (about 4 9/16"), about 63mm high, rounded, and about 2mm thick
> >at the top edge.
> >
> >The spectrogram allows us to see, in a scrolling chart, over time in
> >the horizontal axis, the frequency components in the vertical axis,
> >with the amplitude of each component indicated by shading.  The lowest
> >tone recorded was about 390 hz, approximately a G.  The first overtone
> >was at about 1070 hz, the next at about 1950 hz.  These measurements
> >are +/5.4 hz with the scale and tool used.
> hm,,, for me overtones are multiples...
> >We attempted to match the tone by ear, to a synth patch that had
> >fundamental and 2 harmonics (390hz,1170hz, 1950hz , fund, 3rd and 5th
> >harmonics).  We compared the audibly matched synth tone to the bowls
> >tone in the spectrogram.  The fundamentals matched in frequency.  What
> >we heard as tones in the bowl, matched what we heard on a minimal
> >overtone synth oscillator.  These sounds differ by the first overtone
> >frequency.  The synth has 1170hz (3rd harmonic) and the bowl has about
> >1070hz which is about 2.74 times the fundamental (390hz).
> may this mean that 390 is not the fundamental?
> Then again, I cannot find a fundamental with overtones 390 and 1070...
> I can easily imagine several fundamentals, so 390 and 1070 could be
> independent vibrations (axial-radial, for esample).
> But why is the third harmonic 1170 present? Did the 1070 "eat" it?
> More even I wonder now how they select the bowls: Could yours be a
> good one because the 5th harmonic appears cleanly... or a cheap one
> because the 3rd does not?  :-)
> >We found no illusion between perceived pitch, and measure pitch with
> >the 2 types of sounds.  The beats in the rubbed bowl do change the
> >character of the sound dramatically, however.
> I am not sure I understand what the beating sounds like...
> Is it a subharmonic maybe?
> Interference between the stick movement and some fundamental?
> --
>           ---> http://Matthias.Grob.org