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Repairman77

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Reply with quote  #1 
Looking at the pages of Indian stringed instruments on these pages it struck me odd that none have sound holes like European/Western instruments. Almost all of these do; Guitar, ukulele, mandolin, etc.

Is there a specific reason or is it down to 'they've always been made that way'?

I wonder if anyone has experimented; surely the volume would be increased with a sound hole on the top of a sitar, etc.?

Just curious,

Mike.
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fossesitar

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Reply with quote  #2 
I am not sure the instrument would be louder except at certain frequecies.

This is about what is called a "Helmholtz Resonator", which is essentially
a sound chamber with a hole in it open to the outside. The acoustics are
different between a Helmhotz Resonator and a close box. In a nutshell,
a closed (sealed) sound chamber has a resonance point higher in the
frequency range than if it has a hole added. Further, the sealed box will
roll off bass response at 12 decibels (db) oer octave from the resonance
point down, whereas the sound chamber witha hole will roll off bass at
18 db per octave. The hole size versus box size must be "tuned" in order
for the response to be smooth and not overly boomy or having a hollow
point in the frequency spectrum. All amplified instruments at least those
in Nashville close OFF the sound hole to avoid or reduce feedback. Some
Indian Classical Instruments do have sound holes, even sitars sometimes
have very tiny ones, surbahars may have bigger, veenas more so, it is just
an individual thing but in general sealed box is easier to setup and optimize.
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Repairman77

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Reply with quote  #3 
Thanks for the explanation fossesitar.
In other words the absence of the sound hole increases bass response which is useful.
Makes sense to me now.
Mike.
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fossesitar

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Reply with quote  #4 
Actually the bass response is somewhat LESS with a sealed box Repairman,
which is why Helmholtz Resonators are used for many loudspeakers (they
are referred to as a ported cabinet in this application). Even though the
bass rolloff is more gradual with a sealed box, the resonant frequency is
quite a bit higher than a ported box can be. In fact the resonant frequency
can be tuned to extend the "flat" bass response by about 1/2 octave in a
well designed ported loudspeaker - but then the bass does fall off very
rapidly at 18db per octave below that. The F-holes in a violin for example
do make the sound cavity of a violin into a helmholtz resonator but as I
posted above, ported cavities need to be tuned carefully to avoid anomalies
and this is why Thiele-Small parameters of a loudspeaker must be used to
design a ported loudspeaker enclosure. Sealed chambers are much easier
to work with as they are simpler and therefore predictable. A sitar for
example DOES have a port at the top of the hollow neck (where the much
maligned upper toomba resides) but I sealed that on my acoustic. GF
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John

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Reply with quote  #5 
I think the term 'soundhole' is a bit of a misnomer, since the vast majority of the audible mechanical vibration (aka sound) of a stringed instrument (be it a piano or a sitar) comes from the secondary vibrator (the soundboard), tabli in the case of a sitar, which is coupled to the primary vibrator (the string). Imagine a tuning fork as the primary vibrator - not capable of moving much air by itself. Stick it on a table and, hey presto, it gets louder. So it is with stringed instruments. The hole's main function/s is/are to allow greater vibration of the soundboard and to facilitate the movement of air in & out of the chamber resonator.

Things get a little more complicated when you introduce the hollow neck, which is home to a vibrating column of air. The physical properties of vibrating air columns vary depending on whether they are open or closed at either end. It's worth pointing out that, in a vibrating air column that is open at both ends, only about 1% of the energy used to excite the air column is transferred out the other end. The rest is reflected back by the change in air pressure between the column and the environment, which is how the necessary standing wave is set up in the first place.

I could probably do a better job of explaining this, but I'm reeealy tired!

PS I always thought the holes on a sitar where more to do with further seasoning of the materials than anything else..?

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Repairman77

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Reply with quote  #6 
Many thanks chaps; I'm understanding it a lot better now.

Mike.
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david

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Reply with quote  #7 
This brings up another point. That is the topic of impedance matching. The reason that a tuning fork does not make a sound in isolation is because it is just not able to impart a significant amount of energy to the surrounding air. This is an extreme example of an impedance mismatch.

Impedance matching is especially important in describing both the the sustain as well as the volume of the instrument of the instrument. If this impedance matching is very efficient, the instrument tends to be loud, but have a poor sustain. However if the impedance matching is not very efficient, then it tends to have a lower volume but with a longer sustain. A lot of instrument design is geared toward having just the right amount of matching.

My understanding is that the sound holes improve the efficiency of this impedance matching, but this efficiency is largely confined to the lower frequencies.

This brings us to the topic of the sympathetic strings.

We must remember that you do not get something from nothing. There is only a certain amount of acoustic energy available. It takes energy to drive a helmholtz resonator. It also takes energy to drive the sympathetic strings. Since there is only a finite amount of energy available, it may be that long ago Instrument makers realised that they had to make a choice. They had to decide whether they wanted to support better bass (helmholtz resonator) or a more reverberant sound (Sympathetic strings).

Let as carry this line of conjecture further. At one time many European instruments also had sympathetic strings. Presumably they were also faced with the same decisions to make as per the allocation of acoustic energy. But the European instrument makers decided to go with an improved bass at the expense of a reverberant sound.

Why? (I might rhetorically ask.)

I think that the answer may be found in the acoustics of the performance venues. European performance venues were highly reverberant and I doubt that the presence of sympathetic strings would have made much difference. However, North Indian musical instruments have a strong mark of the "Kotha" in their construction. (I realise that many Indian readers may be uncomfortable with this.) These performance venues were much smaller and consequently less reverberant. Therefore, sympathetic strings may have been deemed to be more important than improved bass.

Please excuse me if I digress a bit, but a smaller room as one might find in the kothas does not necessarily have to be less reverberant than a large concert hall. However due to something known as the "Haas effect" it will appear to be less reverberant. From the standpoint of music, appearing to be less reverberant and actually being less reverberant are really about the same.

I realise that this post may have digressed a bit from the topic of sound holes, but I think that it does bring up the question as to why these things developed as they did.


Peace

David Courtney
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fossesitar

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Reply with quote  #8 
Excellent post David, than you very much for further clarifying a very murky subject.
I would add to your conjectures that ICM is/was probably performed outdoors in the
open air (a completely non-reverberant "room") a lot more than western due to the
climate among many other factors. Even to this day the big music festivals in India
(Calcutta for one example) are performed under huge tents......
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nicneufeld

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Reply with quote  #9 
The ideal room or environment for sitar music, especially, is an interesting question. Smaller rooms particularly seem to be ideal for me, because when I tried playing in a medium-large hall (one that a classical guitar would sound glorious in) I was surprised how dead it sounded, almost like the tarb and the room resonance were somehow cancelling each other out, or confusing each other. When I've played outside, it seems like a lot of the real subtleties get washed out in the quiet ambient noise. That said, UVK and UIK playing in the Taj Mahal (Raag Chandni Kedar, "Night at the Taj") was one example of heavy natural reverb that sounded very beautiful to me. The growl of a surbahar in a place like that!

My sitar, a "studio" model with a carved wooden tumba, has a sound hole. The electronics in it were worthless so I took off the jackplate while removing them, and didn't bother to replace it!
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Repairman77

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Reply with quote  #10 
Many thanks David and niceufeld for elaborating on the topic.
It's quite amazing how complex instrument design is.

May I take the opportunity to thank David for such an interesting and informative site.

Mike.
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yussef ali k

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Reply with quote  #11 
Hi, all: nice subject, some learning: thanks!
Please let me add (& please care to reply):

I have seen a sitar in which the 2 plastic peacock inserts were actually removable covers (no calculations on hole size) & had an ustad for a listener in the simple experience:

1 of us plucking all main strings open (KP, tarbs muted) at their middle/12th fret, then grabbing & moving the sitar to R/Left (the 'listener' stood still, right in front of the player):

taking turns at it we agreed we found/heard:
1) a much bigger difference w/ it (open peacocks)than any other sitar in the Ud.'s house;
2) The difference was there, though not as noticeable when we A/B'd between w/ & w/out peacock covers.

P.S.: I've been told the 2 very tiny holes on those peacocks are for seasoning (=air in & out), but then (as pointed out above) why bigger holes on some instruments?
Have fun.
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yussef ali k

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Reply with quote  #12 
(- Oooops: sorry!)

As to clarify my above post:
The increased sound happened to be felt when,(pulling the sitar to right & left right after plucking) at the point 1 faced the holes, compared to the peghead end.
(Hope you'll understand this 3rd rate writing).
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JRJ

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Reply with quote  #13 
Can i just follow up with a question that seemed to be missed with the above discussion? ; What about the huge hole with sitars that have an upper
tumba? I can hear a resonate sound when the upper tumba is installed and have thought that a sound hole in the lower tumba facing toward
the player's ears would increase the "stereo-sonic-resonate effect:-)

It has become very popular in acoustic guitar design to add a second
sound hole that is primarily for the player.
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yussef ali k

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Reply with quote  #14 
Hi, all.
JRJ,
Take a look at that 2nd tumba on the sarod played by Ken Zuckerman: it seems to be there.
Have fun.
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plectum

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Reply with quote  #15 
At least for Maihar sarod, the second tumba functions as nothing more than an ornamental stand....so soundhole of not, does not really matter. The sound really comes from the goatskin covered drum. Amjad ali does not have a second tumba in his instrument. As for Shajahanpur sarod, I am not the most informed person on this, but I think traditionally they also did not have a second tumba. Radhubabu and Buddhababu made extensive changes in the instruments they played/play and incorporated 2nd tumba, whether this has any effect in sound production, I would like to know.

An interesting picture is this one where radhubabu plays an instrument with a 2nd tumba but his student Pt. Samarendra Sikdar plays a traditional one.

http://www.sarodia.com/images/Radhika_Mohan.jpg

Another intersting point is that of a Rudraveena, which neither has a soundhole nor sympathetic strings....so the whole energy is transferred in the form of vibration through the player's spine....How does that feel!!!!

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You know, music, art - these are not just little decorations to make life prettier. They're very deep necessities which people cannot live without. ~~ Pablo Picasso
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