Double Bass Top-plate soundpost area support

Sebastianus

Sebastianus

Commercial User
May 19, 2024
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#1
upload_2024-5-27_19-13-4.png

Is it common to glue on a new double basses an support circle on a top plate soundpost contact area for preventing the possible cracks in future? (not my bass, just photo from Benedict Puglisi bass making movie on youtube).

I´ve seen it many times on the old repaired instruments but I am not sure about supporting the area preventively, because in my opinion the carefully well shaped soundpost should make no harm to the top plate.

I am asking because of working on my top graduation and I want to consider all possibilities to get the best long term results out of my instrument.
 
#4
even a perfectly fitted sound post wont prevent a sound post crack if the bass takes a direct hit.

What you see in old Basses is an inlaid patch to repair such a crack. It's very common. Usually the grain is offset by a few degrees so that the repair wood prevent the correct from opening again.

But what I think you are seeing in the photo, is a very thin veneer overlay which provides a smooth surface for setting the post, and may help preventing a sound crack in the future. Many makers do this, including me, and I don't think it hurts the sound at all.
 
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#5
Okay, so I will try to do that with hardwood veneer in slightly different fibre angle for getting some kind of plywood mechanical effect. I will do modal analysis and post there photos of vibrational characteristics in few mods before and after - visualised with Chladni patterns. Good experiment to maybe improve our understanding of this topic here on the forums...

Of course, tensions and therefore the acoustical behaviour along the plate changes a lot when the instrument is assembled and soundpost and bassbar is tensed, but anyway, we will see if there will be ,,any,, difference in the pattern on just bare plate with and without prophylactic inlay.
 
#6
I assume the added stiffness of the soundpost area can slightly alter the coloration or presence of overtones in the midrange. Overall the shaping (process) of the soundbar will have a greater impact on the sound, given a standard size, form and graduation of the topplate. I used a patch on the backplate for extra strength on a too thin graduated backplate .
 
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#7
The Chladni patterns has shown difference. Also the resonant frequency is about 2-3hz higher with the prophylactic plate.
1720204791705.png


I have to do something about the sound because the tone is really high and bright without the deep bass punch in the sound. I think it is also problem of the low quality board with some defects and extremely high density in the middle. 2nd mode is really stiff relative to 1st and 5th... 1 - 27Hz, 2 - 76Hz, 5 - 106Hz...
 
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#8
Sebastianus said:
The Chladni patterns has shown difference. Also the resonant frequency is about 2-3hz higher with the prophylactic plate.
View attachment 6972610

I have to do something about the sound because the tone is really high and bright without the deep bass punch in the sound. I think it is also problem of the low quality board with some defects and extremely high density in the middle. 2nd mode is really stiff relative to 1st and 5th... 1 - 27Hz, 2 - 76Hz, 5 - 106Hz...
Click to expand...
What are the thicknesses of the plate per area?
 
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