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H.R.Fisher

Thin top correction?

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   What is the method used to correct a too thin area on a spruce top. The violin in consideration has an area on the lower left bout that is super activated when playing the open A causing an unusual loud unpleasant sound. I am thinking of building it up with layers of hide glue and saw dust. What are the recommended solutions.  Thanks in advance,   Henry

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I have had the same problem with some violas and have added thin but high  braces across the area on the outside of the top plate.

The braces were gradually reduced in height to remove excess wood until the problem was just beginning to emerge again and then I stopped the reductions.

Of course this was done on violas so nobody cares about their appearance.  For violins I suggest you do the same thing on the inside surface but this then requires several plate removals which can damage the plate edge.  I glue a rim of 3 ply 0.8mm thick birch plywood on the top plate edge to prevent pullout of the spruce wood.

 

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I once had thin areas under the f-holes of a cello which I patched -- chalk-fitting and gluing additional wood -- before closing the box.  There appeared to be no adverse effects.  In fact, the cello was wolf-less.  Leaving those areas thicker in the original build is thought by some to minimize wolf tones in cellos.

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I would not use sawdust, but i used some 4-5 cm plane shavings to patch a few thin spots. Just glue in and sand smooth. It looks horrible but seems to work fine :)

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If the instrument is worth correcting, chalk fitting a patch to the area would an ideal repair. I wouldn’t recommend a glue and sawdust or other filler because the density of the top is likely to be adversely affected. Hide glue is quite hard when dry, so a heavy application could stiffen the top more than you want.

Have you confirmed that the spot is too thin with a caliper? I’d advise against removing the top unless it’s certain that the instrument needs to be opened up. 

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8 minutes ago, The Violin Beautiful said:

If the instrument is worth correcting, chalk fitting a patch to the area would an ideal repair. I wouldn’t recommend a glue and sawdust or other filler because the density of the top is likely to be adversely affected. Hide glue is quite hard when dry, so a heavy application could stiffen the top more than you want.

Have you confirmed that the spot is too thin with a caliper? I’d advise against removing the top unless it’s certain that the instrument needs to be opened up. 

I am only assuming it's too thin because  the area  vibrates excessively when the open note is bowed. When I put a finger on the spot it quiets down. Are you suggesting there may be another cause?

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If you do have to open it up, you might consider gluing a layer of linen over the area. simple to do, totally reversible, and will strengthen the area without adding excessive stiffness or weight.

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1 hour ago, H.R.Fisher said:

I am only assuming it's too thin because  the area  vibrates excessively when the open note is bowed.

Some areas vibrate "excessively" on the most coveted violins in the world. ;)

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58 minutes ago, David Burgess said:

Some areas vibrate "excessively" on the most coveted violins in the world. ;)

May be - but to be one of them, these excessive vibrations have to sound nice - not unpleasant , as the OP told. Besides my assumption, that in general strong resonances never are very fine - better to have higher valleys.

The violin of H.R. Fischer seems to have a too strong/instable B1-  resonance. The usual recommendations to avoid wolves by more thickness below the left f-hole concern the B1 +  ( typical wolf) - resonance, isn´t it ?

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1 hour ago, jacobsaunders said:

If you made the Instrument, you can stick whatever you like in it. If it is a nice antique one, you should leave it alone.

However there seem to be many patches and more things inside nice antique violins.

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6 hours ago, H.R.Fisher said:

I am only assuming it's too thin because  the area  vibrates excessively when the open note is bowed. When I put a finger on the spot it quiets down. Are you suggesting there may be another cause?

I can’t tell what the cause is for sure, but it’s possible it’s something else. Whenever I hear that there’s a problem with sound originating from the bottom left bout, my instinct is to check for an open seam first. That’s an area of heavy contact, so it’s more susceptible. That doesn’t mean it’s the cause of your problem, just something to double check. 

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I can see a loose bassbar end causing unpleasant resonances in lower bout. or loose lining... many things.

I just don't grab the idea that small localized area creates "speaker cone" effect that produces sound that is hearable a separate sound from overall violin tone.

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I would start with blue tak on the outside to determine that mass added to this area will in fact help, if so, install either a patch as suggested by VB or a mini bass bar "strut" which slightly opposes the grain on the inside after pulling the top. The patch will add mass with some stiffening where the bass bar will add mass with more local stiffening which may or may not help more than the patch alone. In either case the wood used should be very well seasoned 

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3 hours ago, jezzupe said:

I would start with blue tak on the outside to determine that mass added to this area will in fact help

If the blue tak works, you could just vanish over that, and leave it as it is:)

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6 hours ago, jacobsaunders said:

If the blue tak works, you could just vanish over that, and leave it as it is:)

Ya I think they call that one the "Lord Wallace' :)

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