soundpost science

September 20, 2011 at 06:20 PM ·

i've got a primitive fiddle-like instrument (lira calabrese) that requires me to make my own soundposts.  unlike the violin, the sound post is in direct contact with the bridge - a portion of the bridge juts out over the sound hole on the treble side.  i understand that pine is the preferred wood to use for these but bamboo seems to work as well.

what's the physics of soundposts? - how do they work?  obviously, they transfer vibration from the bridge to the back of the instrument but, regarding the minutia - 

- does diameter matter? (is there a maximum and minimum?)

- would a soundpost tapered at the end intensify vibration?

- thin strips of wood are traditionally used for the lira: should it have a point at the end, pressing into the back; a knife-edge or be totally flat and in full contact?

- are round soundposts more effective than flat?

- pine has soft wood between harder grain: through which is the vibration conveyed?

- i read here (hope i have this right) that soundposts are more effective if their grain runs contrary to the bridge grain: does cross grain matched with vertical grain make for better transference or should like be matched with like (vertical grain bridge + vertical grain soundpost?)

i've got a stanley-knife; a heap of pine laths in the studio and winter's coming on - any help would be very much appreciated - thank you.

Replies (20)

September 20, 2011 at 09:03 PM ·

I'm sure this will generate some interesting feedback. I'm not a luthier, I do have an engineering background, and I do some woodworking, and I have read some papers on violin sound. So here's my two cents (will be interesting to hear other opinions)


Physics - besides transfering vibration to the back, it also limits the movement and vibration of the faceplate by the higher strings. The bridge will be less restricted on the opposite side (G String), and thus cause the faceplate to vibrate more for the lower notes. I suspect that is also where the bass bar comes in, as it would spread that movement out across the faceplate.

Diameter- I would think that its big enough to handle and manipulate easily, and also has enough surface area to provide some support to the faceplate, and also so that it doesn't bend under the pressure from the bridge/strings, without potentially poking thru or denting the faceplate underside. But it does have to be smaller than the F-hole to get it in there.

Tapered soundpost....I think you run the risk of the tip putting too much pressure on the soft faceplate, potentially poking thru or damaging the wood.

This strips of wood - sorry, I don't understand

Round vs flat - I think as long as long as stiffness is equal and you can fit it thru the F-holes, I would bet it doesn't matter.

Grain of the wood. I have to beleive that the grain direction of the soundpost is to provide strength. If the grain was perpendicular to the length, it would snap while it is being made....

soft vs hard wood (or the grain) and vibration transmission. Vibrations travel fastest and with less loss thru harder materials. Whether anyones ever compared a maple soundpost to a pine soundpost on the same violin, same position, would be interesting to hear about....

Be careful with that stanley knife......


September 20, 2011 at 09:44 PM ·

Grain direction is relative to the top.  You don’t want the winter grain lines to be parallel as they can interlock with each other.  It’s just a practical thing–any other issues don’t even get looked at because of that.

September 21, 2011 at 08:13 AM ·

thank you both.  keeping the grain aligned makes sense - putting the grain at odds would act as a barrier, me thinks.  i also have some dried sticks of a very light, unknown wood (acacia?) which produce a brittle ringing sound when dropped on the tiles in our kitchen.  bolstering support of the soundboard on the treble side is something i hadn't considered but i don't know if these "musical" sticks would be strong enough to take the pressure.  the instrument arrived with a roughly made soundpost that ended in quite a sharp point.  i think you're correct in advising against having anything that sharp jabbed into the soft bottom plate.  unlike the violin, the sound holes on the lira are proper holes - one beside the other with a narrow gap in between, on which you place the bridge - lots of room to maneuver the sound post into position.  i tried placing a sound post under the soundboard - alà the violin - but it made a very weak sound - (soundboard on the lira is flat, unlike the beveled surface of the violin - could that be the reason?)

thanks again - bill

September 21, 2011 at 05:09 PM ·

I once saw a folk-fiddler's violin (perhaps a VSO in that instance?) where the soundpost was held in place by a tiny nail hammered through the back of the fiddle  -  I would have used a small screw :-).  Not to be recommended, even for a VSO. Thankfully, very few players are that crass.


September 21, 2011 at 09:42 PM ·

I'm going to leave this alone for the time being. There's much that isn't known about the function of orchestral stringed instrument soundposts, let alone the offbeat instruments, which have received much less analytical attention.

Arnie has given some plausible explanations, and Andres has provided a solid and generally accepted explanation for one factor, the orientation of the grain in the wood.

September 22, 2011 at 07:43 AM ·

chopsticks make wonderful sound posts - kitchen physics - ever onward! ...

September 22, 2011 at 11:19 PM ·

An old time fiddler here in town had a string attached to the sound post, through the treble f hole and by putting tension on the string he could vary the sound. He had learned that from other fiddlers. I forgot to ask if his soundpost ever fell over during a performance.

September 24, 2011 at 02:36 PM ·

Real fiddlers don't do "performances"! They just play their music and if there happens to be people listening and money ends up in the proverbial hat, well, that's just a bonus.

September 26, 2011 at 01:59 PM ·

There is great effect of beautiful resonance produce from proper sound post adjustment. If you have excellent sound post - spruce wood then your choice of adjustment is either brilliant or sweet tone...I have my SP adjuster and as i observe there are sweet and brilliant spots at the bottom right before the bridge...




September 27, 2011 at 05:24 PM ·

I am not a luthier officially, but I work with a lot of them and I have seen this process a number of times on the violin.

For a violin, the diameter of the sound post needs to be about 6 mm.  If it's too thick or too thin, the sound won't project as well.  The length needs to be exact.  A sound post that is too long can damage the plates beyond repair.  

The ends of the sound post should be flush with curves of the inside of the violin.  The ends have to have full contact with plates otherwise it won't work.  Every violin is different so the shape on the ends will be a little different.  To attain this is a meticulous process.  You have to start with a piece that is too long and cut away bit by bit.  You have to do this by working through the f-holes and looking through the hole the end button leaves you when you remove it. I don't know if your lira has anything like this.  

The "perfect fit" is when the sound post is standing straight up and is snug against the two plates.  However, it should be able to fall out when you remove the strings and lightly squeeze the sides.  

The pine you have is pretty standard as far as materials go.  Other woods used in violin making are maple and spruce.

September 28, 2011 at 01:06 AM ·

would there be any advantage in having a hollow core (wooden tube) in the center of the sound post?

September 29, 2011 at 02:20 AM ·

 Hi Rachel:

Your suggestion here is pretty helpful in terms of mathematical calculation due to the core of that certain point has various effects on bowed string instrument. I'll try at home your idea of fixing the correct placement in millimeter adjustment. There are times that violin maker is not around you to help, my point is we need to do it by ourselves but the caution is dangerous. I got an old friend an amateur violinist/luthier.He has great master violins sold from previous buyers but the thing was his error without professional help from violin maker. He damages the edge of the f-hole to due sound post adjustment. He uses fork instead of SOUND POST SETTER. I know that there are still amateurs out there. My concern is this valuable instrument not to destroy but of course absolute preservation for future use. Stradivari & others will not rise from the grave to build a new masterpiece.This is my campaign: Save the Great Italian fiddles, Educate the Amateurs!  




Caution to all who wishes to safeguard what i did to him because i want to safeguard this valuable fiddle was telling him of correct way of instrument care 

September 29, 2011 at 12:53 PM ·

Actually, that last procedure will indeed work, but only if it is preceded by a sacrifice of a goat to the appropriate gods. If you get the sacrifice wrong in the slightest particular the gods won't play ball - so don't dare to go out in a thunderstorm wearing armour.

September 29, 2011 at 03:28 PM ·

I just had a brilliant idea, and soon I'll be rich enough to be a Republican.  In the beginning there were great violins, and great violin makers.  They made bows too.  Slowly people adapted to the idea that the bow was of great importance to the overall sound, and now there are specialists in bow-making who charge as much for their products as folks were formerly willing to pay for the whole fiddle.  Now it seems the sound post is incredibly important too.  Therefore I've decided to become the first Sound Post Maker.  (Hopefully nobody thought of this already.)  I will make ONLY sound posts, and by virtue of this specialization alone, I will declare myself to be better at making a sound post than a generalist who makes whole violins.  My sound posts are starting at $10,000.  A little more if you want a shaft of pure gold running down the middle of it (because gold always makes things better).  Be the first to own a Deck Post.  Commissions accepted! 

September 29, 2011 at 06:23 PM ·

i've tried chickens and they worked pretty well - apollo and i both enjoyed them, each in his own fashion - but never a goat.  when you say: "rich as republican" - do you mean thick as a post?

thanks, john

September 29, 2011 at 08:57 PM ·

Hey Paul,

Finally a master!  Is there a discount if I order more than one sound post?  Also do you offer any in platinum?  I hear platinum is the new gold. :-)


September 30, 2011 at 02:08 AM ·

September 30, 2011 at 02:57 AM ·

Glass?  Platinum?  Mammoth Ivory?

Let's be Edisonian.  Let's slide the sound post out of some Strad that's sitting around collecting dust, create a precise 3D image, and then fashion thousands of sound posts out of various millable materials using readily available CAD/CAM technology. 

But wait... what's the function of the sound post?  Surely that function can be interfaced to available knowledge in materials science and engineering to select the right substance a priori.  It might be wood after all. 

September 30, 2011 at 10:44 AM ·

Carbon fiber soundpost – any thoughts?

September 30, 2011 at 11:25 AM ·

 how come guitar does not have a sound post?  will it sound different with one?

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