Looking for some advice on soundboard and bridge interaction on lyre.

[David Harrison]

Hello

I've made a 10 string lyre and now im looking to make improvements on it.

Something I noticed was the pressure from the strings was pushing down on the bridge was making the soundboard concave and this created a gap in the middle under my bridge. I put some wedges under the gap just to experiment and found the volume of each string sound would change depending on where the contact was best between the bridge and the soundboard.

Anyway what i've done to glue a very thin strip with pointed top to the inside of the soundbox. This keeps the soundboard flat. I've also make a bridge more like the type i've seen on banjos like this..

Look at this

What im thinking is for optimal sound i need the bridge in contact all the way along with more or less equal pressure.

Does anyone have any advice? Does it sound like i'm doing the right kind of thing here?

Thanks

[Jim McConkey]

Hi David, Please note that we require that all images posted here be original or ones that you have a right to publish, because otherwise it is a copyright violation. You are welcome to add a link to someone else's work instead, and I have changed your picture into a link.

[David Harrison]

Ah sorry about that.

[Michael Lewis]

Can you put up a pic of the deformation? It might help to get an over all view of your instrument so we can see what you are dealing with.

[David Harrison]

Heres a picture, unfortunately I dont have one with the warping but this shows it after i've added the changes. The warping was just a concaveness at the centre of the soundboard, previously the bridge was a much thicker solid piece of wood. There would normally be 10 strings on the instrment too.

The changes i've made seem to have worked, but im just wondering if other people anyone can tell me if theres anything better I could be doing instead.

[Michael Lewis]

Are there any internal braces? And how thick is the soundboard?

[David Harrison]

No internal bracing, I wasnt sure an instrument this side would require it. Is bracing generally considered a better option than a support under the board which runs between the back and soundboard?

I seem to remember the soundboard is about 2-3mm, sorry I cant be more precise.

[Barry Daniels]

Bracing good.

[David Harrison]

Perhaps ill have to learn how to do that and then compare the two techniques.

[Barry Daniels]

Let me revise that:

Bracing good; soundposts bad. (at least for plucked instruments, generally speaking, don't hold me to this)

[Michael Lewis]

Well David, you've thrown a lot at the wall and some has stuck. Now you need to figure out what needs to be changed to make it all stick. The dip in the soundboard is most likely due to the string pressure against the unbraced top. The most obvious answer to this would be to put some sort of brace to counteract the dip. A really stiff and strong brace would flatten the soundboard but likely kill much of the acoustic property, so more likely something in between 'no brace' and the killer brace. As the maker it is up to you to determine what makes the best sound and strongest structure, likely a compromise between both ends of the spectrum. If you take it apart a few times and try different bracing ideas you will learn how it all relates, and at the conclusion you will have more real experience.

[Clay Schaeffer]

Hi David,
Another thing to keep in mind is that a bridge also functions as a brace. If you look at the bridges on the old "potato bug" mandolins you will see that they extend past either side of the strings. This helps spread the down pressure on the sound board over a greater area.