Live Back question

You can ask questions here about Trevor and Gerard's exciting new book on Luthiery.

Moderators: kiwigeo, Jeremy D

Post Reply
User avatar
ozziebluesman
Blackwood
Posts: 1529
Joined: Wed Oct 10, 2007 9:12 am
Location: Townsville
Contact:

Live Back question

Post by ozziebluesman » Mon Mar 25, 2013 10:06 pm

Hi Trevor,

I would like to have a go at your live back design. In the book you say thickness your back to about 3mm. How critical is that measurement. I have started an OM build with some nice quilted mahogany, When I thicknessed the back I was going to go with the standard four ladder brace design and have thicknessed it to 2.5 mm. Is that too thin for a live back design? If so, I will make sure I plan it in one of my next builds.

Thanks for your fabulous books, they are a great source for me to learn and be able to build a better guitar.

Cheers

Alan
"Play to express, not to impress"

Alan Hamley

http://www.hamleyfineguitars.com/

User avatar
Trevor Gore
Blackwood
Posts: 1605
Joined: Mon Jun 20, 2011 8:11 pm

Re: Live Back question

Post by Trevor Gore » Mon Mar 25, 2013 11:34 pm

Alan, the backs should be thicknessed using the same methodology as thicknessing the tops. Measure the Elong, Ecross and G using the tap test method, then use the infamous Equ. 4.5-7, but this time with a vibrational stiffness factor of f=55.

If you use very dense back wood, (> ~900Kg/m^3) you'll need to knock some mass out of the back (make it thinner) or it's monopole mobility will be too low for it to couple effectively, and you won't get a very live back. However, if you do that, you'll also need to raise the brace heights to get the stiffness back and a high enough resonant frequency [T(1,1)3]... So, until you get the feel of things a bit, stick with wood in the normal density range for back woods (~600-800kg/m^3).

User avatar
ozziebluesman
Blackwood
Posts: 1529
Joined: Wed Oct 10, 2007 9:12 am
Location: Townsville
Contact:

Re: Live Back question

Post by ozziebluesman » Tue Mar 26, 2013 7:11 am

Thanks Trevor! Better do some more study of the books me thinks!

Cheers

Alan
"Play to express, not to impress"

Alan Hamley

http://www.hamleyfineguitars.com/

Post Reply

Who is online

Users browsing this forum: No registered users and 6 guests