Depth of Sides

Construction and repair of Classical Guitar and related instruments
johnd
Posts: 144
Joined: Wed Feb 03, 2016 3:50 pm

Depth of Sides

Post by johnd » Sat Mar 18, 2017 1:25 pm

What influence does the depth of the sides of a guitar have on sound?

Deeper - louder? Deeper more bass?

printer2
Posts: 290
Joined: Sat May 02, 2015 9:20 pm
Location: Winnipeg

Re: Depth of Sides

Post by printer2 » Sat Mar 18, 2017 8:20 pm

Maybe.
Fred

Alan Carruth
Luthier
Posts: 2545
Joined: Mon Dec 24, 2007 6:56 pm

Re: Depth of Sides

Post by Alan Carruth » Sat Mar 18, 2017 9:59 pm

Fred Dickens did an experiment many moons ago that showed that side depth did not have a great effect on the pitch of the 'main air' resonance. Cutting the sides on a guitar down from about 6" deep to something like 2" deep only changed the pitch by 7%. As far as I can tell it has to do with the way the top and back couple with the air in the box. Making the sides shallower would raise the pitch of the 'Helmholtz' resonance if the walls of the box were rigid. However, it also increases the strength of the couple between the top and the air in particular, forcing the air mode pitch down. The two effects very nearly cancel out.

What I was not able to find out from him when he told me about this was whether the timbre of the guitar changed. I would expect the shallower box to have a more 'forward' or 'thinner' timbre.

Making the box shallower does alter the strength of the 'air' mode. A given amount of top displacement causes a larger pressure change in a shallow box, and pumps more air through the sound hole. In a spectrum chart a shallower box will tend to have a taller and narrower looking 'main air' peak. This does not necessarily come across as a 'bassier' sound, though. There's more to timbre then you can capture in a spectrum plot.

johnd
Posts: 144
Joined: Wed Feb 03, 2016 3:50 pm

Re: Depth of Sides

Post by johnd » Sun Mar 19, 2017 2:24 pm

Thanks Alan.

My wife and I went to a Mexican restaurant and they played mariachi music. One of the guitars was very deep. Wondered how it changed the sound.

Fred - Thanks for your explanation. I had a hard time understanding the effect until I read your reply.

Tom Sommerville
Luthier
Posts: 187
Joined: Tue May 22, 2012 2:15 pm

Re: Depth of Sides

Post by Tom Sommerville » Mon Mar 20, 2017 2:58 am

Allen wrote: " There's more to timbre then you can capture in a spectrum plot."

Amen to that.

It's a voice that I don't always trust because it is seductive as hell and just short burying string definition and projection: in my experience it's associated with bigger and deeper instruments with strongly resonant back and side woods and more often than not, cedar tops; I'm talking about that piano-like vibrato that seems to bloom out of the body.

I think most would know what I mean, but I wonder: in addition to the thickness and coupling of the plates, could a deeper body contribute to this ?
Again, I think depth may correlate, but others may disagree and even then correlation isn't proof. I just wondered what others thought.

Carey
Posts: 68
Joined: Mon Aug 08, 2016 9:19 pm
Location: Central California Coast

Re: Depth of Sides

Post by Carey » Mon Mar 20, 2017 5:52 am

What I hear as the body gets deeper is more of a 'misterioso' sound. Shallower body = more direct, present sound.

printer2
Posts: 290
Joined: Sat May 02, 2015 9:20 pm
Location: Winnipeg

Re: Depth of Sides

Post by printer2 » Mon Mar 20, 2017 2:30 pm

Here is a guitar that surprised me. Click on the images up top and scroll to the side shot, much thinner than I expected. Sounds not too shabby given the loss of air volume in the box.

http://www.guitarsalon.com/store/p5158- ... -moya.html


I have to try making one now.
Fred

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