Official Luthiers Forum!

Hello anyone who reads this as it is my first posting to the forum.

I have read the FAQ and searched the archives for this subject, so I really do hope it is not a redundant one.


Here goes...
In considering a cutaway, what effect does the shape and size have on
the tone of the instrument?  What considerations/trade offs does one need to take into account when 'cutting away' a portion of the top?  Are there compensations in the the bracing to consider?

It seems that most of the things I've read on the
cutaway indicate that it does not have a massive impact on tone because
the area of the sound board that is missing does not vibrate enough to
make a difference.



Yet in searching for cutaway instruments, most seem to attempt to
minimize the amount of material taken away (which seems logical to me.)



I've seen one shape that stands out from the rest. I really like the
cutaway on the Taylor nylon string grand concert body. It has some
modern look to it that really appeals. But when all is said and done, a
proportionally bigger chunk of the top is gone than would be with the traditional
florentine or venitian.



Below are two designs I'm looking at bending. The first is closer to traditional and uses two 1.75" radius bends.

The other is one I'm interested in doing, but does take more of the top
away, and has one 1.75" curve and one 1.25" curve. I'm REALLY nervous
about the 1.25" radius as I'm worried about splintering and cracking
this nice chocolate piece of rosewood.



I'd love to hear what the experts (as well as the novices like myself) have to say about this.

[QUOTE=livemo1]

It seems that most of the things I've read on the
cutaway indicate that it does not have a massive impact on tone because
the area of the sound board that is missing does not vibrate enough to
make a difference.



[/QUOTE]

Welcome to the OLF! Can I call you Mo?
Ok Mo, well I think you answered your own question at the top when you said it makes little difference. I suppose reducing the amount of airspace will start to have an impact, but from what I've read people choose cutaway styles for aesthetic reasons mostly... what do you think looks better? Will you be able to bend the tighter cutaway? Good luck with whichever route you go, and hopefully some more experienced voices will speak up here.

_________________
Time is a great teacher, but unfortunately it kills all its pupils - Louis Hector Berlioz

Chansen / C hansen / C. Hansen / Christian Hansen - not a handle.

Christian

Welcom to OLF Livemo1.

_________________
Say what you do, Do what you say.

Welcome to the OLF

_________________
Say what you do, Do what you say.

The upper bout has little affect on the air chambers motion. It will have some on its main resonance frequency. i assume lower the frequency some. Even there I expect very little.

When planning a cutaway the thing I always watch out for is bracing issues and the radius of the bends. I don't like to bend radiuses smaller than 1-1/4" radius to avoid stress fractures (cracks). Also you have well avoided one pit fall of cutaways. That is bends that the included angel of the entry bend is over 90 degrees.

That said I am opposite of you I like deep flowing cutaway bends like this

but they do put more stress on the wood at the apex of the entry bend.

One of my customers, who spends a lot of time in the studio, says that it's easier to record cutaway guitars. That's a clue.

It has some effect, that's for sure, but just what the effect is is hard to say. I don't think any really tight experiments have been done on this, as yet.

A small cutaway doesn't seem to have a major effect on the 'main air' resonance, which is the lowest one on the guitar, and the air resonance that puts out the most sound. It will raise the pitch of it a little, but less than you might think.

There are a lot of higher order air resonances that may not contribute directly to the sound, but do effect it in other ways. For example, the 'A-1' air resonance, that has the air 'sloshing' along the length of the body, doesn't give much output directly from the soundhole by itself, but it can work with resonant modes of the top (the so-called 'long dipole' mostly, but others too) to produce sound. Changing the effective length of the body, which a cutaway does, will effect the pitch of many of those other air modes, and thus the way they work with the top and back.

To my mind my customer's observation suggests that a more important effect might be raise the effective loss of the air resonant modes, due to asymmetry. This would make the tone of the guitar less 'peaky', and it could thus be easier to record. It might also tend to cut down on the 'tone color' a little bit. This is speculative, of course, but it fits.

The important thing is that a small cutaway should have less of an effect than a big one (DUH!), and the effect, at any rate, will probably be 'small' for theones you're thinking of.

Wow,
Thanks to all who have responded, and any more who chime in.

Somehow, as a newbie, I couldn't find this posting when I got up this morning and therefore couldn't bring myself to do any work on the guitar.

I actually went to the mall with the wife and kids.  On the bright side, I found a Rockler store that had some great specials!

thanks again for the input, I'll be pushing the fam out the door and heating up the iron.


Dave

Good luck Dave! Post progress pics of you can.

_________________
Time is a great teacher, but unfortunately it kills all its pupils - Louis Hector Berlioz

Chansen / C hansen / C. Hansen / Christian Hansen - not a handle.

Christian

The upper bout CAN be made to be more acoustically active if the fingerboard does not touch it, and there is minimal bracing. Don't totally write off the upper bout...

Update,
On the upside, I made the decision and went with the more traditional cutaway. 
Today was almost an awesome day as the wife granted me enough time to go to the hardware store, get pipe, and make a new bending iron.  I also had time to set up my shop-smith with three thin kerf blades and made up fifty bucks worth of lining before supper.

On the down side,
I realized I bent the side backwards.  So now I'll have to un-bend and re-bend the treble side to match the cutaway as I'm not going through that again today.

OOOOOOPS.