Body Depth? What are the effects?

[mandough]

Hi,
I'm beginning my first mandolins. Got some fine wood from Spruce and have made my templates per the Siminoff book.

I've got enough wood for two mandolins and was thinking about making one of them with a slightly different spec from the blueprints.

I was contemplating making one of the F-styles with a deeper body. Maybe increasing it's depth by 1/2 inch to 3/4 deeper.
Does anybody have any general ideas as to what I might expect from making these changes? What might be the effects on Bass, Treble, loudness, sustain...etc.

I don't know why I'm doing this. Curiosity...the need for the fattest mandolin in town. Maybe just a want for a different sounding mando.

[Magnus Geijer]

I asked a similar question a while back. There's some information in this thread.

/Magnus

[Chris Baird]

A deeper body will give a more complex unfocused sound much like an oval hole. You will gain some sweetness and what some may call a tubby or boxy tone. The mandolin will not have much if any chop. However, don't increase the body depth by more than 1/4". Just an 1/8" makes a big difference.

[Dave Cohen]

It is probably an experiment that has never been done properly on the mandolin. Other things being equal, increasing the body depth would (a) lower the frequency of the Helmholtz air resonance and of the higher air resonances, and (b) increase the mass of air in the body cavity, thereby possibly increasing the strength of coupling of the Helmholtz air mode and nearby body modes. The first (a) is neither good nor bad by itself; it could be either good OR bad, depending on several other factors. The second (b) would have to be considered good if efficiency of sound radiation (i.e., loudness and projection) were the only criteria. There, too, is the catch. Loudness and projection are obviously not the only criteria in building an instrument. It boils down to this; if you change one thing on an instrument, you change several, if not all, other things on the instrument at the same time. Some of those changes might be good, others might be neutral, still others might be bad, and still others might be disastrous.

If you want to play the "what if" games from the vantage point of knowledge, instead of relying on having to ask others for their opinions, you need to know about the "general law of similarity". You can find out about it in several places. One would be Fletcher & Rossing's "The Physics of Musical Instruments", 2nd edition. Another would be Carleen Hutchins' papers on her "new violin family". She used the general law of similarity to design that family of instruments, and most of those papers can be found in back issues of the Catgut Acoustical Society Journal. There was also an extensive article by her in Scientific American, maybe 30 or 35 years ago.

[Michael Lewis]

Thanks Dave. I wish I had known about this stuff when I was starting out. Over the years I have re-invented enough wheels to fill a garage. You are a great help putting things into perspective. I'm patiently waiting for the release of your new paper, translated into 'luthier speak' of course.

It's all about proportion and relationships. But where do we go from here?

[Luthier Vandross]

Add up to about 3/8ths.


M

[mandough]

Hi Dave,
I understand what you're saying.
I also understand that the question I asked sounds like a "don't know what you're talking about" kind of question. The truth is, that's the truth. But...it's not like I didn't think about all of the things that you mention.
I know that by changing one of the factors in the mandolin blueprints, the equation will be completely different.
I'm not trying to create a "new kind of animal".
I'm building two similar F-5 style mandolins for myself (because I have enough wood for two). My thinking was, increasing the depth of the mandolin would be the easiest and most dramatic way to change the sound of the instrument.
I'm sure that loads of other people have done this.
The physics and sound dynamics of instruments fascinate me. For my next ones, I will take all of that into consideration and stray from the F-style.
For now though, I just want to distinguish one mando from the other that I am building.

[Luthier Vandross]

There are 2 good depths.. that I know of, buy a Randy Wood, and I'll tell you which ones.



If I told you, I'd have to kill me.


M