Probably the #1 guitar related question I get asked is: what is the sonic difference between an oval hole and a D hole guitar?
The most commonly heard analysis is that D holes are warmer, have more bass, and are better for rhythm. And that oval holes are louder, have more treble, and cut better for leads.
However, I haven't really found this to be the case. We often have two Dell Arte Hommages models in the stock, one a D hole and one an oval. The exact same guitar, same woods, same builder, etc. When compared, the results were inconclusive. More often then not, it was the D hole that was louder, brighter, and had more treble. Sometimes not, but there definitely wasn't any sort of generalization I could make between the two. Other factors, such as the woods and other construction details seem far more important in the overall sound then the sound hole.
Much of this myth seems to stem from the fact that the original D holes were always 12 fret guitars. And the oval holes, except for a few transitional models, were always 14 fret guitars. Totally different designs, hence the obvious sonic differences. For some reason people attributed these differences to the sound holes. However, the short scale length of the originals D holes was the most important factor in giving the guitar a "warmer" sound with more bass.
In recent years it has become very trendy to make 14 fret D holes. So now there seems to be a lot of confusion, with people attributing the sonic characteristics of a 12 fret sort scale to D hole to a 14 fret D hole. As mentioned earlier, I haven't found that the sound hole itself makes that much of a difference.
Interestingly, Michael Simmons, the editor of The Fretboard Journal
, just sent me the recent issue. The cover story is about Tony Rice's famous pre-war D-28, which at some point had it's soundhole greatly enlarged:
This guitar has been copied and mass produced by the Santa Cruz guitar Company, Collings, and Martin. Just like with Selmer's, there seems to be a lot of conjecture about what sort of difference the larger sound hole makes. Richard Hoover, the founder of SCGC, remarks that:
We can put the whole subject on sound scientific footing - and put all the myths to rest - by invoking the acoustics physics principal called the Helmholtz effect: "The larger the aperture of a resonating chamber, the higher the fundamental pitch of the chamber." So, in guitar terms, this means that the bigger the soundhole, the more midrange and treble are accentuated.
This would suggest that 14 fret D holes should have a more pronounced high end then their oval hole counterparts.
I'd like to know other people's observations and opinions.