Soundhole size and effect on body resonance

[Dave Bagwill]

Good stuff Bob. I have heard of Helmholtz a bit.

So far, I need a built-in humidor, an access panel to allow for brace shaving the completed guitar, and now an adjustable diaphragm for the soundhole.

If there are any noob's reading this, I'm joking! :-)

[Tim Benware]

If I remember correctly, the duct is tuned to the cone and the box area is part of the formula. In a guitar the cone is the top and the hole is the port. What complicates things is the shape of the guitar (speaker volume is generally H x W x D) and determining the volume accurately, although I wouldn't be surprised if you couldn't find something on the internet to figure it out. The "port or vent" in the picture is a tube of a certain diameter and length. Tuned properly the vibrations from the driver on the back stroke bounce or reflect off the back wall and exit the port in phase with the vibrations on the forward stroke making use of the overall energy of driver movement and increasing the volume in theory by 2.

[Ray Ussery]

Lot's of folks would tell you that the over sized sound hole in Clarence White's D28 Brazilian made all the difference in the world....and I think it DID! In Clarence's hands.

Tony Rice, who now owns the guitar and plays it regularly, says he can't tell any difference...and I Believe him! He isn't Clarence white.
Everybody holds and plays the guitar differently.... because of that, it really does sound different.

Proof? Take ANY guitar and hold it in your lap, pull it tightly to your belly and play it....then move it away from your body so there is no contact with the back of the guitar and play it...the tone and the volume will differ greatly.

There have been thousands try to duplicate the sound of Steve Ray Vaughan and his Strat...isn't going to happen, even with all the electronics we have today, even with the same guitar...nope...his own brother admits he can't do it!

So many variables..and yet, there are SOME who can build with repeated success...why? what IS the secret?...the tech builder will tell you it's testing grain strength, thickness, bracing... the other end of the spectrum will tell you they can Just "HEAR it" they don't measure anything..they will all tell you to some degree anyway...it's the type of FINISH or lack of it...thickness...right, I've never seen a ruler on a spray gun...then there's the wood...I've seen and played one of Taylor's "Pallet" guitars (Made from an oak pallet he picked up in the lot out back) and I can tell you it was superb!

A couple of years ago in Denver, Wayne Henderson told me it was quality of workmanship and paying close attention to dimensions, properly glues joints and repeatability. From the guitars of his that I've played, including #400, he's doing something right!

Who really knows? :)

[Dave Bagwill]

So the same amount of energy results in 2x the volume; interesting. The obvious question is: why not a second port, or a third, each one tuned to the rest of the box? I must Google.

[Dave Bagwill]

Considering the spectrum of theory and practice, a fella just has to choose what works for him. I haven't had the opportunity to compare 400 guitar tops - actually, 7 so far - so I am not as trustworthy an 'ear' as someone more experienced. OTOH, the technical testing I want to do will yield repeatable results so that I can compare more closely, from instrument to instrument, what the heck is going on. Over time, perhaps the 'ear' will become a reliable intstrument for testing as well.

I appreciate your post Ray - I get it.

[Tim Benware]

So the same amount of energy results in 2x the volume; interesting. The obvious question is: why not a second port, or a third, each one tuned to the rest of the box? I must Google.

In theory it should double but in reality there is more that comes into play and it doesn't. Extra ports won't help. Think of it in this respect there are two movements of the cone (driver) forward and backward the forward facing cone takes advantage of the forward movement and the tuned port takes advantage of the backward motion of the driver by sending the reflected waves of the backward movement out the port in phase with the next forward movement. Remember, sound is fast. So no need for more than one port.

[ken cierp]

When we were selling mountain dulcimers -- the light went on regarding the increase volume and improved tone of an instrument that was place on a stand vs the same one played on the performer's lap -- the improvement was not subtle -- significant, quantum is more like it. So what I have on the drawing board is a true double back design with the inner reflective back totally insulated from the outer back. I am thinking that the inner back could be made with different woods different thicknesses, different braces etc. I know it adds to the confusion (I think of it as opportunities) --- one thing for sure the volume of the instrument will louder then the traditional guitar.