Reguarding Sound Hole Shape And Placement

[Mr. Preston Swift]

I couldn't find enough information on sound hole placement anywhere so i thought i'd ask the best in the business (you guys).

How would the different shapes and placements of the sound hole affect the tone and acoustic volume?

I know Ovation uses all those weird little sound holes on the sides of the top.

Where would a good alternative placement for the sound be?

[biliousfrog]

I've read that small holes enhance the bass frequencies, large holes reduce them, I don't know whether anyone more knowledgable can confrim or deny this?

[fryovanni]

Soundholes are going to set up your Helmholtz resonant frequency(like when you blow on a soda pop bottle and it creates a tone). The size of the soundhole opening and volume of air in the box will give you your resonant frequency. Do a quick search on the subject and you will get a better idea as to how it works, and you will also find formulas if you would like to do the math.

Placement, size, are all personal choice based on what you want to achieve, depending on the size and design of your guitar.

Peace,Rich

[GuitarEng]

Soundholes are going to set up your Helmholtz resonant frequency(like when you blow on a soda pop bottle and it creates a tone). The size of the soundhole opening and volume of air in the box will give you your resonant frequency. Do a quick search on the subject and you will get a better idea as to how it works, and you will also find formulas if you would like to do the math.

Placement, size, are all personal choice based on what you want to achieve, depending on the size and design of your guitar.

Peace,Rich

Here's a cool pic - this is from a very simplistic Finite Element Analysis model that I ran for a prototypical acoustic soundboard. Without going into the details, I think it is indicative of the deformed shape that an acoustic takes on when it is under load. I'd also propose that as the strings vibrate, they basically form a bellows...with the back portion of the body "pumping" air out the soundhole...and the "tone" of which is probably dependent on the Helmholtz frequency. This tells me that you should put your soundhole wherever you think you'll get the most deflection...and that this should give you the most volume...

[fryovanni]

Soundholes are going to set up your Helmholtz resonant frequency(like when you blow on a soda pop bottle and it creates a tone). The size of the soundhole opening and volume of air in the box will give you your resonant frequency. Do a quick search on the subject and you will get a better idea as to how it works, and you will also find formulas if you would like to do the math.

Placement, size, are all personal choice based on what you want to achieve, depending on the size and design of your guitar.

Peace,Rich

Here's a cool pic - this is from a very simplistic Finite Element Analysis model that I ran for a prototypical acoustic soundboard. Without going into the details, I think it is indicative of the deformed shape that an acoustic takes on when it is under load. I'd also propose that as the strings vibrate, they basically form a bellows...with the back portion of the body "pumping" air out the soundhole...and the "tone" of which is probably dependent on the Helmholtz frequency. This tells me that you should put your soundhole wherever you think you'll get the most deflection...and that this should give you the most volume...

Keep in mind that picture is a hugely exagerated bit of modeling to try make it easier to see what may be happening. Now just to maybe add a bit more depth to what may happen inside the box when it is being played. Your soundboard will vibrate(different parts of the soundboard will tend to be more responcive to different frequencies* or maybe be more active is a better term). When the soundboard compresses the air in the box, the back is going to deflect and react/reflect the energy back tward the soundboard and so on and so forth. This compression and decompression is going to move the air(maybe make the air flutter) in and out of the soundhole. A bellows may give you the picture of an air pump that is moving a lot of air out. A couple thoughts on placement(right or wrong thinking here is up to you to determine), Placing sound holes in a location that is not a very effective part of the vibrating system may allow for better use of the more functional space. Generally a good place to start is above the waist of the guitar as it is generally braced very heavily to resist the neck trying to colapse the body(making it a less efficient). Some people go for the upper horn area, and of course the classic location below the fretboard. Another thought, regarding how F holes are used to help make the plate on an archtop move more freely, placing the sound hole above the bridge may also facilitate more free movement of the bridge to a degree. Anywhooo... I can't say for sure where the best place is to put it/them, but it is an important consideration and something worth playing with.

Have fun

Rich

Peaec,Rich

[GuitarEng]

one last thought to add to fryo's would be that you probably aren't going to drastically change the way the instrument sounds if you 1) build it out of normal woods 2) build to pretty standard dimensions 3)brace it using a standard pattern and 4) put the sound hole in a normal spot.

You gotta play big to win big..if you're only making $1 bets, it's hard to strike it rich! And even then...there's always the possibility that the time tested designs we all play today are pretty darn close to an optimized design...