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I have to admit that I have seen some beautiful sound port designs, executed with impeccable craftsmanship. That being said, over the years it has been drilled into me the importance of air tight construction and the effects of even varying the sound hole size -- likewise I have preached about these points. Likely its been posted before (I don't like the PHPBB search engine) but what is the acoustic justification for sound ports? I am sure there are pro's out there that have some experience and data relative to this subject. Amateurs too.

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Ken Cierp

http://www.kennethmichaelguitars.com/

ashtray....

Seriously I'm too much of a traditionalist to find great value in an acoustic sound port but I do know what that value for those who are sound port fans is - it's a monitor for the player and hopefully if not located under an arm pit.... or next to the neck joint the player has a monitor and all the benefits of same.

Got no use for them. Just as you said, a leak in the box. Think you loose projection.

Yeah it would seem if the instrument can produce "X" amount of sound energy and a portion of that goes up into the players face -- the loser would be the audience - not sure if that's how it works however.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Ken that would be my impression as well except that a sound hole is not the only source of the sounds that an instrument makes. Sound also radiates from the top surfaces as well and even a few other places if we want to get specific. Think piano and sound board.

That has always been my instinct, but when I asked Paul Heumiller his take, he said he he believes ports can actually increase projection by allowing more air to pump through the box. Whether it not that's true, I'm not sure, but from my limited research, it doesn't seem to reduce projection, but does, of course, alter the resonances of the box, which needs to be accounted for in the build process.


Ken Jones
Mountain Song Guitars

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Mountain Song Guitars www.mountainsongguitars.com

Don't know the logic or science but I've put them in almost all of my 10 or so builds and probably always will. Again no science to back any claims but when I cover the hole the guitar doesn't sound as good to me as when the hole is open. As far as the audience's experience I did have an audience of one older neighbor (with no acoustical experience) once who simply said, when I uncovered the hole, "Wow, it seems to let the sound out." Now there's some hard science for you, so cut away those sound holes.

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Thank You and Best To All

I put a sound port in a guitar that was already built up 'normal.' Honestly I didn't notice much of a difference. It was one experiment on a cheap guitar not scientific in the least bit. I played a guitar once that had no traditional sound hole but rather only a sound port. It actually sounded good, different but still good.

Basically I got nothing to offer

I sell the sound port as a monitor for the player, as Hesh stated. I know Al Carruth has done extensive tests on sound ports and their placement so he may chime in here as well.

one older neighbor (with no acoustical experience)

Holy crap now that nails it!

Moving the instrument against and away from the torso can have a huge effect on output, technique even taught by some instructors.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Yup, I told you that was some hard science. Did I also mention he was hard of hearing?

You know, funny thing is, I place more importance on his off the cuff comment than information many other over analyzed scientific studies might provide.

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Thank You and Best To All

Here's the Charles Fox blurb regarding the adjustable sound port on his $15000 Ergo model

Adjustable sound port - The optional adjustable sound port allows users to vary the ergo's sound field by selectively opening or closing this second opening into the air chamber. The sound port can be opened to surround the player with sound when playing for pleasure or closed to focus the sound for full projection when performing and recording.

He does mention on one of his videos interviews, that partial opening has zero effect (and than states I probably should not have said that)

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Ken Cierp

http://www.kennethmichaelguitars.com/

Well, having no experience with them, I suppose I got caught speculating...something I don't usually like to do. Still won't use them, I can hear my guitars plenty well even with tinnitus. Guitar couch slouch works too.
Larsons and Oscar Schmidt never used them, good enough for me. Just one of them newfangled gimmicks like arm/gut slanty things or wedgies.
Yea, I'm a luddite...misanthrope too.

So here is the science and Non science I know (or kind of know). I am building 2 guitars now with my first sound ports. With the box closed but without the binding on, I tapped the box at the bridge location and measured the resonance peaks with the sound port open and with the heal of my hand covering it. For both guitars the Main Air Resonance dropped 5 Hz. This was more that I was expecting. Early on, I considered reducing the size of the main sound hole to compensate (I may still bind the sound hole on one). Gore in his book, gives an equation to calculate the Main Air change as a function of sound hole diameter. However, If I understood a post by Al Carruth, the sound hole and sound port are not fulling coupled so the sound port size would have less affect on the main air. I intuperated that a "little affect" and did not compensate. I have not gone back yet and calculate what the coupling is in these guitar (I will wait until I do the binding) but my impression is the coupling is pretty high, close to 1. Now that begs the question of; in future guitars does one reduce the sound hole diameter to hit a Main Air resonance target. I am not sure yet. I will wait until I have a finished guitar to play.

Now for the non science part. I have played 2 guitars by well known builders with sound ports. For both guitars, as a player, I preferred the sound of the sound port open. But more importance in each case I had others there to report on the sound difference the audience experienced. In both cases, the people in front of the guitar preferred the sound with the sound port open. They all reported that the sound was more complex and pleasing with the sound port open. Not a huge sample but it does agree with the other account in this tread. Also I have recently heard Gerald Shepard describe the sound ports in his guitars as "opening up" the sound. That description would fit what was reported to me about the affect of the sound hole.

Great tread. Looking forward to hearing more details.

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EddieLee

I have only heard one classical guitar that had an adjustable soundport.

Sitting beside the player I could hear no difference in sound or volume with the soundport open or closed.

When sitting about 5 feet in front of the player, when the soundport was closed the guitar resonated more and when the soundport was open the guitar sounded cleaner. Not scientific....but the difference in sound was easily heard.

If I recall correctly the luthier said he built the guitar with a soundhole slightly smaller (1-2 mm) than a guitar without a soundport.

Alan Carruth has posted a very nice discussion of his research and experiments with sound ports here:

http://www.alcarruthluthier.com/Downloads/sidePorts.pdf

The MIMF search engine will take you to many other useful discussions of "sound ports" and "soundports."

Basically, the answer to your question, "What is the acoustic justification for sound ports?" is "It can provide a useful way for the player to 'monitor' the sound produced without having a negative effect on the overall sound, especially if the port is not large and the other sound hole is slightly reduced in diameter."

Not everybody agrees that there isn't a negative effect on the overall sound, although in part this may reflect the influence of preconceived ideas. Whether or not to make a sound port, and how to execute it, ends up being a judgment call of the individual luthier.

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Tim Allen
"Never hurry, never rest."

Monitor for the player/ashtray/handy place to lose your joint when officer O'Malley of the FBI shows up... Ain't life great!

For me it is important what lay folks perceive because at the end of the day (and tune) their perceptions will be the measure of value that the market must meet and/or exceed.

I took a piece of plastic tubing and dropped one end into the guitar and plugged the other end directly into my ear. I could hear all kinds of beautiful overtones that I ordinarily never hear from anybody playing. But it looks dumb.

When I was a lot younger I used to love listening to the sound of the guitar while I finger picked and laid my ear on the upper bout. I was a lot more limber then I find the sound port gives me some of that back, mostly while practicing alone. I have also found that when I'm playing on stage with a bunch of acoustic instruments the sound port makes a useful monitor.

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Steve Smith
"Music is what feelings sound like"

Kind of like a giant fiber optic. Hope you did not get that tubbing from the bathroom.....

That link to my article has some useful information, and I've done some more work since then. At risk of repeating:

Opening a port causes the 'main air' pitch to rise, and the overall output at the 'main air' frequency to increase. On a Classical 'test mule' I made a few years ago, with a port 2" diameter in the 'usual' place (the right side of the upper bout), the 'air' pitch rose from 95 Hz to 105, and the level went up about 3dB at the (changed) resonant pitch. This is about twice the power, but is only a 'just noticeable' difference in loudness out in front, where the measurements were taken.

There is a slight decrease in sound level at the 'main top' and 'main back' pitches, which change much less in frequency.

Above that 'bass reflex' range it's harder to say what the overall result is. Some frequencies increase a lot in output, as the port 'hears' things that the main sound hole does not. In every case, throughout the range, any increase in output in front of the guitar is only over a very narrow frequency band, so that it is only likely to affect one pitch.

These results are qualitatively pretty much what I see out front on all the guitars I've tested. The exact changes, and the magnitude of them depends very much on the size and location of the port.

Putting a mic near the port, about where your ear would be, gives a different picture. There are lots of peaks and dips in the spectrum curves, of course, but overall there is an increase in output that seems to average 5-10 dB. At frequencies of internal air resonances that the port can hear the change can be as much as 50-60dB. The change tends to be greater at higher frequencies, where the 'out front' sound may become weaker with the port open.

Blind listening tests of player response have come up with mixed results. R.M.Motolla did a small study, using my first port 'test mule', and found that players could not hear the difference. However, his tests were done in quiet, reverberent spaces, where you might expect room reflections to provide good feedback. I did a rather larger study at the last two Montreal shows, a folk festival and a GAL convention, to see whether the port made a difference in a noisy room. The spaces ranged from the usual 'dead' hotel ballroom to more 'live', but in every case there was about 72 dB-A of background noise, which proved to be 'white' noise. Basically, in those circumstances, when the port was not changed the players were guessing as to whether it had been or not, but when it was changed they got it right almost every time. Listeners in front seldom seem to hear the effect.

Overall, then, it seems that a side port does change the sound of the guitar in a way that's far more useful to the player than the listener. I tend to feel that it would be most useful for somebody who plays a lot of 'restaurant gigs': more or less large and 'dead' spaces where there is some background noise, where you're not likely to get high frequency feedback from room reflections. If you mostly play in livelier or smaller spaces, a port may not be as much help.

The closer the port is to the regular sound hole, the less the effect. A larger port does more of whatever it does than a smaller one. For the player to get much advantage of it, they have to be able to see into the port. It's probably best to try to design the guitar with the port in mind to avoid moving the 'air' pitch up into a range that leaves the lowest notes weak. Its a little hard to know exactly how much to change the size of the main hole, though, so it might be best to allow for some adjustment by leaving a wide margin between the hole and the rosette.

YMMV

Tin cans and string.

I have no scientific data, but the guitar that I put a sound port in seems to have additional ambience rather than a distinct direct sound as a monitor pointing at you. I made a plug (ziricote with cork underneath) to cover the hole. That way you can decide to use the port or not. I like the additional ambient sound. It makes the guitar inspiring to play. I doubt that an audience would be able to tell the difference and I mostly play for my own enjoyment anyway.

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

I don't purport to understand all of the physics behind side ported or traditional non-ported. A few years ago I attended a clinic put on by Grit Laskin. The audience all noted a noticeable increase in projection and volume when the port was open. Not something the player would hear. It is fun playing a side ported guitar and having the benefit of the "monitor" effect. So I don't think that is all hype and ashtray talk (but if someone figures out a fixture that will hold a scotch glass that doesn't take away from the guitar's sound....I am in .