Official Luthiers Forum!

I have seen some awesome OLFer guitars with sound ports and although I have yet to incorporate one in my own guitars I want to.

There are a few things that I don't understand about how a sound port works, or, is supposed to work and after reading the archives I still have these questions.

With some things such as screening RF emissions the size of the unshielded openings dictate which RF frequencies are screened and which ones are not.

When considering sound waves I am assuming that the size and shape of a sound port could benefit from some tuning. I understand that a sound port is little more than a monitor for the player but does the shape and size dictate the tonal response that the player will hear from the sound port?

With the sound holes on the top we know that typically.... decreasing the size of the sound hole may increase the bass response of the guitar. Does the same hold true for a sound port?

Also what effect does the sound port, in conjunction with the sound hole, have on the Helmholtz resonator part of the equation? When using a sound port do you change the size of the sound hole in an effort to tune the overall response of the guitar?

Many thanks!

I think there was a series of articles in GAL not too long ago.

Hesh,

Obviously the more developed minds should chime in here, but I figured I would at least list my thoughts...

When looking at the vibration analysis of a guitar - it is typically treated as a drum head, where all dominant motion is occurring in the top, and the back and sides are more or less static. Obviously, this is not fully true...BUT, working on these assumptions, you would not be "tuning" the sound port so as to achieve the maximum and most efficient energy transfer to encourage the most balanced movement...the sound port would just be another accesss with which the guitar could "breathe" or move air into and out of the cavity...With that in mind, I am sure that changing it size and shape will affect the response of the guitar as you are changing the propagation of how and where the sound moves through the fluid...

So, you knew that already...oh well...
Stephen

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www.ziegenfussguitars.com

Hesh, I have built one with a soundport (not a particularly good one) and also listened to Grit Laskin talk quite a bit on the subject.

The size of the hole definitely affects the main body resonance so you can adjust that size to influence the resonance somewhat. I can't say what effect the location would have. Grit commented that he does not adjust the size of the soundhole when he includes a soundport. If you do the math, you will see the offsetting reduction in soundhole diameter is actually pretty small.

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David White, Toronto

"All my favourite singers can't sing."

Where is Alan when you need him?

Hesh my experience is that if you maintain the original sound-hole size in the top and add a port on the upper bout (say 1" x 1 1/2" oval) the main air freq. raises about a semitone on OMs and SJs. I have not put one in an MJ or Dread as of yet but would expect near the same

You can adapt for this by reducing the size or the main sound-hole and of course the sound port. Location plays a part and Alan post a bunch of info on his plugged port experiment guitar.

That is really all I can add definitively As I just have not worked that much with them.

Interesting to not it seems tht there is a stronger draw to the sound port than expulsion. I assume this is some what due to a venture affect

Thank You Gentlemen!

I just received an email from a very well known and talented player who is lurking on the OLF and he wanted to help me out. So he pointed out an article in this month's Fretboard Journal about John Monteleone's guitars and sound ports.

I am going to go read that right now and see what I learn.

Hesh, my soundport size and location was determined as were a lot of the design elements of my guitar. Trial and error. I keep trying to do things and keep making errors.

It would be interesting though, in tuning a sound port like a speaker. By extending a port tube into the hole and changing the frequency. I think it would be safe to assume that positioning it on the waist side of the upper bout would be the best spot for it, as your body position wouldn't interfere with the sound waves.

The engineer type guys will have mucho information, I'm sure. I wont be able to understand any of it however.

Darrin

Do let us know the outcome.
Lars

The newer ones all seem to go onto the upper bout area, I wanted one above the waist area, but it may be too close to the soundhole? Maybe a tut is in order....?

This is not a new concept, I wanted to put one in 10 years ago(Square with a 'door').Why? Just play the guitar with your ear to the side of the guitar, to hear what they really sound like!

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Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

Darrin that is very interesting - do you mean employing wave guide technology like the insanely priced plastic Bose Wave Radio and other family of products?

That is just it - how do you eliminate or reduce the trial and error, error, error...... when building the actual guitar? I guess that experiences such as Michael's give you some guidance for what to do to get the desired effect.

I am hoping that Al sees this and weighs-in here and also tells us about his corker.

Oh and I forgot to post this - here is an example of port placement that is not only beautiful but probably helps to keep the player cool on hot days.....

This is one of Kevin Ryan's beauties:



Also the article that I just read left me with some more questions, perhaps for another thread but it was mentioned that the guys who have been classically trained in violin making have learned that bridge placement needs to be in the center of the top. Then I hear the echoes of an OLFer who recently commented on a bevel design taking away too much top real estate. I'll hold off on that one for now for fear of high-jacking my own thread and getting someone mad at me....

Hesh,
I got to play Al's corker a bit ago and, to my ear, it sounded best when I uncorked the holes at the bend of the upper bout. At least in terms of giving the player an ear shot. However, I was interested to learn that most players didn't have a preference so it is a subjective thing.
I also got to play one of Burton's latest that had a huge port about 2 inches or so. That one was way loud for the player but I think he played around with some lighter bracing scheme to compensate some how.
I think it was Al also who mentioned if you think you went too far with the port size, you could add binding to close it up a bit.

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Wade
Nashua, NH
http://www.wadefx.com

Hesh, And all...
I put my first soundport in this year. A Bazilian rosewood "SJ" with a really nice, stiff Engelmann top. The guitar turned out beautifully (thank goodness, it's the most expensive one I've sold to date)
Though a "study of one" is pretty much useless, this is what I observed.
The top was thin, & braced very lightly. I expected it to to be very loud with a big boomy bass. What actually turned up was a lovely even toned well articulated sound, with moderate loudness. The balance is the best I've yet achieved, but I tried several new things at once on this guitar. Who knows which elements contributed what, to the overall "sound" of the guitar?
I used Macassar ebony for the bridge & fingerboard, two graphite rods in the neck. Brazilian rosewood for the bridge plate, etc etc. All new stuff on this instrument.
Another surprise was how subtle the monitor effect from the soundport is. I expected the port to emphasize the highs & add the brittle string sounds one hears when you lay an ear on the side of the guitar while playing it. What we really got sounded much the same as what was coming out of the soundhole, but quieter. Very mellow, with no string noise & no distracting overtones.
The big bodied, lightly braced guitars I have built in the past have a tendency to ring on one string (usually the A or the D) when playing a lead on the high treble strings. This one had no such problem. Whether the soundport canceled that effect or not is a matter of speculation at this point.
I did reduce the diameter of the soundhole by a little over an eighth of an inch. Quite a bit less than the area of the port.
The results on this guitar definitely got the juices flowing & I plan to put ports in my next few guitars in hopes of getting some more "data".
I'd be very interested in hearing from other builders who've added a port to their guitars.
Oh yeah... Ports are pretty too, but I need to clean up my interior finish a bit. Every break in the kerfed linings & glue stain are visible through that darned port! Luckily, the owner wanted a K&K Trinity P/U installed & the pre-amp & wiring hide a multitude of sins!

As for tuning them, all I know is that Linda Manzer and others used to make sliding doors to adjust the size of the opening. At Healdsburg last year, she said she is no longer doing that because people always seemed to like them (and leave them) wide open. That may have only been on arch tops though.

I also recall somewhere Doolin talking about adding a tube on the inside of his ports to drop the main air resonance back down to where it was pre-port. I get the impression that all of those refinements have fallen by the wayside as being a lot of work for little or no gain.

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http://www.chassonguitars.com

Let's see.....

Adding a port does raise the 'main air' pitch. The larger the port and the further it is from the regular soundhole the more it changes the pitch. You can get the pitch back down by making the main hole smaller, but given the variables involved it's a little difficult to say by how much. If I'm putting a 1" hole in the wide part of the upper bout I'll make the main hole about 8-10mm smaller in diameter.

The closer the port is to the main soundhole the more the output of the port sounds like the output from the main hole. As you get farther away the port hears different internal air modes than the main hole does, and this alters the sound. A port right up next to the neck seems to put out more sound for it's size, but that's due mostly to the fact that all of the internal air modes have sound pressure maxima there. It will thus tend to change the sound of the guitar more than one further down.

You could add a sleeve to the port to get the main air pitch down, but that's more complication and cuts into the output of the port.

SO ! am I right in my thoughts : if I make a "tony Rice" soundhole, would that be the same as building a normal sized soundhole + a small soundport ? os does a soundport alster the sound in other ways ? summary: larger soundhole same as usual soundhole + soundport ???.

another thing to consider with a soundport is that an artist might not be able to record and sing at the same time, as the sound from the soundport is aimed towards the microphone, wish most of the time needs to be isolated from the vocals. !! just a thought.
But in the other hand, it might be a cool way to stereo mic the guitar. "one mic on the soundhole and one on the soundport.

Lars