removable sound port plug

[j. Kinnaird]

Al bought one of my guitars at BIG a few years ago and called me up a few months ago wanting me to make him a sound port plug. This was plowing new ground for me and I was a little unsure how to proceed. It seems the specs for such a plug would be that it not fall out unbidden, that it not rattle or buzz, that it does not detract overmuch from the looks of the guitar and that it is easy to remove and put in. My initial design involved using brown duct tape. certainly it would be easy to attach, removal might be a problem and it did not look that good. Later design refinements led to the following:

1. a laminated plug whose curvature matches the sides at the port and that fits well into the port.

2. an "O" ring on that plug to firm up the fit and prevent rattle

3. an outer more decorative layer attached to the plug that covers the port opening



the "O" ring


The sound port showing the port tube into which the "O" ring will press.


Port in Place




I could have made the outside cover thinner but in fact the original design used magnets to hold the plug in place so the thickness was there to imbed the magnets, but the "o" ring was so effective the magnets seemed to be an unnecessary addition and I was able to avoid gluing magnetic material inside the guitar.

I played the guitar for my wife. She was out front and said she could not tell a difference with the plug in or out. From my players perspective the plug blocked some of the high frequencies of the bass strings favoring fundamentals and lacking the crispness that I prefer to hear from the bass strings.

[Joe Whitman]

Makes me a lot curious as to why he would want to plug the sound port. Regardless your execution of the request looks first rate!

[j. Kinnaird]

Originally Posted by Joe Whitman

Makes me a lot curious as to why he would want to plug the sound port. Regardless your execution of the request looks first rate!

Thanks Joe
Perhaps Al will chime in here and tell us what he is after. I understand that he had a temporary plug made whose effect he enjoyed and I will be the first to admit that his musical acuity and talent far exceeds my own.

[jt1]

Cool.

This is one of my favorite guitars I've ever had the privilege of playing:

[sinistral]

Like making a time machine out of a DeLorean, if you’re going to make a plug for a soundport, you might as well do it in style!

[Guitars44me]

Originally Posted by sinistral

Like making a time machine out of a DeLorean, if you’re going to make a plug for a soundport, you might as well do it in style!

I’m with sinistral. Very stylish indeed

Not going to ask for one myself, as I LOVE Johns soundports wide open for business…

Cheers

Paul

[Jaimoe]

Nice work! I’ve though about (some day far in the future) making or commissioning “soundport” plugs for some of my guitars that have 90s-style active electronics—eg Fishman Matrix. Some of those electronics could probably be removed and leave soundport-sized openings that are decently placed enough to be useful, but my dream would be to have something nice on the eyes that I could open or close as I saw fit.

Anyone seen/done one of those conversions?

(Note: please assume that if I did something like this it would be a labor of love, so responses like “you could buy another guitar for less” are not useful to me).

[soma5]

OK, I'm Al. Let me be the first to say what a spectacular guitar this is. It is a guitar that never fails to impress the listener. I've owned it for well over two years so it has gotten a lot of play, even among the other guitars I own. I intend to keep it for a long time, and I would not have asked John about this otherwise.

The tonal balance in the tone that is heard by the player is shifted in a guitar with a sound port. I've played acoustic guitar for many years. I feel that I have a good sense of what the guitar sounds like in front, and I depend on that sense when I play. This has kind of been creeping up on me. At the last BIG, I played some excellent guitars with sound ports, and I felt that some resonances were different enough so that I could hear the differences and I could no longer rely on my sense of what the guitar sounded like in front. Of course, once you start noticing stuff like this, you can't (or I can't) get it out of my head and I found it to be distracting. I talked about this to some of the luthiers at BIG. I am not sure whether I was able to communicate well about this, but that is my own issue. I think that I'm in the minority in that the difference bothers me, especially judging by the popularity of sound ports, but once I heard the difference I couldn't un-hear it.

Anyhow, John kindly agreed to think about my issue. Apparently the thinking progressed ahead to doing, and John has come up with a very nice-looking workaround. I am looking forward to playing this guitar again. Thank you, John! I will be in touch via email.

Added in edit: my first plug, if you want to call it that, was a couple of layers of blue painter's tape. Not very attractive and certainly not anything I would want to perform with.

[RJVB]

Does the soundport "tube" have a function (something tornavoz-like)?

I plug the soundport on my Cabaret too most of the time at home, for 2 reasons. With the guitar in classical position she gets a bit too loud for comfort (ah, those nylon-strung classicals ) and when I'm not playing her she's out on a stand and I hate the idea of dust and maybe even the wrong kind of critters getting inside.

I always keep some packaging material from the various shipments I get, and had some "classy" black layered foam that IIRC had help a notebook computer. I cut a 3 cm high oval out of that that's just a tad wider than the soundport. It works but gets pushed into the guitar way too easily so I leave it out when the guitar goes into her gigbag for transport.

An o-ring design as here probably wouldn't work because the sound port is really just a hole in the side with a somewhat rounded edge.

It'd be nice to have matching Lute Hole plugs for this!

[GillanderGuitars]

To add a little science to this, I built a dreadnought with an adjustable toneport. I wanted to see what effect it had and I was inspired by John Monteleone’s archtops that I had first seen at the Met about 10-12 years ago. Anyway, the graph shows the frequency response of the guitar with the port open v closed. The orange line represents the closed port, and the blue is with it open. While there are some changes in the upper frequencies, the biggest shift is that of the first peak. This peak represents the resonant frequency of the air inside the body of the guitar. By opening and closing the door, you can, to a point, tune that resonance. This could be useful in eliminating an unwanted wolf tone. At the Woodstock show, I was talking with Sam Guidry. He is using tubes in the tone port that are cut to a specific length as a means of tuning the air resonance as well.

[jt1]

Originally Posted by GillanderGuitars

To add a little science to this, I built a dreadnought with an adjustable toneport. ...

Very cool!

Originally Posted by GillanderGuitars

... At the Woodstock show, I was talking with Sam Guidry. He is using tubes in the tone port that are cut to a specific length as a means of tuning the air resonance as well.

Interesting. I've built but one guitar (revealing me to have no business commenting here or, well, anywhere guitar-related). I played around with the "tube" of my soundport. You can just see it in this pic if you squint just right:

[TomB'sox]

Originally Posted by GillanderGuitars

To add a little science to this, I built a dreadnought with an adjustable toneport. I wanted to see what effect it had and I was inspired by John Monteleone’s archtops that I had first seen at the Met about 10-12 years ago. Anyway, the graph shows the frequency response of the guitar with the port open v closed. The orange line represents the closed port, and the blue is with it open. While there are some changes in the upper frequencies, the biggest shift is that of the first peak. This peak represents the resonant frequency of the air inside the body of the guitar. By opening and closing the door, you can, to a point, tune that resonance. This could be useful in eliminating an unwanted wolf tone. At the Woodstock show, I was talking with Sam Guidry. He is using tubes in the tone port that are cut to a specific length as a means of tuning the air resonance as well.

I am not sure what kind of measurable difference is noted in that graft, but from the mirroring of the graphs to one another, I would highly doubt I would ever be able to note any difference.

Steve Sheriff of Edwinson guitars was the first I know of that build a sliding door to allow the user to open or close the port. I know he posted about that. Mark Hatcher has also built a very unique sound port with a tunnel to "guide" the sound through the port. He called it his throated sound port. Here is a link to a thread showing a picture: https://www.acousticguitarforum.com/...hroated&page=4

BTW John, that cover looks very nice indeed and seems like it will be 100% functional.

[jmagill]

Do you mean the little cupholder in the upper bout? A favorite beverage plugs it pretty well...
.

[RJVB]

Originally Posted by GillanderGuitars

While there are some changes in the upper frequencies, the biggest shift is that of the first peak. This peak represents the resonant frequency of the air inside the body of the guitar. By opening and closing the door, you can, to a point, tune that resonance. This could be useful in eliminating an unwanted wolf tone. At the Woodstock show, I was talking with Sam Guidry. He is using tubes in the tone port that are cut to a specific length as a means of tuning the air resonance as well.

This corresponds to research by Alan Carruth; for all practical purposes it appears that adding a soundport is equivalent to shifting the (sole) soundhole upwards: the main air resonance shifts to higher frequencies. (This is part of the reason why 12-fretters usually sound warmer than 14 fretters, IIUC.) And from what I understand from the above, a tube in the soundport must indeed act like a tornavoz.

It would be interesting to add an axis to your graph: distance from the guitar, and plot the difference between the open vs. closed frequency responses so we get a visual representation of the frequency shift as a function of "note played" and distance from the guitar. My guess would be that this shift decreases with listener distance, provided the soundport is relatively small compared to the area of the soundhole.

EDIT: it would also be really cool to have a closing mechanism ("diaphragm") that opens into a tube shape. 8)

Originally Posted by jmagill

Do you mean the cupholder in the upper bout?

Lol, back when PCs still had CD trays some very tech savvy users took them for cup holders - memory from moonlighting as a hotline slave

[GillanderGuitars]

Originally Posted by TomB'sox

I am not sure what kind of measurable difference is noted in that graft, but from the mirroring of the graphs to one another, I would highly doubt I would ever be able to note any difference.

I probably should have clarified a little bit about what is being shown in the graph, but I didn't want to take away from the original intention of the thread, highlighting John's lovely work.

This graph is not showing what the player or audience would hear. What you're looking at is the sound of the instrument with the strings dampened while the bridge is gently tapped with a rubber mallet. We all know that guitars vibrate in a complex way with multiple things vibrating simultaneously, most notably the air inside the box, and the monopole of the top. The frequency of the back, assuming it's active, and the vibration of the dipoles, and tripoles are also important. Of equal importance is how these vibrations interact with each other , and the vibration of the string at various pitches. When things are working properly the guitar will be equally responsive across the range. However, resonances can also cancel each other out, or amplify certain frequencies. This is where small shifts in the frequency of one variable can influence the overall performance of the guitar. This graph is useful in isolating which part of the guitar might need to be adjusted to help the guitar perform better. I was just trying to show that we can see the effect of plugging or opening the tone port on the graph by the shift of that first peak resonance, and how that shift can also influence the resonant frequencies across the spectrum. Many ask how the tone port can change the sound of the guitar, and I thought the graph was a great visual. I have no doubt that there is an audible difference to the player. That difference may vary to the audience depending on the instrument, the room, proximity to the performer, etc.

Hopefully this doesn't come across as word salad... I get a bit excited about this stuff.