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I've punched a side port in just one of my guitars so far. My immediate response was WOW! I gotta do more of these!

When I had a doctoral candidate (in guitar performance at U of Texas) try out the guitar, he remarked, "Cool -- it's like I have my own monitor."

Exactly.

But this was a really crude operation. I just took a hole saw to the top bout of the guitar and cut about a 1.5" hole in it about 3" up from the neck joint. Actually I wasn't planning for the hole to be that big. I was hoping to cut a purfling ring about 1.5" diameter, and a smaller innner hole, but the purfling ring didn't work out quite the way I wanted. So I wound up with a really big hole.

Still, it really is amazing how much it improves the guitar's sound.

So to my point. I've had a look at the discussion Al Carruth has at his website regarding porting guitars. In fact, I read through it more than a few times before finally punching a hole in my guitar. But what really has me wondering still is how Al cuts that hardwood insert that he lays into the hole. It's easy enough to cut the hole and smooth the edges. It's even easy enough to put the contour of the side onto the insert so it fits flush against the side. But what has my stymied is that apparently there is a lip the extends below this flush edge, down into the guitar. Yet the insert seems to be a single piece of wood.

So, what's the secret here? Al? Do you cut all the contours by hand, or have you come up with an exceptionally clever jig that allows you to contour the "face" of the insert so that it fits flush against the side, where there's a "lip" that still fits beneath?

Best,

Michael

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Live to Play, Play to Live

Michael

I don't know how Alan does it, but if we are talking about a circular soundport, one way to do it is to use a circle cutter in a dremel or laminate trimmer. Cut the outside diameter over the size of your hole, then cut th outside diameter of the hole, but not full thickness so it leaves a lip, then cutout the center hole.

Not sure if this is the type you meant, hope it helps.

I should mention this is for cutting one from a solid plate of timberRussellR38571.2825462963

I finished a quilted cherry cutaway dread in November and my grandson has virtually taken it away . Not like he needs another. He has 10 (most of them I gave him!Shame on grand pa!) But he wants an under the string pickup with onboard controls. I bought the thing . That was the easy part. I have not been able to cut the hole in the guitar to install it! I made a template , taped it on . There I sit with scribe in hand and decide to put it off again. As much as I`d like to try a side port I don`t know if I could bring myself to cut the hole! It`s irreversable and almost a sacrelidge!

I just 'toughed it out' on that insert. Drilled the hole, marked the size of the opening it was to go into, started to cut around that, rouged in the curve of the side, and chalk fit from there. Took forever. That's why I didn't use one on the second ported guitar I made....

I've got a couple of ideas for easier ways, but haven't tried them yet.

I've gotten a bit sidetracked lately, but I really must get back to work on the paper on ports. IMO they don't add any power to speak of overall, they just redirect it and change the timbre. They sure can be useful as monitors: most of the time I play the 'corker' with the #2 holes open, just because I can hear it better, ad plug the main hole a bit to keep things in line.   

I'm not sure if this is really relevant to the discussion, but I just saw two performers who are very good guitarists, and both had major problems with tuning their instruments between songs. I thought of the port while I heard them playing out-of-tune, and wondered if they heard themselves through a port if they would have been able to tell that they were out.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Al,

Recently I read an interview of Kenny Hill somewhere in the 'net, in which he was talking about a collaboration between Robert Ruck and him regarding side ports. He stated that Ruck had found there to be a small, but measurable increase in overall volume. Had something to do with relieving the slight vacuum and compression caused by the plug of air being sent back and forth through the soundhole. That kinda makes sense to me.

Oh, and about your port, I'm glad it wasn't a trick as obvious as the nose on my face. I think what I'm gonna do for future ones is lay up some squares of black/white headstock laminate inside the guitar, so that there will be a little bit of visual interest there. It'll also stiffen things up pretty well, I think.

Best,

Michael

Michael McBroom38571.8630902778

_________________
Live to Play, Play to Live

[QUOTE=Michael McBroom] Al,

Recently I read an interview of Kenny Hill somewhere in the 'net, in which he was talking about a collaboration between Robert Ruck and him regarding side ports.[/QUOTE]

I've read that they have a patent on their holes. Upper bout; one on each side near the heel.

There _is_ a slight increase in output with the ports: about 1-2% overall in the room when averaged over the spectrum. This is not much extra power. This is based on my own measurements done on the 'corker' in my shop, and backed up by measurements made by Chaigne in Paris in an anechoic chamber with better equipment (JCAS 3.8:24-31, Nov 99).

This added power comes from a fairly large increase in output (sometimes as much as 4dB; more than double the power) over a restricted frequency range, along with a decrease over the broad band. It has to do with the internal air resonant behaviour. The exact frequencies enhanced will depend on just where you put the port, among other things, so dependng on what the particular guitar is doing the effect may be a benefit or a detriment. In any case the narrow band increase and broad band cut are two sides of a coin, as it were: you can't have one without the other, it seems.

Remember, that 'pent up energy' is another way of saying 'resonance'. Yes, putting in a port 'relieves a pressure/vacuum' and allows the plate to move more easily: that's probably part of the reason for the increase in output over the narrow band covered by the particular resonance in question. But there is no way to effect only one resonance, or one part of the guitar without effecting all the others at least some. Remember that those inside air resonances also push on the top and back, and even if they don't produce sound directly through the hole they can often color the tone and add output in other ways. In theory you could relieve _all_ of the pressure/vacuum 'problems' by simply punching holes all around the sides of the guitar so that there wuld be no effective air resonance. I can do effectively that with the 'corker' by pulling all the corks. The result sounds 'tinny' and 'flat'. The body of the guitar exists, in part, to produce just those pressure and vacuum conditions that the ports 'relieve'.

I don't know everything about how the guitar works; that's why I keep doing silly experiments. It's possible that there is a particular hole configuration/location that really improves a particular guitar design and gives a useful increase in power output. But based on the experiments I've done, and my limited understanding of how the guitar works, I doubt it. If anybody knows of any better experiments (objective measurements, please, not just 'I liked that') I'd love to know about them. In the meantime, I'll keep talking about what I've measured.

Does the placement of the hole relative to the waist make a difference?

The closer to the 'normal' hole the port is the less effect it will have on the timbre, because it's 'listening' to the same resonances the main hole is. I settled on a port in the right side, just above the wide part of the upper bout, as being a spot that will be heard by the player and won't change the timbre too much.

One interesting thing: within reason the size of the hole does not seem to matter is terms of the power output. I got the same sort of (very small) change with two 5/8" holes that Chaigne got with one that was several inches long. The bigger hole has more of an effect on the timbre, though.