Sound Ports?

Construction and repair of Classical Guitar and related instruments
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Sound Ports?

Post by DTut » Fri Sep 08, 2017 3:09 am

Ninety-nine percent of the time I play the guitar for myself only. I know the sound is much fuller and louder to someone in front of the guitar.

Do sound ports really help bring more sound (volume) to the player? Any thoughts before I take an auger to the upper bout?

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Re: Sound Ports?

Post by oski79 » Fri Sep 08, 2017 5:01 am

A number of years ago I did just that on an old guitar-- cut a hole about one and a half inches in diameter. I noticed the difference immediately.
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Re: Sound Ports?

Post by astro64 » Fri Sep 08, 2017 3:41 pm

I noticed a difference too when I did this on one of my guitars and did not like it at all. The A and D resonated more strongly through the hole and were out of balance.The soundport is kept closed! YMMV. But I would not repeat the experiment and won't buy a guitar with sound ports. You may hear more, but it is unlikely that it represents the actual full guitar sound you would hear from the front. That largely comes from the top, not out through a hole.

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Re: Sound Ports?

Post by Alan Carruth » Fri Sep 08, 2017 4:38 pm

I've done more experimenting with sound ports than I ever meant to over the past several years. These include building three 'test mules' with various port configurations, making reams of measurements such as spectrum charts and resonance plots, and a 'bind' listening test that involved more than 100 players over a couple of years. Here's what I found.

Ports work, at least for the player.

At low frequencies the sound of the guitar goes out in all directions; it's a 'point source' for the fundamentals of the lowest notes. As you get up around the pitch of the open G string it starts to become more directional, and at high frequencies most of the sound is coming off the top and out of the hole, going toward the audience.

You, as the player, only hear those high frequencies if they get reflected back toward you. Having played once in a large, dead space with a sound system that had no monitor, I can tell you that it's disconcerting (note pun), particularly if it's also cool enough that you lose sensation in your finger tips. A port 'hears' some of those high frequencies, and one that you can look into will send some of that sound out toward you. It doesn't have to be very big to work pretty well: your hearing tends to get more sensitive at high frequencies, so you don't need much to fill in the blank.

Naturally, as an added sound hole in the box, the port can change the timbre of the guitar. Any port will raise the pitch of the 'main air' resonant mode and make it a bit more powerful. how much it changes depends on how big the port is, and where it is: basically, the larger the port and the further from the main sound hole, the greater the change. Usually the pitch change has more of an effect on the timbre than the added power, but where you end up depends a lot on where you started out. Because there are so many variables it's hard to predict exactly what a port will do in a given guitar.

The listening test I did used a rough, but decent sounding test mule guitar with a 52mm diameter port in the wide part of the upper bout facing the player. This is larger than I often use, but is fairly common. The port has a 'door' that can be removed and replaced quietly. I had people sit with a blindfold on, and handed them the guitar. Once they had played it, I took it back for a couple of seconds and had them play it again. I then asked them if it sounded 'the same' or 'different'. Each time I handed it to them I used a coin toss to decide whether the port would be open or closed. About 50% of the time the configuration was 'the same'. The tests were run at two successive Montreal Festivals, a GAL convention, and a local folk festival. The average noise level was about 70 dB-A.

When the port configuration was unchanged, the players guessed, getting it right about 50% of the time. When it was different, they got it right almost every time. The people listening were not polled, since for them it was not a 'blind' test, but many of them volunteered that they really could not hear any difference when the port configuration was changed.

Other testing, done by an associate, using a different test mule I loaned him in quiet, reverberant spaces, showed that players could not hear any difference when the configuration was changed.

So, the bottom line is that a port might well be useful to you if you tend to play a lot in large, 'dead', or noisy places (a 'restaurant gig'). Otherwise it might not help much. Some feedback I've gotten indicates that people with hearing loss often find a port helpful. That makes sense, since the usual hearing loss involves decreasing high frequency acuity.

I could fluff this out with a lot more detail, but that's the gist.

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Re: Sound Ports?

Post by UKsteve » Fri Sep 08, 2017 4:51 pm

I have a nylon guitar with a port. I play for myself, at home so thought it would be a good idea.

Initially, I was impressed - sounded more direct, fuller, more "reverby".

However, I came to dislike it intensely. The diffuse quality that it bestows to what I'm hearing really gets on my nerves - the notes are less fundamental and have less focus. That's a pain if the guitar is otherwise a really good one (which this one is).

As Al mentions above, the box resonance does change - it's easy to examine this; just stick a sock etc. in the hole and then pull it out. Mine is higher with the port uncovered.

YMMV: Many of my friends like the port. I've concluded that I don't.

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Re: Sound Ports?

Post by GuitarB » Fri Sep 08, 2017 5:23 pm

I was considering to purchase the guitar with the sound ports. Is it true that you will hear what the audience hear?

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Re: Sound Ports?

Post by souldier » Fri Sep 08, 2017 5:43 pm

I've owned or played several guitars with ports. They definitely make a difference for the player and I personally like how it makes the guitar sound. The guitar will sound louder, more resonant with a more prominent bass to the player. I've always tested going back and forth closing and opening the port to see if someone directly out front can hear a difference. At first they couldn't hear any difference, but with very careful listening they could hear a difference. The difference however was so miniscule that it doesn't make a difference for the audience.

If I were having a guitar made, I'd love to have a single player side sound port with magnetic cover as seen on guitars made by Stephan Connor, Douglass Scott, Joshia de Jonge, etc. I like this solution as it gives the player the option to open, close, or open partially depending on the desire of the player. It is also important to note that when you open a sound port, it causes the resonance of the guitar to go up a semitone which can definitely change how certain frequencies respond on the guitar.
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Re: Sound Ports?

Post by MessyTendon » Fri Sep 08, 2017 8:16 pm

What you hear at the port is not the same and also the main soundhole. Think of it as wimpy monitor...

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Re: Sound Ports?

Post by celestemcc » Fri Sep 08, 2017 9:11 pm

I have a Connor with a port. When I played guitars in his shop to decide on what I wanted, I made a point of closing the ports -- didn't want to be seduced, frankly! Loved the guitars anyway, so had him make me one. Now I play it with the port open almost all the time. I've also heard others play it with and without the port cover: the big difference is to the player, really, not to audience.
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Re: Sound Ports?

Post by Tom Poore » Fri Sep 08, 2017 9:51 pm

Interestingly, when sound ports were first becoming a thing, we were told that they clearly increased the volume to the audience. (Something about certain frequencies trapped within the standard soundbox being released by the ports—I may have that wrong, as my eyes usually glazed over during these abstruse explanations.) Nowadays sound ports are almost always billed as an advantage to the player. Not much is said about sound ports increasing volume to the audience. Probably because most players trusted what their ears were telling them.

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Re: Sound Ports?

Post by JohnH » Sat Sep 09, 2017 1:31 am

If you want to preserve the Helmholtz resonant frequency the size of the front sound hole needs to be smaller so that the total area of the main sound hole and the side port would be the same as the area of the original sound hole without the side port.

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Re: Sound Ports?

Post by Jim Frieson » Sat Sep 09, 2017 12:06 pm

A good feature of soundports is : If by chance the guitar has a wolf note problem , drilling a hole for a port is remedial . I found this to be the case on a few occasions . Of course , the side has to be fortified in the are a of drilling during construction .

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Re: Sound Ports?

Post by Abel Schmitt » Sun Sep 10, 2017 7:38 pm

I've tried several guitars with soundport. I confirm a volume increasing, but sincerely I don't like it because I consider the sound too aggressive for the player

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Re: Sound Ports?

Post by Alan Carruth » Sun Sep 10, 2017 8:29 pm

Reducing the main soundhole size when building a guitar with a port really helps to preserve the 'normal' sound. Some of the 'brashness' of guitars with added ports seems to be related to the high 'air' frequency. It's a bit tricky to figure out how much to change the size of the main hole, since the effect of the port varies depending on where it is, for a given size. A port at the base of the neck will raise the 'Helmholtz' type resonant frequency a lot more than one just below the wide part of the upper bout, and a small hole down at the tailblock can have an even greater effect. One solution is to make the main hole smaller, and have a fairly wide margin of wood between the edge of the hole and the rosette. Then, if you have to, you can enlarge the hole a bit. It's not so easy to make it smaller...

As always with the guitar, when you look closely this gets very complicated. Not everybody is going to like all of the effects of a port, just as some folks prefer spruce to cedar. The more you (ad your luthier) understand about what they really do, the better you'll be able to make a choice you'll be happy with.

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Re: Sound Ports?

Post by Martin Woodhouse » Mon Sep 11, 2017 12:10 pm

You can also add a shallow tornavoz to the main soundhole to lower the 'air resonance' frequency - I did a simple experiment to test that a few years ago, and found that, on average (though different guitars respond differently), 2.5mm of tornavoz depth will lower the air resonance by about 1Hz, so you can use that as a rule-of-thumb to tune the resonance to whatever frequency you want (within reason).

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