Soundport experience

[Gerald Sheppard]

I remember waiting for a few years before I started offering sound ports. I would go the guitar shows and play a guitars that had them. I was concerned they might be fads too, so I interviewed dealers to see if their popularity was solid. I also spent time talking with other makers. I finally I started offering them a few years ago. I place them wherever my customer wants them but I actually prefer them on the lower bout a few inches off the waist. It's subjective to a point but I will mention some of my reasoning for my preference.

Air flow and volume - I've found that sound ports open a second point of flow for the lower bout as the guitar is played. Instead of the air trying to move in and out of the guitar simultaneously through the one soundhole (which causes some resistance), when the port is in the lower bout, it allows a cross flow; therefore the top is able to move more freely allowing it to yield a touch more volume and sustain (I know, I know - if everything increased sustain that people advertise does, guitars would never stop ringing, haha!).

Sound blockage - Contrary to some beliefs, the players arm does not block the sound from a port placed in the area I mentioned above.

Proximity to the ear - this is subjective, but as a player, I like to hear a blend of sound from the port and ambient sound from the room. If the port is too close to my face I get that closed-in feeling - like when I was a kid and would get in a cardboard box and talk. Just ain't natural!

Sound ports aren't for everyone and their locations are very preferential. If you are in a location where they are available in shops, it might be a good idea to play some guitars with ports in different locations a see which you like best.

[Alan Carruth]

I've done 'way more research on ports than I meant to. The 'corker' was just the first test mule I built for that: I've got three now. As with everything having to do with the guitar it can get complicated, but it can also be simplified to some extent without doing too much violence to the data.

As Chuck said, guitars tend to put out sound differently at different frequencies. Since the guitar is 'small' compared with the wave length of the lowest notes it's trying to make, those sounds go out more or less uniformly in all directions. The player hears as much of those as anybody. As you get up around the pitch of the open G string it starts to get more directional, and the highest frequencies are pretty much going off the top and out of the hole toward the audience. A port that you can look into will send some of the highs in your direction, and even a little of that can help a lot.

Opening a port is an existing guitar does alter the sound a bit. Most of the change is in the lowest frequencies, the so-called' bass reflex' range from the lowest notes up to around that open G pitch. There are two main resonances in that range; the 'main air' resonance, which works pretty much like blowing across the mouth of a wine bottle, and the 'main top' resonance, where the lower bout of the top moves like a loudspeaker diaphragm.

Since it's easier to move air in and out of the box when there is an extra hole the 'main air' resonance always gets stronger. Since there is less pressure change in the box to resist top movement, the 'main top' resonance can also get stronger. Generally speaking the 'air' resonance gains more than the 'top'.

The exact amount of the change will depend on how big the port is, and where it is. In general, the larger the port and the further it is from the main sound hole the greater the effect. A fairly large port at the widest part of the upper bout on the side can increase the 'air' resonant strength by as much as 4dB in measurements I've made. That's more than double the power, and more than the 'just noticeable difference' in loudness of 3dB, so it could be audible. A pair of ports with the same total area cut into the side and top at the base of the neck ('Thurman mulitdimensional ports') can increase the 'air' output by 7dB. Both of these measurements were made on the center line of the guitar a meter out with the mic between the hole and the bridge in height. These impressive looking gains in power take place over a very narrow frequency band; less than a semitone, usually. Averaging over the entire spectrum of the guitar there does not seem to be any gain in output: the port doesn't seem to make the guitar more efficient over all so far as I can tell.

Given that it's easier to move air in an out the pitch of the 'air' mode also rises when a port is opened. Again, how much depends on where the port is, but generally a change in power corresponds to a change in pitch: more of one means more of the other.

A port in the side of the guitar can also 'hear' internal air resonances that don't normally communicate well with the main sound hole. Often enough these are 'losers' on the non-ported guitar; any energy that goes into them tends to be wasted, and they can show up as 'dips' in the guitar's spectrum. If a port 'hears' one of these it can become a 'peak', although often a low one, and, of course, the pitch is usually raised as well.

I suspect that it's these changes in pitch that are what people hear out in front more than anything else. We're not usually very sensitive to even fairly large changes in power so long as the spectrum remains the same. However, there's a real survival value in hearing 'new' sounds, or sounds that stop, even at a low level, so we're very sensitive to those. When I took the 'corker' to Healdsburg people would play it, pull out a couple of corks, and say: "Wow! That's louder!" After a few minutes of playing they were not so sure: it took just as much effort to be heard in that noisy room, so I'm pretty sure the initial reaction was to a change in spectrum more than power.

One experiment that was done by another researcher using the 'corker' found that players could not hear the difference in a blind test. The sample was small, and the tests were all done in reverberant rooms where reflections from the walls and such could provide high frequency feedback. Also, of course, those corks are small, and don't change things much. The third test mule I made has a larger port, that is easy to cover up, and I got over a hundred people to do a blind test at two Montreal shows, a GAL convention, and a local folk festival. The venues were fairly large rooms with background noise ('white' noise) averaging about 72 dB-A. Basically, when the port state was not changed between playing tries people were guessing. When it was changed they almost always got it right. When I showed the numbers to my statistics guru he didn't even bother to run them through the software the result was so strong.

The upshot is that listeners out in front may or may not perceive any change in the timbre of the guitar in a 'blind' test when a port is opened, but the player probably will if the port is in a place where they can look into the guitar. It seems to me that the primary use of a port is as a 'monitor' for the player in large, 'dead' or noisy rooms (think 'restaurant gig'). When I design a guitar to use a port I reduce the size of the main soundhole a bit to keep the resonances in the range where I want them. It's a bit of an art to tell how much to change things, since the port size and location make so much difference.

That's my story and I'm sticking with it.

[Gerald Sheppard]

Good info Alan!

[Wade Hampton]

I'll just chime in and add that I found for my playing that soundports definitely affect how much sound from the guitar I can hear when I'm fingerpicking. But I'm not even remotely a fingerstyle player, and what fingerpicking I do do is bare-fingered on the pads of my fingers, not with picks or my nails.

I use a pick for anywhere from 90-95% of my playing, and I have a strong right hand that probably came from playing mountain dulcimer as my first instrument and needing to get the tone and projection out of it.

This isn't to say that I thrash and play full throttle all the time on every instrument, but what it does mean is that I get a lot of volume and projection when I use a pick.

So when I play with a pick, I've found that the soundports offer me no advantage: I don't get any more volume on guitars equipped with them than I do already. I've owned two spundported guitars, and still own one of them, and it's like flipping an on and off switch for the soundport when I play bare-fingered and then reach for a pick.

So if you play with a light touch, and especially if you're a fingerstyle player, soundports do offer the player some advantages. But for the way I mostly play, I neither need nor want soundports.

Hope that makes sense.


Wade Hampton Miller

[Alan Carruth]

Thanks Wade. The test I did was with Classical guitar, and I didn't think to see if there was any difference in people's experience when they used a pick, since so few did. Another experiment that needs to be done!

[Wade Hampton]

Originally Posted by Alan Carruth

Thanks Wade. The test I did was with Classical guitar, and I didn't think to see if there was any difference in people's experience when they used a pick, since so few did. Another experiment that needs to be done!

Well, the player's attack with a pick is a factor there, as well. Back when I still lived in Kansas City I played with a really superb musician named Don Young. Don had learned to play on an electric guitar, and had a very light touch on acoustic. You could barely hear him when he played acoustic guitar, so his attack and mine were quite different, even if we took turns using the same pick on the same guitar.

I suspect Don is one of those guys who would benefit from having a soundport on his guitar.


whm

[The Bard Rocks]

I became a believer at one of the Montreal shows. Yes, it definitely sounder louder to me, easier to hear above the din of the crowd. We did some uncontrolled "experiments", having someone cover and uncover the port while I was playing. What surprised me was that my audience (which changed from time to time), with eyes shut or open, could not tell when the port was covered or uncovered. They were surprised, too. It seemed only logical that there would be a difference. After all there is a certain finite amount of air moving inside and if some gets out of the port, it stands to reason that there is less to come out the soundhole and therefore it should be a bit quieter to the audience. So much for theory; our practice did not bear that one out.

[doublescale1]

I had a Breedlove Ceder/Mahogany guitar with a sound port that had a rubber stopper in it - I really liked it for sitting by myself and practicing and just playing while sports were on tv. I eventually sold the guitar because I mostly strum not finger style play and the Cedar top really compressed too much and got all mushy. Other than that, I found no compromise in overall tone when playing with the tone-port stopper in or out. It really didn't make any difference when I ran the guitar through an amp. That was my experience any way.

[kmcmichael]

Originally Posted by bohemian

"saying it's silly makes it directed at anyone that think they are worthwhile. "

That is your opinion and your interpretation, I am only speaking for myself and do not foist my opinion on others.. I do not project...

Saying they are worthwhile is saying everyone thinks they are groovy...
they are an affectation.. a fad, a new age phenomenon.


It is MY opinion only that it is a silly affectation that will fade away..

Time will tell.

I believe this to be incorrect.

[Big_Al]

I've added side sound ports to several guitars . . . a Seagull S-6, a Larrivee L-03, and three Alvarez jumbos. I'll report that the change was noticeable and positive. I play in a choir with a piano and other guitars. I could hear myself better in the group, and the guitars sounded better at home too.

My current guitars are plenty loud, so I don't plan to port them. Unless they came that way from the builder, I think it does make them a little harder to sell.

[Alan Carruth]

The Bard Rocks wrote:
"After all there is a certain finite amount of air moving inside and if some gets out of the port, it stands to reason that there is less to come out the soundhole and therefore it should be a bit quieter to the audience. "

Actually, the guitar becomes more effective at producing sound at certain frequencies when the port is open. One way to think about it is from the viewpoint of air trying to get into and out of the box. When you open another sound hole it's easier for the air to move in and out, just as opening another door in a room allows people to enter or exit more quickly. Since the air can move in and out faster the resonant pitch rises when the port is open, and it makes more sound at that pitch. How much everything changes depends on how big the port is and where it is. A port of a given area at the wide part of the upper bout can increase the output at resonance by 4 dB ( a bit more than double the power at the resonant pitch, which is, of course, different). The actual pitch might rise by 7 Hz or so. A pair of ports, with the same total area, at the base of the neck cutting into both the side and the top increased the output at resonance of the same guitar by 7 dB, and changed the pitch by more than 9 Hz. I'll note that doubling the power may niot sound much 'louder' up close, but will tend to 'carry' further.

It bears repeating that these changes are at specific frequencies: even a little off resonance the spectrum is not affected much, if at all. When I summed over the output from the lowest pitch up to about 1000 Hz the port didn't seem to make ant positive contribution, and may actually have reduced the output by a small amount.

Overall, then, any change you hear is most likely due to spectrum changes that alter the timbre of specific notes, and also changes in the directionality of the sound radiation pattern. The timbre changes are really only noticeable in an A/B comparison for the most part, since it's hard to remember tone very exactly for any length of time. Thus the main utility of the port seems to have to do with the change in the direction of the sound output, particularly at high frequencies, for the player. My data says it's most useful when high frequency feedback from room reflections is absent, in a big, 'dead' or noisy space.

[Tim McKnight]

Originally Posted by Bearclaw Spruce

Richard Hoover would argue something along the lines of the air gushing out the soundport will decrease the amount of air gushing out the soundhole and therefore have some sort of impact on tone. I can't remember the exact wording he used but he addressed this to that effect on the SCGC forum a while back.

I would respectfully disagree, at least according to the testing that I have done. Every sound ported guitar, that I have measured, has ALWAYS been louder in front of the main sound hole. Some are louder than others but there has always been a forward projecting and measurable gain in volume. If you care to read more you can by clicking here.

[Poutine]

My Eastman AC822CE-FF Prototype has a sideport and I feel that it's an essential piece to the guitar as it improves my enjoyment of the instrument. Gotta get one added to my Guild 12 string!

[sleepjeep]

If someone would like to see the effect a sound port has on air movement you can set up a simple experiment to visualize this. (I'm referring to Alan's statement that increases the air moving out of the sound hole)

Take a can filled with a liquid. Punch a hole in the top and pour. Now punch a second hole and notice the liquid pours out faster. (You can move the second hole and change size to optimize flow.) This part of fluid dynamics, which was the fun part of physics for me.

[Coffeeaddict]

Originally Posted by sleepjeep

If someone would like to see the effect a sound port has on air movement you can set up a simple experiment to visualize this. (I'm referring to Alan's statement that increases the air moving out of the sound hole)

Take a can filled with a liquid. Punch a hole in the top and pour. Now punch a second hole and notice the liquid pours out faster. (You can move the second hole and change size to optimize flow.) This part of fluid dynamics, which was the fun part of physics for me.

That reminds me of the can Pepsi came in back in the 80's.