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Any info about how a soundport changes the sound?
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Author:  Alain Moisan [ Mon Nov 04, 2013 9:24 pm ]
Post subject:  Any info about how a soundport changes the sound?
Hi all,

Maybe this has been asked before, but I didn't find any information about it. I'm wondering if anyone ever tested how (or if) the presence of a soundport changes the sound of a guitar from an audiance perspective. We all know it has a great impact from a player's perspective, but I couldn't find info about the audiance prespective.

If someone can share information about that, I would appreciate it.

Thanks!
Author:  Peter J [ Mon Nov 04, 2013 9:36 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
Al Carruth is the only one I know of who has done some objective research on sound ports. He covers it thoroughly on his website:

http://www.alcarruthluthier.com/Downloads/sidePorts.pdf
Author:  Alain Moisan [ Mon Nov 04, 2013 9:42 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
Thanks Peter!

I actually found this on Delcamp, which seems pretty detailed. But I will most certainly go through the link you sent.

Cheers!
Author:  Alan Carruth [ Tue Nov 05, 2013 1:45 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
I'm just writing up my most recent experiment, on whether players can hear the difference with an open or closed port in a noisy room, where they don't get the usual feedback from room reflections (they can). In the course of it, I stuck my Classical 'test mule' in the 'anechoic closet' and got some measurements that might be useful here. Keep in mind that these are for this guitar: YMMV.

The big change was out to the side, where the player's ear is, as you might expect. The biggest increases in output were between 400-500 Hz, and in the 2k-4kHz range. The shift around 450 Hz was about 60dB, and was due to some pitch shifts that helped increase 'coupling' of the top and air when the port was opened. You won't always see this. However, there were several other shifts in the 20dB range.

Out in front the picture is different. Almost none of the changes were greater than 10dB, and most of them were simply due to pitch shifts. For example, opening the port raises the 'main air' pitch from about 98 Hz to 108 or so. With the port closed there's 10dB more sound at 98 Hz than there is with it open. At 108 Hz there's around 12 dB more sound with the port open than with it closed. S, the port made the guitar a little louder at the 'main air' pitch out front, but not so much that you'd pick it up right away. Wright, and others, have shown that simple pitch shift is not usually noticed by listeners unless it falls right on a played note, when it wil come across as a change in timbre of that note. In this case the 'closed' 'A-0' mode at 98 Hz is right on the pitch of the G note on the third fret of the low E string. You'd expect a 'wolf', and there is one, but most people don't notice it! The 'open' air pitch is between G# and A, and so does not reinforce either note all that strongly.

There was an increase in the average sound out front between 2-4kHz with the port open, of about 3dB, iirc. That's an audible difference, but not huge. I'd think it might come across as more 'projection' if you were listening carefully, but I'm not sure how useful it would be.

In all the testing (at two Montreal shows, a GAL convention, and a local folk festival) I don't recall any listener saying that the guitar sounded particularly different when the port configuration was changed, but blindfolded players picked it out very reliably. I suspect, based on a little testing at the GAL convention, that the port would make as effective monitor in a quite, dead space as it did in a noisy one. But it doesn't really seem to do much for the audience.
Author:  Alain Moisan [ Tue Nov 05, 2013 3:15 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
Thanks a lot for the extra information Alan!

Alan Carruth wrote:
But it doesn't really seem to do much for the audience.


That corresponds to my personal experience. Glad to know your tests go this way too.
Author:  Alan Carruth [ Wed Nov 06, 2013 2:22 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
I get real suspicious of tests that run counter to most people's experience. OTOH, what's happening is not always what people think is happening. Experiments can help you sort out what's really happening.
Author:  Goodin [ Thu Nov 07, 2013 9:25 am ]
Post subject:  Re: Any info about how a soundport changes the sound?
I have a friend who is a touring professional musician who believes that the side sound port makes the guitar louder from the audience perspective. This is of course anecdotal and just his personal experience with a few instruments but I do trust his judgement (one really develops an ear playing and performing often). I am building a bouzouki for him with a side port. I'll try to remember to report back when it's done. I have another zouk just like it without a sound port that I can compare it to.
Author:  Alan Carruth [ Thu Nov 07, 2013 4:07 pm ]
Post subject:  Re: Any info about how a soundport changes the sound?
One of the reasons scientists use blind tests so often is that people really do listen as much with their eyes as with their ears sometimes. People hear what the expect to hear. If you play a guitar for an audience, and then drill a hole in the side, they will hear a difference. After all, what sort of nut would drill a hole in the side of a perfectly good guitar if it didn't make it better?

The problem with blind tests is that you have to do a lot of them, with a lot of different instruments, to be really sure. My latest tests are pretty clear regarding that guitar, but some other instrument, where things line up differently, might give a different result. You can't generalize too freely from one, or a few, examples, unless you've got a really clear theory, and even then...
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