My little sound port test

[jklotz]

I'm getting ready to do a bit more recording, so I decided to do a little testing first. This was solely for my purposes but it occurred to me some folks might find it interesting, so I'm going to drop it here for my friends. Before I do, please understand there was nothing scientific about this test and I didn't make any effort to match levels. There is no eq, reverb, compression, etc, whatsoever. So please don't rake me over the coals for the faults of my testing methods or inadequacies of my scientific prowess.

I have a guitar, an Edwinson Eclipse, that has dual sound ports.



It seems to me that the air that the body of a guitar can move is finite and I was wondering how sound ports effect the tone coming out of the front of the guitar. What would happen if I recorded it both with the sound ports and with the sound ports closed over. Would I get a better tone with them closed from the front of the guitar, as in for a recording? That was my mission.

So I tried it. (I realize painters tape is not the ideal solution to stopping up the sound ports, but that's the most invasive thing I'm willing to do to my guitar, so that's what you get). Mics are Neumann KM184's going into an apollo preamp then direct into Logic Pro. Levels were not touched.



First, the front of the guitar. Open sound ports first. Mics are about 12" in an x/y pattern:



So what do you think? Can you hear a difference?

So while I was at it, I changed the mics to be over each shoulder, just behind my ears. The goal was to try to simulate what I hear from the playing position. Again, no level changes, one with ports open, the other with them taped over. This is for you guys, I was only interested in the above. But I'm curious, hear a big difference? (First is taped up, 2nd is open)

[Rosewood99]

Sound ports are for the benefit of the player, not the listener. Are you worried that the sound port will degrade the sound for the listener?

[Gee Man]

I hear a difference. The open sound ports make for a rounder tone, not as clear and bright as with the ports covered. I noticed it in both clips.

[Robin, Wales]

With a set of reference headphone on, and jumping back and forth from the same point on the covered to uncovered recordings, I can hear a little fuller sound with soundports covered on both the in front and overhead recordings. More so on the overhead track - which was surprising as I expected the open soundport recording to have distinctly more volume on the overheads but, if anything, it was the other way around.

I like the fact you made me think hard as the two tracks (front and overhead) were recorded the opposite way around! I have had to listen a number of times to check what I was hearing.

[jrb715]

I also hear a difference--and it is significant in the second clip. Assuming I have it right and the first sample in each clip is with the sound ports open, then I hear a more focused, crisper, better tone with the sound ports open. The second sample with the sound ports closed sounds more vague, almost smeared. This is barely apparent in the first clip, but very clear in the second clip. The guitar sounds much better--assuming the recording is something like the actual non-mic sound--with the sound ports open. This is what I would expect in a well designed guitar. It would be tuned to sound its best with the sound ports working effectively.

For the headphone system, I'm listening through Focal Stellia headphones and a Schiit Gugnuir DAC and Jotunheim headphone amplifier.

Through the speaker system I'm listening through ATC 10 monitors, the Gugnuir DAC and a Roksan K3 integrated amplifier.

[jricc]

Hi James, thanks for this interesting test. In the "Front" test, I can hear a difference, with the ports taped, it seems the sound is a little warmer fuller in the mids. If I have this right, the first bit of the "Front" sample is taped, the 2nd is half is ports open?

I find this interesting because I have one of the new Generation Gibsons, the
G-00 with a port. Someone made me a wood cover that wedges in the port, and with the port in, it seems to warm up a bit, of course that could be there is less sound coming out at my ear.

Anyway, thanks again, good experiment.

[Robin, Wales]

Originally Posted by jrb715

I also hear a difference--and it is significant in the second clip. Assuming I have it right and the first sample in each clip is with the sound ports open, then I hear a more focused, crisper, better tone with the sound ports open. The second sample with the sound ports closed sounds more vague, almost smeared. This is barely apparent in the first clip, but very clear in the second clip. The guitar sounds much better--assuming the recording is something like the actual non-mic sound--with the sound ports open. This is what I would expect in a well designed guitar. It would be tuned to sound its best with the sound ports working effectively.

For the headphone system, I'm listening through Focal Stellia headphones and a Schiit Gugnuir DAC and Jotunheim headphone amplifier.

Through the speaker system I'm listening through ATC 10 monitors, the Gugnuir DAC and a Roksan K3 integrated amplifier.

In the second recording (overhead) the first section is with the ports taped closed. The second section is with the ports open. It is the reverse of the first (in front) recordings. Or at least that's how I'm reading the OPs post?

[Howard Emerson]

James,
Did you stay absolutely still while somebody pulled the tape off in between takes to make sure that the proximity to the mic did not change at all?

Howard Emerson

[steelvibe]

Thanks for doing this experiment. Assuming you changed nothing other than mic placement it is about as good as one can get to hearing the differences. To my ears (and the Skullcandy cans I used in the listening) the guitar sounds a bit brighter with the ports open both out in front and overhead. I agree with Robin on this; while completely my opinion and realizing this is all so subjective, the guitar was suited more to my tastes with the ports closed.

This is a bit surprising to me.

[zmf]

Thanks. Interesting. On the "front" recording, the higher frequencies seem more prominent with the ports open (the first half of "front" recording, right?). The volume of the lower frequencies seems to increase with the ports closed, resulting in a fuller, "warmer" tone.

So more low frequency is lost at the front of the guitar due to the sound ports?

[fitness1]

Originally Posted by Rosewood99

Sound ports are for the benefit of the player, not the listener. Are you worried that the sound port will degrade the sound for the listener?

There is a reasonable body of evidence against that theory. To make a blanket statement like that would not be completely correct.

Ports change the air resonance, and if they are done correctly, can change a lot of the instruments tonal qualities and volume.

My guess is the OP is just trying to find out what those differences may be in the ears of others via recording (which is terribly hard to produce!)

Jklotz, may I suggest rolling up a pair of socks or something similar and putting them in the holes? I use some good quality foam and squeeze it and insert and let it expand when I do similar tests.

[MikeMcKee]

Since the purpose of this was to get a feeling prior to recording, my ears would prefer front recording with the ports closed. I assume the second mic placement was solely for getting the feel of what you would be hearing, not an actual mic placement for recording.

I pretty much ended up stuffing a sock in any sound ports I had in the past. Just not for me.

[jklotz]

Hi guys, OP here. A couple of things:

The reason the order of the clips (open vs closed) is reversed is I first played with them open then put the tape on, then for the 2nd clip, since the tape was already on, well, you get the picture. Guess I could have edited them to be the same, but I didn't. Part of me wishes I had not given the answer yet and saw who could have guessed it correctly.

Another eye opener for me was how much of a difference I heard that got lessened going from the DAW to sound cloud. I think Doug Young had a thread about that here recently over in the record section. That streaming soundcloud really eats the detail off the track! The difference is much more apparent when listening to the original recording. If anybody is really interested, PM me and I'll email you the MP3's.

Another observation was how difficult it was to capture what I hear when they are closed vs open, from the players perspective. First, no way to get the mics where my ears are while I'm playing. Secondly, I probably need omni directional mics, which I don't have. In other words, I heard a much bigger difference in person than I did in the recordings.

[jrb715]

So, if I have the open/closed backwards with the second clip--and the first sample of the clip is with the sound ports closed--then I much prefer the closed sound port recording. This might not be, perhaps is likely not to be, the case were I to hear the sound live; and the smearing I hear is the mics not being able to entirely or accurately pick up the envelope of sound the guitar throws. But if I were recording the guitar with that mic set up, I'd tape up the sound ports.

[fartamis]

I hear a warmer sound with the ports closed. with the ports open I find the sound more thinner and a little less loud.