Soundholes

[Tony Done]

I've been idly wondering about soundhole sizes. This comes from a recent
trip back to the UK where I was reunited with the second (steel string)
acoustic guitar I ever bought, after a gap of maybe 40 years. Someone
had enlarged the soundhole from about classical size to about 4", and it
sounded a lot better than I remember it. Much brighter, even with very
old strings.

How much difference would a bigger soundhole make to a standard dread,
as Martin have done with the Clarence White model? How about a port in
the side? Maybe adjustable the way the tune ocarinas. - I'm thinking you
could remove a side-mounted preamp and convert it into a (adjustable?) port.
--
Tony Done

http://www.soundclick.com/bands/default.cfm?bandID=784456
http://www.flickr.com/photos/done_family/

[Alan Carruth]

Soundhole size sets the pitch of the 'Helmholtz' resonance, which is the main determinant for the 'main air' pitch. I believe it may have an effect in the very high frequency range as well.

If the guitar body were rigid the size and location of the soundhole would be about all you'd need to know to find the pitch of the Helmholtz resonance pretty closely. As it is, the flexibility of the walls, and the top in particular, make the guitar into a 'bass reflex cabinet' in it's low range, and shifts the 'air' mode pitch down from where it 'should' be. The hole still works the same way, so making it larger raises the 'air' pitch just as opening another hole in the ocarina does, it's just that it's harder to predict exactly what that pitch will be.

Adding a port also raises the 'main air' resonant pitch, but, again, it's not straightforward. Generally speaking the larger the port and the further away from the 'main' hole it is the greater the pitch rise. Opening a port also makes the 'main air' resonance stronger, and usually augments the 'main top' output (the other half of the 'bass reflex couple') as well.

In some ways, you can think of the sound hole as if it were a speaker in a baffle. We all know that small speakers don't produce low tones well, and it's the same with soundholes. It makes a lot of sound at the low 'Helmholtz' pitch, but that's mostly because the top (and back, too, maybe) is pumping so much air that it can't help it, even at low efficiency.

As you go up in pitch, then, the hole becomes more and more efficient, and, at some point, when the wave length of the sound in air is about equal to the sound hole diameter, the efficiency will approach 100%. This is the 'upper cuttoff frequency' of the hole. Above that pitch, if there's any sound energy in the box, it's being radiated out as fast as the guitar can produce it. Note that the larger hole, with the lower cuttoff frequency, reaches that 100% efficiency level at a lower frequency, so it's going to tend to have _more_ high end output than the smaller hole. I think this is one reason why guitars with larger holes sound 'brighter'.

The range of soundhole sizes we normally use yields cuttoff frequencies in the range from 3000-5000 Hz or so; just where normal ears are most sensitive, and in the range of consonant formants. In other words, these are sounds that carry well, and tend to convey a lot of information. It's my opinion that this is why seemingly small changes in soundhole size can be so noticeable in the sound. Making the hole 5mm larger in diameter doesn't change the 'air' pitch much, but it can alter the cuttoff frequency noticeably. Benade did experiments with this sort of thing in woodwinds, and found that a semitone change in the cuttoff pitch (6%) was sufficient to entirely alter the character of something like a clarinet. I don't see why the same would not hold in guitars, at least to some extent.

Of course, just because something is reasonable, that doesn't make it true. One of the many experiments I want to try.

[Tony Done]

On 15/02/2013 5:55 AM, Alan Carruth wrote:
> Soundhole size sets the pitch of the 'Helmholtz' resonance, which is the main determinant for the 'main air' pitch.
>

Thanks Al, I was hoping to get a reply from you. I already knew about
the Helmoltz thing, but hadn't appreciated the rest of it. I would
really like to try the experimental approach, but I'm reluctant to hack
into any of my current guitars - they were, after all, bought for their
already-decent tone. I might try removing the preamp from one, then
cover the resulting hole by various amounts. Unfortunately the guitar in
question is already bright to start with, so I'm not sure that any
change would be for the better.

[Tony Done]

On 15/02/2013 6:32 AM, Tony Done wrote:
> On 15/02/2013 5:55 AM, Alan Carruth wrote:
>> Soundhole size sets the pitch of the 'Helmholtz' resonance, which is
>> the main determinant for the 'main air' pitch.
>>
>
> Thanks Al, I was hoping to get a reply from you. I already knew about
> the Helmoltz thing, but hadn't appreciated the rest of it. I would
> really like to try the experimental approach, but I'm reluctant to hack
> into any of my current guitars - they were, after all, bought for their
> already-decent tone. I might try removing the preamp from one, then
> cover the resulting hole by various amounts. Unfortunately the guitar in
> question is already bright to start with, so I'm not sure that any
> change would be for the better.
>

Just another thought. Does a side port 1) increase the players
perception of tone and/or volume and/or 2) does it do either of those
for the audience perception?

[Alan Carruth]

" Does a side port 1) increase the players

perception of tone and/or volume..."

Yes, and no. (don'tcha love definitive answers?) Basically, the benefit you get depends on where the hole is, and where you're playing it.

Several years ago RM Motolla borrowed my 'corker' guitar to do an experiment on side ports. He did a blind test with a number of players in different venues, to see whether they could hear the difference with the port open or closed. He determined that they could not. When he published this in 'American Lutherie' magazine people went ballistic. Some of the responses were pretty funny: "I can never hear anything in blind listening tests, but I _know_ that ports work!!!"

One of my students does statistics for a living, and pointed out that the sample size he used was marginal. In his defense, it's hard to recruit people for these things. My main objection was based on the places where he did the tests: a luthier's workshop, and the practice rooms and a small auditorium in a music school. Based on the changes I've measured comparing a guitar that ported or not ported (in fact, the very one he used), I'd say those were the wrong venues for that test.

Aside from the (sometimes major) shift in output in the low range, the port also radiates high frequency sound. Normal guitars act as 'point sources', more or less, for the low end sounds, because the box is much smaller than the wave length of the lowest notes in air. As you go up they tend to become more directional, particularly above the 'bass reflex' range around the pitch of the open G string. By the time you hit 1000 Hz or so, a lot of the sound is going off the top and out of the hole toward the audience. The player generally only hears this from room reflections. In small, quiet, lively rooms, such as the ones he used, there's enough high-end feedback to the player that opening a port doesn't help a lot. The real test is the 'restaurant gig', a fairly large, dead room with some background noise, or so it would seem to me.

I did some testing at the last two Montreal shows, as well as at a folk festival last spring, and at the GAL convention last summer. In every case the rooms were fairly large, at least somewhat 'dead', and there was considerable background noise (roughly 70-72 dB-A in frequent measurement with a meter). One recording of the sound showed it to be 'white' noise.

The results I got were pretty clear: blindfolded players were just guessing when they played the guitar twice with the port unchanged: closed-closed or open-open. When the configuration was changed they got it right almost every time.

One possible objection to this is that noise is noisy: in this sort of setting you can't guarantee that there was not more noise, or worse noise, for some trials than for others. I did 120 trials, overall, so I think it's unlikely that there would be significant bias in that way. The results were consistent in all three (or four, depending on how you count Montreal) venues, so that does not seem to have been a source of problems.

It's entirely possible that large, dead, quiet spaces (the beach) would give the same results, but I have not tested that enough to know. It would also be nice to test a small, lively, noisy space. I could do that: playing white noise at 70 dB-A over my computer speakers in the shop while people played the guitar, but I'm not sure how much of that my students would put up with.

These trials were conducted with a 'test mule' classical guitar, with a port about 30x35mm in size just above the wide part of the upper bout on the right side. Logically it seems to me that the 'right' place for a port is where you can see it, since your ears are more or less behind your eyes. Ports at the base of the neck have a larger effect on the output for a given size, but may not give as much feedback.

" and/or 2) does it do either of those for the audience perception?"

The jury is out on that one. Even fairly large changes in power may not be very audible to the audience, and they're already getting most of the high end signal. There seems to be a consensus building that ports don't change things much for the audience, but this is muddied a bit by claims to the contrary, mostly by folks who have some sort of stake in the game, it seems to me. We won't know for sure until some blindfold tests are done on that.

[Tony Done]

On 16/02/2013 4:55 AM, Alan Carruth wrote:
> " Does a side port 1) increase the players
> perception of tone and/or volume..."
>

Thanks Al. I would guess that in my environment, the living room, I'm
not going to hear much difference. I know from things I have done that
the guitar sounds brighter from the front than it does from the back.
The same is true of guitar amps, what sounds comfortable from the side
can sound overly bright from the front. There is also a psychological
component, my guitars, especially the electrics, sound brighter when
someone else is playing them, even when I sit in the same position
relative to the amp.

Changing the subject a bit, my mate was trying to sell me one of these
the other day:

http://www.musiciansfriend.com/accessories/planet-waves-o--port

I've tried putting non-rigid reflectors in reso guitars, and all it does
is kill the tone by absorbing vibrations. I could bring it home and try
it, but my expectations are low enough that I don't want to bother
installing it.

[Kevin Hall]

"Tony Done" <tony...@bigpond.com> wrote in message
news:kfgsug$h0e$1...@speranza.aioe.org...

Had to chuckle while reading this thread. Many years ago, early '70s I
guess, I noticed that Jean Larrivee and all his disciples were using tiny
soundholes on their steel strung guitars. When I asked Jean about this he
gave a convoluted answer which boiled down to ' the small hole accentuates
the bass'. I suggested, half kidding, that the real reason was that
he'd had his classical style rosettes made up as a custom order during his
early days when he was building almost all classicals, and he was using up
the remaining rosettes. He vehemently denied that, perhaps a little too
vehemently. ;-)

Years later, early '90s, I visited Jean in his shop in Vancouver and
noticed that his steel strings were now sporting a more common ( and
practical) 4" soundhole and 'conventional' steel string rosette. When I
asked him about that change he assured me that ' the larger hole accentuates
the bass'.

Always good for a giggle, this stuff.

From a repairmans' perspective a 4" or better soundhole has the single great
benefit of allowing far more work to be done through the hole, especially
on a dreadnaught or other model which has sufficient body depth to allow a
good portion of a relatively skinny arm through it. Being of the
streamlined persuasion myself I can get my elbow through a 4" soundhole on a
dread, although it's more comfortable through a 4 1/8 incher for jobs like
bridgeplate removal, brace repairs etc. I went to 4 1/8" soundholes on my
dreads and jumbos years ago mostly for that convenience alone, but it
hasn't hurt the sound a bit.

All the best,
KH

[Tony Done]

Great story. How's the book going? First draft off to the publisher yet?

The soundhole thing reminds me of Gary Brown fixing my ancient L-00. The
action had got too high, and rather than reset the neck, he decided to
rebrace the lower bout - through the soundhole. He is a pretty muscular
bloke, and when I visited him a few days after he had done the work he
still had grooves and welts on his forearm. The repair has lasted about
18 years, but the action has again got too high; I'm contemplating a
neck reset this time, or maybe just trade it as-is.

All this also reminds me of the gynecologist joke. He decided to do a
course in car maintenance as a change from his day job. As the final
qualifying test the students had to pull down and rebuild the engine.
The gyno finished the job weeks after everyone else but nevertheless
came top of the class. He asked the instructor how this could be, and
was advised that he was the only one who did it all through the exhaust
pipe.

[Tom from Texas (The Tom Risner Fund for Deserving North Texas Guitarplayers is not liable]

Ask Norm Draper if ye can borrow one of his guitars. He won't notice
the difference if ye give it back to him and he'll probably forget he
loaned it to ye in the first place.

Tom (gotta try this for myself sometime) from Texas

[Tony Done]

On 19/02/2013 3:59 AM, Tom from Texas (The Tom Risner Fund for Deserving

maybe if I just gave him the hole and kept the rest of it.....

[Tom from Texas (The Tom Risner Fund for Deserving North Texas Guitarplayers is not liable]

On Feb 18, 2:15 pm, Tony Done <tonyd...@bigpond.com> wrote:
> On 19/02/2013 3:59 AM, Tom from Texas (The Tom Risner Fund for Deserving
> North Texas Guitarplayers is not liable wrote:
>
>
>
>
>
> > On Feb 14, 2:32 pm, Tony Done <tonyd...@bigpond.com> wrote:
> >> On 15/02/2013 5:55 AM, Alan Carruth wrote:
>
> >>> Soundhole size sets the pitch of the 'Helmholtz' resonance, which is the main determinant for the 'main air' pitch.
>
> >> Thanks Al, I was hoping to get a reply from you. I already knew about
> >> the Helmoltz thing, but hadn't appreciated the rest of it. I would
> >> really like to try the experimental approach, but I'm reluctant to hack
> >> into any of my current guitars - they were, after all, bought for their
> >> already-decent tone. I might try removing the preamp from one, then
> >> cover the resulting hole by various amounts. Unfortunately the guitar in
> >> question is already bright to start with, so I'm not sure that any
> >> change would be for the better.
>
> >> --
> >> Tony Done
>

> >>http://www.soundclick.com/bands/default.cfm?bandID=784456http://www.f...

>
> > Ask Norm Draper if ye can borrow one of his guitars.  He won't notice
> > the difference if ye give it back to him and he'll probably forget he
> > loaned it to ye in the first place.
>
> > Tom (gotta try this for myself sometime) from Texas
>
> maybe if I just gave him the hole and kept the rest of it.....
>
> --
> Tony Done
>

> http://www.soundclick.com/bands/default.cfm?bandID=784456http://www.flickr.com/photos/done_family/- Hide quoted text -
>
> - Show quoted text -

That would be wholy up to you.

Tom from Texas

[David Hajicek]

Alan, I remember your 'corker' from Healdsburg.

I thought I could tell a slight difference between corked and uncorked. But
it was subtle enough that it would be hard to do a blind test.

Dave


"Alan Carruth" <alanc...@gmail.com> wrote in message
news:bde072ee-0880-4c82...@googlegroups.com...

[David Hajicek]

"Tony Done" <tony...@bigpond.com> wrote in message

news:kfm7e5$ttm$1...@speranza.aioe.org...

Well, that is a sound hole modification and is rigid enough for the purpose.
But it is no guarantee of improving the sound of any given guitar. It
might, might not.

I find my guitar sounds better when someone else is playing it and I am
facing it. Also, I can concentrate on the sound better when I'm not
playing.

Dave

[Alan Carruth]

Somebody sent me a couple of the O-ports to experiment with. So far I have not had the time to do much more than stick one in a guitar for a few minutes and see if I could hear a change. I don't know when, or if, I'll get around to anything deeper: I'm always a little leery of putting a lot of time into testing something that's patented. If I find out that it works the maker will trumpet the results to the sky, and if it doesn't, they'll ignore me. Either way, I don't get paid for the time.

[Tony Done]

It would still be good to know what opinions you have formed, but I can
see how you might want to keep them to yourself.

And Dave. I've found it difficult to interpret the reviews I've read.
The closest I've got is that it might strengthen a weak bass, and that
it might improve the tone for strumming but not fingerpicking by better
note separation. It still seems to me that if a guitar was chosen for
the sounds we like, not on looks, make or price, then the odds on making
it better aren't very high. The idea of possibly improving "tightness"
appeals to me - most guitars I try that sound right in most respects of
fall down on being to open sounding - and the possibility of note
separation improvement might do that

[Benoit Meulle-Stef]

I have 2 here, I did some tries, and yes funny it's works great on some guitars but not on others.... I will do some more blind test soon with my friend David Evans...

Cheers
Benoit

[Tony Done]

What kind of differences did you think you heard in the guitars where
there was a perceptable effect. I'm thinkin of getting one this w/e, but
still undecided.

[Benoit Meulle-Stef]

In the guitar who was improved, I think it was a Washburn solid top jumbo, the basses where more focused and volume and projection... I didn't remember what guitar didn't got improved but the result was: no change or maybe a little muddier...

Benoit

[Tony Done]

Thanks, might try one in the cedar-topped Maton, the bass isn't as tight
as it could be However, this guitar is used exclusively for slide, and
if I lose complexity in the highest registers it will be a failure.

In any event I'll report back.