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ok troops, we all know that acoustics have a soundhole.

McPherson & Tacoma migrated it from the centre, but for my 50th build I want a keeper, preferably something well off the beaten track.

I'm pretty sure it'll have fanned frets and a sound port, maybe even a manzer style wedge.

but.

if it has a sound port, does it actually NEED a front facing soundhole?

the soundhole isn't for the sound to escape or to enter from the strings, and it's the top vibrating that gets a the sound out there. the soundhole allows some air to move in & out as the top vibrates and blocking it without a port will reduce it's freedom to travel, so will an acoustic with a port and no front soundhole "work"?

95% of my playing is plugged in strumming through a PA if that makes a difference.

thanks for your wisdom!!

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Hi Martin,
I've never played one, but Batson guitars only have a soundport, no soundhole. Maybe you'll find something there that inspires your design...

http://www.batsonguitars.com/

cheers, Christian

The thing I noticed about the Baston guitars is the size of the sound port. I assume you have to make it at least the same area as a standard sound hole if you leave the sound hole off. Someone else may have more insight into this as it pertains to wolf tones or whatever... Just an observation.

I seem to remember that Bill Moll made a guitar with no soundhole whatsoever and was surprised by its tone and volume. Stan Thomison might know more about it.

Why not make provision for a side sound-port but not cut it until the guitar is finished? Could be fun. Should be interesting.

You have a few choices here, and, as usual, they do have consequences.

No hole and no port= no 'Helmholtz' resonance. This is generally the lowest pitched resonance on the guitar that can radiate any sound, so losing it will mean that the acoustic tone of your lowest notes will be less 'full'. For your uses that might not be a bad thing. One thing I think I learned from working with some of the jazz guys years ago was that guitars that sound 'full' acoustically tend to sound 'thin' through the amp, and vice versa. It's almost as if the acoustic activity takes all the good stuff out of the string and dumps it into the room. What's left for the pickup to hear is the stuff you don't like.

Compared with 'the same' guitar with a hole, the holeless one will probably have a somewhat lower pitched 'main top' resonance. It will also feed back less, which is why they tend to leave the holes out on 'acoustic-electrics'.

Port but no 'main' hole:

You'll have a 'Helmholtz' resonance, and thus the 'bass reflex couple' will be working. The pitch of the actual Helmholtz resonance will depend on the size and location of the port. Basically, the smaller the port is, the lower the Helmholtz resonance, and the closer the port is to the end of the guitar, the higher the Helmholtz mode will be in pitch. So you could get the Helmholtz mode to turn out at the usual pitch by using a somewhat smaller hole up by the base of the neck, or in the tailblock.

All hollow bodies have a number of internal air resonances. On ones with standard holes most of these don't put out sound directly; most of the effect they have on the tone is through their losses, eating up energy, or else through the influence they have on the way the top (mostly) vibrates. A side port will tend to 'hear' internal modes that the main hole doesn't. As a rule, the further from the main hole location the port is, the more 'different' will be the sound it's putting out, compared with that coming from the 'normal' hole.

You tend to get feedback at resonant pitches, of course. A port that 'hears' a lot of interesting stuff easily could as easily feed back at those pitches.

Port and 'normal' hole:

I feel that some of what we feel is the 'normal' guitar sound has to do with the way the usual soundhole works with the internal air modes. The more you mess with that, the more likely it is that your instrument will sound 'different'. Whether that's good or bad is hard to say until you try something. The less radical the experiment, the less likely you are to screw something up beyond hope of repair.

I've mostly used small ports up on the wide part of the upper bout, along with a somewhat smaller than usual 'normal' soundhole. In this configuration the port is a 'monitor' for the palyer. which does not unduly alter the sound. You might want to go with something more radical.

I remember years ago stopping in at Ithaca guitars works on my (our) way back from a ski trip to lake Placid "hey honey, lets drive thru Ithaca ..yeah" ..., and was lucky enough to be there on a day when the main builder (cant remember his name now for the life of me, maybe Kent ... ???) had made the trip "into town" ....

he built guitars with no soundhole whatsoever, to be played plugged in .. remember the ads with the catchphrase "plugged" in the 90s in AG ???

As well, he showed me pix of the bracing ... almost none .... two curved (think bow and arrow bow) braces under the wings of the bridge, maybe 8 inches long .. thats it.

Want to see what a guitar made that way might sound like .. take a std one and plug the hole ....

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Hey, that's kind of fun, it was either Dan Hoffman, who now is building very traditional violins, violas and cellos, or Eric Aceto, who is my father. That guitar was named the "onieda" and a bunch of people still use those. It was heavily influenced by the whole Kasha/Schneider thing, but constantly mutating. The bracing you saw a picture of sounds like it was for an archtop, the flattops did have the two curved braces, but also a bridge plate and bunch of smaller tone bars radiating out from the center. Most of them also had fairly small sound ports, on the bass side near or on the panel for the preamp controls. Some also had soundholes either in the upper bout or even sometimes in the "normal" spot, but not many. They also usually had fairly shallow sides, without much taper.

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Jordan Aceto
Ithaca, NY

So this got me thinking and I did a quick little experiment based off of Alans response. I have Taylor 714CE (cedar top) that I pulled the electronics pack out of the side, leaving an effective sound port. Sounds great. The plug up the hole and see how it sounds comment made me realize I could do that quite easily. I dug out the old Feedback Buster out of a box and threw it in the sound hole. Much to my surprise, but not really surprising after I thought about it after the fact, the low end went through the roof, in a good way. I had the low E dropped to D which made it that much more apparent. That rubber Feedback Buster adds a lot of weight to the top, so it surly has some negative affects. But this is a small confirmation that my thoughts on a Baston like acoustic with only a sound port would make a great players guitar, or at least that the idea is worth exploring.

Yep, Jordan, it was Dan Hoffman, and the Oneida .. he was extremely nice to a guy (me) who walks into the shop and starts asking all kinds of "hey, how did you do that" kinda stuff !!!

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

also, check out Boaz Elkayam's work.
one of the main ideas behind his design is that , just like you said, it's the soundbaord that makes the sound so it only makes sense to leave it solid without any holes in it or super stiff constructions to support the "hole" - that is allow it to vibrate and "create sound" through it entire length.

and i can attest that his guitars sound like cannons!

Udi.

It probably doesn't if its got a piezo bridge pickup for live performance and studio work or you just intend to play it for your own pleasue and not an audience. The sound port would probably be good enough.

I would like to ask a question prompted by Alan Carruth's comments. If we moved the sound hole toward the bridge, say an inch or something, on an otherwise standard guitar design/specs being built, would it help the bass or the treble?

hemet asked:
"If we moved the sound hole toward the bridge, say an inch or something, on an otherwise standard guitar design/specs being built, would it help the bass or the treble?"

It would raise the pitch of the 'real Helmholtz' resonance. All else equal (right!) this would be lilely to raise the pitches of both the 'main air' and 'main top' peaks in the output spectrum. since these are the two lowest pitched resonances that can produce much sound, you'd expect the end result to be 'stronger treble', or, at least, 'less bass'. It might not be that simple, though: these are pretty complicated boxes. The only way to say for sure what would happen is to actually make the guitar.

I was just looking at a Martin style, dont know if it was that brand or not, 12 000 size guitar and the soundhole was almost parallel to the waist. I am familiar with 14 designs and as you know the sound hole is quite far north of the waist. I would expect that the 12 vs 14 fret bodies and bridge locations would produce different sounds but why not have the soundhole on the 14 fretter where the 12 fretter is or visa versa. Well I know it makes it easier to do the rosette by covering it up but I am thinking of things that can be done to customize the sound of a guitar. I am a little confused because Alan Carruth says that moving the sounhole to the neck will make is bassier while moving it to the bridge will make it brighter and then he says you cant predict what will happen. You just have to try it and see.
So lets say you have a customer that wants a guitar built that is bassier than a certain body style usually is, say a parlor. It shouldnt matter if the principle is valid. So you move the soundhole closer to the neck and it has more treble than usual. Both you and the customer are going to be a little upset at this point having to try again.
I dont build professionally but just using this scenario to say the "just try it and see" idea isnt attractive to me. As a person that is building a guitar for myself I want it to sound a certain way so I do this and do that and I was just wondering if the soundhole location would be a way of shaping the sound. We know that the size of the hole makes a difference. We know that scalloping makes a difference. We know that size of braces, thickness of top, stiffness of top etc make a definate difference. Can soundhole location be added to the list?

Ok gang, interesting reading, thanks for your thoughts!!

right,

the idea at THIS point is a concert sized cutaway body.

Ovangkol back & sides (and headplate), Engleman top, mahogany neck, ebony fretboard & bridge

body depth........ 3, maybe 3/12"......

fanned frets.....

bone saddle nut & pins.....

I THINK I have some leopardwood that came off the edge of a set of sides I could use for binding........

probably a few small soundholes along the top bout......

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As I was reading this topic, I remembered a set of EV speakers my dad owned that used an "acoustic suspension" enclosure and found this on wiki:

A variation of the closed-box enclosure, using a smaller box to exploit the almost linear air spring which results. The "spring" suspension that restores the cone to a neutral position is a combination of an exceptionally compliant (soft) woofer suspension, and the air inside the enclosure. At frequencies below system resonance, the air pressure caused by the cone motion is the dominant force. Although no longer popular in commercial designs, the acoustic suspension principal takes advantage of this relatively linear spring. The enhanced suspension linearity of this type of system is off-set by rather low efficiency. Drivers for these designs rely more upon the enclosure characteristics than typical drivers, and most modern woofers are not well suited to acoustic suspension use.

Don't know how this applies to guitars but thought I'd throw it in the ring for your review.

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hemet wrote:
"I am a little confused because Alan Carruth says that moving the soundhole to the neck will make is bassier while moving it to the bridge will make it brighter and then he says you cant predict what will happen. You just have to try it and see."

I didn't mean to sow confusion, but I'll note that you'r mis-quoting me.

Physically, what happens as you move a hole of a given size from the middle of the length of a box out to the end is that the pitch of the 'Helmholtz' resonance goes down. This is physics, and it works every time. But....

Note that I said the pitch moves 'down': an objectively measureable thing. 'Bassier' and 'brighter' are terms that relate to your perception of the sound, and that's something different. _Usually_ if the pitch of the Helmholtz resonance drops, the guitar does tend to be 'bassier', but I'd hesitate to say that it always does.

Guitars are very complicated boxes, in some ways. Things don't always happen the way you'd expect them to. Although there's always a reason why they do what they do, you don't always understand it. Relating what happens to your perception of it is even tricker.

So: I can say with some assurance that if you move the soundhole up toward the upper edge by some appreciable amount, the pitch of the 'main air' mode is likely to drop, all else equal. If you change the bracing around to move the hole, then all else is not equal, and so on. Given the differences in perception, variations in tastes and preferences, and the fact that, with all that's going on in there, you're altering a few dozen relationships between resonant modes when you move the hole, it's hard to say exactly what else might happen, and impossible to say whether you'll like it. I'd expect it to be 'bassier', but it might be 'brighter' and it could even be both. The only way to find that out is to build the guitar.

Ok thank you for explaining to me the the Hemoltz and the, hummm what can we call it, impression of the guitar are two different things. I see now that the Hemoltz is just one factor influencing the sound of a guitar. I have played two guitars that were exactly the same size and built the same but one was bassey sounding and the other trebly for lack of better words. These were classical guitars built by different builders. I am understanding from your explanation that the Hemoltz was not the reason.

But doesn't the soundhole emit sound that's been bouncing around inside the box, and continue to do so for a small interval after the top stops producing that sound? That's usually given as the main drawback of a bass reflex speaker cabinet, since you don't want a speaker enclosure to add any sound to what's made by the movement of the cone. In a guitar it may be an asset.

Also: in a speaker cabinet, where it's much easier to quantify the various factors and calculate the ideal port, the port's length is usually greater than its diameter. But I've never seen a guitar soundhole or side soundport with a length other than the thickness of the wood. I wonder if there's an inherent reason for that, or if it's just never been tried? Wouldn't that port length lower the system resonance frequency and increase the delay in the decay of the sound? And wouldn't a 1/8" thick strip of spruce forming a cylinder around the soundhole be a nice lightweight way of contributing to the top bracing and also reinforcing around the cut edge?

I've seen acoustic Bass guitars with a tube in the soundhole but not on a guitar.

as to the over all sound, well, time will tell.

I play 95% of the time through a PA and a 2x4 with a piezo will sound fine throuh a PA.

acoustically?

I'll let you know!!

Bracing options are really open as there's no soundhole to avoid!!

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So how would one brace a top optimally with no soundhole to deal with?

qwrtz asked:
"But doesn't the soundhole emit sound that's been bouncing around inside the box, and continue to do so for a small interval after the top stops producing that sound?"

Certainly there is sound coming out of the soundhole. Mostly what it emits is around the pitch of the 'main air' resonant mode, somewhere around G on the low E string for most guitars. There are other frequencies too, but most of what you lose if you leave out the hole is that low 'main air' pitch.

I'd guess, without making the measurement that if sound comes out for a little while after you stop driving the top, it's a _really little_ while. The guitar is pretty effective at it's 'main air' pitch; it gets the sound from the string and out into the air quickly. As a result I would think it would die off in a very few cycles, which would occupy only a small fraction of a second. The diration would be similar to the 'thump' you get when you tap the top.

In the low range the guitar is a 'bass reflex' system, but , unlike what I understand is the norm in speakers, the 'top' and 'air' resonances on the guitar are not at the same pitch, but more like a fifth apart in isolation. This, and somewhat lower losses on the guitar, gives the guitar two peaks in the low-range spectrum, rather than a single, broad one with a slight dip.

The soundhole size on the guitar is usually chosen to get the 'Helmholtz' pitch to be in the right place to make the 'correct' sound without any sort of sleeve. This is a good thing. When I've tried putting sleeves in guitat soundholes I've found that they not only drop the air mode pitch, but also add a lot of loss. With so little power to work with in the strings, we try hard to avoid losses like that.

I'm not sure I'd make any major changes in top bracing if I was making one without a hole. It's an interesting thing to think about, though.

Very interesting. But I think bass reflex speaker design does involve that dual resonance, one of the speaker and one of the port, and usually quite a bit farther apart than a fifth. My understanding is that the port somehow creates additional sound in a narrow range centered at its own resonant frequency, which is designed to be sufficiently below that of the speaker in a closed box so that the combination of the two frequency/response curves creates a flattish area between them in the roll-off area of the whole system's curve.


I've never really understood that concept that the extra sound is actually created by the port, and not just allowed to escape from the rear as with a non-enclosed speaker. But I know that when I cover the soundhole of my guitar it makes a huge change to the bass output of the internal microphone, so I assume it's the same there also.

Well, I'm NOT a 'speaker guy', so I'm going on what may be flawed understanding, too. Still, FWIW, I'll put it up: anybody who knows better please correct me.

The idea behind a 'bass reflex enclosure' is twofold: to capture some of the energy off the back of the speaker, and to give a more even response. It turns out that the best way to get the even response is to have two resonant systems, both with high damping, that are tuned to the same pitch, or very nearly the same.

You would expect that two coupled resonators tuned to the asme pitch would give a tall, narrow output peak, but this doesn't happen. Instead you get one of them changing phase relative to the other as you approach the resonant frequency, so that the overall output of the system actually drops. You can see this if you look up a 'Butterworth filter' which is essentially the same thing implimented in 'tank circuits'; capacitors (stiffness elements), inductors (masses), and resistors (loss elements). The output becomes a two-hump spectrum, with the dip occuring at what would be the resonant peak frequencies of the seperate tanks.

How 'flat' the spectrum is will depend on the overall resistance of the circuits: if that's high the height difference between the peaks and dips can be less than 3dB, which is more or less inaudible. The overall circuit also maintains relatively high output as you go up from the double-hump in the low range.

In a bass reflex speaker cab it is assumed that the cone itself has fairly high damping: it's light weight, and has to move something like it's own mass in air as it vibrates, so the amount of energy stored in the system is small relative to the output. The cab itself is usually lined with acoustic foam or fiberglass: something to broaden out the Helmholtz resonant peak. Using a sleeve in the port does two things: it adds damping, and it also allows you to establish the 'upper cuttoff frequency' of the radiation from the port independantly of the Helmholtz frequency.

As you go upward in frequency, the port becomes more and more efficient. As the wave length of the sound it's trying to put out approaches the diameter of the port it works better and better. At some point the port becomes essentially 100% efficient. The smaller the port, the higher the upper cuttoff frequency. On a speaker cab that is meant to be part of a system you'd want to be able to predict the relationship between the port's upper cuttoff and the crossover frequency of the tweeter driver, so you need to have the port be a certain diameter. You tune the Helmholtz pitch by altering the length of the sleeve.

Of course, with high damping in both elements, you don't need to get the frequency match too exact. This allows you to mass produce acceptible bass reflex cabs assuming decent quality control in the speaker construction. I have read, though, of audiophiles measuring the exact resonant pitches of speakers so that they could be matched up with the appropriate cabs, or tuning the cabs by changing the port lengths.

Closing the port or covering the soundhole on the guitar eliminates the Helmholtz resonance, and thus the low peak of the 'bass reflex' output. There's not as much cyclic pressure change in the box for the internal mic to pick up because there's no flow through the hole.

Is that just with magnetic and piezo pickups? Or even with a microphone?