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OK, so I went WAAAY to far in-depth here. Skip this whole post if you wish - I won't cry.


The difference between f-holes and a circular sound hole is the least of the reasons that a flat-top sounds different than an arch-top guitar. The greatest of the reasons are the top itself, and the string anchoring. (Most arch-top acoustic guitars have an end-mounted tailpiece)

One of the first things my guitar prof made me learn was the aspects of the acoustic guitar as a mechincal device. It is a mechanical thing in the sense that it functions through purely physical movement of parts. Some of the things he taught are contrary to popular notion and thus seemed odd to me at first, but he convinced me.

"Sound" is vibration in the air. What vibrates the air? The top. The strings vibrate the top, which in turn beats the air. Imagine a regular guitar string with one end attached to the floor and the other to the ceiling - no guitar, just a string strung up in the room. Tensionize it. Now get out your trusty pick and give it a twang. Can you hear it? (Even though you probably can't actually perform this experiment, I think you know the answer.) Sure, you can hear it but it isn't very loud at all. That is because a skinny little string can't move much air. Remember this example, I'll refer to it later. I'll call it "the bodyless string".

Now, take an identical string and put it on an ordinary guitar with a 'soundboard' (top) and the string vibes the top, which in turn beats the air - now it is louder. The soundboard is the single most important factor in sound production for an acoustic guitar. A dreadnaught or a jumbo is louder than a 000 or parlour guitar mostly because it has a bigger top.

Your acoustic guitar has a lot in common with a drum. It is essentially a membrane with a supporting structure around the outside which holds the shape and keeps the membrane tight enough to resonate.

The guitar-drum similarity is more evident when one considers a banjo. The body of a banjo even looks like a drum.

The more freely the soundboard can move, the louder the guitar will be and the more efficiently it can produce extended freqs (like the 'harmonics' that come with every note. The better you hear them, the more 'character' the sound has). This is why adventuresome luthiers experiment so much with hole and brace configurations.

You may remember the trend toward 'scalloped' braces on guitar tops of a few years back. The soundboard MUST be braced to hold up under the string tension, but the lighter (& more nimble) it can be, the better it will sound. 'Scalloping' some of the wood out of the braces was intended to reduce the mass of the brace without taking away the strength. The lighter top can manouever more quickly, and so respond to the strings in a more detailed way.

Endpin-tailpiece guitars, such as many arched-top guitars, have the big disadvantage of connecting the string ends to the rim of the guitar. This means that the string tension is pushing down on the top at all times. That REALLY dampens the movement of the top. Imagine a cable over each of your shoulders. All four cable ends are anchored to the ground. Someone turns a huge Grover Rotomatic tuner on one end of each cable and puts some tension on it. THEN they ask you to jump up and down. You aren't going to move very freely. In this example YOU represent the soundboard of an archtop acoustic guitar, the cables represent the strings.

Arch tops (with endpin talpieces ) need no bracing - you never see the strings pull the top apart - because the string tension does not anchor in the soundboard itself. This comes at a high cost in terms of tone. You may notice that archtop guitars are typically much quieter than 'flat-top' guitar of the same size. This is why the old archtops hadda be so HUGE to be audible -the soundboard couldn't move much so they had to use a great deal of surface area. Many of them had an eighteen-inch lower bout, which is a very large guitar body.

Our current soundboard-stopped bridgepin-mounted string design allows the top to vibrate like crazy, which is why the F-hole & endpin tailpiece design is seldom used any more. The lower bout of a contemporary dreadnaught measures a bit under 16" and is usually WAY louder than a traditional archtop 18" or more in width.

Let's go back again to the idea of you & the cables & the huge Grover tuners. This time instead of having the cables pushing down on your shoulders, we'll anchor one end of each cable into the ground and have you hold the other end. Now can you jump up and down? Sure you can. In this example you are acting like the top of a modern acoustic guitar - holding the strings and free to oscillate.

Now, as far as soundholes... this is where traditional assumptions begin to break down.

Ready?

The sound doesn't come out the soundhole.

The sound doesn't go in the soundhole.

"Soundhole" is a misnomer - a bad name. That hole isn't really about sound.

Yes, the top beats the air in there and so if your head (or your microphone) was inside the guitar body, it would be very loud. Nevertheless, the function of the 'soundhole' is NOT to let sound pass. The 'soundhole' is only there provide ventilation so that the top can move freely. If the 'box' (body) were glue-sealed all the way around then each time the top tried to vibrate it would have to compress the contained air, so the vibes would be dampened considerably.

Did you ever slam a door unintentionally - because you didn't know there was window open in the room? You go through that door every day, and you know how hard you have to push it - but usually the windows in the room are closed. Then one day a window or another door is standing open, and you push the door with the same force you usually use. SLAM!

Same concept. The door you slammed could move more freely because the air had someplace to escape. Your soundboard can move more freely because the 'soundhole' allows the air to escape.

It is odd at first to think the the 'soundhole' doesn't serve to move sound. Have you ever seen a studio engineer mic an acoustic guitar? Did he point the mic at the soundhole? Probably not. He probably pointed it somewhere near the bridge or center of the lower bout.

If you still have doubts about the soudhole's role, I suggest you actually perform the 2 experiments below. Test the theory:

Experiment #1 - soundboard yes, soundhole no.
Tape something over your soundhole. Maybe get onea those dampits that goes in there, or onea those feedback-reducer gizmos. IF the soundhole is for sound, then plugging your soundhole should make the guitar almost silent - about as quiet as the 'bodyless string' mentioned earlier. If youve got nothing else, tape a piece of cardboard over your soundhole.

Pluck a note or two. Is it quieter? A little bit - but not nearly as quiet as the bodyless string. You have just played a guitar with a free soundboard but no soundhole.

The reason it is a bit muted is just because you've lost your ventilation.

Experiment #2 - soundhole yes, soundboard no.
This time we'll leave the hole unbothered but hamper the top. It might be beneficial to have a helper. Hold the guitar in an ordinary way but place your palm wide open on the big open part of the soundboard and press down slightly. Get your friends to do likewise. Flop as much llve fleshy meat as you can on that soundboard. Have everyone use some pressure so as to hamper the vibrations - (WITHOUT pushing so hard they break your guitar).

Pluck a note or two. Is it quieter? A LOT quieter. It is almost inaudible. It is about like an electric guitar unplugged.

So, we've demonstrated that you lose most of your sound by defeating the soundboard, but you lose relatively little by defeating the soundhole.

The reason is that the soundhole is not responsible for sound. The soundhole's primary function is to allow air exchange.

Guitar makers are still experimnenting with soundhole configurations which will optimize soundboard vibrations on new-technology guitars. Ovation's upper-bout array of small holes has already been mentioned here, it is one of many examples.



Now, on to the guitar's back and sides....

As you may have already guessed, the back & sides have a suprise or 2 in store. Just like the top, they don't perform the kind of function I though they did when I was a kid.

The back and sides do not amplify or reflect the sound and throw it back out the soundhole. The function of the back and sides is to use reflected pressure to optimize the top's vibrations.

Let us think of a note being played in super-super-super slow motion. The top bows out toward the room, sending a pulse of air pressure out that way. Next, it bows back toward the inside of the guitar, sending another nearly equal pulse in a direction 180 degrees opposite of the first. The thoeretically ideal guitar body takes that pulse and reflects it back toward the top in a precise way. There is more than one aspect of this reflection.
-it should not lose much energy. The body should absorb as little of this energy as possible, to bounce back as much as possible.
- the pressure pulse should bounce back in such a way that when the top is again pushing out toward the room (still with residual energy from when you plucked the string) the reflected pulse will hit it from behind at the same time, reinforcing and constructively adding energy to the vibration, and thus the note.


So, anyway ..... cutting a hole in the side of the guitar probably won't hurt the sound as much as you might think, or least probably not for the same reasons. It may help you hear the guitar , but if it does it probably won't be as loud as you might think.

I am actualy surprised that we haven't seen more nontraditional experiments for soundholes. I've envisioned them as being very small vent holes, perhaps around the sides or back of the guitar. I'm sure someone besides me must have though of this, so I assume the ideas have proven impractical in one way or another.

Apologies for going all Dr. Smartash on ya. Thanks for your patience.

"Archtops probably don't need bracing because the pressure of the strings is distributed by the arched shape of the top."

I wasnt' referring to braces being required because of downward pressure of the strings - yes, the downward pressure is handled nicely by the arch in the top.

The tension element I was making reference to was the string tension wanting to pull up & tear the bridge off.

Thank you. In payment I shall require you all to make "ooooh" and "Ahhhh" noises the next time I post a headstock project.

Credited to account for OTM:

-"Ooooh", Qty 1
-"Ahhhh", Oty 1


*hands him a receipt*