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I was wondering why the vast majority of guitars have
the shape they have..i.e
shoulders/waist/hips..(.figure 8 shape),why has the
guitar evolved this way? Are the reasons
ergonomic?tonal.?aesthetic? Are there more
'efficient' shapes...meaning that if the top was (for
example) circular (or square,or octagonal..etc..you
get the idea...) would it sound any better?
I know that some shapes would render the guitar
very difficult to hold (!)..but I just wondered how and
why we arrived at this shape.
Any thoughts chaps?????

Men have always been and will always be drawn to that shape. The only way to make it more irresistable to us is to make it walk away....   

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Seriously, though, that is a big question. Builders of guitars and guitar-like instruments have been experimenting with different shapes for centuries. I think, because of companies like Martin, etc., who have popularized the instrument, there is a certain "standard of identity" associated with the label "guitar" and we have come to expect them to look and sound within a loosely organized range of shapes and sound profiles. I think as time goes on, it gets harder to deviate from that standard and still call it a guitar, even while it is possible to make changes to optimize the playability (e.g., beveled armrests) and sound quality (e.g., bracing systems).

John may be right in his assessment, too, even while joking. The human form is consciously used in many types of art. Makes sense to me!

IMHO

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

Some years back I read a small book on Flamenco guitars. One of the builders interviewed used to put on a shirt and tie every day for lunch, come up from his basement workshop, and watch the girls go by. He said it gave him inspiration for the plantilla.

That's probably as good a reason as any for the guitar to start out with that shape. There's also the fact that one name for an early from of guitar was 'vihuela', which is cognate with 'viola' and 'fiddle'. Early guitars seem to have been rather easily converted into bowed instruments, and the waist was needed, once you got past a certain top width, to enable bowing.

None of that, however, explains why we still make them that shape. All sorts of shapes have been tried in the past; lyre guitars, bell guitars, trapezoidal and rectangular, lute bodied, you name it. Some of them have caught on for a time as fads, but somehow we keep going back to the same old shape, more or less.

Certainly the shape has acoustic effects, although they're hard to sort out. Most of the sound is produced by a 'bass reflex' action involving coupling between the top and the inside air, with help from the back on many guitars. That's mostly related to the volume of the box and the soundhole size and location, and is not very shape dependant. However, the higher air modes in the box certainly depend on the shape, and it's likely that some also depend on the location of the hole. In particular, I have seen two interior air modes that can effect the tone more or less directly, which depend on the shape.

One is a second 'Helmholtz' type air resonance. These sorts of modes, which are what you hear when you blow across the mouth of a bottle, are 'breathing' modes. Air flows in and out of the soundhole and the pressure in the body changes. Most of the time something like a bottle, with a simple shape, will only have one such mode, with the pressure changing everywhere inside in the same way at the same time. On the guitar we call this the 'main air' mode, although, strictly speaking, what you hear on a guitar is the result of cooperation between the air and the top, as I've mentioned. However, because of the waist, and the position of the soundhole near it, it's possible for the flow to be 'short circuited', with the pressure changing only in the lower bout. The dynamics of this are tricky: it seems also to involve the motion of the top, as it doesn't show up in a rigid guitar shaped box. It is also not there on at least some Dreads I've measured: not enough waist, I guess.

Acoustically, this 'A-0-2' air mode tends to happen a little above the 'main top' mode pitch. This top resonance has the wood in the lower bout working like a loudspeaker. The flow through the soundhole from the 'A-0-2' mode is out of phase with this top motion, so the air mode decreases the output of the guitar in that range. This has an effect in determining the timbre of the instrument in the mid-range. The seeming lack of this mode may be part of that 'Dread' sound.

There's also an interaction between the 'A-1' air mode, and a top mode that is often called the 'long dipole'. The A-1 mode has the air 'sloshing' the length of the guitar body like water in a bathtub. The pressure changes occur at the end blocks, and, since the soundhole is near the center where there is not much pressure change, this mode would not be expected to radiate much sound. However, the top 'long dipole' mode, where the areas in front of and behind the bridge are moving in and out in opposite phase, can couple strongly with the 'A-1'. When this happens in a system you will see two resonant modes involving both parts, but at different frequencies. This, in itself, would not always make much difference in the tone.

However, again, I beleive, because of the waist and the soundhole location, the 'shape', if you will, of the two resulting A-1 air modes are different. On one the pressure null is moved up further into the waist than you'd expect, closer to the soundhole, which leads to even less sound output from it. The other, though, has it's null shifted downward toward the bridge, and the flow through the soundhole is enhanced. Interestingly enough, at least on many classical guitars, this tends to happen at a frequency right around A on the high E string, where there is a sort of 'hole' between wood resonances that can effectively put out sound.

I don't think either of these effects is a coincidence. Both of them contribute noticably to the characteristic 'guitar' sound, and are absent, for example, in the lute. Again, the one guitar shape that seems to lack one of these features, the Dread, has a 'signiture' tone that is different from other guitars, even ones, like the Jumbo, that are as large.

Again, I'll note that these are complex things that happen because of the interaction between the different parts of the guitar. Exactly how they work, and what effect on the sound they have, depends on a lot of little details, and would be difficult to predict. The texts I've seen on guitar acoustics, for example, don't mention the 'A-0-2' mode, since it doesn't show up in the rigid boxes that physics people like to study. It does come out in complex computer models that take the wall vibrations into account along with air motion, but that takes some pretty fancy programming and a fair amount of computer power, even by today's standards, I think. It's sort of cool that the old boys hit on this just by trial and error. They could not have been looking for it, but they were smart enough to recognize the benefits once they hit on it, and to get it under some level of control.

So that's why I think we tend to stay with that shape, as much as it's a pain to build sometimes. Besides, it looks so sexy....

I think, as Alan touched upon, that the original idea came from the violin-family shape. Some builder probably thought to himself, "I wonder what it would sound like if I built it like that?", so he did, and liked the sound. So did others. I think the feminine allusion came after the fact.

Alan explained why it happens, but to put it simply, if it's not shaped like a guitar, is won't sound like a guitar. It might sound good (a lute, for instance), but not guitar-like.

A friend of mind was over in a Muslim country, Can't remember which one.
He said they weren't allowed to display guitars in windows because of the
feminine shape. Of course I asked about veils but he only laughed.

[QUOTE=DannyV] Of course I asked about veils but he only laughed.[/QUOTE]



I went out with a girl who wasn't allowed to wear court shoes to school becaues they might show the cleavage between the toes...... and who knows where THAT would lead!!! (not that it did, mores the pity)

I recently finished a guitar shaped bouzouki which sounds pretty guitar like, more so than a zouk...

If it looks like a duck, maybe it'll quack like a duck too!!martinedwards39106.7459375

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John, you're a real riot!

Thanks Chaps...some really interesting replies.....
I woder what the guy who designed the banjo was
thinking......round women(?)..no accounting for taste I
suppose....

I think if any of you played the lute, you would realise why the guitar is shaped the way it is! Ergonomically it is just more comfortable. Sitting with a lute on your lap and trying to stop it slide onto the floor when you start playing and then reaching round to get to the strings, is an acquired skill.

The development from the viol family is of course a better answer, but they only retained the waist because it fits the knee.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

A little thick on the lower bout and itl be sure to catch my eye

I think that when you look at the problems that you need to solve to make a guitar, you will quickly end up with the standard guitar shape. Here is my model of how it all works. I don't have any scientific data to back this up and it is more likely than not that I'm completely wrong. But I think that it has some self consistancy.

I makes sense to me to put the bridge near the center of the main vibrating surface. That would put more of the string energy into the fundamental pitch. This is somewhat like plucking a string near the bridge vs plucking it over the 12th fret. That is the case for the guitar because the lower bout accounts for most of the sound. It is also true of the bozouki.

On the guitar, the sound hole and the bracing do a pretty good job of isolating the lower bout from the upper bout. The bozouki doesn't have an upper bout. The bozouki also has a pretty thin sound. To get a deeper sound you need to add volume to the box. You could make the box deeper but that would make it harder to play. So the logical choice is to add volume above the sound hole. You still want to isolate the upper an lower bouts acoustically. So, constricting the width of the top right near the sound hole helps to do that.

The air inside the guitar sloshes around when a string is plucked. When the air moves between the lower to upper lower bouts, it whistles just like a constriction in an air duct. The constriction is pretty slight so the whistling is only adding some color to the sound. When the constriction is less, such as in a dreadnaught, there is less of this color being added.

The "easier to hold" argument seems less likely to me. Primarily becuase the shape came into being long before the steel string guitar was built and the classical playing position does not have the player resting the guitar on the knee at the waist.

[QUOTE=Mike Mahar] I think that when you look at the problems that you need to solve to make a guitar, you will quickly end up with the standard guitar shape.[/QUOTE]
Mike, I think that all the points that you brought up were realized well before the guitar was invented. Bowed instruments have the same concerns, so guitar builders/inventors just went with common knowledge.


[QUOTE=Mike Mahar]the classical playing position does not have the player resting the guitar on the knee at the waist.
[/QUOTE]
Ummm...yes it does. Left knee--hence the usual classical player's foot stool to raise the knee so the instrument is in playing position. Historically, some players have advocated other approaches, but most since the 19th century have used the raised-knee technique.

[QUOTE=Raj Snake] I wonder what the guy who designed the banjo was thinking...... [/QUOTE]

forget the shape, just what was he thinking!!!!

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[QUOTE=CarltonM] [QUOTE=Mike Mahar] I think that when you look at the problems that you need to solve to make a guitar, you will quickly end up with the standard guitar shape.[/QUOTE]
Mike, I think that all the points that you brought up were realized well before the guitar was invented. Bowed instruments have the same concerns, so guitar builders/inventors just went with common knowledge.


[QUOTE=Mike Mahar]the classical playing position does not have the player resting the guitar on the knee at the waist.
[/QUOTE]
Ummm...yes it does. Left knee--hence the usual classical player's foot stool to raise the knee so the instrument is in playing position. Historically, some players have advocated other approaches, but most since the 19th century have used the raised-knee technique.[/QUOTE]
I didn't mean to imply that all this was invented by guitar makers. Most of these issues have been around long than the guitar. My point was that once you try to build something like a guitar, you'll end up with a similar solution to what we have today. The fact that other instruments used the same sorts of solutions simplified that journey quite a bit, I'd recon.

As for the classical playing position, I stand corrected.

Hmmm SJ is just my speed in that case John!
indeed
Cheers
Charliewood

The American banjo was developed from a whole family of African instruments that were built around gourds, and had skin tops. The precursor of the lute was one, but the Arabs substituted a wood top. Some people think that's where the name came from; 'al'oud' means 'the wood'. Some disagree. In this country they used things like coffee cans or stove pipe to make the rings, as well as wood, when they couldn't get gourds. My favorite member of the family is the 'kora', the west African 'harp' that is really a banjo with about 33 strings, each tuned to a particular note.

I won't even go into the sexual symbolism one lady on a classical guitar list once elaborated to counter the 'feminine' one so often used; suffice to say that the banjo might have been even a better fit. ;)

A banjo? Harmless compared to one I saw on another guitar forum I moderate!!!

A little TOOoooooOOOOooooOOOooo graphic for my liking, and I ain't a prude...

[QUOTE=Alan Carruth] My favorite member of the family is the 'kora', the west African 'harp' that is really a banjo with about 33 strings, each tuned to a particular note.

I won't even go into the sexual symbolism one lady on a classical guitar list once elaborated to counter the 'feminine' one so often used; suffice to say that the banjo might have been even a better fit. ;) [/QUOTE]

As used brilliantly by Afro Celt Sound System - a fantastic fusion of African and Irish music. See the kora in use here where you'll see what Alan means (Sam - you may want to look away ), also catch the "tribute to Hendrix"

Also check out Release with Sinead O'Connor, written in tribute to one of their band members who died suddenly. Iarla O'Lionaird their singer is Ireland's leading Sean nos singer. I heard him in Dublin in a small cellar bar and the hairs on the back of my neck stood on end.Dave White39108.2008680556

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". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

[QUOTE=Dave White]

As used brilliantly by Afro Celt Sound System - a fantastic fusion of African and Irish music. See the kora in use here where you'll see what Alan means (Sam - you may want to look away ), also catch the "tribute to Hendrix"
[/QUOTE]


HAH HAHHHHAHHHAHHHHHAHHHH HAHHA HHAHHAHHAAA!!!!!!!


FANTASTIC Kora playing!!!! Now who would be ashamed of something THAT size?!?!?!?!?!? WOAH!!

Seriously. That music was great, both clips.... Fantastic afro-celt fusion. I'm gonna check out some more, thanks Dave!! I would love to learn the Uilleann pipes one of these days being a Celtic nut, but might be a little too tricky.



I LOVE Sinead's voice. I really like her work.

Sam Price39108.239837963