Thread: Symmetry and the acoustic guitar

To my knowledge, the symmetry of the top is nothing to the asymetry of the bracing. There are strange cancellation effects with completely symetrical tops, note cancellation and dead spots (apparently). There are asymetrical guitars out there, built specifically to cancel this problem, but I suspect that the asthetic of a symmetrical guitar is more pleasing than an oddbodd shape. Also a symmetrical shape would mean an easier mass produced guitar.

Originally Posted by mongrel

Also a symmetrical shape would mean an easier mass produced guitar.

I agree Mongrel, that, and tradition, instruments are supposed to look a certain way.

Different, check out Wildwoods' website for some neat takes on other instrument shapes.

Symetry is not absolute on many accoustic guitars, but some is undoubtedly there for aesthetic reasons.

There are three distinct styles of "cut away" guitars, where the body curves away from the neck joint parallel to the neck axis in order to permit fretting high up on the neck. The only double cuts (and back to symetrical) I've seen are on electric guitars where body cavity resonance is undesirable.

Locating sound ports is also somewhat traditional, but you can find them on the top side (that nearest your face when playing), on the upper left bout, as 'F' holes and in combinations. You can put them anywhere, but the common locations are quite good compromises.

There are two shops that I know of that build a bevel to the left side of the lower bout. This is for player comfort, that edge can dig into your arm.

All incursions into the basic shape remove volume and raise the hemholtz resonance. This is generally undesireable as it leads to interaction with notes on the lowest string (a reason that you don't see low tuned strings on stadard ukuleles.)

The shape of the modern guitar comes out of Spain, but no explanation from the originator(s) as to why the double curve. One might speculate that the lower waist curve was to make holding the guitar on the right leg more comfortable. Another possibility is that the incurve at the waist stiffens the top and back, giving the entire box a fair amount of structural integrity.

Whatever the reason for the general shape, it is firmly establish in popular conception and selling other shapes is quite difficult. The same with woods for the box and neck. Stray very far from the accepted and your guitar becomes a curiosity.

Bracing was mentioned earlier. A cute trick there is to use a truss support anchored to the bottom side of the bridge and pushed against the tail block. This cuts down on the need for bracing of the top and is reported to have greatly improved the performance of a number of poor performing guitars. It also all but eliminates distortion of the top in a long term response to the pull of the strings trying to rip the bridge off the guitar.

Bridges are not quite symmetrical, they are almost always slanted to make the lowest string longer and generally having a step back on the 'B' string. Both are compensation for effects on tuning caused by the string being fretted - the higher the action on the string, the greater the compensation needed. Poor compensation will cause the strings to become noticably off tune by the 12th fret (an octave below 0th fret.) This drives most musicians up a tree.

If you are contemplating building your own, subscribe to the Yahoo group Left Brain Luthiers. There is a wealth of information and help available from the members as well as links to books and writups. A word of warning, the number and kinds of tools needed is amazing. The reward is producing some of the most beautiful and practical pieces of wood art one can imagine.

Originally Posted by Sebastiaan56

I agree Mongrel, that, and tradition, instruments are supposed to look a certain way.

Different, check out Wildwoods' website for some neat takes on other instrument shapes.

Yep have seen Wildwoods gear and while it did not precipitate my question it does add some substance to it.

Ross

Originally Posted by microsuffer

Symetry is not absolute on many accoustic guitars, but some is undoubtedly there for aesthetic reasons.

There are three distinct styles of "cut away" guitars, where the body curves away from the neck joint parallel to the neck axis in order to permit fretting high up on the neck. The only double cuts (and back to symetrical) I've seen are on electric guitars where body cavity resonance is undesirable.

Locating sound ports is also somewhat traditional, but you can find them on the top side (that nearest your face when playing), on the upper left bout, as 'F' holes and in combinations. You can put them anywhere, but the common locations are quite good compromises.

There are two shops that I know of that build a bevel to the left side of the lower bout. This is for player comfort, that edge can dig into your arm.

All incursions into the basic shape remove volume and raise the hemholtz resonance. This is generally undesireable as it leads to interaction with notes on the lowest string (a reason that you don't see low tuned strings on stadard ukuleles.)

The shape of the modern guitar comes out of Spain, but no explanation from the originator(s) as to why the double curve. One might speculate that the lower waist curve was to make holding the guitar on the right leg more comfortable. Another possibility is that the incurve at the waist stiffens the top and back, giving the entire box a fair amount of structural integrity.

Whatever the reason for the general shape, it is firmly establish in popular conception and selling other shapes is quite difficult. The same with woods for the box and neck. Stray very far from the accepted and your guitar becomes a curiosity.

Bracing was mentioned earlier. A cute trick there is to use a truss support anchored to the bottom side of the bridge and pushed against the tail block. This cuts down on the need for bracing of the top and is reported to have greatly improved the performance of a number of poor performing guitars. It also all but eliminates distortion of the top in a long term response to the pull of the strings trying to rip the bridge off the guitar.

Bridges are not quite symmetrical, they are almost always slanted to make the lowest string longer and generally having a step back on the 'B' string. Both are compensation for effects on tuning caused by the string being fretted - the higher the action on the string, the greater the compensation needed. Poor compensation will cause the strings to become noticably off tune by the 12th fret (an octave below 0th fret.) This drives most musicians up a tree.

If you are contemplating building your own, subscribe to the Yahoo group Left Brain Luthiers. There is a wealth of information and help available from the members as well as links to books and writups. A word of warning, the number and kinds of tools needed is amazing. The reward is producing some of the most beautiful and practical pieces of wood art one can imagine.

Microsuffer
All good points and very helpful. My original observation was not so much that we dont see much innovation in instrument shape in the commercial world the reasons for that are clear but rather after so long an evolution in the design of this instrument it seems that not much thought has been put into egronomics or the fact that the half of the instrument nearest the bass strings could well need a different shape than that side nearest the treble strings. Other things like the top half of the instrument soundboard also has more contact with the players arm etc might all add up to an improvement in sound if the shape was different.
I see some people have experimented on these things like Cumpianos odd shaped sound holes and unsymetrical bridges but little has been said about their merrits or otherwise.


Ross

Hi Ross,
Interesting discussion, even though I know nought about it. I just love acoustic guitar music, and the instruments themselves are beautiful objects. I have seem cut away acoustics, so I suppose that's assymetrical....I don't know if its about sound quality or bridging some perceived gap between them and solid body.
Returning to symmetrical, have you seen any Weissenborn style guitars, there's a different take on a standard form?! Reeves introduced me to them, and I've heard a few players using them, mostly at Woodford. I'm a bit a slide guitar/bottleneck/dobro fan so it suits my ears.
I found a Brisbane based guy who makes them, here
they look great!

Cheers,

Hi There

Interesting question you have posed! I heard somewhere that the shape of the guitar was based on the curves of the womanly figure! I know not if that is true or not but there does seem to be some correlation, don't you think?

The mass standardisation of acoustic guitars does intrigue me as it would seem this world thrives on continually trying to produce newer, more inovative products and features for commercialisation. The electric guitar (admittedly a chunk of wood) has taken on a bazillion different forms, but not the acoustic.
To say that to deviate from the standard form will gain nothing more than curiosity, would seem a little short sighted to me. If nothing ever varied then we would all be playing lutes, or even banging rocks together like cavemen. You cannot dismiss something before you have tried it, yet alone before it has been created.

I have made many different shaped guitars over the years, and each has its own unique sound. The shapes have not been the only variables, ie. I have used different timbers, finishes, inlays etc. so a direct comparison in sound to shape is somewhat affected by these other factors. Overall, the shape of the instrument (quite obviously) does affect the sound produced, just like the choise of timbers, bracing, finish etc. However, it is not necessarily an adverse effect, it is just another variable that can be moulded to suit your needs. There are certain frequency responses, volume ratios, active surface areas etc. etc. plus ergonomics and asthetics that need to be kept in mind but that is not to say that something slightly different can't be just as good (good being very subjective!). A lot of reaserch would need to be put into creating a new shape to hone it into a fine instrument, possibly that is a restricting factor for makers when there is one readily available that already works.
I now produce a range of fairly unconventional smaller instruments, of which I derive my sole income from, ie. they sell!

Don't get me wrong, I don't think the guitar needs reinventing, but a little diversity could be a good thing!

Cheers
Nick

Originally Posted by Wildwood

Hi There

Interesting question you have posed! I heard somewhere that the shape of the guitar was based on the curves of the womanly figure! I know not if that is true or not but there does seem to be some correlation, don't you think?



Cheers
Nick

Nick I think the nameing conventions might have something to do with my mother in law. Jumbo, Dreadnaught etc!

The instrument pictured to the far left in your post is exactly the type of asymmetry I would expect as a result of evolution in design I love it !!!

Ross

Originally Posted by Different

Nick I think the nameing conventions might have something to do with my mother in law. Jumbo, Dreadnaught etc!

The instrument pictured to the far left in your post is exactly the type of asymmetry I would expect as a result of evolution in design I love it !!!

Ross

Makes you wonder about leo fenders missus then, or the guy that designed the sg

Then there is Picasso's missus......

I don't know much about steel strings but I wouldn't want a classical guitar any other shape. Even the cutaways Maccaferri and others have built seem quite wrong to me (although Maccaferri's are beautiful).

I wouldn't want the edge bevelled as it would tempt a greater incursion of the forearm onto the soundboard. Cutaways are completely unnecessary, one can reach the whole hand up over the neck if required. The classical pantillas are well proportioned for the classical seated position. I suspect they simply developed from the lute shape which in turn arose from the gourd. Add a bulge at the top to facilitate seated playing and you have the modern guitar.

I assume you know bracing on nylon string guitars isn't usually symetrical. I don't know if steel string bracing is ? The sound hole is where it is because that's a prt of the top that doesn't vibrate much. It needs to be stiffened to support the string tension.

Often people play the steel string differently, so perhaps there are ergonomic or astetic needs there.

Traditionally unconventional guitar designes don't meet with acceptance. The electric guitars short history is littered with failed innovations. Guitar players are very conservative. It's good to applaude experiments, but nearly all don't sell. Greg Smallman is one standout exception, haveing created essentially single handed a whole new class of nylon string, but he is the exception not the rule and he was helped very much by one of the worlds great masters embracing his design and showing what could be done with it.

There was a spectacular and unusual accoustic on the mimf a few months back. Still fairly symetrical but certainly not conservative. Marylin I think it was called.

Acoustics are generally not entirely symmetrically braced. Some more so than others. The pull is greater than with a Classical, but the problem of making the top a suitable transducer is pretty much the same.

Sound hole location can move to either corner of the top bout with little loss of live surface. In fact, it frees up the area above the bridge to contribute to sound coupling. What you loose moving the hole to an upper bout corner you gain in the central surface.

Changing shape changes the Hemholtz resonance as well as surface modalities. Then again, the next flitch of wood can also contribute to a difference in sound. Lots of study on this, not a lot of hard rules derived. An expert, for instance, can tell a Taylor guitar from other brands by listening, but not which grade.

The modern guitar shape is rather new, and, I would point out, it resembles the violin family more than its immediate predecessor, the lute.We'll never know for sure, but my theory was the change was to attempt to gain some of the volume available in the violin. Lutes are all but inaudible at any distance if there is competing sound. Steel strings were the answer to gaining even more volume, but require a truss rod in the neck.

I like the bevel trick. You can counter brace the guitar against barre chords without damping the guitar as much.

If I could talk SWMBO into it I would buy a Weissenborn and learn slide guitar. It is nice to play something different now and then. If only I could actually play. That might be why she is discouraging me.

Interesting question, but instead of asking 'why haven't acoustic guitars changed much?', it might be interesting to ask 'why should acoustic guitars change much?'

Firstly, I suspect the effect of geometry on sound is not really all that huge. For example, a good cutaway acoustic sounds a lot like its non-cutaway brother, and the difference between the best sounding guitar and the worst one is usually due to factors other than the shape. A guitar is essentially a wooden box that goes twang, and as long as it is made by a skilled luthier from quality materials, it can probably be persuaded to produce whatever sound the luthier seeks without having to stray too far from the classical shape.

Secondly, why would a luthier WANT to make a guitar in a radically different shape? Aside from minor conveniences and comforts, what is to be gained? Perhaps he could affect the lower frequencies, or the higher frequencies, or the harmonics, or the volume - but wouldn't it then sound less like a 'guitar'?

Originally Posted by Different

Nick I think the nameing conventions might have something to do with my mother in law. Jumbo, Dreadnaught etc!

Ross

The Dreadnaught was named after the design of warship of the same name.