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So, I'm hoping this isn't a stupid question...but has anyone ever tried to combine a spruce and cedar top? I love the way a spruce top sounds in the bass register, and I love the sweetness of cedar in the upper register. So, couldn't someone create a soundboard with the bass side made of spruce and the treble side made of cedar? I know it would look odd, light and dark. Just curious to know if others have pondered this and if someone has actually tried it.

Almost, only the other way around:



Dovetail Madness by Howard Klepper

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

https://www.facebook.com/FenskeGuitars

Yes, there have been guitars built like that. It's also not uncommon for double tops to have one skin made of spruce and another of cedar.

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Jim Watts
http://jameswattsguitars.com

Not a stupid question at all, though it has not been shown conclusively that the bass and treble sides of a top respond to the respective ranges.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Hmmm...I guess I was under the impression that the bass side of the soundboard would respond more to the bass frequencies and the treble to the higher frequencies.

So, how does it work? Any recommending reading on the matter?

The Klepper guitar is quite a looker! I wonder how it sounds.

Dang! That's neat as hell, ain't it?

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"Act your age, not your shoe size" - Prince

While I am sure there are differences of opinion and also of fact, many years ago Brune mentioned to me that there isn't really a side of the top that reponds to treble and another side to bass, but that various areas respond to the various frequencies, and those areas can be anywhere and be effective. I am not sure if that is still his opinion.

If you have to divide the top up into sections, the bass, generally is most prevalent in the area between the bridge and the tail of the guitar, and treble in the wings and just above the bridge on both sides of the instrument, but all areas respond in different ways to the vibrations from the strings and the pulsing of the air in the box.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Seems to me that when I pluck ANY string on ANY fret, the whole top vibrates.

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Old growth, shmold growth!

I went back and did some listening. The bass in my guitars is most prevalent at the soundhole.

From the bridge to the tail is very midrangey.

The neck is extremely bright, while the brghtest parts seem to be the fretboard and strings themsleves.

But it still seems like the whole guitar is reacting to just about everything I do.

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Old growth, shmold growth!

Here's my understanding...

"Bass side" and "treble side" are merely labels because "left" and "right" are confusing in the case of guitar tops.

Stiff and light weight = high resonant frequency, flexible and heavy = low resonant frequency.

The lowest frequency modes of the guitar generally involve the whole top, back, or air volume moving in some way, so having a bass side in the sense of that half responding more to low frequencies doesn't make a whole lot of sense.

That said, some people, when doing asymmetric bracing patterns, go for stiff and light on the treble side, and heavy and loose on the bass side, simply as a matter of convention, as well as proximity to the attachment points of the supposedly favored strings... but in general, the effect of that should be very minor if any, so you could mirror the bracing and get a similar sounding guitar. But why bother going against convention, when it makes such natural sense for the "bass side" to be the loose and heavy side, and vice versa for the treble?

As far as I can visualize, the biggest effect of asymmetric bracing has to do with the cross dipole mode (bridge rocking side to side). With symmetrical bracing, the half of the top going up and half going down should cancel out eachother's effect on the air pressure inside the box. But with asymmetric bracing, one side moves more than the other, thus pumping air in and out through the soundhole and making more noise. Although whether that's a good thing or bad thing depends on the sound you're going for, I guess. Especially since the different stiffness/mass will affect all the other modes in some way or another too.

As for half spruce half cedar tops... I'd probably taper the thickness from one side to the other so the spruce side wouldn't be too stiff. But there'd still be a discontinuity in the middle, and I'm not sure what kind of effect that would have. Need to decide what is your goal; to have one side stiffer than the other, or to get some of the "flavor" of each top wood at as close to symmetrical stiffness as possible.

The sound a guitar makes are almost entirely determined by the amplitudes, resonant frequencies and "Q" values of its main modes of vibration.

The vibrations of the strings excite bending waves in the guitar's top (primarily) which travel across the top much like waves on the ocean. However, due to some fairly complex relationships between the speed of the bending wave and the speed of sound in air, these bending waves don't radiate very much sound at all. BUT, fortunately, the bending waves reflect back into the top when they reach the sides of the guitar, and at some frequencies standing waves are formed, much like the standing waves you see on a vibrating string, but in two dimensions. The pictures below show how some of these standing waves form and they can be seen by using Chladni techniques, where particles (dried herbs in this case) gather in places where there is not much movement, called nodes. There is much more movement in places where the particles do not collect, and this movement of the guitar top pushes around the air near it and so sound is radiated.

The left hand pic shows one of the monopole modes of vibration, which gives the impression that the top pumps in and out like a loud speaker. It doesn't really. It's just the way the reflecting bending waves, which form the standing waves, make it look.

Whilst these modes of vibration have particular resonant frequencies at which they move the most and so radiate the most sound, they also operate at other frequencies, but with less amplitude. It is the summation of the movement of the modes of vibration that characterise the sound of a guitar, and no sound is effectively radiated by movements other than the modes of vibration, which is why I opened with "The sound a guitar makes are almost entirely determined by the amplitudes, resonant frequencies and "Q" values of its main modes of vibration".

So you can see, now, why there isn't really a side of the guitar that radiates the bass and a side that radiates the treble. The bass sounds are primarily radiated by the modes of vibration with the lower resonant frequencies and the treble sounds are radiated by the modes of vibration with the higher resonant frequencies (those to the right, in the pic).

The resonant frequencies of the modes of vibration can easily be identified in the guitar's frequency response function. And, of course, the shape, amplitude, resonant frequency and "Q" of the modes of vibration are affected by how the woodwork is shaped. That is how the link between the shaping of the woodwork and the sound of a guitar is formed.


Not sure I'm the right person to answer that one! Anyway, there's a review of a good book on the subject here.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Harry Fleishman has been building cedar and spruce and redwood and spruce topped guitars for years. http://www.fleishmaninstruments.com/

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

I have Trevor's books and although I have not read them cover to cover, I can tell you they are chock full of the kind of info he posted here. Highly recommended.