Official Luthiers Forum!

Hello friends
First of all happy new to all of you...

Every one know that sound of engelman spruce is mellow and little bassy
im planning to build another classical with laminated back and sides and engelman spruce
can we achive higher trebles in spruce ??
what should be thickness of top. the bracing system and thickness of braces
hope all of u contribute ur experience to me

I'll give you the same answer here.

"I believe your premise is wrong. Engelmann Spruce is not bassy, and it projects trebles as well as any other Spruce. IMO, keeping the correct stiffness in the area above the wings of the bridge is one of the keys to getting strong treble sustain. There are many ways to accomplish this, and each depends on the wood in your hand."

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Waddy,
Can you, or anyone, elaborate on this a little or point to another thread, or publication, or something?

Thanks,
Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I'm with you Kevin. This could be an excellent learning opportunity.

_________________
Joe Beaver
Maker of Sawdust

Rats: I just answered this one on another forum.

Engelmann spruce tends to be less dense than European spruce, and thus usually has lower stiffness along the grain. If you make a typical Engelmann top the same thickness as you would a typical European top, it will be a bit on the thin side, and will tend to be bassy and lack clarity in the trebles. Used right, it works fine.

I have found that thinning the top behind the bridge tends to bring up the basses. Thinning in the wings, from the bridge ends out toward the edge of the box,tends to give a bit more 'cut'. I think it's due to the fact that the cross dipole mode bends a lot in this area, so thinning there lowers the cross dipole pitch. This, in turn, tends to 'steal' energy from the monopole in the upper part of its range, making the output peak in the spectrum narrower. Guitars with a narrow 'main top' peak tend to sound 'sharper' and can even be irritating if the peak is too narrow. You need a bit of this on a classical guitar, which is why they stick with fan bracing rather than X bracing. Flamencos need it even more, and often leave out the two outer fans to loosen the edge.

Alan can you elaborate on the term "cut" so I can better understand your comment ?

Thanks

I use 'cut' to refer to the ability of the guitar to 'cut through' and be heard: 'carry' might be another term you could use. Usually, in my mind, the difference is that guitars with 'cut' have a transient that makes them noticeable, while 'carry' seems to depend more on the output spectrum, particularly in the high end (2-4kHz). You might think of these things in different terms. From what I can tell, the way we perceive a sound is usually a complicated mix of the way it develops over time, as well as the frequency content and how that changes. I've seen guitars that had a 'bright' and 'punchy' sound that actually did not put out much power in the high frequency range, and some that sound 'full' that do. That's one reason its hard to say with any certainty how you might go about 'improving the treble'. You have to know what aspect is missing, which presupposes that you know what the person wants.

Thanks Alan that may have helped.

I am working at letting all this dipole info work its way around in my head. So if I make no sense it's because of the wolf tones I created....

So thinning from the bridge wings to the rim of the guitar as it loosens the top actually "compresses the sound" since it "steals energy" from the upper range from the main dipole sound... yet overall increases the air pump motion bringing out a punch or cut into a room mix.

Whether I understand or not I sure like having thoughts bounce through my head...

D.Ramsey wrote:
"So thinning from the bridge wings to the rim of the guitar as it loosens the top actually "compresses the sound" since it "steals energy" from the upper range from the main dipole sound... yet overall increases the air pump motion bringing out a punch or cut into a room mix."

Not exactly.

The main sound producing mechanism of the guitar is the 'bass reflex action' of the 'main air' and 'main top' resonant modes. Working together these are thought to produce most of the actual output of the instrument up to about 1000Hz. Air moving in and out of the hole, in the same way it does when you blow across the mouth of a wine bottle, is pretty effective, if not outrageously efficient, at making sound around the pitches of the lowest notes. The 'main top' mode acts like a loudspeaker tuned near the pitch of the open G string, and seems to be very efficient, although such things are hard to measure. The important thing to notice is that, around the 'main top' pitch the whole lower bout is moving the same direction at any given time, and that's the main reason it's so effective.

All of the 'higher order' resonances involve more than one area in motion. As you go from one moving area to the next the direction of motion changes as you cross the non-moving 'node line'. Thus, for the top 'cross dipole' mode, as the treble side of the top moves 'up', the bass side moves 'down'. There is at least some cancellation inherent in this: air that's being pushed away from the treble side can find it easier to just slosh over to the bass, rather than actually producing sound. The sound that is produced tends to be in 'lobes': like beams of light in a way, but not nearly so well defined. If you drive a top with a pure tone just at the 'cross dipole' pitch, you'll hear sound going out at an angle toward the treble and bass sides, but won't hear much, if anything, if you listen right in the center.

Guitar strings don't produce pure tones. Also, although we talk about these modes as happening at particular frequencies, they can actually be driven over a pretty wide range of pitches. Thus, when you play a string, you tend to get a number of different modes going to a greater or lesser extent, and each puts out sound in the way that it would by itself. What you actually hear coming out of the guitar is a sum of these different sound producers. In some directions the power adds, and in others it subtracts, so the sound field can get pretty complicated, even at fairly low pitches.

On the whole, though, any power that goes into driving the 'cross dipole' type of motion is going to tend to produce less output than power that goes into the 'monopole' of the 'main top' resonance. If the cross dipole is close in pitch to the main top resonance, that loss of efficiency sets in close to the monopole's own pitch, so the output peak that's formed is not as broad.

One audible result of this is an increase in the 'sharpness' of the sound. This is pretty much characteristic of any sound with a 'peaky' spectrum: one that has tall peaks and deep dips in between, rather than a 'flat' characteristic. It probably has to do with the fact that closely spaced tones will end up with much different overtone mixtures, which gives your ear and brain something interesting to home in on. 'Flat' sound just tend to sound, well, 'flat'. There are limits to this, of course. Too 'peaky' gets 'irritating', and maybe even 'boring', as it gets to be too hard to keep track of something that comes across as random. As usual, there are 'Goldilocks' values for things: neither too much not too little, but 'just right'. Just as naturally, the 'best' level of 'peakiness' varies, depending on what you're using the guitar for, and individual tastes come in, too.

Does that help?

Actually it did.
Thanks for opening my mind a little more.
I find visions in my mind of those "like beams of light in a way".......

That alone gave me a way to follow the motion of sound inside my head to feel like I grasped what you are saying.

Now seeing it and building it are two whole different things.
Gaining Theories and proving Theories are steps I feel so far from as I have so much trouble completing my builds
(I do not have a love for the step of putting on a finish on wood.)

I did get your DVD on free plate tuning and felt a bit overwhelmed and will spend more time trying to gain a good understanding even if I do not choose that method to build I appreciate the knowledge gained.

Dennis