Official Luthiers Forum!

Let me just carve my braces please!

Oh yea the whole world will be affected but much animal or plant life is likely to survive tie immediate on slot for a thousand miles of the epa-center. Most of the fossils dating from the last super eruption showed that most animals died from siliceous induced by the fall out. Even as far south as Texas and almost all the animal live in the Dakotas to Nebraska were gone

Hesh asked:
<<...a question that I have had for a while has been the potential damping impact of epoxy as a pore fill on tone. >>

Two things:
'Damping', as we try to use the term, has to do with the dissipation of energy: how much gets turned into something other that what we want (usually heat). Adding mass by itself does not add to damping, even though it cuts down on the amplitude of vibration, all else equal.

Epoxy resin should have about the same specific gravity as the shellac used as a binder in FP fill, but the pumice is much denser, so I'd think that the epoxy might add less weight, and thus be 'better'. Unless, of course, the material has higher damping than shellac.... ;)

Colin wrote:
<<I'm afraid that Alan has over-simplified the case of wave motion through the material of the guitar.>>

Sure. As far as I know the bending waves are the only ones that actually produce sound, so I talked a little about them. I'd be interested to find any papers about the influence of other wave types on guitar tone. Until then it seems to me that discussion of them is of primarily academic interest.

"In terms of the velocity of a wave through any material the density is a greater influence than the modulus of elasticity. The latter will slow down the wave but an increase in density will result in the wave travelling faster with less loss of amplitude."

Are you sure that's not backward? Higher stiffness should give higher wave velocity, all else equal, and higher density should be lower. At least, it always works that way for me.....

In justice, I must point out that I _never_ make those sorts of mistakes...NOT. ;)

" So yes the type of glue will make a difference, you want one that with a low elasticity. Hot Hide in fact! "

When I took physics, just after the local glacier melted, an 'elastic' material was one that rebounded fully after being deformed, while the other kind was called 'plastic'. Various elastic materials have different moduli of elasticity: they are more or less 'stiff', but that does not effect how 'elastic' they are. For example, aluminum has a lower Young's mpdulus than steel, but, with lower losses, some aluminum alloys rebound better, and are thus more 'elastic', which is why they use them for tuning forks. In that sense, then, hide glue is _more_ elastic; it defoms less under applied loads than Titebond or white glue. HHg also has a higher _modulus_ of elasticity: it's stiffer. It's still better, though.

I think I would rather talk about love waves in guitars.
Does anyone think that is why tone faerie are attracted to them.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I meant that for the volcano talk (scary) not Alan, would walk over lava to listen for as long as he talked.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

[QUOTE=Alan Carruth]
"In terms of the velocity of a wave through any material the density is a greater influence than the modulus of elasticity. The latter will slow down the wave but an increase in density will result in the wave travelling faster with less loss of amplitude."

Are you sure that's not backward? Higher stiffness should give higher wave velocity, all else equal, and higher density should be lower. At least, it always works that way for me.....

[/QUOTE]

I believe Alan is correct on this one.

This was covered extensively in my ultrasound/sonography physics classes.

Some basic principles.

1. Sound wave velocity is 100% media dependant. The same sound wave at any given frequency will change velocity through various media.

The stiffer the media (less elastic)of the same densities the faster the sound waves will travel.

The density of two media with the same stiffness will be inversely proportional to the velocity of the sound waves.

In the "real world" it is very difficult to change stiffness independant of density or to get a hold of two materials that are identical in one of these variable but significantly different in the other.

What we generally find in nature most often is that more dense media tends to be more stiff but there are exceptions such as spruce (high in stiffnes and lower in density than most other wood) and lead wich is very dense but compressable (not so stiff) in its pure form.

Kevlar and carbon graphite are obviously prized for being uniquely stiff and light weight (lower density).

2. Stiffer media transfers sound waves more efficiently than more compressable media.

3. The biggest influence in sound wave reflections are impedance mis-matches where the greater the difference in Q value (density x stifness) between two specular reflectors (flat surfaces that are flat for at least one wave length of the sound wave) the greater the percentage of sound energy will be directly reflected back leaving less sound energy to continue on its original merry path.

Conversely the more similiar the Q values are the more efficiently the sound waves will transfer from the intersection of one media to the next when encountering specular reflectors.

Non specular (reflecting surfaces whose linear intersection is less than one wavelength) will scatter the sound waves in multiple directions rather than a direct reflection.

All the above ignores sound wave interactions as they pass each other and hit each other head on in various longitudinal and transverse waves.

These intersecting waves can cause contructive and destructive intereference where certian primary frequencies from one wave will be amplified when combined (when the peaks of the waves are in phase when combined) or destructive interference (when the peaks of one wave merge with the troughs of the other waves).

Of course these waves rarely intereact perfectly in synch so you get various degrees of modulating frequency boosts and cuts at each primary frequency initiated from a single pluck of a string or tap on the sound plates.

The other two forms of directional sound waves are such a smaller percentage of the total energy that I agree with Alan that these effects are most likely more academic than a significant influences in tone and effeciency of sound transmission.

Tommorow we can get into Doppler effects and Fast Fourier Transform analysis so be sure to read ahead

Scooter B39035.9746296296

Ouch!!! Alan, Colin, Scooter - Y'all stop it now! ...yur hurtin me. I don't think brains were made to think that much.

All this has inspired another question – but in a slightly different direction. Another topic.

Scooter B wrote:
"...the greater the difference in Q value (density x stifness)..."

Oh-oh. In all the literature I've got Q is the measure of damping: the amount of energy 'lost' or dissipated in vibration. Sqrt(density*stiffness) is proportional to impedance, which is commonly designated by Z. What you're describing is the outcome of impedance matching/mismatching. I have no problem with anybody using any letter they like to designate any variable, but we'd all better use the same ones here or we're in trouble.

BTW, P waves in strings _do_ seem to effect the high frequencies by altering the distribution of tension in the strings. Do we _really_ need to go there?

[QUOTE=Alan Carruth] Scooter B wrote:
Oh-oh. In all the literature I've got Q is the measure of damping: the amount of energy 'lost' or dissipated in vibration. Sqrt(density*stiffness) is proportional to impedance, which is commonly designated by Z. What you're describing is the outcome of impedance matching/mismatching. I have no problem with anybody using any letter they like to designate any variable, but we'd all better use the same ones here or we're in trouble.

BTW, P waves in strings _do_ seem to effect the high frequencies by altering the distribution of tension in the strings. Do we _really_ need to go there? [/QUOTE]

Yeah they do some weird things on the ultrasound side of the physics such as reversing the Doppler shift to where Blue represents going away from the source and Red going toward the source. That is plain backwards from Johan Doppler original astronomical observations with Red having the higher wavelength and Blue the relatively shorter wavelength shift.

That being said I did not pull out my physics books so I may well be inverted on my Q formula.

Nah we don't need to get into the strings P waves but there are lots of complex waves going on to produce different timbre of sounds having the same fundamentals.