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"No such thing as a stupid question" ...try this one!

2K views 30 replies 12 participants last post by  BMW-KTM 
#1 · (Edited)
In a fully hollow bodied arch top guitar, how are the acoustic properties able to influence the sound/tone... vibrations of the top through the pickup(s)?
Or do they (i.e., is this a myth)?

This is a beautiful example of what I'm referring to...


This is might be more to the liking of others...


Thanks in advance. I have asked this question many times and have never been given much of a convincing (preferably scientific/acoustically based) answer.

Most often, I got blank looks or a short "Don't know" or "Beats me" from those that I expected would know.
 
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#4 · (Edited)
... All I know is hollow bodies + my small ass studio = feedback!
Not an expert on acoustic science by any means, but I suspect that this is part of the answer. The hollow body will resonate more readily and this probably translates to more sustain or otherwise affects the vibration of the strings, which is in turn picked up by the pick-up. I don't imagine that the vibration of the top is picked up as there is nothing metal to generate a current/magnetic field, however, it might possibly cause the pick-ups to vibrate relative to the strings (perhaps along a different plane or axis) which might also somehow affect the tone.

Interesting question!

Edit: I always tell my kids and students, "The only stupid question is one that you already know the answer to."
eg. "Should I practice more?"
 
#6 ·
Both instruments shown have "floating" bridges. Such bridges will vibrate and emphasize those frequencies the vibrating top favors. The vibrating top will favour frequency ranges depending on bracing, body shape/size, wood properties, scale, etc. And of course, they will use the sort of tailpieces shown, to provide as little downward pressure of the strings on the bridge as possible, permitting the top to vibrate longer.

As always, remember that the steel string "wants" to come to rest after it is plucked. The harmonics produced, when the string is set in motion, will decline before the fundamental, such that the tone of the guitar will depend on how all the stuff noted above damps the harmonics over time-since-pluck. But of the top and body don't damp the string too much, the string will continue to vibrate for a while after the harmonics have died out.

Is that enough detail?
 
#7 ·
Both instruments shown have "floating" bridges. Such bridges will vibrate and emphasize those frequencies the vibrating top favors. The vibrating top will favour frequency ranges depending on bracing, body shape/size, wood properties, scale, etc. And of course, they will use the sort of tailpieces shown, to provide as little downward pressure of the strings on the bridge as possible, permitting the top to vibrate longer.
This is now making it much easier for me to understand. Your explanations always have such clarity and flow so well.

Thanks very much!
 
G
#11 ·
Can you not shout into a pickup and it can pick up your voice? If so I think that will also allow some of the acoustic sounds to come through.

I have a Gibson 335, 137 and a custom jazz guitar. They do have more of an acoustic sound to them. Sort of on the fringes of the normal electric guitar sound. When played clean. When overdrive is on they also have a different tone than a solid body.
 
#18 ·
Starting from the top, when a string is plucked (given energy), it vibrates in a series of nodes, collectively referred to as a mode. These change proportion and number, as the vibration (energy) decays. Although the initial energy was imparted in a particular direction (vector) via the pick, the polarity or plane of vibration rotates as it decays. This sweeps the acoustic environment of the instrument with energy, stimulating sympathetic resonances, particularly in hollow bodies. The resonant energy is coupled, or ‘heard’ by the vibrating string as it decays, influencing its mode of vibration. Just like the string’s vibrational modes, the body surfaces (particularly the top) also demonstrate vibrational modes wherein various portions of the wood serve as separate dynamic resonant zones coupled according to pitch. The physical makeup of the instrument reins over the net result of what one hears; body depth, width, flat/arch top, wood type/moisture/density/thickness, etc.
 
#19 ·
When I had a tour through the former Gibson-now-Heritage-Guitars building in 1982, it culminated in being shown what was, at the time, the most expensive carved-top guitar Gibson made, the Kalamazoo Award ( Gibson Kalamazoo Award ). "Just breathe on it" my tour-giver said (I think, but don't know, that this was Marv Lamb, who became one of the co-owners/founders of Heritage). I did, and the strings resonated for a while. That was some responsive instrument.

So I have little doubt that if one shouts at a decently made archtop, equipped with a pickup, you can hear it. In the case of solid-bodies, any yelling-generated sound would, as Dave/Greco indicates, be a result of microphonic pickups.
 
#21 ·
Don't know if it'll help answer your original question, but I'll offer this anyway.............
I have a Heritage H155, which is referred to as 'semi-solid', being a chambered hunk of mahogany with a maple cap. Size is approximately that of an LP. 24 3/4" scale.
I also have a Heritage H535, a semi-hollow roughly equivalent to a 335, with laminate top and back, solid maple sides, and F-holes. So the H535 has a lot more internal air than the H155. It's 24 3/4" scale as well.
With identical pickups (Seth Lovers) and identical strings, these two guitars do not sound alike at all. The H535's sound is considerably more mellow, with greater depth, width, and sustain. Its notes have a very pleasing 'bloom', not found on the smaller H155.

So I figure the tonal difference is a result of either the differing woods, differing construction, differing internal volume, or all of the above.

Here's the H155:


And this is the H535:
 
#22 ·
I do know that my full hollow Ibanez has a faster decay than my solid body electrics
Could there be other factors as well?
Sure, but the different decay & so shorter sustain affect the sound--and the way the strings attach can affect how they vibrate--which I believe will affect the tone.
Some might pin all the different tone on the pickups or something like that--but it doesn't seem to work hate ya to me
(Of course others overstate the impact of other things on a guitar as well)
 
G
#23 ·
I had a '92 Epi Emperor II that squealed big time (microphonic feedback).
First I wax potted the pups. I caked them thick.
Helped a little, but not much.
Swapped them out for Gibby's that I found on 'jiji. That helped.
Did a little research and what I did was pressure wedge a coupla' of sound posts (dowels) under the floating bridge.
That did the trick.

Yellow Orange Macro photography
 
#24 ·
I had a '92 Epi Emperor II that squealed big time (microphonic feedback).
First I wax potted the pups. I caked them thick.
Helped a little, but not much.
Swapped them out for Gibby's that I found on 'jiji. That helped.
Did a little research and what I did was pressure wedge a coupla' of sound posts (dowels) under the floating bridge.
That did the trick.

View attachment 221932
Now THAT makes sense. Any sympathetic vibrations of the guitar body are most likely to have the biggest impact at bridge/saddles and nut, since that’s where the strings are attached and any movement there will change/vibrate string pitch. There will also be acoustic vibrations from a hollow body that will affect (vibrate) strings at other locations, but that would be a much lower magnitude effect (but still present in a hollow body). I don’t find all this focus in this thread on microphonic pickups compelling or logical at all.
 
#25 ·
I had a '92 Epi Emperor II that squealed big time (microphonic feedback).
First I wax potted the pups. I caked them thick.
Helped a little, but not much.
Swapped them out for Gibby's that I found on 'jiji. That helped.
Did a little research and what I did was pressure wedge a coupla' of sound posts (dowels) under the floating bridge.
That did the trick.

View attachment 221932
I did that to a Pyramid semi-acoustic I picked up in 1990 or so. In this case, because it was a budget guitar and made of less-than-optimal materials, it improved the sustain a bit too, on top of curing feedback.
 
#26 · (Edited)
The pickups don't pick up anything from the wood.
They only respond to the changing magnetic field above them which is caused by the metal mass in the strings vibrating close to them.
Since the wood is non-magnetic it does not affect the pickups.
Any affect that the guitar itself may have on tone, volume, sustain, etc. is only due to how things like mass, density, stiffness, hardness, etc. may affect how the strings vibrate.
Of course, I am talking about amplified guitars.
The hollow/solid tone discussion is the same as the tone-wood debate.
In both cases, the materials used and the construction methods used can have an affect on how the strings vibrate.
Usually the materials and construction methods have a damping affect on the strings.
How much damping occurs and at what frequencies is at the heart of the issue and is the reason for the differences we hear.
Woods (or other materials) that are hard, stiff and light usually have less damping and so the guitar can seem louder, brighter or with more sustain.
In a hollow bodied guitar there is the added component of how sound pressure may come into contact with the strings and have an affect on how they vibrate.
The fact that sound pressure can affect the vibration of guitar strings can be demonstrated by turning the amplifier up loud and facing the amp.
I think we all know what happens in that situation.
In the case of a solid body electric and a loud amp, some think the amp is interacting with the pickups but that is not the case.
It's basically the same effect as an acoustic and a loud amp, just with a different outcome.
Sound pressure is non-magnetic, at least for the purposes of this discussion.
The sound pressure from the amp interacts with the strings.
The pickups pick up the strings.

Hope that helps.
 
#29 ·
How much damping occurs and at what frequencies is at the heart of the issue and is the reason for the differences we hear.
In a hollow bodied guitar there is the added component of how sound pressure may come into contact with the strings and have an affect on how they vibrate.
Extremely interesting and helpful for this inquisitive idiot. Thanks
 
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