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Rayleigh surface waves and "tone amplification"
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Author:  Howard Klepper [ Wed Dec 10, 2008 4:42 pm ]
Post subject:  Rayleigh surface waves and "tone amplification"
Has anyone looked at this guy (Frank Geiger)'s site? He says he has a way of making surface waves audible and calls it a "tone amplifier". He posted recently on a bunch of forums. He offered ways to build his products for yourself, which seems sincere. But from what I've been able to find out, the amount of energy in these waves would be very small in a guitar top or side, and I frankly do not understand how his thingamajig is supposed to make the energy of these waves audible.

I'm showing a link to Geiger's Theory page, and also a very nice page that offers a visualization of what these waves are (a hybrid of longitudinal (compression) waves, which are the main component of audible sound, and lateral displacement waves, which are the main way a string vibrates). Googling seems to indicated that these waves are mostly of interest to people doing supercooled fluid dynamics.

Al? Can you 'splain?

http://www.geigeracousticdevices.com/Ge ... heory.html

http://www.kettering.edu/~drussell/Demo ... otion.html
Author:  wbergman [ Wed Dec 10, 2008 5:38 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
http://cgi.ebay.com/Recitalbox-Fantasti ... 7C294%3A50

Here is an ebay listing for a "recital box" (found under "famenco guitar"). Based upon the famous endorsers, it might really work. It is claimed to not only improve and amplify tone while attached to the guitar, but to actually modify the guitar so that the guitar is improved even upon removing the device.

Any comments on this?
Author:  Jody [ Wed Dec 10, 2008 5:50 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
I dont know, but it seems if they are selling enhanced tone, they could have easily done a before and after the recital box.....hearing is believing ... Jody
Author:  Lars Stahl [ Wed Dec 10, 2008 6:16 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
I am with Jody ! Sounds like humbug to me !
Would be good to get a sample of before and after.

Allthough that RECITALBOX is really cool.
Author:  Jim Kirby [ Wed Dec 10, 2008 8:08 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
Howard Klepper wrote:
Has anyone looked at this guy (Frank Geiger)'s site? He says he has a way of making surface waves audible and calls it a "tone amplifier". He posted recently on a bunch of forums. He offered ways to build his products for yourself, which seems sincere. But from what I've been able to find out, the amount of energy in these waves would be very small in a guitar top or side, and I frankly do not understand how his thingamajig is supposed to make the energy of these waves audible.

I'm showing a link to Geiger's Theory page, and also a very nice page that offers a visualization of what these waves are (a hybrid of longitudinal (compression) waves, which are the main component of audible sound, and lateral displacement waves, which are the main way a string vibrates). Googling seems to indicated that these waves are mostly of interest to people doing supercooled fluid dynamics.



Rayleigh waves are one of the two main paths for transmitting seismic disturbances over distances along the earth's surface, the other being direct transmission of body waves along straight paths through the earth.

Thanks for the link - as a wave guy, these things pique my interest.

Jim
Author:  Marc [ Wed Dec 10, 2008 8:44 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
Howard Klepper wrote:
... Googling seems to indicated that these waves are mostly of interest to people doing supercooled fluid dynamics....


and geophysicist, they can sometimes be a problem if your doing a seismic survey .
Author:  jfmckenna [ Thu Dec 11, 2008 8:59 am ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
Ah yes as a trained Geologist I seem to remember some of this stuff :)

I am sceptical. Once you pluck the string the energy diminishes. You can only amp it with power. Howard if you ever try one please let us know.
Author:  Wade Sylvester [ Thu Dec 11, 2008 12:32 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
Howard,
Some of this seems to make sense.
The idea of properly shaped objects that are sensitive to frequencies already traveling through the wood via the strings. Maybe they are not really amplifiers so much as sympathetic devices. If they are the right length to respond to high frequencies and the right shape to dispense that tone into the air, I could see them working like a tweeter cone in a speaker system. The power is provided by the strings. You just need the proper sympathetic devises to help dispense them into the air or maybe support a boost of those frequencies sympathetically along the guitar’s top surface.
They look a little strange tacked on to the outside of a sound hole.
What is to keep us from building these into the insides of our instruments?
Then again..
Author:  Howard Klepper [ Thu Dec 11, 2008 12:47 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
I take "amplifier" to be used loosely; of course you can't amplify without a power source. And tone is not something that you can have more or less of, as long as we're getting technical. The claim seems to be that the energy in these surface waves can be transfered into audible compression waves in air.

The problem, as far as I understand it, is that these waves would only be in a microscopically thin surface layer and carry a tiny amount of energy.
Author:  meddlingfool [ Thu Dec 11, 2008 1:44 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
He he he!
I've heard one of those things years and tears ago when I was just learning guitar in highschool. If it's the thing I'm thinking about, inside the box are springs, very similar to tremolo springs,and the bridges' vibration excites them, giving you, of course, spring reverb. Hence your "cathedral like sound". It's actually a nifty sounding device, but like all effects it wears thin real fast, especially for strummy kind of stuff cause it doesn't stop when you do. However, I'm glad this post exists 'cause I've been looking for one for years!
Thanks
Author:  Alan Carruth [ Thu Dec 11, 2008 2:19 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
I followed the links on some of this when it first came up, and it didn't seem to make much sense. Meddlingfools' post clarifies it somewhat if what he saw is indeed what the link is talking about. I fear siesmic science is not my strong suit, so I will have to look up 'Rayleigh surface waves' to be sure about it.

I did see something that may be analogous when I was looking at string vibrations a few years back. We usually think about only the transverse displacement waves (you pull the string sideways and it vibrates when you release it), and the tension changes associated with them. However, there are also torsional waves in the string (it rolls off your finger or the pick), and longitudinal compression waves. The former die out pretty quickly as far as I could measure things, but the latter turn out to have an effect sometimes. It's a bit tricky, but the compression waves in the string can take energy out of the tension change signal, and, if the frequencies line up, build up to a fairly high level. If they do they can effect the transverse vibrations because the tension is no longer uniform over the length of the string at all times, so the higher partials can be messed up. The longitudinal wave frequency varies depending on the string length and material, and can range fro around 4000 Hz or so (iirc) on a plain steel or nylon string down to below 1000 on a wound string. If Rayleigh waves involve this sort of compression then they could work similarly in two dimensions on a top, for example. Again, I want to look some stuff up on that.

If this is the case he's right in noting that this sort of wave won't drive much air or contribute much to sound except, perhaps, to mess it up in special cases. OTOH, there are plenty of ways for the usual structures to deliver high frequency sounds. If the Rayleigh waves are highly damped they could 'eat' some energy, but it's hard to think of ways to get rid of what is, after all, a natural phenomenon.
Author:  David Collins [ Thu Dec 11, 2008 2:23 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
I thought at first it was the deep thoughts that was giving me a headache, but it turned out to be just the white on black tiny text. Copy that text to word, switch it to black verdana, and suddenly it's a much simpler read. Really, that seriously hurt my eyes....

I can kind of see the reasoning behind it, but I can't help but think it's something more academic than practical. Yes, I'm sure there is some small amount of energy in surface waves that are not being put to work moving air, but two main questions quickly come to my mind.

First of course would be, if we've been conditioned to appreciate a certain timbre by instruments played over the last 80 years, what would make one think "amplifying" them in the overall tone would automatically qualify as an improvement? That's obviously more a philosophy question though, where of course we'd never expect a consensus. Not much point in arguing good or bad.

On the technical side, if the energy contained in those surface waves is so small, how much can a passive unit like this bring them to be noticeably heard? If they do indeed carry so much in higher overtones that the instrument in it's current design does not translate to the air, do those waves contain enough energy to even overcome the losses as it moves the mechanism and still have any positive sum in the end to turn to audible sound? Pretty much the same as you were wondering Howard, I think.

When measuring or listening to controlled comparisons, what means of testing did they contrive to deduce that the difference in timbre was due to the addition of these surface waves to the spectrum, and not just the limiting of other frequencies in the top by clamping this thing to it, partially blocking the soundhole, changing air flow, etc.? Do the differences in tone result from it acting as a "tone amplifier" for these upper harmonics, or a selective tone soak?

It seems if one really wanted to accentuate these overtones, the best answer is already out there in the transducer and electronics. I can kind of see their theory, but I'm really not sure I believe the end effect is due to the properties they aim to utilize. Of course I've never played with one, and haven't seen all the research, so I'm really just talking out my @$$ here. Could be better than sliced bread for all I know.

Honestly, the first thing that popped in to my mind was "oh look, the Virzi plate of the 21st century". It is a bit reminiscent of it's philosophy I think. We all know how great those went over though.

I would love to hear Alan's ideas on this as well.
Author:  Erik Hauri [ Thu Dec 11, 2008 6:13 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
'nuther geophysicist here - yes Howard, you are correct in thinking that these waves will have very little energy in a guitar top.
Author:  MacD [ Thu Dec 11, 2008 7:24 pm ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
meddlingfool wrote:
He he he!
I've heard one of those things years and tears ago when I was just learning guitar in highschool. If it's the thing I'm thinking about, inside the box are springs, very similar to tremolo springs,and the bridges' vibration excites them, giving you, of course, spring reverb. Hence your "cathedral like sound". It's actually a nifty sounding device, but like all effects it wears thin real fast, especially for strummy kind of stuff cause it doesn't stop when you do. However, I'm glad this post exists 'cause I've been looking for one for years!
Thanks


Meddlingfool - I think what you're talking about there is an Aspri reverb - it's a black plastic box with reverb springs in it which attach mechanically to the strings at the bridge. They were quite effective but tended to mess up the intonation.

As for adding resonators to make use of longitudinal or surface waves on guitar tops, the amount of mass that has to be added to make any use of them would surely interfere with the operation of the rest of the system. I'm sure they'll change the sound and might even improve the tone of specific instruments, but I can't see them improving a well made and voiced guitar.

Cheers,
Bri
Author:  meddlingfool [ Fri Dec 12, 2008 11:26 am ]
Post subject:  Re: Rayleigh surface waves and "tone amplification"
Thanks for the tip!
I seem to recall the one I saw being made of plastic. I guess I was thinking of something besides what was actually being discussed. Ah well...
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