stethoscope tone test

Mike Scaggs · From: Nashville, TN

So my dear buddy Wayne Dahl and I were in the shop messing around when I remembered having a stethoscope with a small metal tube on the end. I used to use this for finding noises in my old hot-rod motors.

Anyway we got to playing around with my push pull and discovered how each piece on the guitar was exhibiting tone. You could strike a string and hear sound through each bell crank for example. You could hear differences all around the body and end plates. The cross shafts themselves were ringing like bells. Even the pulls rods had audible tone!

We found this to be a very valuable lesson in materials used in building guitars and how each part in of itself contributes to the end game.

Try it yourself, go to Harbor Freight and buy on of these stethoscopes for a few bucks and test it out. You will probably be as surprised as we were.

https://www.harborfreight.com/mechanics-stethoscope-69913.html
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David Weisenthal · From: Arizona, USA

Interesting Mike...I have a stethoscope in my garage, I can try with my Derby...
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Stephen Williams · From: from Wales now in Berkeley,Ca, USA

maybe some new micing techniques will arise from this research.
Direct in plus ambient microphone on bell crank 2 and pull rod 4

Mike Scaggs · From: Nashville, TN

gary pierce · From: Rossville TN

These are great, I finally found that squeaking bearing on my Cummins.

Mark Hepler · From: Virginia, USA

Amazing info, Mike.

Opens up the idea of contact micing the cabinet somewhere to get dobro tones or who-knows? . . . with one of these:

https://www.amazon.com/SUNYIN-Transducer-Microphone-Classical-Cello-Black/dp/B01M1GG05L/ref=pd_lpo_vtph_267_bs_img_2?_encoding=UTF8&psc=1&refRID=TNS5CC5JP4Q7KKPZ287N

Mechanical noise might overwhelm the notes, so maybe we'd have to lay off pedals while using it.

Mike Scaggs · From: Nashville, TN

Mark Hepler · From: Virginia, USA

It's a very interesting insight into how much components affect tone.

Fred Treece · From: California, USA

Do those overtones and resonances actually make their way from the various parts back to the string and into the pickup? Or do they affect the pickup more directly somehow, after the string causes them to vibrate?

Bob Hoffnar · From: Austin, Tx

I had a long talk with Bud Carter one day where he told me about testing the resonant frequencies of every part in a pedalsteel. Really facinating stuff. Paul Franklin Sr and Bobby Bowman both have very involved ways of making sure every part of the steel worked together to create the tone.

Dale Rivard · From: Ontario, Canada

I believe it's the combination of different materials and the way they're assembled that affect the overall tone and sustain of an instrument. I agree with Bob about pickups. If an instrument has poor sustain when played acoustically, changing pickups won't help that. The pickup only amplifies what the instrument delivers. This being said, you can alter tone somewhat through pickup changes.

Pat Chong · From: New Mexico, USA

The results of the stethoscope use is interesting. Since the parts/rods themselves are vibrating, one would wonder if padding between the rods might dampen the sound or sustain, a little bit? Just a thought.

...........Pat

John Goux · From: California, USA

I've had rubber bicycle handles on the knee levers. It feels good on your knees and makes playing in shorts more comfortable.

It had not occurred to me me, those rubber pads might be dampening the instrument. One day I removed them for travel.
I noticed the steel seemed more lively with them off. So I put them on and off a few times.
It seems even the hanging knee levers add to the resonance. Subtle, yes. Maybe inconsequential. But I've kept them off for a while now.

The pickup is going to hear what the strings do. But the instrument does vibrate and resonate as a unit(or not).
This reminds me of discussions about the how tight to make the necks on push pulls.

Also, "lighter" does not necessarily equate to "more resonant". Sometimes lighter parts dissipate energy. I read Paul Franklin experimented, and has stayed with the heavy legs in his steels. He described the difference as "very subtle" or something to that effect.
John

Fred Treece · From: California, USA

It might be even more interesting to find out which resonant frequencies match the various materials an instrument is made from. The bell crank might be singing while the corner braces are out catchin' a smoke.

http://www.intuitor.com/resonance/tesla.php

Georg Sørtun · From: Mandal, Agder, Norway

Back in the early -90s I put the "stethoscope" testing to good use - using a contact mic, headphones and scope - as one of the tools, when I modified my Dekley S10 and put on a floating neck.
As a Dekley is more of a "soundboard-in-a-heavy-frame" design than most PSGs, and the floating neck acts like a 12 inch rigid and heavy, bridge attached to that soundboard, my goal was to find and eliminate unwanted parasitic vibrations, increase sustain, while keeping the typical Dekley-sound I had become used to.

I was not particularly interested in how mechanical parts vibrated by themselves when excited, except for those parts that returned vibrations back to the strings and PU area for amplification. Dampening vibrations to and from parts was as important - actually more important - as making them "sing" and contribute positively to the instrument's tone.

Details about the process are "lost in the fog" over the years, but the modified Dekley is still here and is "singing" the way I want it to when played: pretty pure and massive tone with minimal unwanted parasitic vibrations, and about twice the sustain it had originally.
Much of this can be contributed to the fact that I intentionally lowered the overall resonance frequencies by a couple of octaves, and delayed spread of vibrations to and from the bridge/PU area, and thereby made the instrument sound larger and heavier than it is without it sounding "boomy".

The "trick" is that one has to know beforehand what one wants and what to look for and listen to in an instrument, as "good/strong vibrations" in parts of the instrument may, or may not, contribute to good overall tone. A little insight, and some lucky guesses, helps too Very Happy

After a "service trip" to Canada back in 2010 (Bent Romnes' workshop), I had to repeat the "stethoscope" test and trim a bit in the keyhead area, as we had tightened the keyhead a little too hard against the soundboard and had lost some good vibrations there without noticing. Listening to the soundboard and neck made for an easy fix.

robert kramer · From: Nashville TN

My theory is the light weight of the Kluson tuners account for the open sound of the Emmons guitars. (Or I might have heard that from some one a long time ago).

Mike Scaggs · From: Nashville, TN

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