Official Luthiers Forum!

So, is there any use for an ocilliscope in acoustic guitar making? Can it be used to measure modulous of elasticty and stuff like that (you speed of sound through wood?). Any good references would be appreciated! (I know nothing about these things but just bought one!)

Thanks

Shane

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Canada

Good question! I have an old Dumont Cathode Ray Oscillograph, that works just fine, but it's pretty much a cinder block in my hands. I haven't a clue what to use it for. I tried to use it for biasing amps some years ago, but never got that right either. It was too easy to just do it with a meter.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Uses in guitar building - I'm not sure. I have several and also use them at work so I certainly know how to use them and what they can do but I have yet to see a reason to drag one down to the shop, at least for acoustic building.

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Steve Smith
"Music is what feelings sound like"

If you have some backs that are potato chipping, stack them up and set the Dumont on top. After a few months they might straighten out.

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If you can't do something well, learn to enjoy doing it poorly.

Jim has it about right. You could put it under your bench and leave it on during cold spells - it will warm the air around your feet nicely. That's about all it's good for IMO.

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Wood density is sometimes used as a proxy for the speed of sound in wood - they are roughly correlated. 20 MHz may not be quite fast enough, but more than once I've thought of using a fast scope to directly measure the speed of sound in wood billets (I have a 1 GHz one at work).

You need dual piezo elements fed into separate channels of the scope, one element at each end of the board. Bonk on one end and you'll get 2 pulse arrivals on the scope, separated by the time it takes the sound wave to travel from one end of the board to the other. You can measure the time difference between pulses down to a few nanoseconds on a good scope. Length of board divided by time = speed of sound.

At least in theory - I haven't tried it.

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The member formerly known as erikbojerik....

Thanks Erik. That is kind of what I was thinking about. I don't have an idea how to do it but I thought that a scope was useful for that purpose as I had rad it somewhere, maybe from Siminoff. This is a Tektronix and I was also wondering if 20Mhz was enough, if not I guess I will use it for other purposes of some kind or another or something!

Thanks

Shane

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Canada

You can measuire the speed of light with that, I imagine it could handle the speed of sound.

I have one and it comes in handy so much that i forget where i actually stashed it. I use to tinker with electronics so thats why i have it. You can actually tune a guitar with it. But since most here have a guitar tuner laying around whats the point since it's no easy process.

As I remember I think it actually comes down to the sampling frequency, which on my work scope is 5 gigasamples/second. I can measure time differences approaching a nanosecond. But this is a fairly new digital scope - if yours is an older analog model, it may not be up to the task.

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The member formerly known as erikbojerik....

Various sources seem to agree that the speed of sound through wood (along the grain) varies around 5,000 m/s. Assuming you test a piece along the grain that is 1/2 meter in length then the sound should take 1 s/5000m x 0.5 = 100 microseconds per 1/2 meter (approximately). A 20Mhz scope should be able to measure this quite easily.

If the scope does not have a single-shot function then using a "bonk" won't work well. It would be easier to use the piezo element on one end to inject a tone and then use a piezo element on the other end to receive the tone. Then you can use the scope to measure the relative phase difference and calculate the time.

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Steve Smith
"Music is what feelings sound like"

I think it might be fun to mechanically attach a low mass LVDT (Linear voltage differential transmitter) or a piezo electric crystal to the top of the guitar and measure the movement of the top with the scope while striking notes. As the frequencies of the notes are known, comparing the vibration data of the top might be kind of cool. I might give it a try once it gets cold around here....food for thought from a geek..LOL. Might be an insightful tap tuning aid as well......

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John Nowicki

... might be kinda cool.

I wonder if that's how Al got started on his journey of inquiry?

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Steve Smith
"Music is what feelings sound like"

If your scope is new enough (Digital) you should be able to hook it to a computer to store the data.