Working them out

[DarwinStrings]

I have this graph and would like to know exactly what those three peaks beyond the main top mode are. They occur at 351Hz, 379Hz and 441Hz respectively. Then there is one more at 674Hz.

I have a Fender 210R amp (small transistor amp) and wondered if pulling one of the two ten inch speakers out and using that amp with a tone generator on my PC would be enough to do a tea leaf reading or am I going to have to buy different equipment.

Jim

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[Trevor Gore]

10" is going to be a bit of a handful and will definitely make a mess if you drop it in the wrong place.

I'd suggest going to the local Jaycar/Dick Smith/car radio place and buy a 4" speaker (or two; sometimes they come in pairs, but having a spare is good.) You should get change out of $20. Make sure you wire it so you get the right drive impedance for the amp.

Those three peaks are likely the cross dipole, long dipole and maybe the first partial of the long air, possibly in that order. The big peak up at ~675 is possibly the cross tri-pole, but there's only one way to be really sure.

[DarwinStrings]

Cheers Trevor, I will take that advice and go get a 4 inch. Have been advised to get a 4ohm and bypass both ten inch speakers using the new 4ohm one or if I can only get 8ohm then I leave one of the Fender speakers running.

Jim

Oh and if that one is the cross tri-pole how do I go about getting it down on the next guitar, maybe lower the CF in the bridge? Hmm or thinner edges of the sound board?

[Trevor Gore]

Oh and if that one is the cross tri-pole how do I go about getting it down on the next guitar, maybe lower the CF in the bridge? Hmm or thinner edges of the sound board?

All the answers are in the book, Jim!

On my SS guitars the cross tri comes in at 500-550Hz.

[DarwinStrings]

Thanks Trevor, I did read in there that you were suggesting that getting that one in a good spot was something worth doing. Back to more bookwork, so many words in there you must be able to type fast.

Jim

[DarwinStrings]

Today I learned two things, the first was a good thing as it seems at least I am making good use of the sound board for a 14 fret to body guitar. The second thing I learned not long after the first thing was that speakers are not supposed to have mini built in smoke machines (seems a infinite baffle and I might not need to turn it up so much)

Jim

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[kiwigeo]

Nice monopole...

Heres my Chladni set up. Its a Bradley 50watt signal generator and a 6" 50watt speaker I got from Jaycar.

[DarwinStrings]

I bet you get bucket loads of power out of that Martin.

I didn't think of that way to solve the phase cancellation problem of the un-housed speaker(I tried to solve it by turning it up, 50w speaker + 65w amp = smoke machine) but it looks like a good way of doing it to direct the sound. In the end I bought a new $15 50w 4 inch and shoved it in PVC pipe with a bit of foam and a polystyrene plug in the back( I got the plug from Stu, If you need any polystyrene just buy one of his lino prints and he will pack it in some handy material you can add to your pile of useful junk)

I tested it and it is plenty loud now with out much volume from the amp then I put it all down, opened a beer and started reading that black book again to try to work out how to get that cross tri-pole in a better place.

Jim

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[DarwinStrings]

BUGGA! I got the cross dipole which was the 351Hz peak but then burnt another speaker so I am not sure of the rest and have given up. Will just move on to the next guitar and try again when that one is complete. Maybe I will buy a cheap 15 or 20w amp for next time.

Jim

[Trevor Gore]

Hmmm. I've never had a problem burning out speakers and getting decent patterns. My amp is 15 watts RMS. Maybe check that your speakers are rated RMS rather than "music power" or some equivalent marketing term. Another tip is to hold the speaker over where you think an antinode is going to be (which is the advantage of a smaller speaker) so that you are not trying to excite poles of opposite phase with the one phase of excitation.

[DarwinStrings]

I have to guess that the amp is too big for the cheap speaker. If I get to a point of frustration I leave it alone for a time but will get back to it. I'll keep my eye out for a small amp at cashies and when I find that I will go buy another 4 inch speaker and go again. No sweat really Chladni can wait as I am happy with the guitar as a first and look forward to improving on it with more of the same basic design.

Jim

Life is good when you are amongst the wood.