Chladni of Main Air Mode

[Dave M]

This has been sparked off by the discussion of Simon Ambridge's pictures of a Hauser. And what good eyes you must have Trevor...

I have been checking a couple of my boxes and my patterns look just like the top monopole patterns though messier. The air mode certainly isn't out near the sides on either of them as Trevor has pointed out one would expect. Below are pics of my old Aranjuez which is lightly built, lightly fan braced guitar. The other is a falcate braced with side masses.

Does anyone have an interpretation of what is happening?

Sorry should have said the discussion was over on the Delcamp Forum

[Trevor Gore]

Does anyone have an interpretation of what is happening?

In a word, No!

The smaller diameter of the node line for the T(1,1)2 mode is something I routinely see, though. So here are some possibilities:

Make sure the guitar is not constrained from moving in the expected modes. I use foam supports, which I try to position where node lines are developing, though I'm not particularly pedantic about that. I tend to excite the T(1,1)1 via the sound hole (rather than off the top) and so may be getting the back to move more because of that. Your T(1,1)2s seem to be "cleaner" than your T(1,1)1s and that might be why. Keep the speaker ~ its own diameter away from the sound hole, though, or you effectively partially block the sound hole. (I use a 4" speaker). It's also possible to get interference from the bench itself which can produce odd effects, so I try to keep the guitar supports fairly high, about 100mm (4").

Let us know how you go.

[Dave M]

Just as a holding reply I do have those conditions pretty much nailed down. Foam support, used a more solid bench today, excitation a reasonable distance above the soundhole. I am using VA to provide the sound, through a domestic amplifier into a speaker around 100 mmm diameter in a closed box ...

What I did do today was to excite the top monopole with the frequency indicated by VA, in this case 194 Hz, then changed to the main air at 101 and nothing moved at all so I am exciting that same resonance.

The fact that it happens with two very different guitars suggests a setup problem but I still can't see what it is.

As an aside I can see the Chladni patterns very clearly on both guitars for the cross dipole, though at widely different frequencies, which suggest the setup is working.

I will continue experimenting.

Cheers Dave

[Trevor Gore]

What I did do today was to excite the top monopole with the frequency indicated by VA, in this case 194 Hz, then changed to the main air at 101 and nothing moved at all so I am exciting that same resonance....

I guess that' a another possibility when resonances are close to an octave apart. I would have thought those frequencies are far enough from the octave, though, unless something is giving you a wrong frequency (e.g. reading off an analogue dial)...

[kiwigeo]

You could try a different blend of tea leaves??

[Dave M]

Yes Lapsang souchong is probably the answer. Less of this builders tea!