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DIY CLD Plinth Design--A measured Approach
DIY CLD Plinth Design--A measured Approach
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Old 13th September 2021, 09:07 PM   #331
hjam is offline hjam  Canada
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Ok, thanks Bryan.
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Old 14th September 2021, 03:56 AM   #332
hjam is offline hjam  Canada
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Quote:
Originally Posted by cats squirrel View Post
I wouldn't bother, Hugh, even if you could devise a way of damping those frequencies.


A panel the size of a turntable plinth will have its fundamental resonance frequency in the 100 to 500 Hz region. The fundamental resonance has the largest amplitude, usually followed by all the rest. Higher frequencies will have much lower amplitudes, usually. So the real problem to solve is with the fundamental and lower harmonics.
Bryan,

I had a good look at some older tests on Plinth sized material. Looks like you're right about the lower frequencies dominating - especially if I ignore the suspect spikes above 3khz.

I also tried the Accelerometer on a speaker cone at different frequencies. It looks OK up to 2500 hz. (6db/oct slope). Then it drops like a rock above that.

I think I'll still have to concern myself with resonances above 500 hz for the Linear Arm. Some of the supports will be much smaller than a plinth.

Thanks again.

Hugh
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Old 14th September 2021, 08:18 AM   #333
2wice is offline 2wice  South Africa
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Quote:
Originally Posted by cats squirrel View Post
A panel the size of a turntable plinth will have its fundamental resonance frequency in the 100 to 500 Hz region.
Does this mean there are no topologies possible in plinth sizes that have a fundamental around 3khz?
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Old 14th September 2021, 01:51 PM   #334
cats squirrel is offline cats squirrel  United Kingdom
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even a panel of ply 100mm thick (yes, they do exist!) has a fundamental resonance around 600 Hz, but very close to the critical frequency (so havoc would ensue!). The fourth, sixth and eighth harmonics would approach 3 kHz though, but at a much reduced amplitude, compared with the fundamental.


Note, as the fundamental resonance frequency and critical frequency are very close, it will mean that there is no (or very little) help from the mass controlled region, the very reason to add mass! Irony indeed.
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Old 14th September 2021, 07:18 PM   #335
2wice is offline 2wice  South Africa
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That all seems very true for a solid (no void), but that is very limiting when there are other topologies that do offer a 3Khz fundamental.

You can tune these forms to a wide range, I'm curious if they can serve a purpose.
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Old 14th September 2021, 07:47 PM   #336
cats squirrel is offline cats squirrel  United Kingdom
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well, if you can find that 3 kHz fundamental, the structure will be very small, I'm sure you can work out how to damp it.
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