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Multi-Way Conventional loudspeakers with crossovers

constrained layer damping with MDF and Ply
constrained layer damping with MDF and Ply
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Old 18th July 2019, 01:38 PM   #131
HammerSandwich is offline HammerSandwich
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Quote:
Originally Posted by Dave Zan View Post
I dimly recall a claim that the Newtonian reaction force of the driver was the main cause of vibrations rather than the air pressure in the enclosure.
I don't recall the author except that it was someone with some credibility, which is why I took note of their claim.
Just going on memory, isn't that in the KEF LS50 whitepaper?
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Old 18th July 2019, 01:39 PM   #132
HammerSandwich is offline HammerSandwich
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Originally Posted by seanny View Post
some guitar pickup is tuned to peak at high frequency.
Don't use it to measure any thing.
What's your opinion of using one only for relative comparisons?
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Old 18th July 2019, 10:13 PM   #133
Dave Zan is offline Dave Zan  Australia
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Originally Posted by HammerSandwich View Post
...isn't that in the KEF LS50 whitepaper?
My recall is that I read it in posts by "Speaker dave", his bio says he worked for KEF so makes sense it's in that white paper.

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Old 18th July 2019, 10:19 PM   #134
seanny is offline seanny  United States
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Originally Posted by HammerSandwich View Post
What's your opinion of using one only for relative comparisons?
I overstated.
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Old 19th July 2019, 02:50 AM   #135
HammerSandwich is offline HammerSandwich
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Originally Posted by Dave Zan View Post
My recall is that I read it in posts by "Speaker dave", his bio says he worked for KEF so makes sense it's in that white paper.
Not sure if he was still at KEF for the LS50, but he's definitely made a lot of posts about damping cabinets & decoupling drivers.

Anyhow, I skimmed the LS50 whitepaper again, and it does cover this well. Their sims indicate that you can ignore air pressure effects until you've decoupled the driver. Example attached. Worth a (re-)read.
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File Type: png ls50fi8.PNG (110.2 KB, 84 views)
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Old 19th July 2019, 03:13 AM   #136
Dave Zan is offline Dave Zan  Australia
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Originally Posted by HammerSandwich View Post
Not sure if he was still at KEF for the LS50...
Yes, I didn't mean he necessarily was involved with the LS50, just that he was from that school, his posts and the white paper take the same view.
I knew of that paper but never actually tracked it down until now, indeed worth a read.

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David
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Old 19th July 2019, 03:23 AM   #137
Dave Zan is offline Dave Zan  Australia
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Originally Posted by seanny View Post
I overstated.
I think it's a fair point to raise and at least check.
Art didn't claim any absolute measurements, used for comparison.
There are not-too-expensive accelerometers available, member "Gdan" sells a kit and can calibrate the accelerometer.
The ACH01 that he uses is ~$50, probably cheaper ones with similar performance are now available - accelerometers have almost become a commodity item.

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David
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Old 19th July 2019, 04:00 AM   #138
seanny is offline seanny  United States
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That graft above looks scary.
Most of the radiations happen in the range where our hearing is most sensitive.

Mass Damping

When we add mass to our car, the ride got smoother.
Tall buildings use mass of pendulum to dampen swaying.
Ships use mass of water to dampen rolling.

I call those Mass Damping.
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Old 19th July 2019, 08:05 AM   #139
andy19191 is offline andy19191  Europe
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Quote:
Originally Posted by Dave Zan View Post
Earl says the fundamental mode dominates, Art comments that this was not necessarily the case, to his own surprise.
I dimly recall a claim that the Newtonian reaction force of the driver was the main cause of vibrations rather than the air pressure in the enclosure.
I don't recall the author except that it was someone with some credibility, which is why I took note of their claim.
Anyone remember the thread or author?
I don't know about people but just about every FE simulation of a speaker cabinet which includes the internal air pressure (it is often dropped) will show it to be small-to-negligible at the frequencies of the lowest cabinet modes compared to the forces from the driver hammering on the baffle. The figure below is from some working notes for a subwoofer with a small sealed cabinet which has perhaps the largest internal forces relative to the forces from the magnet. The resonances start at around 500 Hz but are shifted mainly higher in frequency by various design modifications. The lowest pair of resonances (2 symmetrical modes) are not really driven and would radiate weakly to the listener even if they were. It is the mode above which is the nasty one.

BTW speaker dave has worked at plenty of speaker companies but is US based and I don't think he has worked at KEF here in the UK. Andrew Jones used to work at KEF and has posted here about cabinet vibration.

Placing particles on panels to reveal standing wave patterns is of limited practical use. As mentioned by someone above, Earl I think, the lowest and most problematic modes tend to involve the whole speaker bending and not higher order panel vibrations. These obviously do occur but normally at frequencies sufficiently high and weakly driven and/or radiating that they are not a practical problem. An exception might be something like a large thin walled cabinet with no bracing so one cannot be absolute about it.
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Old 19th July 2019, 10:51 AM   #140
andy19191 is offline andy19191  Europe
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PS I have found out how to lookup people and speaker dave does indeed list KEF as an ex-employer. I really am going to have to rely less on my fading memory. Is there any chance Earl mentioned the lowest modes being whole speaker motions?
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