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In Reply to: RE: Apogees and ethics - comments posted by josh358 on February 16, 2012 at 17:24:02
The idea is that larger magnets and thicker tweeters end up with larger relative magnetic forces vs. air resistance and damping. Thus less compression.
In the torsioning case, I know from listening and from the basic physics of it that it can't be damped effectively, only prevented - as magnepan do with their little beads - which allows them to have no torsioning and no significant lengthwise resonance.
One of my tweeters is loose, while the other is nice and tight and beaded. The loose one torsions when playing signficant output below 5 khz, but performs just fine with the 10khz XO. The higher frequencies don't seem to be affected by the torsioning when playing at lower XO, but the 2-3 khz range becomes rough and screechy like the Apogees can sound.
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Once it starts oscillating the damping would already have proved insufficient, so it makes sense that it wouldn't stop while still driven. But I assume that if you could achieve critical damping, you wouldn't get the torsional oscillation in the first place.
I gather the Apogee ribbons had foam supports to achieve the same thing as Magenpan's adhesive. But of course they still had the torsion problem, I assume due to the width of the ribbon.
Not any measurements done by myself but from the book "Ribbon Loudspeakers Theory and Construction" ISBN: 1-882580-24-X.
Corrugated ribbon have larger/more THD then an uncorrugated ribbon in 3kHz and 10kHz except for 1kHz where the uncorrugated ribbon has slightly higher THD.
IMD is higher for corrugated in 2&5kHz and slightly higher for an uncorrugated ribbon in 5&7kHz.
Interesting I would think.
The one who succeeded was the one who didn't know it was impossible.
I was looking for that book a few days ago, the only copy I could find was going for more than $300. But I saw the web page that had that info. I wonder whether an uncorrugated ribbon would be more susceptible to torsion. Also, whether it would allow sufficient displacement to play at high amplitudes at the lower end of its frequency range.
There are sadly no comparisons in those areas in the book.
But it mentions and shows a research of how a corrugated ribbon does behave as a uniformly moving piston, but has many modes imposed and torsional movement in, what they call 8th resonance mode, that would be 244Hz.
The one who succeeded was the one who didn't know it was impossible.
Edits: 02/17/12
Now that's really ineresting. Wish I could get hold of that book. I'm going to see if I can get it on interlibrary loan.Meanwhile, I found the paper mentioned in the caption:
Edits: 02/19/12
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