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Old 29th April 2005, 04:02 PM   #1
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Default Martin Logan frequency correction???

Hi experts,

I have read some different opinions regarding the way the curved ESLs of Martin Logan work.
Some claim that the crossover of for example the Sequel2, has frequency corrective elements. Others claim that this is not the case and it is all about impedance correction.
Because beaming of high frequences is largly reduced by the curved design, one should expect that there is only little correction needed in the frequency response.
Who knows about this???
MartinJan
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Old 29th April 2005, 07:04 PM   #2
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If you post the schematics it would be easier to see what is what.

The curve reduces slightly the HF beaming, but not entirely.

In general the ML's interface - at least the ones I've seen - are somewhat inferior to some of the patented schemes that have been used for matching the xfmr(s) to the cells... for this reason they ended up with a hyper low imput Z with their original CLS design...

Generally speaking, you can't "match" a step up device to a given "full range" cell and still have good sensitivity - the tradeoff is sensitivity vs. bandwidth. This was shown nicely by Peter Walker in his 1950s articles on ESLs in Wireless World. Similarly, if you match for good HF extension, you'll probably have weaker bass... which will "work" if you knock the HF down so that you end up with a nominally "flat" response... this may be what ML was doing with the CLS. Not sure.

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Old 30th April 2005, 07:31 PM   #3
Calvin is offline Calvin  Germany
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Default correction

Hi,

Martin You guess right. The Sequel 2 needed quite heavy equalizing. First of all the frequency response of the panel itself wasn“t that linear. Second the quality of the audio trannies was quite cheap, with a too great leakage inductance, that lead to a resonance peak around 7kHz with a -12dB slope above that resonance frequency. See the attached pic.
C1 in togetherness with L1, R1 and the ESL gives a very steep highpass response with a lot of overshoot (R1 is used to damp the overshoot) to correct the phase cancellation of the panel itself. R5 is used to get the efficiency down to woofer level and C2 corrects the falling response above 7Khz. The notch (C3, R3, L2) corrects the midrange around 3kHz.

PDF:
black: principle frequency response of panel and trannies
green: electrical frequency response of ESL with crossover but without C2 and notch
blue: electrical frequency response of ESL with crossover but without notch
brown: electrical frequency response of ESL with crossover but C2=5µF
orange: electrical frequency response of ESL with crossover but C2=10µF
red: electrical frequency response of ESL with crossover (original, C2=15µF)

yeah
Calvin
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File Type: jpg sequeliisimu hf-circuit b.jpg (93.1 KB, 1131 views)
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Old 30th April 2005, 07:33 PM   #4
Calvin is offline Calvin  Germany
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Default electrical amplitude

Hi,

the electrical amplitude response of the Filter looks like this:
Attached Files
File Type: pdf sequel2 elektr amp.pdf (11.2 KB, 270 views)
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Old 30th April 2005, 07:40 PM   #5
Calvin is offline Calvin  Germany
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Default different responses

Hi,

this pic shows the frequency responses of the Sequel2 panel with and without crossover and using the original audio transformer or the excellent Amplimo toroids.

black: Panel with original trannie without crossover
blue: Panel with original trannie and crossover
green: Panel with Amplimo trannie without crossover
red: Panel with Amplimo trannie and crossover

yeah
Calvin
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File Type: pdf sequel2 simu1.pdf (17.4 KB, 279 views)
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Old 30th April 2005, 07:50 PM   #6
Calvin is offline Calvin  Germany
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Default different responses

Hi,

this pic shows the same responses but to compare the quality of the trannies.

black: Panel with original trannie and without crossover
blue: Panel with original trannie and with crossover
green: Panel with Amplimo trannie and without crossover
red: Panel with Amplimo trannie and without crossover

Without crossover the superior high frequency response of the Amplimo (greater bandwidth) is obvious. The linearity of the panel itself is not the best.
With crossover the differences are much smaller. Like in a clockwork the corrective features of the crossover help to minimize the linearity probs of the panel and the low quality of the trannie. The overall result is very accaptable. Nice work indeed

yeah
Calvin
Attached Files
File Type: pdf sequel2 simu2.pdf (17.5 KB, 193 views)
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Old 30th April 2005, 07:53 PM   #7
Calvin is offline Calvin  Germany
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Default Newer panels

Hi,

here“s a nearfield measurement of a Prodigy panel using the Amplimo trannies.
These newer constructions show much more linear frequency responses than the older ones.

yeah
Calvin
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File Type: pdf ml prodigy 10cm amplimo.pdf (23.6 KB, 238 views)
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Old 30th April 2005, 07:56 PM   #8
Calvin is offline Calvin  Germany
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Default far field

Hi,

same measurement but different distance (170cm) and variations in polarizing voltage

yeah
Calvin
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File Type: pdf ml prodigy 170cm kv var amplimo.pdf (33.5 KB, 180 views)
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Old 30th April 2005, 08:16 PM   #9
Calvin is offline Calvin  Germany
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Default comparison

Hi,

here“s a comparative measurement of my own DIY panel versus a Prodigy panel (which is roughly half the size of the Prodigy)

I use a curved panel with smaller holes and greater opening factor and an even smaller spacing than ML. Therefore the efficiency of the panels is nearly the same.
My film is thinner than ML“s which could be the reason for the extended bandwidth and higher efficiency above 8kHz. The fundamental resonance is higher with the ML because the thicker film can be stretched harder. It is quite clever of ML to “use“ the frequency response of the panel down to the fundamental resonance. With a damped 12dB HP filter You can get a very linear amplitude response together with very high efficiency without the need of a lot of corrective crossover components. Dynamic headroom is exceptional because of the hard stretching of the membrane and the low diaphragm travel above 200Hz.
Such panels can play easily soundlevels above 110dB and can even reach very high efficiencies of around 100dB/2.83V/m

yeah
Calvin
Attached Files
File Type: pdf vergleich ml prodigy-esel.pdf (19.3 KB, 233 views)
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Old 1st May 2005, 07:56 PM   #10
thomsen is offline thomsen  Austria
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Hi,

The measurements are very interesting. But I always thought that elektrostatic panels itself have a linear frequency response automatically (at least to a very large extent). Only limited by the mass and tension of the film. How is such a non flat response possible (like the Sequel). Where is the difference between the Sequel and the Prodigy? Mechanical difference?

Thanks for each explanation.

Thomas
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