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Old 30th August 2007, 11:13 PM   #1
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Default ESL low frequency rolloff

Hello All,

First off, I am new to the board. My goal is to build an ESL with subwoofer.

Before I do so though I would like to understand as much as possible. I have read the books by Sanders, Fikier and Wagner. I have browsed the web for days on end and read a lot on diyaudio.

But still, questions remain.

The big one right now is the falloff in ELS SPL towards the low frequencies. And if this is different for wire stators and plate stators.

For example Sanders claims in his book (page 16) that the rolloff starts at the frequency for which the minimum width is 1/4 of the wavelength. He further claims that this is due to phase cancellation (from the backside).

But in Fikier's boek, he shows a measurement of the ESL 175 in fig 9.16 where the rolloff is at about 60Hz. The width of the ESL 175 is only 260mm, which according to Sanders should have the rolloff starting at around 4.5Khz.

Unfortunately Sanders does not provide measurements but shows only calculated frequency charts.

Wagner does not mention this effect at all, though he does mention directivity on page 76/77.

At first I thought that the discrepancy between Fikier and Sanders could be due to the use of a wire stator by Fikier. As the wires act as an acoustic lens, they would disperse the higher frequencies more effectively pushing the rolloff frequency lower.

However that cannot be the case as in fig 9.4 he shows the frequency curve of a metal plate ESL that also has the rolloff below 100Hz (but which according to Sanders should have been at about 2.5kHz)

Thus I am left puzzled. Does the effect mentioned by Sanders exist? And if so, how can it be that Fikier did not see it?

I would be grateful for any answers.
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Old 30th August 2007, 11:34 PM   #2
SY is offline SY  United States
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It's not a matter of wire versus perf- for the same geometry, the rolloff will be the same. The issues are effective width (not the same as actual width, you have to account for the length, too), room effects, and bass boost from the diaphragm fundamental resonance.
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Old 31st August 2007, 08:27 AM   #3
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hI

The wires won't act as a lense, as the wavelength of the highest frequency is larger than the dimensions of the wires. It would act as a lense in case of a single slit as shown in different books of physics. Such single slit can be found in the beveridge esls. So there should be no difference between perforated sheets and wire stators regarding dispersion.

There have been some measurements performed by amateurs of the esl175 which shows a cancellation dip indeed. It is centered between 100 and 250 Hz roughly. So this is at a lower frequency as predicted by Sanders.
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Old 31st August 2007, 09:09 AM   #4
EdwinR3 is offline EdwinR3  Belgium
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Hy Skyseeker,

The difference is caused by the setup off the measurement.
If you do a close distance measurement (say 10 cm), the dipole cancelation does not (or hardly) occure.

If Fikier had made the measurement at say 2 to 3 meters, the LF rolloff
would show up.
You should also check out the web site of Linkwitz (I don't remember if he mentions the effect of the distance on dipole cancelation).
See http://www.linkwitzlab.com



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Old 31st August 2007, 06:46 PM   #5
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Sy: "The issues are effective width (not the same as actual width, you have to account for the length, too)"

Thanks, I would like to find out more about this. Any suggestions?


Dijkstra: "The wires won't act as a lense, as the wavelength of the highest frequency is larger than the dimensions of the wires"

Yes, I wondered about that too. Still it seems as if the dispersion characteristic of the ESL175 is much better than the "laser focus" Sanders talks about. Are there any other explanations?


Dijkstra: "It is centered between 100 and 250 Hz roughly"

That is very useful information. Thus a crossover to a dynamic woofer would need to be at say, 200 or 300 Hz.


Edwin: " ... measurement at say 2 to 3 meters, the LF rolloff would show up."

Unfortunately Fikier does not say how he did perform the measurements. But as he also included 30 degrees of-axis measurements, so I think it is safe to assume that it must have been more than 1 meter. Otherwise even 30 degrees of axis would be in front of the speaker. Distance is a factor though, as also Sanders says that having the speakers really close makes it a much more immersive experience (than at a distance).

Oh, and yes, I spend a few days over Linkwitz's website. He almost convinced me to stick with dynamic dipoles instead!
(I will use an open dipole dynamic [sub] woofer though)

--------------

Does anyone know of direct comparisons between a metal stator ESL and a (identical size, transformer etc) wire stator ESL?

And for a wacko idea: How about an ESL with one metal plate stator and one wire stator?
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Old 1st September 2007, 08:04 AM   #6
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[QUOTE]Originally posted by SkySeeker


Dijkstra: "The wires won't act as a lense, as the wavelength of the highest frequency is larger than the dimensions of the wires"

Yes, I wondered about that too. Still it seems as if the dispersion characteristic of the ESL175 is much better than the "laser focus" Sanders talks about. Are there any other explanations?


Dijkstra: "It is centered between 100 and 250 Hz roughly"

That is very useful information. Thus a crossover to a dynamic woofer would need to be at say, 200 or 300 Hz.




Hi,

Several people have build the ESL175 and this type of speaker has been demonstrated frequently during esl-club meetings. I have build them several times too. Yes, they are directive and are not comparable with many other (dynamic) speakers. Added to this, there is a rise in high freq. So a basic esl175 sounds quite harsh with too much highs. Electrical segmentation will improve this and actually turns the esl175 into an audiostatic es100 ! The speakers Sanders build have a much larger width than the esl175 and will be more directive as a consequence, so this could explain the differnece between those two.

Crossing at 200 to 350 Hz will work.

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Old 21st September 2007, 12:04 AM   #7
JonFo is offline JonFo  United States
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My experience with balancing the low end of ESL's is that a 315Hz is indeed a sweet spot for crossover to some dynamic drivers.

The best solution is to build a companion line-array of mid-bass drivers for the 40 or 60Hz to 315Hz range.

This maintains the same depth of field characteristics of the ESL line source in the critical mid-bass.

For more details, measurements and theory on how I applied this to create a very capable, large Center Channel to match my MartinLogan Monoliths, read this thread:

http://www.martinloganowners.com/~td...ead.php?t=2018

This is the result:

Click the image to open in full size.
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Old 22nd September 2007, 08:42 AM   #8
Calvin is offline Calvin  Germany
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Hi,

the broader distribution character of a wire stator against a flat metal stator is solely due to electrical segmentation and not a matter of stator building material. You can achieve similar results to a electrically segmented stator by curving the stator -as ML and other do.

Acoustic phase cancellation starts above 1kHz with usual panal widths.
So You have to equalize the freq-response in any case or You get the -sadly too often heared anemic, thin sound. The lower You chose the crossover-freq the more You have to equalize. Experience shows that a equing does no sonical harm as long as You eq less than ~6dB. To stay below this value most panels should be crossed over around 300Hz, with wider panels allowing for lower crossover-points and thinner panels for higher ones.
I agree with R. Sanders when he says that a too low crossover point is a trap in which most ESL DIYers fall. It kills output and distortion figures and doesn´t gain on sound quality on the other hand!
The imo optimum way how the problem is solved is shown in the ML Statement2, JonFo´s setup and -as I may humbly add- my own setup.

jauu
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Old 23rd September 2007, 08:29 PM   #9
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Floor dip/bounce.

That will create a hole or "suck out" in the response of any speaker that is some distance above the floor (or other surface). This can not be overcome with simple means.

One way to tell if this is happening is to get the speaker by some means onto the floor (lay it down?) and remeasure, and/or do a FFT type measurement with the mic very close to the diaphragm so as to avoid the measurement of the acoustically created suckout.

Briefly stated, this suckout effect sucks.

Don't overlook its contribution to these issues.

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Old 24th September 2007, 07:56 AM   #10
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"To stay below this value most panels should be crossed over around 300Hz, with wider panels allowing for lower crossover-points and thinner panels for higher ones."

My current plans call for a 400mm wide (wire) stator, 1.5mm DS, 1600mm height. Slightly curved (20 dergees opening). Crossover at 500 Hz to a (one per channel) peerless XXLS 12" in an open dipole.
http://www.tymphany.com/datasheet/printview.php?id=321

(3KV bias, 1:100 audio transformator, 100W amplifier, but the amplifier might change)

Any suggestions?
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