What X-over for a hybrid ESL?

[bolserst]

Originally Posted by john65b

I also want to make a passive to compare. But since I built the electronics for the CLS panels (bias circuit and stepup transformer), I have no idea what the impedance is of my ESLs are. I put a voltmeter on them and get just under 2 ohms, and the maggies are 8ohms. Would it be correct to design a passive xover around these two measured impedances?

The 2 ohm you measured is the DC resistance of the transformer primary windings and any resistance you might have in series with the primaries. This is not the AC impedance which would be needed to design passive crossovers. The impedance of an ESL varies wildly as does the phase. You would need to measure the impedance with something like the Dayton Audio WT3 tester. Many of the computer based audio measurement systems also have the capability of measuring impedance.

The maggies on the other hand will have an impedance that is pretty close to their DC resistance measurement. They do have a small amount of inductance the will cause an increase in impedance and rotation of phase as frequency increases.

Here is a posted example of what you might expect to see for the maggies.
The inductance is low enough, impedance doesn't start rising til >1kHz.
Planar magnetic DC resistance vs. impedance?

[john65b]

The 2 ohm you measured is the DC resistance of the transformer primary windings and any resistance you might have in series with the primaries. This is not the AC impedance which would be needed to design passive crossovers.

Yes, this is exactly my issue. I know the actual impedance, if I were to measure as you indicate , would fluctuate wildly with frequency.

Now I think it was you who had recommended a 15ohm across the ESL Speaker binding posts (in parallel across the primary of the step-up tranny) and a 50uf cap in series with the speaker positive input would get me the 250hz cross...is this accurate? What ESL impedance was this based on?

My apologies if it was not you...

[CharlieM]

For those of us like myself who aren't skilled enough to design a passive crossover that works well with an ESL, and/or don't want the headache, an active crossover with adjustable gain provides easy, real-time tweaking capability to precisely balance the woofer and panel outputs, and I would say you get tighter/cleaner bass when you don't have a passive inductor between the amp and woofer. Active is the easy way to go. I've used an analog op-amp crossover and [now] a DSP crossover with my speakers and they both work great.

[bolserst]

Originally Posted by john65b

Yes, this is exactly my issue. I know the actual impedance, if I were to measure as you indicate , would fluctuate wildly with frequency.

Now I think it was you who had recommended a 15ohm across the ESL Speaker binding posts (in parallel across the primary of the step-up tranny) and a 50uf cap in series with the speaker positive input would get me the 250hz cross...is this accurate? What ESL impedance was this based on?

I think this was the post you were thinking of.
Martin Logan CLS Power Supply

The technique of putting a 10ohm - 15ohm resistor across the primary of the step-up transformer goes a long way to stabilizing the impedance magnitude and bringing the phase close to zero (ie resistive). Basically the low value resistance put in parallel with the primary swamps or overpowers the varying impedance, so it isn't terribly important what the verying impedance was. You are left with an impedance that is fairly constant at 10ohm - 15ohm and will work well as a load for a high-pass network made up of a single capacitor.

Lower values of resistance result in a more constant impedance. The trade off is that lower values of resistance will need to be able to dissipate more power than if you chose a higher value. In my experience, 10 - 15ohm is a good range to choose from. Much lower than 10 ohm and power dissipation becomes a problem. Much higher than 15ohm and the impedance isn't as constant and resistive as you would like for an easy passive crossover.

[AcoustatAnswerMan]

Originally Posted by bolserst

Speaking of companies promoting full-range crossover-less ESLs....what about Acoustat?
The patent that their design was based on is in fact a method of combining output from HF & LF transformers thru a crossover.
How could they then promote this as a crossover-less design?

I don't recall Acoustat ever waving the 'crossover-less' flag, or using that terminology in their marketing. The patented Magne-Kinetic design, of using a high and low frequency transformer with outputs combined into a full-range signal presented to the panels, is certainly NOT crossover-less in the strictest sense. But, those speakers did not use different drivers for different frequencies. That is, all panel area was identical, and played full range.

The later Spectra Series was a little different. Although the transformer implementation is completly different, the result is the same, with different sections of the transformers handling different frequencies. The big difference is that not all panel area produced full range. The panel was split up into vertical strips, with one strip playing full range, another area playing lows and mids only, and the final area playing lows only. This was done using all the same type of panel, regardless of operation. The frequency roll-offs are accomplished using simple resistors acting against the inherent capacitance of the panels. So it could be said that the Spectra Series actually had two crossover systems.

However, I believe this thread is getting off topic a bit, as I believe the original question related to how to implement a crossover between an ESL panel and a woofer. There is no correct answer to this question, as it all depends on the skill and inclinations of the builder. Certainly the cheapest way to go would be passive. Acoustat used passive crossovers for its hybrid designs, with a 6-dB/octave high pass for the ESL, and a 12-dB/octave low pass for the woofer. The down side to this approach is that it can take quite a bit of fiddling to get the values correct. You may also find, as I did when voicing the Spectra 11 and 1100, that the best results might be obtained by having the poles of the low-pass slightly mis-aligned. But this would depend on your design and the actual LF performance of your ESL.

Using a commercial or home-brew active crossover would offer the most flexibility for tweaking final values, but the down side is that it adds the cost of the crossover AND a second amplifier.

My suggestion would be to go with a passive design first, and see if you can get acceptable results.

[tyu]

I well be the frist to say passive crossover can eat power...an sound bad if all is not right but as for althings Active ..... i had the best crossover i could find for my Apogees in the 90s an it was a all KRell setup...an i could still hear the Active crossover..Just one more thing in front of the sound

Here you go
.My suggestion would be to go with a passive design first, and see if you can get acceptable results.

Vary good info...if you can get the sound you wont out of passive frist... good luck with all the other..

just my 5cent

[bolserst]

Originally Posted by AcoustatAnswerMan

I don't recall Acoustat ever waving the 'crossover-less' flag, or using that terminology in their marketing. The patented Magne-Kinetic design, of using a high and low frequency transformer with outputs combined into a full-range signal presented to the panels, is certainly NOT crossover-less in the strictest sense. But, those speakers did not use different drivers for different frequencies. That is, all panel area was identical, and played full range.

Hello AcoustatAnswerMan,

My comment was meant as humor, not accusation. Sorry if it didn't read that way. I personally think that the MK transformer interface is an elegant solution for driving and providing EQ for full range ESLs. I particularly like the later Spectra series transformer arrangement where the series capacitors on the primary side can be dispensed with, and the high voltage AC across the mixer capacitors is half that of the pre-Spectra interfaces with the same step-up ratios. Also, as you mentioned, Acoustat was one of the first to implement resistor ladder networks to provide increasing driven panel area with decreasing frequency.

However, in essentially every pre-Spectra brochure or manual I have ever seen(included Stricklands white paper) the term crossoverless appeared...see below. I am sure what was meant was that no acoustic crossover was used between different panels or panel areas. This opinion is supported by the fact that the term crossoverless was never mentioned in the later Spectra series brochures or manuals. But I'm not sure the average consumer would have picked up on the distinction.

From the Acoustat White Paper:
“All Acoustat speakers are, and have always been, crossoverless full-range-element design”

From an Acoustat Brochure:
“The Acoustat full-range-element electrostatic loudspeaker systems represent the culmination of over 20 years of design and development - beginning with the bold assumption that it was possible to build an electrostatic speaker system of no compromise, one that would be of full range design, capable of high sound pressure levels, have no crossovers, and be more reliable than any speaker of any type.”

From an Acoustat Manual:
“The Acoustat pure electrostatic speakers(1+1, 2+2, etc) utilize full-range element electrostatic panels to reproduce all frequencies in the audible range without splitting the frequency sprectrum with separate drivers or crossovers”

However, I believe this thread is getting off topic a bit.

Agreed.

[DjSinae]

Originally Posted by CharlieM

I've used an analog op-amp crossover and [now] a DSP crossover with my speakers and they both work great.

Hi charlie, I was wondering if you think something like this would be nice
CO3 Three Band Phase-Linear Crossover Filter Kit (Bass, Mid-range, and Treble)_Filter_Accessories Kit_Analog Metric - DIY Audio Kit

I will use minidsp at first but i would really like to have linear phase and also lower latency than DSP...

[CharlieM]

Originally Posted by DjSinae

Hi charlie, I was wondering if you think something like this would be nice
CO3 Three Band Phase-Linear Crossover Filter Kit (Bass, Mid-range, and Treble)_Filter_Accessories Kit_Analog Metric - DIY Audio Kit

I will use minidsp at first but i would really like to have linear phase and also lower latency than DSP...

I'm thinking something like that would probably work fine, once you've settled on the crossover frequencies.

About a year ago I decided to take the plunge and go digital throughout my entire signal path, with a single D/A conversion coming out of my new DSP crossover. I know this is blasphemy to analog enthusiasts who still spin LP's and shun digital, but I like the sound just fine and I've gotten so spoiled by the convenience being able to play my whole library via a digital music server without ever getting off the couch that I haven't even played a CD since. And while I liked the sound of my old DBX analog crossover, I also like the sound of my 24 bit/96khz DSP crossover and it gives me a whole lot of flexibility for tweaking and experimenting with different setups. Analog or digital, I think you will be happy either way.

Good luck with your project!

[Calvin]

Hi,

of course may something like this "CO3 Three Band Phase-Linear Crossover Filter Kit (Bass, Mid-range, and Treble)_Filter_Accessories Kit_Analog Metric - DIY Audio Kit" work fine....
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but
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and this is a major BUT
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only if the circumstances are all right.

This means that such a filter will give good results only if the speaker behaves close to a theoretically ideal bandpass, which no speaker does.
In other words: a filter that dosen´t take the speakers own behaviour into account will not give good results.
In the end its the acoustical output that counts not the electrical.
The main difference between most passive filtering and (analog) active filters is the lack of equalizing functions with the latter.
Especially ESL always require some means of equalization.
So a filter without equalizers won´t lead to good output.
The great advantage of digital filters like the minidsp is that they allow for filtering and equing at the same.
As such they fulfill the requirements of the speaker.
Personally, I never came across a OPamp graveyard Xover that did music any good and I know lots of opportunities to spend $89 for better.
One may just spoil a thought or two about the signal path in a analog crossover vs a digital crossover.
Is there any reason to believe that a analog OPamped crossover featuring thousands of active parts will do any better than a AD-DA conversion and some calculus in between?
If the analog crossover were carefully build with discrete parts for one specific speaker (as such much more costly), the outcome might be more pleasing than with a digital filter.
In any other case I´d say forget analog filters that offer just filtering wo. equalizers.

jauu
Calvin