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Old 11th March 2012, 10:54 AM   #1
markusA is offline markusA  Sweden
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Default What X-over for a hybrid ESL?

I find myself with a little extra time to consider the finer details of my current project, a hybrid ESL. (Check my blog for project updates)

A while back Calvin was nice enough to walk us through the development of a passive crossover for a ESL.
Today I find myself asking a pretty relevant question.
What kind of XO should I choose?
The cross will be somewhere in the 250Hz +/-50Hz area.

The options are active, passive or digital?
The easiest would without a doubt be to buy a commercial active x-over.
The most difficult to build is probably the passive one.

My question is which one is the better and why?

A good amp will cost money, passive could end up being the cheap solution.
Digital would offer a lot of fun parameters to tweak.
Maybe a passive XO with a digital EQ?
The floor is yours...

What to build and why?
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Old 11th March 2012, 11:57 AM   #2
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Quote:
Originally Posted by markusA View Post
I find myself with a little extra time to consider the finer details of my current project, a hybrid ESL. (Check my blog for project updates)

A while back Calvin was nice enough to walk us through the development of a passive crossover for a ESL.
Today I find myself asking a pretty relevant question.
What kind of XO should I choose?
The cross will be somewhere in the 250Hz +/-50Hz area.

The options are active, passive or digital?
The easiest would without a doubt be to buy a commercial active x-over.
The most difficult to build is probably the passive one.

My question is which one is the better and why?

A good amp will cost money, passive could end up being the cheap solution.
Digital would offer a lot of fun parameters to tweak.
Maybe a passive XO with a digital EQ?
The floor is yours...

What to build and why?
The ESL presents many more design challenges than just choosing frequency or how that frequency is obtained. Here is a good start attached that shows a voltage multiplier coupling transformer loading choke, audio transformer and crossover components. The design was in production for over 25 years and is highly regarded as one of the worlds best speakers. It is known as the Quad ESL 57. it is very much a trusted design suitable for and designed around the ESL panels that Quad produced.

There are also many other excellent references on ESL DiY designs right here on the forum, but the ESL 57 is an excellent starting if not finishing point on the subject of ESL's

Opening up a Martin Logan Quest Z one will find enormous effort put into crossover and electronics. Martin Logan opt for the approach of the ESL panel reproducing upper frequencies, rather than full range. So their approach is different to Quad.

What this should say is that ESL's are a serious speaker, requiring serious design effort
with high voltage components, that is a symbiosis of many parts dedicated toward producing excellent sound.

Cheers / Chris
Attached Files
File Type: pdf quad_schematic.pdf (47.4 KB, 126 views)
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Old 11th March 2012, 12:31 PM   #3
markusA is offline markusA  Sweden
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I'm not entirelly sure what to make of your post?
Are you an advocat of passive crossovers?

I'm very much aware of the fact that it'll be long and hard work to get a passive XO optimised.
I'm more concerned with which one is actually better and why?
There are some designers claiming that passive is better above 200Hz.
Some swear that active is the way to go?
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Old 11th March 2012, 12:38 PM   #4
Calvin is offline Calvin  Germany
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Hi,

I´d choose the Xover after having measured the drivers.
Basically I´d opt for as much bandwidth for the ESL part as sensible.
Sensible meaning here to HP-limit the lower bandwidth to at least 1/2 octave above the fundamental resonance of the panel, or a frequency point requiring no more than ~+6dB equalization for acoustic phase cancellation, whichever comes first.
The probabely biggest advantage of an hybrid against a FR is its largely increased dynamic range and low distortion figures. It results from the restriction to a frequency range where the diaphragm excursions become very small (<1mm) which is typically the range >150Hz.
Depending on segment sizes and mechanical diaphragm tension the fundamental resonance may be in the range rom 100Hz -200Hz. This suggests an X-over range from 150-300Hz, if the 6db-rule and the requirement for the dynamic range, i.e. panel size allow for such low Xover -frequency.
Since ESLs need some form of equalization, passive crossovers mean a loss of efficiency in every case, in extremes -as for example the old SequelII- up to 15dB. After my experience xovering actively is the only way to achieve top-notch results. Wether You xover with analog filters or digital filters doesn´t matter much sonically if OPamps are involved. Almost all commercial analog Xovers miss on the EQ-capabilities required for ESLs.
The digital filters offer alot more flexiblility, convenience, filter capablities and will probabely even cost less (see MiniDSP et al).
It may be possible to top the sonic results with elaborated discrete-circuits analog xovers, but as long as You haven´t found the final set of parameters I´d suggest You use a digital filter.

jauu
Calvin
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Old 11th March 2012, 12:47 PM   #5
john65b is offline john65b  United States
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I have a DCX2496 biamping a pair of ML CLS with a pair of Magnepan Tympanis. Currently crossed over at 250hz. 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?

Anyway, I will continue and watch thsi thread...
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Old 11th March 2012, 12:53 PM   #6
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Quote:
Originally Posted by markusA View Post
I'm not entirelly sure what to make of your post?
Are you an advocat of passive crossovers?

I'm very much aware of the fact that it'll be long and hard work to get a passive XO optimised.
I'm more concerned with which one is actually better and why?
There are some designers claiming that passive is better above 200Hz.
Some swear that active is the way to go?

What I am referring to is that conventional active crossovers are designed for preamp type voltages - and they can do an excellent job when placed in that role, ESL's though are high voltage devices. The ESL 57 schematic shows the audio transformer stepping up the voltage to the passive crossover components. So here we have Quad purpose designing that there is some benefit in having the crossover components running at high voltage... You could look at the Wireless World articles from 1957, and I am confident in amongst the myriad of mathematics is an answer for why it is better to have the crossover of frequency done at HV

Your design possibly needs to consider this voltage step up and the exposure of components to that voltage. Very few active crossovers that I know of are designed for such voltages or could survive such voltages. Hence the wisdom of passive crossovers.

Relative to the ESL 57: The audio transformer is used to step the voltage up which comes from your amplifier. The transformer has a single primary and two secondary windings. The primary winding is what you connect your amplifier too. The secondary windings eventually connect to the bass and treble panels (after the signal goes through the crossover). This means that all the components in the crossover have to be rated at high voltages. The secondary windings are nominally 55:1 and 110:1 for the treble and bass panels respectively. This means that at the maximum input voltage of 36 volts you are getting about 4000 volts on the stators of the bass panels !! The transformer is totally encased in wax.

Cheers / Chris

Last edited by Chris Daly; 11th March 2012 at 01:02 PM.
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Old 11th March 2012, 01:09 PM   #7
markusA is offline markusA  Sweden
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I suppose that pretty much sums it up?
My initial thoughts of a digital XO is probably both the easiest as well as best way to go.
I guess there isn't much to do except start saving up for the DAC/DSP combo.
I predict a regular active crossover like the Behringer will be the safest bet to get the system up and running while I save up for the real deal. Lol
I got to get myself a good paying job, this is going to require a bigh chunk of $$$. :P

Like I stated in the beginning, work is gently moving along and I had a little time left over. I'm currently shopping around for a local powder coater for the panels.
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Old 11th March 2012, 01:39 PM   #8
Calvin is offline Calvin  Germany
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Hi,

maybe the ´wisdom´ in using the HV-side is simply marketing?
Up till today, the ill myth holds that a fullrange ESL is the superior ESL.
Now what should all the people think if they realized that their beloved Quad company didn´t built nor sold true fullrange ESLs but rather multi-way/multi-paneled ESL-speakers with secondary-side Xovers?
They could and do market such a speaker still though as xoverless speaker, thereby claiming to fulfill an ideal, that no other speaker could offer.
The same principle as with MLs XLS (which in contast relies on a primary side Xover), which isn´t a fullrange ESL like its predecessor the CLS.
If it weren´t for other than marketing reasons they surely had not opted for a clearly inferior ESL panel as bass part.
All issues and problems are solved if You just claim: "Its a Fullranger!"

jauu
Calvin
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Old 11th March 2012, 02:20 PM   #9
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Here is a reprint of the 1955 article by Peter Walker, showing development of what was to become the ESL57. Much wisdom on many fronts. the use of bass and treble panels and a crossover at HV from what I can ascertain, was to improve efficiency. As can be seen many design issues and criteria are proposed, including actual use, sound pressure levels, and PW answers each to propose the use of ESL panels as near perfect sound radiators.

Wide Range Electrostatic Loudspeakers P.J.Walker Wireless World May 1955 part 3

Also remember this was 1955 and production of the 57 led to arguably the best loudspeaker that was mass produced ever, with production numbers to over 25,000 pairs. 53,151 apparently the last one.

Cheers / Chris
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Old 11th March 2012, 03:09 PM   #10
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Quote:
Originally Posted by Calvin View Post
maybe the ´wisdom´ in using the HV-side is simply marketing?
Up till today, the ill myth holds that a fullrange ESL is the superior ESL.
Now what should all the people think if they realized that their beloved Quad company didn´t built nor sold true fullrange ESLs but rather multi-way/multi-paneled ESL-speakers with secondary-side Xovers?
In Quad's defense, I have never seen any documentation that would lead me to believe that they promoted their original ESL-57 as a crossover-less design. In fact, Walker and Baxandall provided a great deal of information on the ESL-57 and why they chose to use a 3 way design, how they implemented their crossover and how they dealt with the high-Q diaphragm resonances.

Now, I have not read any mention of why they chose to use a HV-side crossover. But, I would think the most likely reason was cost savings. If they had used primary side crossovers they would have needed 3 separate step-up transformers.

As to whether it was advised for QUAD to use ESL bass panels for their ESL-57 or cross to dynamic drivers, I could only say that having listened to some of the vintage woofers of the 50's I think they made the right choice.


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?
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