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Old 18th February 2016, 11:54 PM   #21
golfnut is offline golfnut  New Zealand
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Hi

ESL63 transformers are not suitable - that is a different class of ESL again

Essentially there are three classes of ESL depending on their impedance.....

Single segment ESL (e.g. perforated plate)
These radiate as a rectangular source (typically) with poor polar response (narrow listening position)
ESL load is single pure capacitor
best transformer (for maximum bandwidth) has high capacitance and low leakage inductance
larger (50VA) toroids good - commercial ESL transformers good
Leakage inductance a few mH, capacitance several 100 pF - see the Amplimo transformers for example

LC Transmission line (ESL 63 family)
This is multi-segment ESL connected as LC transmission line. The LC transmission line uses annular segments radiating with LC delay sections to simulate a point source = spherical wave front and wide listening position - LC transmission lines have a resistive input impedance, hence
ESL load is pure resistor over audio band
Best transformer has low capacitance and high leakage inductance
(ESL63 transformers are about 1.5 H and 30 pF I think)

RC Transmission line (multi-segment PCB or wires, with resistors)
This uses the RC transmission line to simulate a line source = cylindrical wave front= broad listening position.
ESL load is equal mix of resistor and capacitor
The best transformers have middling leakage inductance and middling capacitance, below 200-300 mH and below 100 pF respectively.
15VA transformer has 16 mH and 100 pF (unloaded bandwidth 130 kHz), when stacked the inductances add in series and capacitance add in parallel (fall) mostly.
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Old 19th February 2016, 12:10 AM   #22
WrineX is offline WrineX  Netherlands
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15 inch is pretty wide. its ok but stability of the mylar can be an issue. there is a reason why acoustat and quad used more smaller panels.. they used multiple to get the desired spl, and they used smaller ones because a resonance of 10 hz is not needed and not desired, and will result in mylar being stuck to one stator.

if you want to reach 50 you could go sligthly bigger then a quad panel for instance.
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Old 19th February 2016, 12:20 AM   #23
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by golfnut View Post
Hi

ESL63 transformers are not suitable - that is a different class of ESL again

Essentially there are three classes of ESL depending on their impedance.....

Single segment ESL (e.g. perforated plate)
These radiate as a rectangular source (typically) with poor polar response (narrow listening position)
ESL load is single pure capacitor
best transformer (for maximum bandwidth) has high capacitance and low leakage inductance
larger (50VA) toroids good - commercial ESL transformers good
Leakage inductance a few mH, capacitance several 100 pF - see the Amplimo transformers for example

LC Transmission line (ESL 63 family)
This is multi-segment ESL connected as LC transmission line. The LC transmission line uses annular segments radiating with LC delay sections to simulate a point source = spherical wave front and wide listening position - LC transmission lines have a resistive input impedance, hence
ESL load is pure resistor over audio band
Best transformer has low capacitance and high leakage inductance
(ESL63 transformers are about 1.5 H and 30 pF I think)

RC Transmission line (multi-segment PCB or wires, with resistors)
This uses the RC transmission line to simulate a line source = cylindrical wave front= broad listening position.
ESL load is equal mix of resistor and capacitor
The best transformers have middling leakage inductance and middling capacitance, below 200-300 mH and below 100 pF respectively.
15VA transformer has 16 mH and 100 pF (unloaded bandwidth 130 kHz), when stacked the inductances add in series and capacitance add in parallel (fall) mostly.

what is the difference for the transformer if there is a delay line ???? quad uses resistors as well. the the bass panels for instance are segmented(it has a high roll off). adding a delay wont change the fact the trannies need to drive the whole surface area full range.. in the schematic there are resistors. on almost all rings and bass panels. as far as i know. when you listen it is quite obvious the center ring emits most of the high frequency from 12khz and up. especially when you know it should increase 6db oct (or was it 3?) so the high frequency are heavily damped by some sort of filter... if it was only a delay i should be able to measure it still.

well enlighten me please on how they are capable of driving 1:250 without problems, since i dont get it. the delay line itself and the wave front is not the reason so what is it ?.. no offence i am just curious!

you could still use audiostatic transformers if needed

Last edited by WrineX; 19th February 2016 at 12:41 AM.
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Old 19th February 2016, 01:08 AM   #24
golfnut is offline golfnut  New Zealand
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Hi Wrinex

In a true LC transmission line, all of the segments are driven at full voltage , as you say. However, the phases are different. At low frequencies, all of the segments are driven in phase.

At high frequencies, all of the segments are driven at different phases (due to the L between each C), so some of the sound from one segment will be cancelled by the audio from another. At high frequencies there is a lot of cancelation going on.

Another way to look at it ...You might recall Walker's equation, which says that the on-axis SPL is proportional to stator current. If you drive a pure capacitor with ac, the current increases with frequency. - so you would expect the SPL to increase with frequency. The LC transmission lines fiddles with the phase of the stator current in the different sections in such a way that the vector (i.e. include phase effects) sum of all of the stator currents is independent of frequency => and therefore the SPL is independent of frequency.

The extra resistors do something extra - they slightly attenuate the signal towards the edges of the ESL so that it does not have big diffraction effects. Also, as you note, the bass sections are more like RC network too.

Re step-up ratios

Single segment ESLs are very sensitive to inductance, including amplifier output inductance. The amplifier inductance as 'seen' by the ESL is the amplifier OP inductance times the square of the step up ratio. So 10 uH OP inductance with a 1:100 transformer, looks like 100 mH in series with the ESL. With a (medium sized) 1 nF ESL, the cutoff frequency would be 16 kHz. If you were to increase the step up ratio to 1:200, the bandwidth would fall to 4 kHz - intolerable. By the time you include the transformer inductance etc with a big ESL, the maximum step up ratio is about 1:80 and you must avoid high inductance transformers. The problem is the high capacitance of the ESL.

The Quad ESL 63 has a pure resistor load impedance, which means that inductance is not so important. If the transformer and everything else is made with as small a capacitance as you can, the inductance can be very large, and the step up ratio can be large For example a 1:250 step up ratio on 10 uH OP inductance means the ESL would see 0.625 H in series - this only makes a small difference when the capacitance is very low and the total transformer inductance (two transformers) is 3H. Hence the ESL 63 favours transformers with low capacitance and high inductance.

As above, the RC transmission line ESL lies midway between these two cases, requires medium inductance, medium capacitance, tolerates medium step-up ratio (200 is high unless you know your amp has low OP inductance).

regards
Rod
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Old 19th February 2016, 08:41 AM   #25
WrineX is offline WrineX  Netherlands
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Thank you golfnut!!

then the audiostatic is a kandidate. or indeed the teroids
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Old 20th February 2016, 04:50 PM   #26
CharlieM is offline CharlieM  United States
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Originally Posted by golfnut View Post
Hi Wrinex

I found that 32 small toroids at wholesale rates was cheaper than a set of commercial ESL transformers. Also there are no commercial transformers made for segmented ESLs - they all have the wrong balance of leakage inductance and winding capacitance and would seriously limit the bandwidth - same problem as big toroids.

The number of transformers required also depends on the low frequency required, if I was happy with a response down to 100 Hz instead of 50Hz, I could halve the number. Actually, when segmented speakers are used in hybrids or not for really full range applications, choosing a bunch of 10VA toroids is really a no brainer. You just need to avoid the ones with the twin 110 V windings - capacitance is really high.

The best solution is of course a purpose made transformer - that can be done for less than US$150 for a pair, I understand - that's the approach I would take in the future. Most transformer manufacturers will do them if you provide the design. But that requires a bit more expertise than I had when I started playing this silly game.

regards
After reading the above I'm thinking my tandem 50VA 230V/2x6V toroid setup isn't ideal for my segmented hybrid panels. And the smaller toroids I've seen advertised online also have the two 115V windings, which I gather we want to avoid due to capacitance. Any recommendations?

Regarding segmentation:
I'm about halfway through building a wire stretching jig for 90-wire panels. The jig will use pins rather than threaded rods. But I'm at an impasse insofar as I can't drill the plates for the pins until I decide on a segmentation scheme.

The panel has 2 vertical spacers dividing the diaphragm into 3 equal sections, each driven by 30 wires (90 wires total). I'm torn between these following schemes:

Config 1: 10-wire group + (16) 5-wire groups in (9) electrical segments
Config 2: (15) 6-wire groups in (8) electrical segments

I'm completely deaf above 10Khz so I'm not sure it makes any difference which scheme I choose. My hearing actually starts rolling off dropping off around 5Khz so I have to apply some boost to get the treble to my liking.

I figure that with my hearing, if one configuration gives brighter treble above 5Khz, that's the one I should go with. Any thoughts on which configuration I should choose?

Chaz
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Old 20th February 2016, 06:50 PM   #27
golfnut is offline golfnut  New Zealand
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Hi Chaz

generally, the smaller the segments (the greater the number) the better, although there is little to be gained from making them much smaller than about 12 mm wide. There are several benefits...

1. Good smooth equalisation requires a minimum of about 10 segments. Play with the Excel simulator to see this.

2. Smaller segments improves the off-axis response a little bit. The segments must be less than 20 mm wide to avoid high-frequency zeros and phase reversals somewhere off axis, but there is little benefit to segments smaller than 12 mm wide.

3. More segments means more resistors, which means that the power is more widely dispersed, and the voltage drop across the resistors is less. For a good full-range ESL, say > 450 mm wide, you will need maybe 30-40 segments, so you can use resistors with quite modest ratings ~ 300 V 1W - good surface mount resistors make for a nice compact design. The power and voltage ratings are not a big deal unless you test them with pure sinewaves > 5 kHz.


regards
Rod
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Old 20th February 2016, 09:12 PM   #28
bengel is offline bengel  United States
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Originally Posted by CharlieM View Post

Regarding segmentation:
I'm about halfway through building a wire stretching jig for 90-wire panels. The jig will use pins rather than threaded rods.

Chaz
I would love to see pics of that rig. I've been thinking thru ideas myself for a setup that will allow me to make those stator panels quicker.
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Old 21st February 2016, 12:10 AM   #29
CharlieM is offline CharlieM  United States
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Originally Posted by bengel View Post
I would love to see pics of that rig. I've been thinking thru ideas myself for a setup that will allow me to make those stator panels quicker.
Hi Bengel,

I plan to build wooden lattice stators and assemble them azz backwards. That is; the supporting lattice pieces will be assembled over the wires, as opposed to stretching the wires over a pre-assembled lattice. The tensioned wires will lie on a flat jig surface covered with wax paper. The wooden wire supports will then glue down one piece at a time, onto the wires and spacers. This method should yield flat stators with glue lines perfectly flush to the wires. I tried this on a small scale already and it looks like it's gonna work.

Of course, I shamelessly stole ideas from Bazukas, Bolserts and Golfnut for laying out the wires and pins. The pins will be set into 3/16 thick aluminum plates. A pair of 3/4 threaded rods with coupling nuts will serve as jackscrews to stretch the wires.

I hope I don't come to regret using wood rather than rectangular metal tubing for the jig frame but I'm trying to save some coin. Besides, I already had some hefty pieces of wood lying around; not to mention I almost had a stroke when I priced ($$$) steel tubing.

I will post some photos when it's done.

Jazz

Last edited by CharlieM; 21st February 2016 at 12:20 AM.
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Old 21st February 2016, 06:12 PM   #30
lowmass is offline lowmass  United States
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I have zero experience with ESLs but if yal dont mind would like to add what ive experienced with a bunch of planer magnetic panel builds to perhaps help make decisions. Specifically with respect to the "curved" panels.
To avoid all the crossover issues etc I experamented for some time with curved. Built two types, one tru curve, the other multiple flat sections. The tru curve fist off is a very different animal largly as it does not really follow the typical very low mass possabilities of flat diaphragms. By this I mean that construction of the tru curved diaphragm required me to use very thick mylar. I think in the end I had to use 2 or 3 mill thick !!! thats typically about10 times as much mass as can easily be constructed with flat diaphragms. The reasion was I simply could not figure a way to mount thin films in a tru curve. With the tru curve arraingment I used the structural properties of much thicker film that heldits shape easily as you simply layed it carfully over the supporting frame work wich BTW was an exact copy of the Martin Logan design. Simple perf steel with foam strips. The foam strips acting as the support for the curved film. In such an arraingment the film becomes a riggid curved structure and the foam strips have some damping property terminating the film. It was very easy to construct once you had the suporting structure built. Now I dont know and maybe someone can educate us here but IMO this is all Martin Logan is doing. Its not really exotic and not elaborate tensioning of the diaphragm is going on at all. However the drawbacks were a heavyer diaphragm and the rigid film structures resonances were more obvious to my ears. Also very limited lower frequencys!! Need a huge panel to get to even 100hz.

Much better sound was the multi flat section unit using very thin film, as thin as u want. I used the same foam strips to divide up the vertical sections appox 3 inch wide over a curved perf steel / magnet structure. The hard part was tensioning the damn diaphragm over this. Fortunatly with very thin film the exact tension seemed unimportant so long as not too tight and I got a nice response down to 50 hz on a panel approx 3 ft tall and 2 feet wide. A tru full rage planer magnetic with at least a reasionable horiz directivity. It was my refrence but it was limited in SPL.

So the tru curve as I see it is limited in low freq response unless huge. The multi section is tricky to apply film. At least in my experience

Last edited by lowmass; 21st February 2016 at 06:16 PM.
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