My first ESL and definitely not my last!

[chinsettawong]

Hello friends! I have learned a great deal about ESL through the making of my headphone. So, I decide to try to make a pair of ESL. The stators are 120x10 cm and 120x25 cm. I use 1 mm spacer for 120x10 cm panels and 1.5 mm for the 120x25 cm panels. The bias voltage now is set up at 1800V for the small ones and 3600 V for the big ones. At the beginning I used a pair of line output transformers for each channel, but I found out that the transformers couldn't take the load and was saturated after around 10 minutes of listening. It was very obvious because the sound was so very distorted. I now use a 8.5K push pull transformer for valve amps for each channel. The coating material I use is the same glue formula I used for my headphone. The sound is really sweet.










I thought that the bass would be bad, but I was wrong. The bass is actually not bad at all. So, I'm going to listen to them without woofer. We'll see how it goes.

Thanks everybody for sharing with me valuable information to help make my ESL a success.

Wachara C.

[arend-jan]

Hi Wachara,

those are two might fine looking ESLs! How do you like the sound? With those two 25cm panels you have quite a lot of surface area which helps with the reproduction of the low end. I suspect they could do pretty nice bass.

Do you have a microphone to make some measurements? You may want to do a basic frequency response measurement to tune the crossover. Do you have the 25cm panels running full range now or do you have them low pass filtered with series resistors?

[chinsettawong]

Hi Arend-Jan,

I like the sound very much. I really like to do the frequencies response measurement, but I don't know how to do it. Could you teach me, please?

I am running them all full range right now. They seem to go together very well. I do not know how to do the low pass filter. Perhaps you can teach me.

I am using only one transformer per channel. Is it still possible to do the low pass filter with one transformer?

I checked with the guy who made the transformer for me and he told me that the step up ratio of the transformer was only 46.5:1. I am wondering if the ratio is too low? I am playing the speakers with my EL34 PP amp. It is rated 25 watts per channel. But when I tried to play the speakers with my Nelson Pass's F5, rated 25 watts per channel, I just could not get the amp to play loud enough. It's weird.

Wachara C.

[bacon665]

dont those little pads touching the diaphram keep it from producing sound?

if your building a lowpass filter for woofers you dont tie them into the transformer. They get spliced in before it because the subs most likely cant handle the transformer output.

The simplest low pass filter is as follows...

[chinsettawong]

Hi Bacon665,

I like to try to put a low pass filter on the big panels. I don't know if I can do it with only one transformer. Thanks for your suggestion though.

Wachara C.

[Calvin]

Hi,

a lot of people tend to forget, that the transformers are not only used to step up/down voltages/currents, but to match the impedances. So to know if You´ve got the right transformer it means to measure the impedance of the speakers. 46:1 is a bit low for a panel of this size. But it could be enough if the impedances were alright. In Your case 1.5mm of d/s is a bit high for a hybrid panel and a bit low for a FR-panel. This means a lower capacitance, hence higher resistance of the panel. This in turn means higher transformation factors are needed.
Anyway, the capacitance of the panel as is should be around 900pF, which translates to ~9kOhms@20kHz. This value divided by u² (1/46,5²) gives ~4Ohms. That´s too high. No wonder Your amp doesn´t drive the panels to full volume. While the amp is optimized for low ohmic value loads the ESL presents a too high ohmic value load. regardless of the capabilities of teh amp, power is wasted simply because of the impedance mismatch.
The impedance matching is off of the optimal value. 100:1 would be a better value here. Even better would be a redesign of the panel, since high transformation factors are always sonically inferior to lower transformation factors.
I use between 60:1 and 70:1 (25x125cm) and 50:1 (40x150cm) for the larger panel which is roughly double the size and capacitance. This gives around 1Ohm@20kHz or slightly less. The tranny´s stray inductance goes into resonance with the panel´s capacity somewhere between 12kHz and >20kHz. The resulting peak in the freq-response can be countered by a series damping resistor (typ. 0.5-1.5Ohms) which reduces the low-ohms-stress on the amplifier, linearizes freq-response and allows for a better impedance matching in the lower freq-range.
I wouldn´t use sheet metal stators for a FR-ESL. Wire stators are the better choice when larger d/s values are needed. Sheet metal stators are superior when the d/s is small --> hybrid panels.
So you have two good choices.
a) a hybrid panel made from punched sheet stators, featuring small d/s values and small transformation factors, or
b) a FR-panel made from wire stators, featuring larger d/s values and high transformation factors.

jauu
Calvin

ps. of course You don´t lowpass filter the thingies but high pass them! The series resistance is solely to control the resonance at the upper bandwidth limit.
An easy and very effective way of filtering is to use a dampened C/LR-Filter (2nd order) whith a slightly raised Q value. This way You can counter the phase cancellation around 200Hz, achieve a linear freq-response and highest efficiency....but....it will be a hybrid panel now

[analog_sa]

Originally posted by chinsettawong

I like the sound very much.

And you are running these panels full range? No beaming, huh? And the amps don't mind the capacitance?

[chinsettawong]

Hi Calvin,

Thanks for your input. I really do not understand much about the technical things. I can get only around 50% of what you tried to explain. I'm sorry for my so little knowledge.

Can you suggest to me what I should do? Since I have them done the way they are now. They sound is nice as is now. But if I want to try to produce only lower frequencies in the bigger panels, what do I have to do? To do the R-C filter do I need another transformer?

My EL34 PP amp when playing with these speakers is only at around 40% volume and the sound is loud enough for normal listening. 60% of the volume then the sound is too loud. However, with my F5, turning the volume to almost full still doesn't make the sound as loud as 40% of EL34 PP. I heard from some friends that vacuum tube amps tend to sound louder than the solid state amp at the same wattage. Is it true?


Wachara C.

[chinsettawong]

Hi Analog_sa,

Yes, I run them all full range. I just connect all three big and small panels together to the same transformer. About beaming, it's not that bad. I'm not sure what effect the capacitance can do to the amp. But so far, so good.

Wachara C.

[chinsettawong]

Hi Calvin,

Referring to your post saying that my current speaker Ohm load is too high at 4Ohm. Could you please show me how you calculate that? I put a 1.8 Ohm resister series at the input of the transformer right now. Does that help at all? Also I connect the one 120x10 cm panel and 2 120x25 cm panels to the same transformer. Does that make the Ohm higher?

What do you think about my bias voltage? Now they are 1800V and 3600V.

Wachara C.