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Building an Electrostatic Speaker
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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Mon Jan 30, 2012 9:20 pm    Post subject: Reply with quote


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Bob,

According to Wikipedia the rolloff occurs when the narrowest panel dimension equals 1/4 of the wavelength and it then falls by 6dB/oct. In practice because of a well placed (preferably distributed) resonance of the membrane the actual 3dB point is lower. Additional support structures line the 'ears' on the Martin-Logan CLX and the angled side supports on my own speakers make the minimum dimension larger and the lowest frequency lower.

A speaker like the ESL-0.88 can easily reach down to 80Hz and the remaining portion can be filled up by a sub woofer. I am sure not if anyone built them in a wall yet but that would definitely remove the back wave cancellation. You would need to be careful of pressure differences (both static and dynamic) between the two rooms, I could imagine pressing the membrane all the way against the stator. It would probably not kill the speaker immediately but over time it will burn off the conductive layer on the membrane.

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Boilermaker




Joined: 21 May 2006
Posts: 527



PostLink    Posted: Mon Jan 30, 2012 11:00 pm    Post subject: Reply with quote

Quote:
You would need to be careful of pressure differences (both static and dynamic) between the two rooms


Excellent point that I never thought of. Static wouldn't be an issue in my case, but all it would take is to slam the door to my HT, and I'd have an arc for sure!


Quote:
A speaker like the ESL-0.88 can easily reach down to 80Hz and the remaining portion can be filled up by a sub woofer.


Yes, I intend on using an electronic cross-over to make each one a two way to not lose the bottom couple of octaves and to enhance overall power handling capability.


Thanks,
Bob
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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Thu Mar 01, 2012 4:33 am    Post subject: Reply with quote

Well. the final chapter has arrived, the speakers are wrapped,



crated,



and finally shipped



This was not an easy process, I booked with a shipping company, gave them the dimensions and weight and they booked a trucking company to pick up the crate. Unfortunately they forgot to tell the truckers how big and heavy it was so the driver just shrugged his shoulders and drove off again. After being hung up in my face by the dispatcher the shipping company re-booked and this time they came out with two people and two trucks. It still took them almost an hour balancing the crate on both lift gates before it was finally loaded.

Lets hope the rest of the journey goes better than the start.

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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Fri Apr 20, 2012 7:14 pm    Post subject: Reply with quote

The crate has arrived completely unharmed at the other side of the pond. The customer has unpacked the speakers and placed them in the room. I am anxiously waiting on his feedback.
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kal
Forum Administrator



Joined: 06 Mar 2006
Posts: 16910
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Fri Apr 20, 2012 7:27 pm    Post subject: Reply with quote

.... and pictures I hope!

Kal

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garyfritz




Joined: 08 Apr 2006
Posts: 11413
Location: Fort Collins, CO


PostLink    Posted: Fri Apr 20, 2012 8:21 pm    Post subject: Reply with quote

Wow, I didn't realize your customer was in Europe! Last time I tried to ship something there, they told me there were no longer any surface options available, and I'd have to ship it by air. It cost a freakin' fortune. But I assume you found some surface shipment option? Otherwise you'd have spent thousands to ship those beasties! (And they probaby wouldn't have taken 7 weeks to arrive! Smile)
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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Fri Apr 20, 2012 9:13 pm    Post subject: Reply with quote

Shipping by boat wasn't actually that difficult to figure out. There are many companies out there that offer LCL (less than container load) shipping. The cost is strictly by volume, they don't seem to care about the weight and some of them have it almost completely web based now.
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garyfritz




Joined: 08 Apr 2006
Posts: 11413
Location: Fort Collins, CO


PostLink    Posted: Fri Apr 20, 2012 11:36 pm    Post subject: Reply with quote

I imagine that's for pallet loads and crates. I just had a box with some HD145 lenses in it -- that little box would get lost in a cargo ship!
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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Wed Apr 25, 2012 7:16 pm    Post subject: Reply with quote

After playing for weeks at my house without any issues whatsoever, one of the panels decided to start sparking barely an hour after being switched on by the customer. The customer made some pictures and videos of the area's where it happened. I have to say I felt almost physically sick when I heard it after putting so much work into them and I was ready to get on a plane with parts in order to fix it on the spot.

Luckily the customer is very handy and he managed to fix it himself by carefully removing membrane around the mounting holes and screws. I had insulated these with tape but I guess that over time voltage breakdown occurred and when is starts to spark it won't stop. I will add this to my lessons learned list and pay more attention in the future.

Another interesting phenomenon was cutting out of the sound at a certain volume level. This was ultimately traced to some interaction between the speaker and one of the digital components. My guess is that the electric field of the stats interfered with the 1's and 0's.

There are still a few problems left:

1) The sensitivity the customer measures is much lower than what I measured. This is still not understood and I will have to compare it to the ESL-1's when I finished rebuilding them for the upcoming Lone Star Audio Fest show.

2) The second order distortion is rather high at elevated listening levels. There are two possible theories for this behavior. One is that it has to do with the spacers. Because of construction reasons the front spacers are a bit wider than the rear's and one theory is that that caused an asymmetrical movement in the membrane and therefore second order distortion. Another possibility is that the transformer is driving too high of a capacitance load and it starts to distort. When I have time I will set up some measurements of just the transformer.

After all the problems here a few unfiltered quotes by the customer.

"What comes to the sound, I like it. They sounds like big electrostatics Smile. Balanced like you said, not too bright nor too dark. Excellent midrange and treble, bass is also quite good. But I have to set them up properly and more importantly get them working properly."

"I have listened with them for 3 hours now straight, that's 6 times more that I could listen to them before the other started to spark. The bass is actually quite good from these, but the capacity is too low for normal semiloud listening. They are not perfect speakers, to be honest in this condition they are not as good as my previous dipole linea array / horn tweeter speakers. The biggest problem soundwise is the high THD. Transients sound too forward and the midrange lacks some of the ultimate midrange delicasy of low THD electrostats. The sound quality is not bad, but not as good as I have heard. The good is that the big stat fills my room with music and they look very good. They have lot's of potential, and they can be made to sound much better. More capacity to the bass, little higher conversion ratio to the trafo (maybe 1:100 - 1:150) to boost the sensitivity and especially the THD has to be get rid of."

"The sound is improving constantly. The bass is not so restricted anymore and I can actually get some dynamics out of them."

I will have to do some work on the distortion, my personal first guess is the transformers and when they are the culprit doubling up on them is the most obvious way to go.

Lastly a link to some photos:

http://s817.photobucket.com/albums/zz95/LegisActio/System/?action=view&current=staatit11.jpg



Kim

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Boilermaker




Joined: 21 May 2006
Posts: 527



PostLink    Posted: Thu Apr 26, 2012 4:47 pm    Post subject: Reply with quote

I would guess that the distortion he is experiencing is either from his power amps or the transformer. Do you know what amplifier he is using? he needs to find out if he is running out of voltage or current. If it happens to be voltage then he can use a transformer with a higher turns ratio, but I doubt that he is voltage limiting. Is the distortion appearing during passages with high frequencies and high output?

If he measured a lower sensitivity than you did, meybe he is measuring differently, or the bias voltage has dropped?
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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Fri Apr 27, 2012 6:53 am    Post subject: Reply with quote

My best guess is still that it is transformer related and there are a few indicators for that. For example at less clamping force the capacitance of the panel goes down and the distortion goes down as well. The bias voltage is increased in order to keep the sensitivity constant.

Removing a few spacers also reduces the panel capacitance and the distortion. I have admit though that both reductions can also be explained by something going on with the spacers.

It is not the amps, those are ginormous.

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Legis




Joined: 28 Apr 2012
Posts: 2



PostLink    Posted: Sat Apr 28, 2012 1:13 pm    Post subject: Reply with quote

Hi everybody.

I wanted to say that the sound has improved constantly, so some of those Kim's quotes are outdated (like that my previous speakers sounded better).

The step-up trafo saturation at the bass is the biggest problem, which is caused by lowish sensitivity. I can get ~95dB clean to the listening spot (only 2m away from speakers) with music material that has normal bass and ~90dB with bass heavy material. The speaker don't sound constrained (at all) at these levels, I can't even see the membranes moving, but one dB more and the Plitron's trafo starts to saturate because of too high primary voltage at the bass. The SPL is measured with digital Radioshack SPL meter (C-weighting, "max", fast reaction time (125ms average)) with fresh battery.

These levels require heavy stress on the trafo because the sensitivity is somehow quite low. Output configured to ~2,83Vrms with sine waves between 300Hz and 1kHz and measured 1m away from speaker (only one playing), the bias voltage set at halfway, the sensitivity is a tad below 75dB. My 3" fullranger is almost 10dB more sensitive, which becomes quite clear if I hook it in parallel at the same time - it totally overrules the ESLs in the SPL at same output voltage. I could boost the bias voltage from halfway to max, to get approx 4dB more sensitivity, but I have not done that yet as I don't see it as a first choice fix for this problem.

I will write some analysis after the problems are get rid of and the speakers are broken in.

Regards,

Legis
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Boilermaker




Joined: 21 May 2006
Posts: 527



PostLink    Posted: Sat Apr 28, 2012 5:03 pm    Post subject: Reply with quote

Legis,

First off I need to admit that I am envious! Several decades ago I built a few 'stats and can tell you that yours makes what I did look like a high school science fair project.

Are you running these full range, or are you using either one or two subs with them?

Quote:
but one dB more and the Plitron's trafo starts to saturate because of too high primary voltage at the bass
.

Its been a long time, but since your Plitron's are air coupled instead of iron, is it possible to saturate? Perhaps you are running out of voltage swing which you could check easily with a scope. Just a thought.


Quote:
I could boost the bias voltage from halfway to max, to get approx 4dB more sensitivity, but I have not done that yet as I don't see it as a first choice fix for this problem.


As long as you don't get any arcing, I would use as much bias as possible, unless I am missing something.

Please do keep us informed as you play more with them.


Thanks,
Bob
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Legis




Joined: 28 Apr 2012
Posts: 2



PostLink    Posted: Sat Apr 28, 2012 8:27 pm    Post subject: Reply with quote

Boilermaker wrote:
Legis,

First off I need to admit that I am envious! Several decades ago I built a few 'stats and can tell you that yours makes what I did look like a high school science fair project.

Are you running these full range, or are you using either one or two subs with them?

Quote:
but one dB more and the Plitron's trafo starts to saturate because of too high primary voltage at the bass
.

Its been a long time, but since your Plitron's are air coupled instead of iron, is it possible to saturate? Perhaps you are running out of voltage swing which you could check easily with a scope. Just a thought.


Quote:
I could boost the bias voltage from halfway to max, to get approx 4dB more sensitivity, but I have not done that yet as I don't see it as a first choice fix for this problem.


As long as you don't get any arcing, I would use as much bias as possible, unless I am missing something.

Please do keep us informed as you play more with them.


Thanks,
Bob


Hi Boilermaker, yes Kim's stats are looking georgeus Cool . The stats are running full range. There is a big polyprop capacitor in series to make a first order high pass around 50-60Hz, but other than that no filtering. It does not really limit the LF response of the panels, but keeps the DC out of the trafo and also limits the infra content from saturating it. Both 18" bass line arrays are running along, crossed (acoustically) over where the stats start to fall, that is around 50Hz. With bass arrays the system digs into infra bass region.

Yes the Plitron's trafo can saturate, I think Kim also experienced this at least when I said he should try to play the Tchaikovsky's 1812 (Kunzel) with real cannons Laughing. Here on page 130 you can find some calculations on this specific trafo's saturation point (17,9V @ 50Hz, I don't know if that holds true for one trafo or is it half that voltage): http://home.kpn.nl/verwa255/esl/ESL_English_2011.pdf Amps should not be the problem, they give approx 715W into 4R, which translates into somewhat over 53Vrms. I have also tried with other monos, that can output 1070W into 4R with same results. With another pair of Plitrons I could get double the capacity, but they are hefty expensive. Maybe we will first try with four Antek's trafos connected in series/parallel. The trafo's capacity could also be increased with higher or steeper high pass filter to limit the LF that goes to the trafo.

I will keep you posted how things are progressing.
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MrAcoustat




Joined: 01 Jan 2013
Posts: 13
Location: Quebec - Canada


PostLink    Posted: Thu Aug 01, 2013 1:06 pm    Post subject: Reply with quote

How would you like to ship these babies - - - Acoustat DIY Spectra 8800 - - - 41x102x 10 inches weight 800 pounds.

[/img] http://cdn-2.dastatic.com/forums/gallery/data/500/medium/Acoustat_Spectra_8800_05.jpg

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beun




Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Fri Aug 02, 2013 4:17 am    Post subject: Reply with quote

Big crate and big bucks.
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