esl horror stories

[flodge]

Hi this isnmy first post and it is regarding safety with the diy esl. A local audio guru(ahem!) has informed my friends of my almost certain death if I continue the construction of my speakers. Because he knows a bloke that ionised the room and lost half of his face etc. I have seen no such worries on the internet. Does anybpody know of any such stories or is a matter of hot air a I suspect it to be. Is there any experimenter out there alive enough to give the low down on this?
Thanks in advance

[SY]

For most ESL designs, hot air. The most spectacular failure I've seen was from a Beveridge wannabe with a metallized diaphragm. One loud passage and... POOF! Flames.

[Bill Fitzpatrick]

Well, there is the danger of becomming permanently invisible.

[SSassen]

Adding to Bill's comment there's the ever present danger of opening a interdimensional portal due to a high-voltage discharge and resulting em-field that rips a hole in the fabric of time-space, imagine that!

But seriously the high-voltage cascades used to charge the foil carry a dangerously high voltage. If you use the tried-and-tested dual transformer design and a bunch of caps and diodes you'll feel a sharp pain when you touch the foil when powered up.

If you go with the 'minimalist' approach of a cascade running straight off the mains you could end up in the ER, as then there's no real current limiting other than the diodes that usually push about 1A, either way high-voltage demands respect.

I'd suggest you Google for ESL Cook Book by R Sanders and read through that to get an impression of the do's and don't's.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

[Andy Bartha]

There is no chance that you will ionize yourself to death and have half your face fall off with your DIY esl speakers. What RUBISH! The only real danger is of getting zapped by high voltage if you are not carefull. You will only do that once.
The only speaker that can ionize air is a plasma speaker that is not enclosed. There was a story going around many years ago about Nelson Pass and a plasma speaker he built. But I doubt if that was true.
Sander makes a very good point about getting the ESL Cookbook. There is a quite a bit of good info on ESL.
Do not pay any attention to your local audio guru. As with most of these audio guru types there mouths are one thousand bigger than their knowledge.

Andy Bartha

[flodge]

Many thanks for your excellent and informed answers to my post. you have put my mind at rest.I have seen the the results of people just playing around with electricity. One fly in the room and blam ..... no more dinner party invites.
Seriously though it is very difficult to stand up in front of people with little or no interest in the subject, ones family generally, and claim that twenty years of reading and fiddling around with components has given you some residual familiarity with the the subject if there is the barfly expert standing next to you telling tales to chill the blood.
What an excellent community.
and many thanks, I was so miserable at the thought of having to stop creating my masterpiece.

[I_Forgot]

The danger is not in the HV bias supply, unless it is not built properly.

By built properly, I mean there should be no high energy parts in it- i.e. don't use a big transformer for voltage step-up, don't use any large capacitances, and put a very large resistance (>10 Megohms) between the supply and the ESL diaphragm. You should be able to touch the ESL bias output with your bare finger and get nothing more than the shock you get when you walk across a carpeted floor and touch a grounded lamp/doorknob/etc.

The real danger in ESLs is the possibility of coming into contact with the stators while the speaker is operating. The audio transformers that step the amplifier output voltage up to a few thousand volts can deliver a very bad shock. I know this from experience. I was left with a very sore arm and an interesting perforation pattern from the stators burned into my thumb and index finger.

ESLs should always be built with some form of mechanical barrier that prevents anyone from accidently coming into contact with the stators or the wiring around the audio transformers. Don't skip this part of your design, and be very careful when testing.

I_F

[Brian Beck]

This is such an important question that I_Forgot’s excellent response deserves to be “seconded”. Fortunately the diaphragm’s HV bias supply already needs a high resistance to ensure constant charge for low distortion. This resistance also is protective for humans. The typically >10MEG resistor should be an integral part of the HV supply (close as possible to the diodes and caps) so that any wiring used to distribute the HV to the diaphragm(s) will be after this resistor and will be current limited against accidental contact.

But the stators can be deadly when music or test signals are playing. Using a HV probe, I have watched on a scope thousands of volts of music playing on my Quad ESL-63 after the step-up transformer (or, in my case, coming from my direct-drive 833 amps). Whether a transformer step-up or direct-drive is used, both sources have the relatively low driving impedance necessary to drive the capacitance of the ESL elements at higher frequencies. This means that not only are high voltages present, but also deadly high currents (relatively). As a side note, I always wondered how Martin Logan, InnerSound or any other ESL manufacturer can get away with exposed stators. The MLs are coated with some kind of epoxy, but still, a scratch or a wet finger finding a tiny hole in the coating could be dangerous. I suppose you’d have to figure out how to touch both stators simultaneously, and maybe that has saved the day. I’ve never heard of anyone getting fried with a commercial speaker, but still I wonder.

[I_Forgot]

Originally posted by Brian Beck
As a side note, I always wondered how Martin Logan, InnerSound or any other ESL manufacturer can get away with exposed stators. The MLs are coated with some kind of epoxy, but still, a scratch or a wet finger finding a tiny hole in the coating could be dangerous. I suppose you’d have to figure out how to touch both stators simultaneously, and maybe that has saved the day. I’ve never heard of anyone getting fried with a commercial speaker, but still I wonder.

Maybe no one has ever lived to tell the tale!

I have always wondered the same thing about MLs. Maybe they put resistors in series to limit current, but not so large as to reduce the speaker output in the audible range (or maybe they do that to act as a LPF to roll off the HF response of the speaker)...

I_F

[bear]

Ummm... contact with the stators should not be dangerous. They are at ground when the unit is NOT playing.

When playing they are at some rather variable AC voltage which depending upon the speaker and how loud it is playing may or may not be high enough current or voltage to bother you under normal home circumstances...

But, I'd rather not be holding the secondary of a step up transformer that is running the stators, or the uninsulated stator AND holding a nice solid ground...

So for merely ordinary people, some touchy/kids/fool protection of the stators is probably essential... grille cloth at a suitable distance from the stators may suffice?

The high voltage supply should NOT be a high current supply. It should be a low current high voltage type - typically either a regulated switcher or more commonly a multi-stage diode "quintupler" or such (like a voltage doubler, but stacked up to produce some HV from something like a wall wart or a small iso tranny). The latter, the wall wart/12vac small transformer virtually eliminates any possibility of injury from high voltage.

Although you can take a nice jump if *you* serve as the discharge path for the ESL panel itself...

As far as ionizing the air in the room, not!

The two speakers that MIGHT ionize the air are a pure plasma speaker - there was one made commercially back in the early 80s and advertised for a short time... spectacularly low output, btw... and/or a plasma tweeter of the ionovac/ionofane ilk will produce some ozone.

Oddly, I kinda like some ozone in a room... via electrostatic air cleaners - a nice clean smell... your preferences may vary on that.

The one that your fiend, I mean friend my have been thinking of is/was the Hill Plasmatronic, which used a HeNeAr or similar gas, (the patent didn't call for the the HeNeAr, but just He, but I thought the purple glow was due to the Ar, but apparently not - but i diverge) which did tend to fill the room with nicely ionized air and inert gas... so a positive ventalation system was a good thing to have with that extraordinary speaker.

_-_-bear