tade no esl

[tade]

so i have a panel that is eight inches by twenty two. a good tester. using gaphite on my saran wrap diaphram. i jacked a HV supply from a night vision camera, and it is capable of dragging the membrane into the stators. so that tells me that i am maxing out my voltage potential. i also bought a pair of tube otuput transformers to use as the step up. the secondary can be four eight or sixteen ohms. I tested with four. the primary is listed at 10000 ohms center tapped.
the volume was pretty pathetic. and when i turned up the amp to get a decent level, not rocking out, i could hear the transformer clicking and hissing. I hope this is just coils moving in the magnetic field and not laquer vaporizing, or layers arching... I am feeling a bit on the low side, any advice you could give would greatly help me!
many thanks

[SY]

The good news: there's not much to go wrong. The bad news: you can't just take any old transformer, turn it around, and expect it to work properly...

How tight is the diaphragm stretched? Thickness?

[tade]

the diaphram was at about twenty hz i would guess. you could hear it vibrate, but it was very low. maybe tighten the heck out of it?i do not intend for these to be full range, maybe i could make the resonance yield a flatter response and high voltage tolerance. the spacing was probably four milimeters on either side. the thickness of the saran wrap is anyone's guess. quite thin i should think.

[SY]

Well, most grocery-store Saran Wrap is about 5 times too thick. Finding 0.5mil Saran requires some hunting. Thinness for Saran is particularly important since its specific gravity (density, weight per unit volume) is considerably higher than Mylar.

For your geometry, a 20Hz resonance suggests that your tension is too low and (possibly) your diaphragm is too massy. If you really have 4mm of spacing on either side, that's pretty high, too. You'd be better off with 2-2.5, the lower number being more appropriate if you're not running full-range.

[tade]

wow, i had no idea how thick saran wrap was in comparison to acceptable mylar, that and its density. The heavier diaphram will limit my high frequency and impulse response? I am going to build a new test panel today. 1.5mm spacing using double sided tape. and i will also stretch the **** out of the diaphram. Ill let you know how it works.
Thank you for the advise!

[Brian Beck]

SY,

BTW, I greatly prefer your new look over the decomposing dwarf

I believe that the mass of the heavier Saran will only significantly effect the high frequency roll-off. This is where the diaphragm mass reactance exceeds the air radiation resistance. Therefore, we would expect an earlier roll-off in the treble with the heavier Saran. Well below that frequency, there would be no difference in sensitivity between heavy and light diaphragms because the air radiation resistance dominates. At low frequencies the diaphragm's stiffness interacts with the air mass reactance to determine the resonance, and not the relatively light diaphragm mass.

[SY]

That's right- the mass part of the motor is dominated by the air load at lower frequencies. In tade's case, he's got an 8" wide panel which will (without eq) not go very low. If I were to guess, the combination of these two rolloffs is one contributing factor to his low output.

I've got some panels about the same width (rebuilt and heavily modified 1+1s) that are putting out very satisfactory levels, but it takes a lot of voltage swing for them to do so. The wussy 1kV direct drive amp I tried on them was fine for background music...

[tade]

i started today on the bigguns. one by four feet. too me an hour to make one panel. i will need four... wish me luck

i was showing my neighbor the test esl i built. he was very impressed. then i showed him the sub i built, a wicked one. that was also impressive however, when i cranked it, it caused the panel resonate and the membrane to hit the stators with no charge on em! give and take.

more news later, and maybe some pics if you are lucky.

[tade]

oh yeah, forgot to ask.
when i make the panel bigger, will my sensitivity increase?

also, when i connect the bias, i get a hissing across the panel. I have a guess that this is charged air being drawn to the membrane from the stator. could this be?

thanks

[tade]

So i built a one by four foot panel. Sounds great. i really like the the beaming. allowa me to be further away with no reduction in quality. which is really neat. I don't notice anything lacking in the upper ranges due to the heavy saran wrap i used. i atribute that to either, rising trebel response caused by the transformer canelling out the damping by the wrap, or my prematurely aged ears!

I used double stick foam tape which is about one mm thick It sticks wonderfully to the stators and the membrane, which leads to another dilema. this panel's tention was too low. i probably got excited during its construction... anyway, this means sometimes i must shake or blow on the panel to stop popping and hissing sometimes. Ill have to tear it apart which i am not looking forward to. the next step will be housing them in such a way as to inspire awe in my fellow human being. this may be harder than i expect.

Also, i will need to pair it with a goldwood ten inch woofer. looking to do this scientifically with measurements and such, but i blew the fuse on my multimeter. so on to another day.

I have three weeks left til they come to school with me finished or not.

peace