Other ESL build with simple materials available from local grocery stores

[Bazukaz]

Hi,
Since this thread is about easily obtainable methods as well , i'd like to continue it a bit to this direction .
Currently , i am experimenting with conductive coatings. I found a few methods to do this , each having its own disadvantages.

One method is to use PVA based adhesives.Some types of these adhesives are hygroscopic , and will attract moisture. However , PVA , being water based , does not wet mylar well.Adhession to film is not very good either. The resistance is on the low side.
Another method is shoe cream rubbing.This method probably works because the cream contains carbon black(?). The resistance is too low as well , though it is possible to rise it by cleaning with wet cloth.
I tried some other methods , like dissolving nylon fishing line in acetic acid. This method gives very high resistance, but is hard to work with due to vapors of acid.

Any other ideas ?

Regards,
Lukas.

[wolf_moses]

Calvin on curved ESLs

Hi Calvin,

Could you share your method of building curved ESLS which avoids Sanders' mistakes?

Thanks,

Wolf

[moray james]

Lukas if you want PVA adhesive like Weldbond to stick to mylar you only need follow the directions. The trick is to dilute with water (5 parts water to 1 part weldbond) and then simply use a small hand held mister bottle to apply a lifht even coating. Let dry and you will hav excellent adhesion. You can also dope the water that you use to make it work better try a non sented dryer antistatic sheet soaked in the water. You can search under Quats

here is part of a theradWeldbond Post #5
Something that I will post to stimulate experimentation. Weldbond white glue which is a modified PVA adhesive is made by Frank T. Ross & Sons Ltd. in Toronto. (www.weldbond.com) when diluted one part glue to five parts water can be sprayed or brushed onto mylar and dries to a fine cloudy thin film. This bonds extreemly well to mylar. You can experiment with quaternium ammonium salts to dope the adhesive to achieve the desired resistivity. The most simple source would be to take a non sented Downy dryer sheet and soak it in some water. Then use the water to dope the adhesive. Many anti static products like hair conditioner or shampoo with added hair conditioner contain such salts and could also be experimented with. Easy to play with and almost free. Weldbond can be found at most any craft store as it is considered a universal adhesive. By the way Weldbond is totally non toxic. Best regards Moray James.

[Calvin]

Hi,

with curved stators I wouldn´t use heat tensioning but solely mechanical tensioning with the highest possible value..of course just tension in the straight direction. The tension in curved direction should be as low as possible....just enough to straighten out any folds. But when You apply very high tension in the straight direction, You even get away with quite strong tension in the curved direction (obeying the 1:70...1:100 rule for d/s)!
You can do this with a mechanical stretching frame with curved ends.
I use only instant bonding glue or tape. After application of the glue or tape to the backside stator I stretch the membrane and lay ist on the stator. The stretching frame presses the membrane onto the glue joint by its weight. With 3M-Tape the instant bond is very strong but increases over some hours to its final value. Then I release the pressure of the tensioning frame and cut the panel free leaving some diaphragm material left. Now I glue some thin doublesided tape on the outside (backside) of the stator and turn the diaphragm over its rim and glue it on the thin tape. This way You have much less trouble with tapes that might not have the shear strenth to hold the constantly high diaphragm tension over a long time for You have much more glued area. If there were some tiny wrinkles left on the frontside of the stator, You could even pull those flat since the foam tapes I use as spacers allow for those small final corrections.
The soft foam introduces some damping to the membrane which I regard as positive for less standing wave-Q and less stress on the membrane itself at this joint. CSD Measurement showed very good results. MartinLogan used to glue the membrane on the stators backside too..but only in the straight direction.

jauu
Calvin

[Audio_idiot]

Hi,
This is super informative!! Thanks guys!!

More stupid questions...

MJ,

Weldbond white glue which is a modified PVA adhesive is made by Frank T. Ross & Sons Ltd. in Toronto.

Don't think I'll find them in my local stores.. Could you help me nerrow down the search by tell me what are their "normal" application? then I can start reading label and contents in the store like I'm in a book shop...


Calvin,

But when You apply very high tension in the straight direction, You even get away with quite strong tension in the curved direction (obeying the 1:70...1:100 rule for d/s)!

I have been told many time about tension high and low but I don't have a feel for thatis ther any indication of "high-tension" , is there any indiction that I can fall on? eg weight for stretching, pressure applied? something? anything...

(obeying the 1:70...1:100 rule for d/s)!

I am getting confused with the d & s value.. is it,
d=Panelwidth, &
s= Panel length?

You can do this with a mechanical stretching frame with curved ends.

Are you saying that the bicycle tube stretch table is no use in your technique? In stead you have a rectangular frame to do the work?

Cheers

[Calvin]

Hi,

d/s means diaphragm-to-stator-distance....usually ~ 0,5---5mm
To ensure that the diaphragm will not touch one of the stators when playing music the membrane should be supported at distances of 70 to 100 times the d/s. For a d/s of lets say 1,0mm supports should be distanced between 70 and 100mm apart. You see those supports by MartinLogan as clear horizontal spacers, or with Audiostatic as simple silicon dots.

When tensioning a material it is first just tensioned. When You stretch harder there will be a point where the material starts to ´flow´ and the tension won´t increase any more but the material starts to become thinner. With a film You can easily feel this point, since the stretching force doesn´t increase anymore but decreases. Furthermore if You listen to the ground resonance by e.g letting fall a pingpong ball on the film the resultant tone doesn´t get higher. Depending on the film this point is reached between 2% and 4% of length increase. I´d first test the film on this property.
I usually stretch around 2% which gives strong tension.

The good point about the tubed stretcher is, that it can develop a very even tension over the complete area and in every direction. With curved panels You need to stretch only in one direction. You could probabely use a tubed stretcher when You ensure that it stretches only in the straight direction as the mechanical stretcher does. The tube doesn´t have an advantage over the mechanical stretcher in this case as it has in the case of a flat panel with tension in 2 directions

jauu
Calvin

[Audio_idiot]

Hi Calvin,

Thanks for clearing my cloud over the tension part Now I'm crystal clear.

But

d/s means diaphragm-to-stator-distance....usually ~ 0,5---5mm

But in the earlier suggestion of having 250mm x 1,200mm panel, using 1mm gap (stator to diapharm), has already exceeded the 1:100 ratio, am I understand properly that we can get over this by havingpoint support or strip sectionalised the panels to keep the 1:100 d/S ration and we can go as big a panel as we wish with still keeping the 1mm gap?

Cheers

[Zvon]

Hi Calvin,

Your method of Mylar tensioning may be too high. While the high membrane tension is desirable for stability, Mylar service life in vicinity of spacers may be considerably shortened (as seen on many failed DIY and commerical ESL panels).

You tension Mylar to yield ("flow") point and the resulting stresses (membrane stresses) are uniform across the membrane thickness. Close to spacers the membrane is subject to significant curvatures and bendig stresses that should be superimposed to the membrane stresses.

Cyclic loading (read fatigue) of this magnitude (close to yield) are responsible for delamination of coatings in this area (read loass of bias) and ultimately tears parallel to the spacers (read panel rebuilding).


Regards

[moray james]

If you are into experimenting with coatings weldbond is an amazing product to play with. You can find information on weldbond and where you can buy it. Your best possible chance of finding weldbond would be in a craft and hobby store. Regards Moray James.

http://www.franktross.com
I am sure if you email weldbond they will inform you of where you can purchase thier product. I hav even seen it on ebay.

[wolf_moses]

Thanks for your very helpful response, Calvin. Plenty of food for thought.

What about the tendency for foam to rot over time, as in woofer surrounds?

Regards,