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In Reply to: Please describe the "blow-dry" procedure Thanks(nt) posted by Seth Speaks on June 22, 2000 at 22:36:27:
Though there are many mylar panel based planar speakers which might benefit from this process, I want to make it clear that I have direct experience only with Acoustat and Dayton-Wright electrostatics. DO NOT try this on Maggies with ribbon tweeters as those are very delicate little critters and likely would be damaged.Perhaps it would be helpful for me to describe the underlying problem we are trying to solve and to recount how it was that I discovered this process before detailing it. Forgive me if you already know these facts. Virtually all electrostatic and some planars like Magneplanars use mylar plastic as the diaphragm material. The chief advantages are low cost, low mass, insensitivity to moisture and aging, and it's ability to bond with other materials. Unlike other e-stat designers, Jim Strickland sourced his special diaphragms from Ampex. They used a proven tape manufacturing process that permanently bonded a graphite conductive layer to the mylar necessary to contain the static charge. This is one reason why twenty year old Acoustats still function like new. The only downside to mylar is that it stretches over time. Consider that it is only .00065 inches thick according to Acoustat literature. With bass response down to the 30's, there is a bunch of excursion going on and consequently, stretching. The result is that the diaphragms become “loose†over time. They lose some of their transient “speed†and are more prone to bottoming against the honeycomb structure when playing low bass. The effect is quite audible. This is where the hair dryer comes in.
When I first saw a friend “blow dry†his Dayton-Wrights, I was both shocked and amazed at its effect. One of the cells on his XG-8 MK I had failed and he had to install a new one. Unlike Acoustat, however, Dayton-Wright used an unconventional method of insuring that the panels would not arc especially due to their use of very high bias voltages. The front and rear surfaces are sealed with enormous sheets of clear mylar forming a "bag" to contain sulfur hexafluoride gas. Huh? One challenge of e-stat designs is that one can get more efficiency by running a higher bias voltage. Beyond a certain point, however, the voltage is so high that it breaks down the dialectric in the air and "arcs". Whereas Acoustat ran their bias around 5 kv, the D-W designs ran theirs around 8-10 kv if memory serves. Their solution was to seal the cells in an atmosphere of SF6 gas to serve as an electrical insulator. Cell replacement therefore required performing a surgery of sorts. He had to slit the bag in order to get access to the cell. Once the cell was replaced, he patched the bag with some very thin 3M packing tape and began the process of refilling the speaker with the SF6 gas. As a funny aside, SF6 has the opposite property to helium – while transparent, it is heavier than air. If you breathe in some and speak or sing, your voice is lowered. My friend who is also a musician and sings bass for the ASO chorus demonstrated this to me. I still remember when he sang a few bars sounding like Lurch at the Met. Anyway, the now sealed bag was loose. Solution? Bring out the hair dryer. He carefully ran the dryer over the surface of the bag visibly contracting the mylar. In about fifteen minutes, the surface was restored to that of a taut drum.
Move forward in time two years with the introduction of the Acoustat X product. Bob Reiman, the President of Acoustat, and Jim Strickland, the designer, flew to Atlanta to bring a pair for review to the same friend who also writes for an audio magazine. I was fortunate to meet them over at my friend’s house and to hear their incredible new product. Over the course of much listening and many discussions, comparisons with the Dayton-Wrights were inevitable. Strickland was quite proud of his panels and their durability. He asserted that due to the new Ampex bonding technology, they would prove to be far more reliable than the D-Ws which used an exotic liquid for the conductive layer. I think time has certainly proven that statement. Strickland said they performed a similar “blow dry†treatment to the panels at the factory prior to shipment using heat guns to tighten the diaphragms. Reiman even boasted that one could “hose down†the panels with no deleterious effects. No kids, I never tested that theory!
Here is the simple “blow dry†process. I have heat treated my panels well over a dozen times, usually about once a year. I use a standard 1200 watt hair dryer set to high. I hold the dryer at a slight angle about three inches from the panel surface. The key is to keep moving and not to “torch†any area. Move slowly across the entire surface of all the panels, front and back. This takes me about thirty minutes to cover my pair of four panel 2+2s. If you have not already visited the electrostatic speaker site mentioned in an earlier post, you might find it very interesting. I particularly enjoyed the section on the Dayton-Wrights since those are the ones that first seduced me some twenty five years ago.
Here is the link: http://www.geocities.com/hzeeuwe/
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Follow Ups
- Heat Treating Acoustat panels - e-static 12:25:22 06/23/00 (2)
- Thanks very much for the info :-)))) (nt) - Seth Speaks 18:11:14 06/23/00 (0)
- Re: Heat Treating Acoustat panels - Brian Walsh 14:49:46 06/23/00 (0)
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