The original Quad diaphragm coating
My original intention was to see if the conductive coating that Gary had come up with was truly the best coating to use for the Original Quad speakers. So I can offer my customers the best possible product I can. I ordered the Phenol, picked up the nylon line, studied the mechanics of mixing up the coating and began my project. As most of you know I am very close-mouthed about the techniques I use because of a promise that I made to a dear friend of mine. However, Gary's work is a public document. So here is my report on his coating for the Quads based on my findings while experimenting with it.
The first discovery I made was that Phenol in crystal form is not something that is found in a corner drug store. In fact, most chemical companies do not stock it. All the companies I found that sold Phenol in an acceptable grade were either too difficult to deal with, or required such large quantity minimum orders that it was not reasonable to order from them. The least expensive supplier I found had industrial grade Phenol at $55 a kilogram. They were rather difficult to deal with and I preferred high grade Phenol for my R&D. I finally came across a company that allowed me to order only 125 grams, that was able to ship to me in a reasonable amount of time. They were the nicest people. I ordered the Phenol from Alameda C&S, Inc. right here in Idaho (208) 463-8358. It cost $80 for the 125-gram bottle and an additional $30 handling fee for hazardous material. I believe it's possible to order the same Phenol directly from the manufacturer for $62 + shipping.
Before starting there were a couple recommendations made to me. The first was to have a fire extinguisher and a Phenol antidote kit (which consists of caster oil or any vegetable oil). When I received the Phenol I stretched my diaphragm and followed the directions that Gary had laid out exactly. I mixed 25 grams of Phenol in 150 ml of water (I used tap water the first time). I carefully weighed the nylon line, making sure there was exactly 5 grams of line. I stirred the mixture until the nylon dissolved. I then spread the mixture on the diaphragm. I reduced the heat on my hot air gun so that I did not heat shrink the diaphragm and dried the moisture off. I turned the diaphragm over and repeated the procedure on the other side. I then put the speaker together and began testing.
I tried several different ways to apply the coating on the diaphragm. The first deviation I tried began by soaking a large mouth Mason Jar lid in Acetone until all the rubber and varnish came off of the lid. I then made up another batch of Phenol/Water/nylon. This time I dissolved much more nylon in the mixture until it was so super saturated that it had a bunch of "snot" in the bottom which is a layer of phenol/nylon (please be careful because the phenol is more concentrated in this layer). I then placed a drop of the "snot" on the jar lid along with a drop of water and rubbed it into the towel. After it was worked into the towel I rubbed it onto the diaphragm in small fast circular motions. This method of application appeared to give a more consistent coating. I experimented with other changes in an attempt to make the coating more consistent.
The technique I ended up using to achieve the most consistent coating was to take a drop of the "snot" and water and work it into the towel. After working it into the towel I moved to the diaphragm and rubbed somewhere off of the speaker diaphragm until the consistency of the coating was correct. I then moved onto the diaphragm in a very slow back and forth motion, trying to avoid creating any friction. It takes so much time that by the time I have finished the second diaphragm the first is usually almost dry, without using a heat gun. You need to be very careful that you do not get the coating too thick (consequences of this is discussed later). If it is too thick, you will have to strip it off and start over again.
After the first couple of speakers I tested I noticed that the efficiency was up close to 5db from an original panel fully charged. The re-diaphragmmed panels seemed to charge instantly which was in total contrast to Gary's findings. I left the speakers running all night. When I tested the speakers in the morning the efficiency was back down to where it should have been. I found that the discrepancy of efficiency was due to using tap water to mix the Phenol. When I used distilled water to dissolve the Phenol I had much better results. The results were so dramatically better I recommend that you do not even consider using tap water. Tap water has lead, minerals, chlorine, etc. depending on where your water comes from. I found these things do affect the outcome. In case you are considering putting a thicker coat on the diaphragm to increase efficiency this will NOT work! Discussions with Gary indicated that he seemed concerned about decreasing the resistance of the diaphragm by having the coating too thick. This has the potential to make the panel hum. Though that is a great concern, it is the least of your troubles if you get the coating too thick on the tweeter. You can load the diaphragm down and roll off your highs significantly, especially if you are using 6 micron or thinner film.
I sat down in front of the speakers to conclude if the new coating was truly better. I allowed the speakers to charge a good 24 hours to make sure that both sets of panels were fully charged. I had to first turn on the pink noise and check the signature of both speakers. The first thing I noticed was that the very top frequencies were rolled off a bit more than my coating. I kind of expected this because the nylon is a much thicker coating than mine is. What I did not expect was that when I moved the mic up and down close to the diaphragm I found that the output was more consistent across the diaphragm from the nylon-coated speaker.
The first question that I had was, "Does the slight frequency response difference really sound better? Or worse?" The speakers with the nylon coating seemed to be more alive and have better control over the diaphragm. As I was listening to the nylon-coated speakers I began to wonder about the top highs I had measured earlier that were a little more rolled off. The highs did not sound rolled off at any time during the listening test. I hear all the time that "The Original Quads do not have the highs that I remembering them having." I wonder if this is from the diaphragms and the original coating getting old causing them to not have the response they used to have. I do not know what it was like to witness a brand new pair of Original Quads off the assembly line and burned in proper. From what I was told the Quads efficiency drops by 15% over the first 5 years then stops decreasing after that. Also the tension of the diaphragm relaxes a bit, lowering the resonate frequency. Plus there is some degradation of dampening tapes used in the high frequency panels. (Another possibility is that electrostatic highs are so natural and smooth. People now days are so used to listening to over exaggerated highs to try and give a feeling of "airiness" to the common dome tweeter. Which makes the listener THINK the highs are rolled off). So if you have a 15 - 20 yr. old speaker that you blew a tweeter out on and you were able to order a new panel with all original parts, the new panel should sound better and not the same. If you were to rebuild a tweeter it shouldn't sound the same, but should sound slightly better as well. That is what I feel that this coating does. It seems to breathe new life into the panels and make them sound new again.
The nylon coating that Gary has come up with is the single best conductive coating for the Original Quad speakers that I have used to date; it beats soap, graphite, and everything else I have tried. It seems to work well only in the Quad type designs. If you need to match a more conductive coating it does not work that well. So it will not work in all situations. There are some drawbacks to the coating that I can think of, they would be as follows:
- It does roll the extreme highs off a bit more than a thinner coating material with the same conductivity. **NOTE** The thinner coating has a slight rise from the original. The nylon coating makes the highs exactly the same as the original coating. The loss of highs from a thinner coating is not bad it is only a couple of dB @20KHz, and it is not something that is heard during a listening test.
- The coating that I was using is a coating that would last as long as the diaphragm material (I was told by the distributor that it was 1000 years) and this coating lasts about 20 years.
- The chemicals used to make the coating take a great deal of care at best to handle.
However, the advantages of the coating well outweigh the drawbacks. Anyone that is rebuilding a Quad '57 panel would benefit from the use of this coating. The first time charge on a pair of tweeters does not take long at all. The first time charge on a pair of woofers takes a very long time. The speakers are playable after 5 minuets, however they really start to sound better and really come alive as more time passes during the first 24 hours. There is not a problem with electrons falling off this diaphragm. After the first initial charge, they seem to charge much faster (The driver is a capacitor, so it may be that it is just holding a charge). The speaker will charge more quickly if you power it up immediately after rebuilding.
** The following is speculation on my part **
At that time all the water has not yet evaporated from the nylon causing the charge to distribute across the diaphragm more quickly.