Posted by Roy on February 08, 2003 at 07:51:15:
I have been away on business for almost 2 weeks and I have missed the recent discussion on “Sound Lab’s answer to recent comments on SLOG”.
Many of you will know of the problems that I have been having with chronic stator insulation breakdown in my A3 speakers. I am in the unique position of having a pair of 1994 vintage panels and also a pair of new panels that were delivered early November 2002. Close inspection of both vintages of panels has given me knowledge of the change in manufacturing procedures between the two.
The text in the Sound Lab response misses out important issues that have a direct reflection on the quality of construction of the panels that were delivered to me early November 2002. It is my opinion that the panels produced in 1994 were in some respects manufactured to a much higher standard than the new panels delivered to me early November last year.
My newly delivered panels had a base response that only went down to ~55Hz. Sound Lab recommended that that the best solution was to heat treat the panels so that the diaphragm would relax. The heat treatment had the desired effect and the response of my panels went down to about 30Hz. After a while I had my first stator tube breakdown and now I am on breakdown number 10.
On reading the Sound Lab response some of the text says………
“During this last year there have been other improvements that do not show
from the outside. We have now started using water-jet machining to cut out
the components of the panel's infrastructure. The benefits are closer
tolerances, no machining chatter marks, and no heat produced during the
machining process which can distort the material and create carbonized
leakage paths. Also, in key high-stress joints in the framework, we now use
an industrial cyano-acrylate adhesive that is considerably stronger than the
standard plastic adhesive that was used for years. Furthermore, the
horizontal ribs that support the stator grids have water-jet machined
precision notches to support and critically align the stator wires. These
improvements have improved both the strength and precision of the panels”
The horizontal Ribs in my October manufactured panels are NOT notched to support the Stator Tubes. The Ribs have been manufactured on a Routing machine and the Stator Tubes are glued to flat surfaces on every Rib, that is 2,880 unnecessary glue joints and points of STRESS and virtually every single breakdown that I have had has occurred immediately next to a glue joint. My experience in designing and building special purpose machinery for over 30 years has given me the necessary expertise to make valid judgements on the manufacturing techniques used by Sound Lab. I felt qualified to enter into extensive discussions with Sound Lab about reasons for the continued breakdowns and in particular the poor mounting technique used for the Stator tubes.
On the 23rd November I emailed Sound Lab and suggested that the Stator Tubes should be pocketed into the Ribs and that the tubes should be glued at one end only so that the remainder of the Stator Tubes would be free to side slightly within the series of Ribs when the frame structure expanded and contracted with temperature changes. Mounting the Stator Tubes this way would prevent the STRESS problems at each glue joint to the Rib and I felt strongly that this was a serious factor that contributed to the Stator Tube breakdowns that I was experiencing. I was also suspicious of the effect that the glue would be having on the surface of the tube. The HDPE Stator Tube used in these panels is notoriously difficult to bond to. Another factor that I think contributes to breakdowns is that coiled tube is used to slide over the stator wire. The tube used is considerably stiffer than the previous flexible PVC tube used, this new tubing would be in STRESS when straightened and passed over the stator wire. Purchasing straight cut lengths of extruded tube costs no more than coiled tubing. I also explored other factors that related to the actual Stator Tube that could be responsible for the breakdowns with my speakers.
Finally, Sound Lab stated that the responsibility for these breakdowns was not theirs because I had carried out the heat treatment process and in some way this heat treatment process was responsible for the breakdowns. This was the process that Sound Lab recommended I carried out to rectify the poor base response. At no time did Sound Lab say that if I heat treated my panels then Stator Tube breakdown would be likely to occur. I found this get out unbelievable.
LESSON. Do not carry out heat treatment if Soundlab recommends that you should do it.
At this point I stripped off the cloth covering the old 1994 panels. When I inspected them I was flabbergasted, the Ribs used a pocketed method of holding the stator tubes in position, Not a drop of glue used on the series of cross braces except for one end. On the 8th December I mentioned this to Sound Lab, they told me the old 1994 cross braces were laser cut and the reason given for discontinuing this method of manufacture was that a sharp edge occasionally caused a breakdown. I inspected these crossbraces very closely and they looked well made to me and I could not see a single sharp edge that would have caused stator tube damage. Even if one or two were present I did not see why the process of de-burring should be too difficult or excessively time consuming, even with a high number of slots.
So it would appear that since my communication pushing for pocketed cross braces on the 23rd November and Christmas Sound Lab have implemented this notched Rib method of construction. Talk about moving fast. Anyway, thank goodness for that. Quality methods of construction and good practice have returned.
I am sure that Sound lab speakers will be much more reliable in the future because of this change.
Sound Lab initially offered to re-build my panels if I would pay the cost price to do so, incredible. After I strongly declined this offer they said that they would repair them if I would bear all the shipping costs both to and from the UK. After that they said that I would have to pay the cost of shipping the panels only to them. It is my opinion that I should not have to pay anything at all. I am in this mess with my speakers through no fault of my own and from the minute I opened the boxes.
I am still left with a glued Stator Tube to Rib method of construction that is producing no end of breakdowns with the type of Stator Tube used at the time.
Time to listen to some music from my fabulous sounding but somewhat unreliable speakers.
Roy