Posted by Roger West on January 28, 2003 at 15:08:48:
Dear SLOG,
This is the first time that Sound Lab has contributed to the SLOG site. In
following the dialogue on SLOG we are aware that there has been some concern
over some issues lately that we feel are important enough for us to address.
We have been reticent to become involved directly as we respect the right of
Sound Lab owners to freely state their opinions without us being accused of
a conflict of interests in what we might contribute. However, we have been
invited to speak up at this time in order to shed light on the prevailing
issues.
One issue is that it has been speculated that we have started using a
"porous mylar film". In fact, we are using the same roll of mylar that we
purchased six years ago. The film is so thin that a 50 pound roll lasts for
years. I've never heard of "porous mylar" and I'd be interested in learning
what it is. We use Type C mylar, which is one of the most refined grades.
It is mainly used in the manufacture of capacitors.
Another issue is that some speakers have been reported as having lost
efficiency or are in the process of doing so. The speculation has been that
Sound Lab has been losing quality control and its products are not what they
used to be. The truth is that there were indeed two problems that resulted
from the introduction of two new technical features which were intended to
improve our products. Furthermore, the truth is that these two problems
have been isolated and corrected and, as a result, our products are indeed
better than ever. One problem had to do with a component that slowly failed
in the new high-energy bias supply introduced last year and the other had to
do with the limited introduction of a new insulating material that failed,
which was introduced about a year and a half ago. I would like to address
both of these items in some detail in order that both the problems and their
solutions are clearly understood. I should mention that the scope of the
problems was much smaller than one would believe after reading the comments
on SLOG. The numbers of speakers involved were a fraction of the total
products manufactured. Hopefully, my comments will put speculation to rest.
Concerning the bias supply problem, initially we talked with a few customers
and from their comments it appeared to us that the bias controls were
failing. A few bias controls had indeed failed and we felt that, since we
assumed that the bias supply was reliable, sending new controls to replace
the original ones should solve the problem. It was anticipated that this
would also save customers the inconvenience of having to send backplates to
us for repair. Our best guess was that possibly line transients could have
pushed the controls past their limit. The circuit was revised to take
stress off of the control, and new controls were sent to the customers
involved, with instructions on how to install the new circuit. The results
were mixed. In two cases the new circuit solved the problem but there were
a few cases that didn't make sense unless the latest bias power supply
circuitry was at fault.
Having the dust settle from our involvement at the Consumer Electronics
Show, I was able to spend time to look deeper into the problem. I found the
source of the seemingly unsolvable bias problem in a DC to AC step-up
converter that we purchase from another company. This circuit, which is the
heart of the bias supply, employs a tiny step-up transformer. Upon
inspection of a defective unit, I found that the secondary coil of this
transformer was open. Upon taking the transformer apart I found that the
attachment of one of the secondary coil leads was burned away from its
terminal and that a carbon track had been created, which made a
high-resistance path to the terminal. This fit the circumstantial evidence
perfectly. Customers had reported that the bias potential slowly reduced
until the control was advanced as far as it could go and that the speaker
was still losing efficiency. I took a second defective transformer apart
and found exactly the same thing, the same lead and the same terminal. The
only difference was that the carbon path was not as extensive as that of the
first unit, which strongly implied that it could be a progressive situation
just as the customers had stated. Close examination showed that the lead
wire to the open terminal was intact before the carbon trace. This
indicated that the transformer coil, itself, was not failing as there was no
charring on the coil. It appeared to me that it was an attachment problem
of the lead to the terminal. The most probable explanation is that in some
units the lead isn't reliably soldered to the terminal and that the high
voltage at this point in the circuit easily jumps the small gap and starts
the burning process. As proof of this theory I found that a small
percentage of the transformers didn't show continuity on the secondary wind
using an ohm meter between the terminals. These units would surely fail.
The percentage of units showing this open circuit was fortunately small, so
I don't expect that there will be many failures.
The vendor of the converter has been contacted and is looking into the
problem and assures us that it will be quickly solved. In the meantime, we
are doing an accelerated test on some of the converters that we know are OK
to test the theory that if continuity is indeed present between terminals on
the transformer secondary, that they will work properly indefinitely. This
is supported in that the large majority of the circuits in the field are
doing fine.
In retrospect, we could have found this problem sooner if we had demanded
that the backplates be returned to us for inspection when we first heard of
the problem. This will be our policy from now on. If any customer is
experiencing slow degradation in the sensitivity of their speakers, please
send your backplates to us for inspection. If your speakers emit a
crackling sound when the bias control is advanced, then your backplates
should be OK. Before shipping your backplates, please contact us first for
directions on how to properly package them for shipment in order to avoid
shipping damage.
Probably due to the problem described above, the notion that Sound Lab
quality control has been permitted to degrade has been entertained on SLOG.
I can understand that this is one possible conclusion, but it is not the
correct one. If the first backplates that exhibited the problem were
returned to the factory, the problem of degrading sensitivity would have
been solved almost a year ago. The most logical conclusion would be that we
didn't insist that the backplates be returned to us, and that our intent to
try to have customers fix the problem in the field was not wise. I predict
that when the defective units have been replaced by units that are proven to
be good, there will be no more incidents of this problem.
Concerning the second problem, about two years ago we decided to try a new
stator insulation material on a few speakers. We felt that this new
material, a type of nylon, was superior to our original material and was
worthy of a limited field test. We carefully tested this material to our
satisfaction, and it appeared to have all of the proper electrical
characteristics along with a greater resistance to abrasion compared to the
original material that we had been using for over 20 years. Several pairs
of speakers were built using the newer material, and after a period of time
(weeks to months) we started receiving reports that the material was
failing. To me, this was astonishing as we had no indication of this in our
lab tests. We immediately started running some accelerated endurance tests
on the material (higher than normal bias and signal potentials) and we
confirmed that over an extended period of time the nylon started giving off
a distinct presence of ozone which, due to its powerful oxidation effect,
led to the ultimate failure of the material. Apparently, the porosity of
the material was such that it was able to initially handle the high
potentials involved, but that it also permitted air to permeate it which led
to the destructive ozone production.
Permit me now to back up in time. Since the inception of Sound Lab in 1978,
we have always looked for better materials with which to insulate the stator
electrodes of the panels. About three years ago, which was well before the
use of nylon, we tested a promising material that we had obtained from a
specialty extruder. At that time our concern was focused on the effects
that humidity had on the stator insulation. Since this particular material
was noted for its extremely low moisture absorption, a pair of speakers was
built and shipped to a customer who lived in an area that had a challenging
environment. The results were very positive, but due to the significantly
higher cost of the material, and the fact that our standard material was
actually quite good in humid climates, we didn't pursue this material
further. However, we did make note of the extremely low hygroscopic
characteristic of the material along with some other of its attributes.
Back to the present. When we became aware of the nylon problem we did two
things. First, we started a program of rebuilding every unit that used the
nylon insulation. Secondly, we decided to look again at the material we had
sent to Singapore three years earlier, since it has survived the harsh
salt-air, humid and hot environment as well as the long, very cold (-70 F)
air-shipping phase. The company that made the material was contacted, and
after some refinements (alloying) of the material we ordered a rush sample
to try. We received the material and immediately gave it an accelerated
endurance test. No problems were found. The decision was made to go with
it instead of the original material. The new material not only had superior
moisture resistance, but it had superior electrical characteristics and was
very inert to most chemicals, including strong acids. Furthermore, it is
very tough and is very resistant to abrasion, which was a significant
improvement over the original material. We used this material in the
rebuilding of the speakers that had used nylon. We felt very confident that
it was the proper choice.
With solid statistics to back me up, I can say that we made the correct
decision. With over a year of experience (actually three years if the
Singapore units are considered) the results have been most gratifying.
What's astonishing is that a pair of M-1s (or A-1s/U-1s) use more than half
a mile of insulation, and we now have many miles of the new insulation in
the field with great results.
In order to eliminate any speculation that the new material has resulted in
a loss of sensitivity, we compared a U-1 panel, using the original material,
with an identical panel using the new material. Armed with a calibrated
real-time analyzer and a calibrated sound-level meter, we compared the
sensitivities of the two speakers, balancing acoustical factors and
carefully equalizing microphone distances. The panel with the new material
consistently showed a slightly higher sensitivity of 1.2dB. This was
demonstrated to several people in our lab with the same results. The
slightly higher sensitivity of the newer material is within experimental
tolerances, so we can at least conclude that the sensitivity of the new
material is, indeed, consistent with that of the original material.
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.
We, at Sound Lab, are committed to continually look for ways to improve our
products. I suppose that there is always an inherent risk factor in this
process. One is faced with the choice of not attempting to improve
something that works acceptably or to take a calculated risk in trying new
procedures, materials and designs in an attempt to offer superior products.
With amplifiers, cables, music sources, etc., continuously improving, we
really have no choice but to continue research and development if we wish to
keep up with other technological advances in our field. We attempt to never
release a change until we are confident that it represents a genuine
improvement and that we have fully done our homework. However, if a change
results in a problem, we are also committed to making things right with our
customers.
It is hoped that this note will ease the fears and suspicions that have
arisen recently. You are invited to contact us directly on any questions or
issues that you may have in order to get first-hand clarification. We are
always open to suggestions that might improve our products and our customer
relations, and we apologize to those who have had to endure the frustration
caused by the problems I've addressed. We are deeply committed to your
musical enjoyment. Thank you for your continued loyalty to our products and
efforts.
Sincerely,
Roger West,
President