(A QUIET WORD TO OUR CUSTOMERS THAT COULD BE TO EVERYONE’S BENEFIT – WE WOULD URGE YOU TO READ ON!)

Over the years we have made no secret of the fact that we consider the Quad ESL-63 (and its many derivatives higher in the range) the best transducer on the planet.  It is superb because it was designed properly in the first place. It was a less hectic world in those days: not many producers now would spend a decade perfecting a design with all the cost and time involved. There were minor modifications: one being a redesign of the audio step-up transformers to improve the  speaker’s efficiency (this occurred in the successor to the ESL63, the 988 series). Beyond that – except some improvement in the protection circuitry – the design remains unchanged.

The “secret” to this marvellous design is the novel and ingenious panel design. Most models in the range use four of these panels (the taller versions six). The annular designs of the audio electrodes (sometimes called stators) enable sound to reach the listener which closely imitates the way sound reaches the human ear in the real world. That is the pure genius of the design – or rather that and some clever electronics which govern the amplitude and frequency the annular “rings” and bass areas receive.

To achieve transparency and accurate information retrieval, it is necessary for the perforated stators to be very thin (just 0.5mm). Down the centre of these two drive stators is a diaphragm which utilises a special coating. The object is that the diaphragm only moves – not the stators which are glued to a solid grid. This latter requirement is perhaps the single weakness of the design, because over the years the diaphragms are required to vibrate billions of times and at different frequencies and amplitudes in response to audio signals generated by the stators.  In time, this can result in  failure of the glue which holds the stators firm. This usually causes the stator to lean into the diaphragm and “sparking” will occur, causing severe crackling in the speaker. Protection circuits are quick to shut the speaker down but usually the damage (to the delicate diaphragm) has already been done. It should be possible in an age where glues can be developed and “stress-tested” to cope with most situations and conditions, for this weakness to have been addressed (the car industry is the major consumer here and an industry has grown up to meet these requirements). However, Quad’s panel – while it can last for many years – seems to have missed out on the theoretically “indestructible” glue and visually declares the end of its life-span by turning into powder form.

So what is our solution to the problem?  We are currently working on the ultimate solution but in the meantime we remove the residue of the old glue and substitute a glue which boasts a certain flexibility. Admittedly we have had only nine years to collate our findings, but so far we haven’t come across a single panel where our glue has failed – the glue merely having hardened somewhat in the passage of time. Only a powerful glue solvent will get rid of the glue that we have used.

So what’s the point of this discussion ?

The point is this: the 4 or 6 panels operating in a Quad speaker are all subjected to the same stresses. The wear-and-tear on them is approximately equal. So the common-sense factor must be applied very stringently: if your car tyres had clocked up fifteen thousand miles, would you insist, for reasons of economy, in changing the one tyre which is now illegal?  “I’ll change the others when I can afford it.”  That seems pretty idiotic and certainly the most expensive way of dealing with the problem in the long run. Yet time and time again, we get Quad owners who will instruct us, “Just do the work that is necessary”.  (Thus implying that some of the work we undertake is unnecessary!)   The question is also sometimes asked, “If your glue is so superior, why can’t you use it on the other panels that might still have some life in them?” The problem here is a purely technical one: When our glue is applied to a rebuilt panel, weights are applied for 24 hours to ensure that the delicate stator lies perfectly flat. Obviously this can’t  be done on an “in-situ” panel – and even if it was attempted, some of the glue would find its way onto the diaphragm. Not good!  In short, there is no effective solution that does not involve replacing all the panels. Yes, there is a cost: but it’s nothing compared to the cost of returning the speakers to us every few months when yet another panel gives up the ghost!  Changing single malfunctioning panels is false economy in the extreme. Some of our customers have learnt this the hard way.

The above applies to speakers that have their original panels and have been in use “from new”.  In some instances one or two panels have been changed over the years.  If, after tests, these meet our criteria – these are panels you won’t have to pay for (obviously). So it’s not all bad news!

Good listening to the world’s most accurate sound transducer!

Ron Best, June 2019