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The sad tale of Celestion.

With age it seems like most of us have a habit of repeating ourselves.
We end up almost like parrot constantly repeating our beliefs as a mantra we have formed through our life only now and the modifying our views.
I am probably doing this to the same extent as most others. So here will I have another go at a topic which I have discussed earlier, timbre quality (or lack of it) of reproduced sound; but this time I will attack it from a different angle than before; a historical angel.

I will tell the story of how the Celestion SL 6/600 was born in glory and how its offspring’s died of because Celestions engineers seemingly didn’t understand why it had a magical sound, and therefore took it down the wrong development route.

In the late 1970’s early 1980’s Laser Interferometry was introduced to the loudspeaker engineers, well at least to those who were so lucky that he/she worked for a loudspeaker company willing to invest in this new fancy technology. One of the very first companies to do so was Celestion, they could soon proved what everyone had actually known before that virtually all loudspeakers of the time were run in breakup mode from around 600 Hz and upwards.
It is obviously difficult to know the subjective listening consequences of this but the folks at Celestion feelt that they now had the engineering tool needed to design a tweeter which behaved like a perfect piston up to 19.000 Hz. This had to be a good thing at least it could do no harm!! So on they went, and designed what became the Celestion Sl 6 and its luxury derivative the SL 600. This/these loudspeakers did behave much better than the previous generation of the speakers, and the tweeter truly did behave as a perfect piston from its crossover point at 2200 Hz to its first breakup point at 19.000 Hz.
The reviews at the time was outstanding, everyone loved the little Celestion and all agreed that here was the empirical evidence that breakup modes in drivers destroys the sound, because this was surely the most sweet and natural speaker sounding speaker ever heard; what a glorious sound!!!
The engineers at Celestion must surely have felt the same, but they were not quiet satisfied yet; because, good as they felt the SL 6/600 to be; they knew that it wasn’t quiet perfect. So soon they started to reengineer it into the supposed much improved SL7/7000.
What did bother the engineers at Celestion was the fact that the tweeter of the SL 6 was made of copper which they had originally decided to use because it is seemingly cheaper to produce than aluminium membranes. The use of copper had 2 side effects they wanted to rectify in the new SL 7/700, first it first breakup mode was just inside some peoples hearing range secondly copper is much heavier than aluminium which meant that the tweeter in the SL6 was absurdly inefficient. Instead of making the SL 6/600 absurdly inefficient, they had originally decided to let the treble play at a level around 2 dB below the level of the bas/midrange driver. So the SL 6 basically had a fairly flat frequency response up to the crossover point at 2200 Hz and then it suddenly dropped by 2 dB for the remaining 3 octaves. The engineers at Celstion must surely have felt that this was unacceptable in the long run so; the main change for the SL 7/700 was the use of an aluminium membrane in the treble (and a new surround for the bas/mid driver), and presto Celestion had what had always wanted, a mechanically well behave loudspeaker to beyond our listening capability with a flat on axis frequency response. There must have been a party that evening at Celestions development department, what they didn’t know was that it was more of a funeral gathering.
Within a few years Celestion would be out of the High End segment, they had just killed the glorious timbre of the SL 6/600, from this moment onwards it was downhill all the way.

What had gone wrong?
Basically they had developed a speaker, as engineers have a tendency to do, as mechanical devises, and they had paid almost no respect to what it in the end is all about psycho acoustics. When they had developed the SL 6 they had by chance/accident ended up with a frequency response which integrated wonderfully with most small listening rooms. There has been made loads of research of which in room frequency response listeners fin neutral sounding, these can be found in papers of Floyd o Toole, on Lyngdorf Audios homepage and several other pages.


The findings do not always agree completely but they are actually fairly close; we perceive an in room frequency response as neutral, when the in room frequency response falls slowly with frequency.
With this knowledge let us then take a look at how the Celestion SL 600 did compare to the Celestion SL 700 in John Atkinsons listening room.


Yes the Celestion SL 700 is the superior to the SL 600 in the mechanically sense, but it is seriously lacking in timbral quality.
I will suggest that Celestion still would be producing high end speakers today, if their engineers had realised this at the time of introducing the SL 7/700.


Best wishes from Denmark.
Yes it is a sad story; let’s hope it will serve as a lesson for all those loudspeaker producers out there who produce ever and ever shriller, harder and more pinched sounding speakers. You have already lost the young generation of listeners who are more interested in computers; beware not to loose us, the music loving community who wants natural timbre, warmth, beauty and envelopment, in our speakers.

Best wishes from Denmark.

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Topic - The sad tale of Celestion. - klausDK 06:38:59 04/02/08 (11)


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