And then there were four

The advantages of stacking Quads vertically were recognised early in their career. It immediately improves the apparent bass, and as they’re a vertical line source you get the much greater presence of the larger area, without any compromise of the stereo image. This would never work with the later ESL-63 with its more sophisticated attempt to recreate a point source.

‘Another thing people like to do is to use two of our panels, one above the other. This is quite reasonable because it is really a strip source, you can extend the strip source without deteriorating anything. All you do is add 6dB at the bottom and 3 dB everywhere else. It gives you a louder sound, a more impressive sound. That’s all right.’

-Peter Walker in Audio Amateur, 1978

It’s been frequently attempted by individual enthusiasts and searching will bring up lots of pictures. The only commercial stacks I know of were part of the expensive ($30,000) Mark Levinson ‘HDQ’ system. This consisted of a pair of stacked Quads with Decca ribbon tweeters between the panels, along with two big Hartley subwoofers and several (6?) of Levinson’s heavy ML-2 25W amplifiers:


This rather grainy image shows Faye Dunaway’s stacked Quads, date unknown:


They seem a bit close to the wall – and the whole room looks very shiny and acoustically reflective: I’m not sure they would have been at their best. Visitors probably gazed at her instead:


Here are two interesting downloads on stacking quads.  For both of these links I am indebted to the most thorough and indispensable of ESL-57 sites online,

Double Quad”  T. Farrimond, Electronics Today International, 1975

Quad ESL Mods and Stacking” C. Beeching


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