Phil Allison wrote:
"Serge Auckland

I wonder if anyone knows how Electrostatic loudspeakers can have any sort
of bass response.

An ESL is a doublet that radiates equally front and back. With a normal
cone loudspeaker on a finite baffle, the bass starts to roll off at a
frequency whose quarter-wavelength corresponds to the smallest dimension
of the baffle. Looking at the dimensions of, for example, the ESL63, the
bass should start rolling off below about 320Hz,


** Huh ???????????????

The width of an ESL 63 is circa 1 metre.

A wave of 4 metres has a frequency of 80 Hz.



but in fact is maintained down to a -6dB point of 34Hz.



** It really does too.

Cos it is taller than 1 metre and there is little back to front sound
transfer - a huge SPL null exists all round at 90 degrees to the central
axis.



How is this possible?


** You cannot do math - or much else, can you.

BTW:

There are many examples of modest sized speakers which radiate back and
front and yet have quite good bass output.

Ever seen a combo guitar amplifier ????

Most have open back cabinets with 2 or maybe 4 x 12inch speakers fitted
neatly inside - so are less than 1 metre square. Output is well
maintained to at least 80 Hz and is still strong at 60 Hz. Been testing them
with sine generators most of my life.

Also, the famous Wharfedale SFB-3 open back 3-way speaker of 1956:

http://www.troelsgravesen.dk/Wharfed...iles/SFB-3.pdf

Pre-dates the Quad ESL57.

Response down to 35 Hz is claimed.

Magic ??



Yep, look out for the books Gilbert Briggs wrote about loudspeaker
design. Also in the case of the SFB-3 (and for that matter my own open
baffle speakers) the tapered side panels also increase the front/back
length.

--
Nick