Serge Auckland wrote:

"Nick Gorham" wrote in message
...

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


The width of the ELS63 is 66cm, a wavelength of 2.64 metres has a
frequency of 130Hz (I mistakenly multiplied by 2, not 4 in my original
post, my apologies.) So, I would expect the ELS63 to have a reducing
bass output below 130 Hz. Why doesn't it? What about other ELS
loudspeakers, like the Dutch Audiostatic that were about 30cm wide, and
yet had a decent bass response. What about the Magneplanar MG3, which
were not electrostatic, but nevertheless doublets, and had excellent
bass response.

What am I missing?

S.



I think yopu have to take both path lengths into account. Also you need
to consider that as the baffle bass response drops off, thats when the
room gain starts to kick in.

As it happens, Septembres HiFi world has a article on the SFB-3 with
some measurements. They find that the bass starts to roll off at about
100-120hz if you discount the effect of the room.

If you can't find a copy let me know and I will try and scan it in.

My OBs use a 15% base unit, the front panel is aprox 20" * 48" with
tapering sides that are 24" deep at the base up to zero at the top. They
measure flat (ish) down to about 40hz in room, when the bass starts to
fall away at about 6dB/Octave

--
Nick