As promised, here is the result of sine wave testing
of the ER Audio ESL-IIIB to examine the limits for applied bass signals.

The conditions of the test were as follows:-

Amplifier, 300W SS, thd 0.005% at 40vrms output,

Oscillator, wien bridge, thd 0.05% between 10Hz and 10kHz.

ESL speaker set up with 27 ohms plus 5mH in series network
connected across the input Step Up Tranny primary input coils,
one end grounded to 0V from amp, live end with 150uF series cap,
and with 1.5 ohms series R.

The 150uF and 32mH of shunt input inductance and 27 ohms form a damped
second order input filter to obstruct very low F from the speakers.

The following voltages were able to be applied with
less than 2% or audible distortions.

An oscilliscope was connected to a microphone signal
which confirmed the gross distortions which occured above the applied
voltages
listed below 220Hz, and also confirmed the clean undistorted signals
above 220Hz.

220Hz and above, 20Vrms OK.
140Hz, 4Vrms, NOT OK,
100Hz, 3Vrms,
85Hz, 1.7vrms,
70Hz, 3Vrms,
50Hz, 2Vrms,
44Hz, 0.7Vrms,
35Hz and below, less than 1Vrms.

The distortions heard coming from the speakers
were either sharp increases in distortions or what sounded like buzzes,
or resonance provoked artifacts.
waveforms from the mic confirmed what i was hearing.

The voltage figures would be a lot worse if there was no LF reducing
input filter.

The performance at bass F compared to my dynamic speakers is truly
100% dismal and unnacceptable, and these speakers just don't like bass
signals at all.

EHT was set at a mild -2.7kV level.

The poor sound heard during last saturday's testing with music is due
therefore
to these panels just being completely unable to handle any bass signals
adequately
below 200Hz.

There is a chance the membranes are being pulled off centre but without
being
pulled right over against a stator so that might explain the buzzes.

But to the best of my ability, the panels have been constructed as per
the dimensions
set by the materials in the kits and its not possible that the distances
either side of the membrane
to stators is grossly different when the membrane is uncharged with EHT
supply turned off.

It is very hard to tell if any parts or whole of the membrane is being
pulled off centre just by gazing at the darn things.

So now an effort will be made to configure the panels for a second order
cut off
at 250Hz, and my bass bins connected to replace the bass produced by the
ESL,
and they should perform well, but with no change to low sensitivity.
so a suitable drive to the bass speaker will have to be devised
if I can find a suitable LF transformer, or use bi-amping
with appropriate filters.


Patrick Turner.