[Patrick Turner]

After last weeks trials of the ever so capricious ERA ESL kit panel I
began testing, the 5th attempt to get things to work,
I was a little miffed with noises at bass F and variations in whether
noises would happen,
since the speaker seemed to change from hour to hour.

I kept EHT to -2kV to avoid the discharge noises and stiction,
and have now put in the silicone tabs along the bass panels to damp the
bass resonance.
Without the silicone tabs, bass Fo was s high Q 12dB peak at 41 Hz in my
panel.
But now with the silicone tabs, the SAME kind of bass resonance occurs
with a 12dB peak
but now it simply moved up to 51Hz, something I was sure not looking to
have happen.

Only a truly tiny 50Hz voltage needs to be applied to the panel before
the membrane rattles against a
stator, so in practice, all bass performance is thus quite ruined.

I also had a close look at where the membrane was in relation to the
stators, and tried slightly
springing the stator plates inwards towards the membrane by pressure
with a plastic tool handle
to avoid a shock.
Sure enough, with a low 50Hz signal present I could make the problem
worse, or not as bad by
either slightly benting the whole panel which is taped vertically for
testing to the back of a timber framed
chair. We are talking about very small amounts of bend.

The panel should NOT be so damn sensitive to very slight movements,
or suffer such resonance caused limitations.

A guy I know said place 75mm wide felt strips vertically down the
middles of each bass panel
on their rear side only, thus tending to trap air between stator and
membrane, thus damping
large membrane movements,
but they have to be glued on to the rear of the stators but without the
glue blocking the
holes in the perforated metal stators, so applying glue is a PITA, and
I though I better try the silicone tabs first, before applying the
felt fix, for which of course, knowing my luck, is likely to make
matters worse
in some way rather than better.

No such felt damping crap is applied in this particular way on ESL57, so
why have it on anything I build?

Patrick Turner.

[g0l]

But now with the silicone tabs, the SAME kind of bass resonance occurs
with a 12dB peak
but now it simply moved up to 51Hz, something I was sure not looking to
have happen.


have you considered trying a notch filter to block out the resonant
freaquency of the panel... there should have been compensation in the
crossover with the kit as suplied but with having altered the recomended
tension on the panel it would shift the values for the compensation network
as well.. tho from your description of this kit the manufacturer may not
have done any research into this aspect of the development of this kit...
tho you now are.

[Patrick Turner]

g0l wrote:

But now with the silicone tabs, the SAME kind of bass resonance occurs
with a 12dB peak
but now it simply moved up to 51Hz, something I was sure not looking to
have happen.


have you considered trying a notch filter to block out the resonant
freaquency of the panel... there should have been compensation in the
crossover with the kit as suplied but with having altered the recomended
tension on the panel it would shift the values for the compensation network
as well.. tho from your description of this kit the manufacturer may not
have done any research into this aspect of the development of this kit...
tho you now are.

ERA may indeed have done a fair amount of research and development to
have come to their designs.

But there is no published detailed history of exactly what form the R&D
took,
or any impedance measurments or acoustic response measurements.
The ERA website invites you to assume they have a wonderful product
without any hint of construction difficulties or
performance worries.

To make a notch filter for 41Hz or for whatever LF resonance occurs,
I'd have to have used a bridged T LCR filter, because any other type of
filter
using say an L and C in parallel and in series with the speaker input
would not
give a high enough Q for the resonance.
Maying the bridged T filter would reduce any bass at the LF as well, and
I expected to get
bass at least down to 50Hz, -3dB.

To get a flat resonse with the ESL-IIIB kits, there has to be a total of
400k from each end of the step up tranny sec to two points from which
100k then go
to each bass panel stator. This then flattens the response between 40Hz
and 2kHz,
and the RC is in effect the crossover to the treble panel.
The treble panel then takes over from the bass and as it directly
connected to the
sec at above 2kHz, but its low sensitivity determines what is done
to set the bass levels.

If the treble panel had spacer distance of 1.2mm instead of 2.3mm the
treble sensitvity
would be 6dB higher, permitting less series R between tranny and bass
panels,
making them more sensitive. But the level at 50Hz would rmain unchanged,
and
the LF cut off would be maybe 100Hz, and resonance problems would still
remain.


Using a series LC notchfilter is entirely wrong because it would
offer the amplifier a virtual short circuit at Fo.

I should not have to do all this jiggery pokery with complex additional
LCR
networks at all.

I am seeking advice from a gentleman in Sydney who has been building ESL
and
repairing Quad ESL57 and 63 for 20 years, and perhaps what might be done
to
salvage these kits may be discovered.

Patrick Turner.

[Peter Wieck]

I am seeking advice from a gentleman in Sydney who has been building ESL
and
repairing Quad ESL57 and 63 for 20 years, and perhaps what might be done
to
salvage these kits may be discovered.

Is there any way you might be able to put a slight positive camber on
the diaphrams? The tension will tend to make a negative camber, so
perhaps weighting either end with a dowel at the center-point of each
section might form a camber if done carefully... and that might keep
the membrane just-enough-that-much-further-out to do some good?

Peter Wieck
Wyncote, PA

[Patrick Turner]

Peter Wieck wrote:

I am seeking advice from a gentleman in Sydney who has been building ESL
and
repairing Quad ESL57 and 63 for 20 years, and perhaps what might be done
to
salvage these kits may be discovered.

Is there any way you might be able to put a slight positive camber on
the diaphrams? The tension will tend to make a negative camber, so
perhaps weighting either end with a dowel at the center-point of each
section might form a camber if done carefully... and that might keep
the membrane just-enough-that-much-further-out to do some good?

Peter Wieck
Wyncote, PA

I think the membrane should just remain central between stators
shortly after turn on without any pulling over to a stator,
and without all the noises of discharges.
Trying to camber anything by curving or bending, propping or swaying,
pulling, yanking,
et all isn't an approach I could have any faith in. Its bodgery.
I have close to the same membrane tension as Quad ESL63, and resonance
went from 30Hz to 40Hz, OK, and perhaps some means other than silicone
tabs
need top be applied to control that; I really don't know what works.

My Sydney contact says he doesn't have any problem using 6kV
on his panels with stator spacing of 2.5mm, about the same as with ERA
ESL-III3 panels.

I will take my speaker panel up to him, and we will examine it
throughout; its is easily
dismantled, and if possible we will measure the membrane coating
resistance.

I need to learn his secret, because I cannot achieve this figure of 6kV,
and if I could the problems of low sensitivity would be tolerable,
providing LF resonances are also not a bother.
My contact likes to use a 1:200 step up tranny for his bass panels
instead of the ERA 1:90,
and coupled with the use of 6kV EHT voltage, he manages to get
far better SPL for a given input voltage, without having low speaker
input impedances.

Quad ESL57 have 1:290 ratio for the bass panels, and because the
spaces for midrange and treble panels are 1/2 that for bass, the
mid/treble panels have
much lower EHT, and have 1/2 the drive voltage of the stators, so they
are much more
sensitive than the ERA panels, also because Quad input step up tranny
has much less shunt capacitance to drive.


In other words, he manages to equal or better the general operation of a
Quad ESL57,
and does not need a huge powerful amp just to get enough volts.

The ESL57 only needed a 20 watt tube amp, and ppl I know find the 8 ohm
tap works fine
with a pair, and 20 watts into 8 ohms is only 12.6Vrms.

I need to learn what I don't know about.

Patrick Turner.