Martin Logan CLS IIz


This is what a CLS IIz looks like with the black finish. (5’10” author added for scale.) The diaphragms are transparent which is not easily discerned due to the camera flash. For much more information you should visit their site.


The system powering them in Nov ’99. The large, amp-sized item on the top left is not an amplifier. It is a Theta Digital Data II combination Laser Disc / CD transport. To the right is a Rotel RDD-980 transport which I originally bought for my CLS II system. The DAC is a Theta ProProgeny A (left 1st shelf). This DAC impressed me so immensely with its construction quality that I decided to replace the Rotel transport with a Theta transport. The pre-amp is a McCormack TLC-1 (right 1st shelf), and amplification is a pair of ’91 vintage PS Audio Delta 250 monoblock amplifiers (left and right bottom shelf). Later I upgraded to an Aragon 4004 (below).


This purchase was not initially stress free.  The frame split on one of the two panels during shipping.  I ended up repairing it myself.

DamageFront1 DamageFront2

You may have heard that the impedance of electrostatic speakers is very low at high frequencies.  I took some measurements of the undamaged speaker, with and without the power applied.  That’s under 2 ohms at 20 kHz !!!


Varis Audio Manual

This is the retailer’s manual that was given to the original buyer. Not much, but at least it shows the hook-ups for the transformer and recommended frequency range of operation.

Speaker III – The Future


??? 2000

Try different back chambers for the Morel tweeter.

Summer 2000

First prototype cross-over design.
After I buy a house and can do some real mid-range measurements.


March 2000

So far I have only done some computer simulation of crossovers.
I really want better measurements than I can perform in my
living room.
I’m thinking that will have to wait for owning a house, which I
hope to be doing sooner rather than later.

January 2000

The mid-range resonance at 1 kHz looks like a cone resonance,
coating the driver basket with bondo didn’t do a think
except make a mess of a couple of drivers.

August 1999

Mid-range testing.
I noticed what looks to be approximately a 1 kHz resonance during early
mid-range tests.
My guess is that this is from the driver basket resonating.
It may be possible to reduce the resonance by coating the basket with
a thick layer of bondo or other material.

July 1999

The mid-range positioning tests were quite a surprise.
I did not anticipate any of the results.
Using the results, I have built a third prototype cabinet.
The basic driver measurements look good, so its time
for port tuning and crossover design.


February 1999

The diffraction tests were basically null results.
I did learn that the mid-range position on the baffle may affect
the tweeter’s response.
The next series of tests will be to determine a good mid-range position
relative to the tweeter.

January 1999

Tried different cabinet types and front baffle dimensions.

July 1998

First prototype cabinet completed.

Copyright © 1998,1999 John Lipp