As part of my commitment to designing quality audio equipment and providing excellent repairs of existing speakers and electronic components, I have invested in a wide variety of measurement tools. For measuring the frequency response and the health of the Quad ESL's, I use PC based measurement software, and either a B&K 4133 microphone or a calibrated Panasonic electret microphone. This measurement capability allows me to constantly monitor my speaker rebuilds to provide consistent, high quality panels that match the original speaker performance as closely as possible. This capability also allows me to assess problems with existing speakers and provide rebuilds which repair any specific shortcomings without the expense of unnecessary repairs.

All measurements are taken 120 cm away from the speaker (front grille), with the center of the speaker and the microphone 100 cm above the ground. the speaker is tilted so the panel is normal to the microphone and perpendicular to the ground. A 3.2 mS time window is used for the measurements to provide a "pseudo-anechoic" response down to about 300 Hz. Panel measurements are taken with my measurement jig and without any grilles.

The original Quad ESL loudspeakers are now at least 22 years old and can be up to 46 years old. Even speakers which have been lovingly taken care of can show the effects of age. The measurements below show the various states that an un-rebuilt Quad ESL can be in, as well as how my rebuilds compare to healthy original panels and how other companies rebuilt panels compare to the original panels.

Unrebuilt Complete Speakers:

These measurements show the various conditions that seemingly undamaged speakers can be in. These measurements illustrate the extent to which non-damaged speakers can change over time. So in many cases even speakers which appear to be in very good shape can not provide the level of performance that was capable when the speaker was new.

Unrebuilt Panels:

I've had the opportunity to measure a lot of original panels as part of my rebuilding services. Here are a few panels which exhibited no signs of damage and appeared to be working well with a brief listen. These measurements show the range of differences that can be expected with aged stock panels. NOTE: no damaged panels are shown here.

Panel Rebuilds:

I have been measuring all my rebuilt panels to insure consistency and to insure that my rebuilding techniques remain constant and the end product is as true to the original as possible from a performance standpoint. I have measured samples of two other panel rebuilders. It should be noted that these are small samples (2 panels and 1 panel), and may not be a true representative sample of each companies products. That said, I'll let the results speak for themselves:

Quad of Germany (one panel)

This panel looks markedly different than the original Quad ESL panels. The stators are made of a different material (FR4 fiberglass?) and is constructed differently than the original stators. The wiring to the treble panel is via a terminal strip rather than leads coming through the dust cover. I really like the construction of the German panel when compared to the original panel construction. The output level of the German panel is about 3 dB low across the midrange and does not exhibit the rising response of the original panels.

One Thing Audio (two panels)

These panels are rebuilds of existing Quad treble panels. They are very professionally rebuilt and look quite good. The treble panels use nylon attachment devices rather than nuts and bolts. The diaphragm coating material is quite visible through the holes in the stators. The two panels measure differently, particularly in the treble region, and I'm concerned about the panel to panel consistency. I would like to get another pair of panels to measure. Measurements were repeated to verify that it wasn't a problem with my technique or setup.

SDS Labs (me)

As I stated earlier, my measurements have guided my rebuilds, both in terms of rebuilding techniques to maximize consistency, and rebuild materials which produce results which are most like the performance of the original panels.