As part of my commitment to providing the best Quad speaker rebuilds possible, I have invested in, and use a variety of measurement tools to assist me. Electronics are tested using high voltage probes, signal generators and an oscilloscope. For panel testing I use a calibrated measurement microphone and either Fuzzmeasure or software that I have written specifically for speaker testing. I test my speaker rebuilds at several points in the process. I often start with an "as received" measurement, then I will measure the individual panels (both before and after dust covers on the original ESLs), and then I measure the speaker when the panels are installed before I put the grilles on. Then I do a final measurement after a break-in period. I provide this final measurement to the customer as part of their invoice.
I primarily use completed speaker measurements as a verification of performance, and matching. I have a setup for the speakers and microphone that works well in my shop, but I have not gone to great lengths to eliminate room artifacts in the data from the measurement.
The original Quad ESL panels have not faired well over the decades. The bass panels often suffer from corrosion. the treble panels are often damaged from overdriving or the plastic has sagged or deformed over time. This deformation can be particularly bad if the speakers were stored in a hot attic. In addition to the vagaries of time, the treble panels on the original ESLs were never made to the same level of precision as the modern Quad panels are. So panel to panel and speaker to speaker matching is typically not quite as good, but with care during the rebuilding process, very good results can be had.
