On the Bench

For all distortion tests, a bandwidth of 80 kHz was used.

At 1 kHz, 100 dB, and 1 foot from the middle of the ESL panel, THD+N was 0.21%, and was primarily second order. This is important, because many speakers out there have primarily third order harmonics, and even-ordered harmonics are easier on the ears than odd-ordered harmonics. Indeed, when I listened to the Spires at high volume, it did not bother me at all.

I was not able to measure THD+N vs. Frequency in the upper frequency regions at 100 dB using my standard tests because the impedance at 20 kHz is so low, the amount of current delivered at a single sine wave frequency was overheating the resistor in the crossover network. So, I performed a series of other tests, and determined that, at 100 dB output and 1 foot, THD+N is about 0.5% from 100 Hz to 20 kHz, and is 10% at 30 Hz, decreasing to 0.5% at 100 Hz. This is excellent performance.

For the room response, I used a distance of 2 meters. I measured the response with the bass control setting at 0 dB and at - 10 dB. You can see the response is quite flat, with the one room mode bump at 60 Hz. Judging from these curves, if I were to leave the speaker in this placement, I would adjust the bass control to about - 5 dB. Obviously, this is a very useful feature to have.

I did not measure the impedance or phase, because the power amplifier input is in the circuit parallel with the speaker binding posts.

Conclusions

MartinLogan's new Spire electrostatic hybrid speakers are fabulous in my book. They play loud for their size, with great detail in the music, and the distortion profile seems to be primarily second order, which is pleasant rather than irritating as it would be if it were primarily odd-ordered. ESL technology has obviously come a long way since I first heard MartinLogans back in the early 1980's, and I am delighted with the improvements. 

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