Floor-standing Speakers

MartinLogan Spire Floor-standing Electrostatic Hybrid Speakers

ARTICLE INDEX

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.