On the Bench

Because of their (relatively) small size for an ESL, low frequencies are not reproduced all that well. Here for example, at 100 Hz (microphone at 10" from the center of the panel), THD+N was almost 6%. Even just an 8" cone woofer would do better than this, and it's why a good subwoofer is always helpful when using ESLs. I would recommend crossing these speakers over at 120 Hz when used with an SSP.

At the higher frequencies, however, ESLs do great. At 1 kHz, about 0.4% THD+N resulted.

At 1 kHz and 1.5 kHz, the A+B IM peak at 2.5 kHz was 45 dB below the fundamental, and the B-A peak at 500 Hz was 40 dB below. If you look at the IM peaks we have gathered for amplifiers, you will see that speakers don't do as well. This is because electrons move faster than cones and membranes which are physical objects. Even though ESL membranes are very light, they still have inertia.

At 5 kHz, THD+N was 0.74%.

And, at 10 kHz, THD+N was 0.43%

The room response showed a roll-off below about 700 Hz. This is because ESLs are dipoles. The sound from the rear comes around to the front and interacts with them, attenuating some of the frequencies. So, again, here is the reason why I suggested crossing them over at 120 Hz. The peak at 90 Hz is a room mode.

The impedance of the 400is is low at about 10 kHz and above. Even though that is only part of the audio spectrum, it is still a good reason to use an amplifier rated into 4 ohms. Electrical phase is mostly capacitive (the part of the red line below 0⁰ is due to capacitive influence, and the part above 0⁰ is due to inductive influence). That is because an ESL acts like a big capacitor. The phase peak at 100 Hz - 200 Hz is due to the transformer.

Conclusions

My little experiment with small ESLs was a big success. Final Sound has managed to design small ones that deliver where it counts: SPL and detail. Even though the panel is flat, dispersion is still acceptable because the panel is narrow.

ESLs are not for everyone, but Final Sound has just enlarged the market, as the 400i will fit in any home theater or music room.

 

- John E. Johnson, Jr. -