Introduction

When you love your job, you can consider yourself very lucky, and I consider myself very lucky. I was trained as a neuroscientist and did research for years back in the 1970's and 1980's. I then stopped the research but continued in the field by becoming an editor of medical journals. Although I like editing journal articles in the field of science and technology, I would not like to go back to being in an animal research laboratory. Working with hi-fi equipment is so much more fun than culturing neurons in plastic dishes.

One of the main benefits of being an audio writer is having so many new toys to play with constantly. I have often referred to my love of flat panel speakers, and Electrostatic Speakers (ESLs) are one of those.

My first experiences with hearing ESLs included MartinLogan decades ago. Recently, I reviewed the MartinLogan Purity.

In May, 2008, MartinLogan released their newest model, called the Spire. It is larger than the Purity, and has a 10" cone woofer to handle the frequencies below 320 Hz, which makes this a hybrid. While the Purity had built-in amplifiers that drove both the ESL panel and the woofer, only the woofer in the Spire is powered.

The ESL panel is 43" high by 12" wide, so it has a rather big surface area. It's not really big enough to be a full-range ESL, but it's getting there. Most full-range ESLs are about the size of a door.

Like all ESLs, you need an AC wall socket to plug them in so that the panel membrane can be electrostatically charged. This also supplies power to the woofer amplifier.

The Design 

The base of the Spire has the woofer enclosure, and on the back are the connections. You can also see a dial near the mid-top of the enclosure, and this lets you boost or attenuate the bass by ± 10 dB. This is important because ESLs are very sensitive to room placement, and it's necessary to be able to bring the bass into line with what the ESL panels are doing.

Here is a close-up of the dial, and you can also see the jumper clips that connect the ESL panel to the woofer. There is a small toggle to turn off a blue MartinLogan logo that is on the top of the woofer enclosure, as it can be seen through the translucent ESL panel.

The stators are curved and are perforated with small round holes. The shape and edging of the holes were researched in order to keep edge diffraction to a minimum. There are some narrow strips that keep the two stators spaced at tight tolerances.