Introduction

Most consumers have never seen an electrostatic speaker, even though they were marketed way back in the 1930's.

The reason for this is that electrostatic speakers, or ESLs, are rather esoteric, meaning that they are not your garden variety speaker, and are not for everyone. Ironically, every woman I have talked to said they love the look of ESL speakers. It's probably because they are slim and transparent, so they don't overpower the room decor. Thus, they have a high SAF (Spouse Acceptance Factor).

ELSs are usually very expensive, because they are not made in great quantities, and they have to be relatively large due to the membrane that moves the air not having a lot of excursion. They also need a wall AC connection to power the supply that provides an electrostatic charge on the membrane. So, you can't just plop them down anywhere in your listening room. Lastly, they really need to be out from the wall, because they are dipoles, meaning that the sound comes out the back just as much as it does out the front.

The Design

There have been a number of ESL manufacturers over the years, including KLH. I remember when I was in high school, and I heard a pair of KLH ESLs. They were the size of doors, and were being driven by McIntosh power amplifiers. I wanted a pair of them so bad, I could taste it, but alas, high school students don't have much cash to buy such things, and they were $1,500 a pair. Rotten luck it was.

These days, there are only a handful of companies that market ESLs. In the US, Martin Logan is perhaps the best known. Innersound also sells them, and we reviewed their complete ESL system in 2005. In Europe, where it is based (The Netherlands), Final Sound is very well known.

ESLs work in the following way. A thin plastic membrane, or diaphragm, is suspended between two metal perforated "stators". An electrostatic charge is placed on the membrane on the order of several thousand volts. The audio signal passes through a transformer that increases its voltage, also to several thousand volts. As the audio signal changes from plus to minus on the front vs. the rear stators, the charged membrane is attracted to, or repelled from, the stators. The membrane moves air through the stators, and this produces the music that you hear.

Final Sound has made some changes in the ESL design by sending the audio signal to the membrane, while the stators have the static charge, positive on one side and negative on the other. Here is a PDF white paper that describes their technology. This is the exact opposite of conventional ESL designs, where the static charge is on the membrane, and the audio signal is applied to the stators.

One of the advantages of this new design is that it does not take as much amplifier power to drive them, and this is important, because ESLs have been notorious for needing lots of amplifier power. In the case of the Final Sound 400i's, which is the model being reviewed here, I found that 10 watts per channel filled the room with sound. Other claimed advantages include lower distortion and greater detail. Lastly, the design allows for smaller electronics (the transformer), which reduces manufacturing cost.

Now that does not mean you can drive them with just any old amplifier. The reason for this is that ESLs are notorious for something else, namely having low impedance. Usually, they will be 4 ohms, or lower, at some frequencies. So, you still need a good amplifier that will work at low impedance, but it just does not have to be a high powered one anymore.

So then, the 400i is the smallest of Final Sound's floor-standers. It is 48" high, 10" wide, and 6" deep. The speakers come with an oval metal plate that you bolt to the base, and then it is ready for placement. As I mentioned, ESLs need an AC wall supply. That has not changed, and the Final Sound ESLs use wall warts that connect to the back of the 400i. This supplies 12 volts to the internal power supply which raises it to several thousand volts for charging the membrane.

Other models include the 600i, which is 61" high, the 1000i, at 74" high, and the 1400i, which is 80" high. Yup, 80". That is 6 feet 8 inches. As I mentioned, ESLs need to be big, because that membrane does not move very far forward and backward. So, the large membrane, with lots of square inches of surface area, will move enough air that you can get high SPL when you want it.

All of the models have a configuration where the panels are divided into vertical sections, each of which reproduces a specific frequency range.

So, why are 48" models even manufactured? Well, not everyone can fit an 80" tall speaker in their listening space. Smaller ones will work fine if you add a good subwoofer (Final Sound offers several models), and if you are putting them into a home theater, it is even more useful if you can get five ESLs that are reasonable in size, namely about 48" high (or wide, in the case of the center channel).

If a good subwoofer can take up the slack at the low frequencies, why build big ESLs at all? The answer is that a cone speaker is much different than an ESL panel, and purists want to have all the frequencies coming from the ESL, rather than having the mids and highs coming from a membrane, and the lows coming from a cone.

But, we are not covering the 80" version here. This is about testing a pair of ESLs that would fit in any listening space, and discussing what the compromises are.

Click Here to Go to Part II.