Floor-standing Speakers

MartinLogan Ethos Hybrid Electrostatic Speakers

ARTICLE INDEX

Design

I usually gather technical information about the products I am reviewing. This information helps me understand, evaluate and report on the products. I typically call and e-mail the manufacturer's technical experts to get this information. They will send me technical white papers that supplement the information on their website or in the product's owners' manual.

In the case of the MartinLogan Ethos speakers, I didn't have to do any of that. The speakers shipped with a most excellent owners' manual which was well written, well organized and chock full of useful information. There was probably more information in the MartinLogan 28 page manual than I find in many other manufacturers' technical white papers. I'd venture that MartinLogan believes (or realizes) that their clientele is suitably knowledgeable and can benefit from this information. I'd bet they are right about that, too.

Most MartinLogan speakers feature a large mid/high electrostatic driver. These drivers and their design and technology are at the core of the MartinLogan "ethos". (How's that for a double entendre?) Seriously, though, MartinLogan has invested a great deal in advancing this technology and one area that the manual covers in detail is the history of electrostatic driver technology. I would like to summarize that history below.

Electrostatic drivers were originally pioneered by C.W. Rice and E.W. Kellogg of Bell Labs in the 1920's to develop a loudspeaker technology for amplified music. They made a working prototype but ultimately recommended the active cone over the electrostatic and some other technologies they investigated. Their original design was patterned after the condenser. It only had one charged plate. The unit was plagued with low sensitivity and they could not get good bass response from a reasonably sized unit. Consequently, the technology was not considered commercially viable at the time.

Later, Arthur Janszen developed a HF electrostatic driver for the Navy that was used for testing microphone arrays. It was favored over dynamic cones due to its inherently benign phase angle and flat frequency response. He developed a viable tweeter element by the early 50's that created quite a buzz in audio circles. It worked well because it was a push-pull arrangement with a constant charge on the diaphragm where earlier designs varied the charge on the diaphragm while maintaining a constant voltage.

In the mid 50's, Englishman Peter Walker carried electrostatic technology even further. His efforts culminated with the introduction of the Quad ESL's in 1956. This is when the technology really became a successful commercial product.

The biggest developmental hurdles for the technology were low power handling, low sensitivity, poor dispersion, limited low frequency response and possible damage of the units due to arcing. The greatest advantages of electrostatics were good transients (because all parts of diaphragm are loaded), low distortion and a non-reactive load (but they did exhibit low impedance at high frequencies).

MartinLogan officially started production in 1983. They have worked continuously to overcome the disadvantages of electrostatic technology while enhancing the advantages of the technology. Their efforts have produced a number of patents and trademarks. These MartinLogan exclusives provide an excellent overview of the Ethos speakers. I thought it would be fun to elaborate on them in this mini glossary:

AirFrameTM – This is the name given to the extruded aluminum structure that surrounds the electrostatic panel. It supports the panel and provides sonic and electrical isolation. The latest version of this technology maximizes the active membrane area and enhances the dipole dispersion pattern of the unit.

ClearSparTM – The clear spacers which suspend the membrane between the stators. These prevent grounding of the membrane. In the Ethos, they appear to be staggered vertically, presumably to avoid resonances or natural modes.

CLSTM (Curvilinear Line Source) – The panel is curved in the horizontal plane to produce a controlled horizontal radiation pattern that is free of the "venetian blind effect" which is common among large flat panel speakers.

EthosTM – The amazing speakers under review here.

Generation 2 Diaphragm – This transparent membrane has uniform surface resistivity characteristics and is nearly mass less. The Generation 2 Diaphragm is just 0.0005 of an inch thick. Its design reduces the possibility of damage because it resists arcing between the stators.

MicroPerf Stator – This is the new stator for the XStatTM panels. It reveals more open vibrating area of the panel so the panel can be reduced to almost ½ the size for an equivalent level of performance. (MartinLogan may consider a honeycomb pattern in the future as the hexagon provides the greatest opening for the least amount of material, but the corners in the pattern may be sites for potential arcing.)

PoweredForceTM – This is the bass unit supporting the Ethos speakers. It is a remarkable achievement for an 8" compact sub to be able to produce 100 dB of continuous output at 50 Hz with a clean spectrum. I was able to obtain this level of performance in the bench testing below. These powered bass units have built-in protection circuitry.

Vacuum Bonding – This proprietary system ensures uniform diaphragm tensioning and precise manufacturing tolerances.

XStatTM – This is the latest iteration of the famous MartinLogan electrostatic panel. It "incorporate a myriad of technology and design innovations including CLSTM, MicroPerfTM, Generation 2 Diaphragms, ClearSparsTM and Vacuum Bonding."