Surround Sound Speaker Systems

MartinLogan 5.1 Home Theater Speaker System

ARTICLE INDEX

Design

What is an Electrostatic Speaker?

Electrostatic speakers are essentially a thin ultra-lightweight diaphragm that is suspended between two stators. The diaphragm is positively charged, while the stators (driven by the amplifier) hold opposite charges where one is positive while the other is negative. The alternating polarity of these stators simultaneously pushes and pulls the diaphragm forward or backwards. This movement is what produces the vibrations that are interpreted by the brain as sound. Electrostatic transducers are superior to traditional (cone) drivers is in both mass and distortion.

When a voice coil drives a conventional cone back and forth, increasing levels of distortion occur as the cone achieves greater excursion and becomes harder to control. To reduce this distortion loudspeaker designers use a stiff cone, spider, and surround, which comes with added mass. The resulting inertia created with addition mass results in potential sluggishness when changing direction. As this change in direction can occur up to 40,000 times a second this becomes a significant audible bottleneck. Compare this with an Electrostatic speaker that uses a huge membrane uniformly driven across its entire surface. The larger the radiating surface used, the fewer excursions required to move the air which in turn reduces excursion-related distortion.

Additionally an electrostatic membrane is very thin (12 microns, about the thickness of regular plastic kitchen wrap). This ultra-thin, low-mass design (with almost no inertia to overcome when changing direction) allows electrostatic speakers to be extremely quick and agile when reproducing the electrical input from an amplifier.

Sounds like everyone should use electrostatic membranes doesn't it? Well, this type of driver is not easy to produce and can be limited in low frequency output. As the frequency goes lower, the panel size increases. To get low bass the panel would need to be at least the size of a door. For example, MartinLogan's full-range CLX speaker is six feet tall and two feet wide, and still only goes down to 56Hz. While I like my speakers to be big and large, most listening rooms, and listening partners will not accept such a large monolithic speaker. To address this MartinLogan uses cone drivers to cover the lower frequencies, allowing for more compact designs and room/spouse friendly designs. This comes with its own issues though, as now you have to make the ultra-lightweight, low-distortion panel blend with higher-mass cone. Where this becomes an audible issue is really only at the point at which the panel passes over to the cone. At this cross-over point there could be integration issues. MartinLogan's solution to the problem using only high quality parts in their sophisticated 'Vojtko' cross-over network named after their lead designer. That and they have been working on this issue for over 25years. Their constant refinement of this integration has created a seamless hybrid design.

MartinLogan Home Theater System

Summit X

At the top of the ESL hybrid line is the aptly titled Summit X. The X indicates this is a new version of the original Summit incorporating the 'XStat' panel adopted from the technology found in their premium CLX speakers. While the overall specifications remain unchanged, MartinLogan claims to have improved the crossover, the panel, and the woofer integration. Unfortunately I was unable to obtain a Summit to compare with the Summit X, so my comments refer to the Summit X on its own.

The Summit X boasts a 44" tall panel, two ten inch woofers, each with their own Class-D amplifier housed in a rather compact sealed box. There is a level control (+/- 10dB) at both 25Hz and 50Hz, as well as a control for the LED's on the box that will illuminate the control panel on the back of the woofer box, the MartinLogan logo, and a set of LED's that shine down underneath the box. You can select all, some or none of the lights. This provides zero audible improvement but adds some fun to the speaker. I was happy to note the glow of the LED's was not detrimental to my viewing experience in my darkened theater room.

In the Summit X the crossover is at 270Hz, this is right in the middle of a Tenor, and the cello. At the crossover point the powered front-firing and down-firing 10-inch woofers take over and handle the lowest most octaves. The complex and creative Vojtko crossover adjusts the phase of the drivers near the crossover point to better integrate with the dispersion pattern of the electrostatic panel. The 25Hz and 50Hz level controls were able to counter-act the minor room issues I have, further allowing the Summit X to blend remarkably well with the Descent i subwoofer.

The Summit X is available in many finish options, and is 100% designed and assembled (as of this article) in America. The finish on the Summit X is flawless. The build quality and construction of all the components is indicative of its price tag.

Vista

The bottom of the XStat line up is the Vista hybrid. Designed and assembled in America, with the woofer section being built in China. The Vista uses a smaller panel than the Summit X, a single 8" ported passive woofer section, which combined with the smaller panel moves the crossover point up to 450Hz. This is in the middle of a Soprano and clarinet (among others). The panel is of the same high-quality construction as the Summit X (just smaller is size); however the quality of the cabinet housing the woofer section is noticeably lower quality. The veneer is close in color and tone to the Summit X's, yet it feels less like real wood and more like fake veneer. There is an obvious difference when compared side by side; on its own the difference is hardly noticeable. I did find the finish to be sub-par when compared with other $4000 (and less) speakers such as the B&W 804s, and the Totem Forests.

Ever had one of those Jaw Dropping moments? Well I did the day I put the Vistas up front in place of the Summits. I was expecting to find the Vistas to pale in comparison to the Summit X's, and was I surprised. What I found was that the Vistas are a very capable loudspeaker. Excellent dynamics and resolution, and they paired with the Stage center better than the Summits. Where they lacked was in the bottom end and the upper most top end. The bottom end was compensated for by increasing the low-pass on the Descent i, from 40Hz to 60Hz, and slightly increasing the subwoofer's 50Hz level control. This complimented the Vistas remarkably well. However this also required that the Descent I sub be placed closer to the speakers to improve the integration (which is very room dependent). As for the top end, the clarity and depth of the Vista was not as accurate and involving when compared directly to the Summit X's.

Descent i

An ingenious cabinet design that maximizes driver surface area and minimizes cabinet induced distortion by placing three drivers 120degrees apart in a well braced sealed box. Mounting the drivers in opposition significantly reduces cabinet vibration and the associated distortion that results. Think of two people on a backyard swing-set. If both people swing in unison you can tip the swing set over, when they swing in opposition the resulting forces keep the swing-set stable. Each driver is powered by its own class-d (ICE) amplifier capable of 250watts (RMS) and 700watts (peak) and is servo-controlled to eliminate distortion if it starts to occur. The sub includes +/-10dB level controls at both 25Hz and 50Hz, multiple inputs allowing for simultaneous connections of LFE and stereo, as well as variable phase and crossover.

The only thing that could improve upon this powerful and flexible subwoofer would be a measurement microphone and automatic equalizer. As I have both an auto-eq equipped receiver and a measurement microphone/software system I was able to accurately and effectively set the controls. When paired to the Summit X's I set the crossover to 40Hz, and increased the 25Hz control 2dB and left the 50Hz control flat. This produced a very clean flat bass response that while not the loudest; it is among the best I have ever heard with all types of music and movies.

Stage

Center channels are essential to home theaters, and yet they seem to be an afterthought for most manufactures. It is not enough to just turn a regular speaker on its side. A driver dissipates its sound waves differently in the horizontal plane than its vertical plane. Therefore placing a speaker horizontally changes it's vertical and horizontal dispersion, as now there is a baffle to the sides of the drivers rather than top and bottom. This is even more of an issue with an electrostatic speaker as they have tight horizontal dispersion (also called Controlled Dispersion, see next page) that focuses the sound energy in a tight beam. Placing an Electrostatic speaker on its side greatly reduces its vertical dispersion which reduces the seamless integration necessary for quality home theater audio. To address this the Stage uses three types of drivers, two 6.5inch mid-bass drivers handle from 70Hz to 450Hz, an Electrostatic mid-range handles 450Hz to 2700Hz and then a 1" soft dome tweeter takes it from 2700Hz to the top. On paper one would think this mixing of drivers would create issues, and certainly it would if not for the advanced crossover network that MartinLogan employs.

Overall the Stage is one of the best center channels I have ever heard. This speaker had excellent tonal quality, usable mid-bass and excellent treble. The only problem I found was a slight tonal mismatch between the Summit X's and the Stage. The Stage is a great center, however the mid-range and high-end of the Summit X's is in a whole other league. This issue was most present with multichannel music, and less noticeable with movies. When paired with the Vista there were no tonal issues noticed.

Controlled Dispersion

A speaker driver disperses its sound in a radiated pattern which then causes the sound-pressure waves to hit the floor, ceiling and walls which in turns reflects back towards the listener. This can create some atmospheric effects and contribute to sound-stage and imaging cues. These reflected sounds can interact with the direct sounds from the speaker and confuse the brain and muddy the sound. By reducing the spread of the waves (controlling the dispersion) you can then minimizes late arrival side and ceiling/floor reflections. . This controlled dispersion is one of the major advantages of electrostatics that creates an illusion that you're in the room with the artist/band rather than 'listening to a speaker/recording. The narrower the beam of sound is the less the room will interfere with the direct sound, which can also translate to a very narrow sweet spot. MartinLogan employs a curved electrostatic panel to increase the sweet spot and still benefit from controlling the dispersion.