MartinLogan Interview on Electrostatic Speaker Design

We recently swung by MartinLogan's headquarters in Lawrence, KS for a tour around the facility and an interview with Joe Vojtko, the company's Chief Audio Technologist. While anyone in the audio industry should know of MartinLogan, there is still a lot of mystery surrounding electrostatic loudspeakers (ESLs). Additionally, many people have preconceived notions about ESLs that don't take into account advancements made over the last 50 years. We covered some of this in our review of the MartinLogan Theos, but we decided to go straight to the source for the best answers possible. Before jumping into the interview, we recommend watching the three YouTube videos below (courtesy of MartinLogan) in order to develop a basic understanding of the technologies that the company uses.

• History of MartinLogan
• Electrostatic Loudpeakers (ESL) Technology
• Busting Electrostatic Speaker Myths

MartinLogan Factory Tour & Interview 2016

AH: What is your history with MartinLogan?

JOE: I have worked at MartinLogan for over 20 years and have developed many speakers starting with the Aerius in the early 1990s.

AH: Do you actually wear a lab coat at work and do people call you professor?

JOE: No, I do not actually wear a lab coat and people do not call me “Professor”. I am not an actual professor; I only play one on the internet. Mostly, I wear t-shirts and people just call me “Joe”.

AH: Many people just group ESL and planar speaker technologies together, how would you explain the difference?

JOE: ESL and planar speakers are both flat and have dipolar radiation characteristics. Ribbon speakers typically use a narrow ribbon for the high frequencies that results in a wide radiation pattern at high frequencies. Because the MartinLogan ESLs high-frequencies are played across a large, wide ESL we achieve a much higher level of controlled dispersion than the typical ribbon.

AH: What do you think is the biggest misconception people have regarding ESL’s?

JOE: One of the biggest misconceptions people have about ESLs is that they are only good for jazz and classical 2-channel music. This simply isn’t true.

AH: What advantage does the curve in the panel give you?

JOE: One of MartinLogan's original breakthroughs, CLS technology, has been an essential ingredient of every electrostatic loudspeaker we've produced. Manufacturing methods enable construction of electrostatic panels as cylindrical sections. Their horizontal curvature solves the problem of obtaining good high-frequency dispersion from a large radiating surface without compromising overall sound quality or reliability.

When a sound has a wavelength that is small relative to the size of the speaker diaphragm, it tends to radiate over a narrow angle rather than dispersing widely into the room. Such high-frequency "beaming" yields a very small sweet spot where the listener can sit and hear proper tonal balance and often results in a dry, sterile sound quality. Since every other design consideration pushes electrostatics in the direction of larger panels, treble beaming is a serious concern.

MartinLogan's curvilinear electrostatic panels are an elegant solution to the problem of achieving the preferred range of horizontal dispersion from a driver having a large diaphragm surface area. Curvilinear panels maintain relatively limited vertical dispersion, which minimizes undesirable floor and ceiling reflections. And they do so naturally, without resorting to tricks such as multi-driver arrays or to horns, which create other problems of their own.

AH: How close or far away from the wall should the panel be?

JOE: We recommend, at minimum, 2 to 3 feet from the wall behind the speaker and the same for the side walls. The out-of-phase back wave is an integral part of creating the three-dimensional soundstage for which our speakers are known.

If placed too close to the wall behind the speaker the back wave of the ESL will bounce back and arrive too quickly after the primary wave.

If placed too close to the side wall the reflection from the side wall will bounce back to the listener. Some distance is required from the side wall so that the controlled dispersion can minimize this reflection.

AH: Have you ever experimented with putting an enclosure on the back of an ESL panel to make it a monopole instead of a dipole design?

JOE: Dipole design is an important feature that contributes to an electrostatic speaker’s special ability to reproduce a 3-dimensional soundstage. Select electrostatic models in the MartinLogan line (such as the Motif center channel) do include back-wave absorption. This decision is always made on a case by case basis depending on the specific requirements of each unique product design. However, for the majority of our speakers we love the transparency and spacious sound created by a dipole design—it’s an integral part of the MartinLogan “magic”.

AH: Have you experimented with different dynamic driver placements before? Such as top and bottom?

JOE: Yes, we have experimented with dynamic driver placement. A well know MartinLogan speaker, the Statement e2, had an array of dynamic dipole drivers flanking the electrostatic panels.

Achieving seamless blending between electrostats and woofers is always a challenge. The alignment and configuration between these disparate technologies must be balanced to blend well. Dynamic driver location is also dictated by room interactions, taking into consideration factors such as floor bounce and its effect on overall low-frequency performance.

AH: With a MartinLogan loudspeaker, the entire ESL panel plays the same frequency, like a typical line array design. Would there be an advantage to splitting up different parts of the panel to play different frequencies?

JOE: No, splitting up the panel is only advantageous in certain situations, specifically when attempting to create extremely low-frequencies from an electrostatic panel. For example, the CLX features an electrostatic bass panel matched with a curvilinear electrostatic panel that single-handedly reproduces mid- and high-frequencies.

The human ear is most acute in the mid-range—and distortions in this area can cause recordings to sound less than ideal. This critical mid-range area is also where most traditional speakers deploy crossovers. By using a single panel to reproduce mid- and high-frequencies our electrostats are inherently free of crossover induced anomalies. When one transducer is able to play nearly the entire frequency range, something magical occurs.

AH: Any cool new technology or products we should know about? Maybe the Dynamo 1500X, Perfect Bass Kit, Motif X or Stage X?

JOE: You’ll have to wait for the story on unreleased products, but the Dynamo 1500X was recently added to our web-site.

The Perfect Bass kit is an interesting new feature that we plan to incorporate in other upcoming products. The PBK system employs a PC, connected via USB to a microphone and a MartinLogan subwoofer, to identify problem areas in a listening environment. The PBK processes information from multiple data points and configures the optimal solution, achieving pinpoint-accurate room response. 

Motif X and Stage X are updates on two of our well-known center channels, replacing the older model’s dome tweeters with Folded Motion transducers. These two models represent the first electrostatic center channels that don’t incorporate a dome tweeter for high-frequencies. We have been so impressed with the performance of Folded Motion technology that we find it to provide a very ideal match when mating with the electrostatic mid-range in these products.

AH: MartinLogan is known for their ESL speakers, but we have seen a huge rollout of speakers utilizing your Folded Motion tweeter. What can you tell us about them?  

JOE: We are proud of the Motion Series. It’s been over a decade since MartinLogan released its first non-electrostatic design. Along the way we’ve had many non-electrostatic products that have been very well received. The compact size of the Folded Motion driver has allowed us to create an array of smaller products and in-wall products that capture many of the performance benefits of thin-film driver technology in a much smaller package.

We engineer everything to high standards. MartinLogan strives to bring an authentic experience to consumers regardless of transducer technology. “Listening Experience” is a term that we use nearly every day in the office.

AH: What is the story behind the Statement E2 speakers (120k/pr)? Would you still consider them, excluding the tower of subs, to be better than the current CLX’s, or just different?

JOE: The Statement e2 is different than the CLX. They were designed with very different goals in mind. It’s difficult to draw direct comparisons between the two.

We want to thank Joe Vojtko and MartinLogan for taking the time do this interview with us. Also, keep tuned for our upcoming review of the MartinLogan Vision Soundbar.