ML speakers are a line source

[kcl]

Although I'm relatively new to this forum, I've 'lusted' after Martin Logan speakers since I first heard them in a high-end stereo shop in the early 1990s, and got my Ascents back in 2002. I've done a lot of reading and research within this forum, but something that I discovered early on about these speakers I've never seen in any messages. So I thought I'd pass this along for those that may not know it. (And if everyone already knows it, my apologies for wasting your time.)

One of the things that originally impressed me was how Martin Logan speakers seemed to 'fill' both large and small rooms with their marvelous sound, especially more so than traditional cone speakers (even high-end ones). Being an engineer by trade and training, I realized what I thought was the reason: Planer speakers are a line source of sound, whereas traditional cone speakers are a point source. "Well of course" you're probably saying, but I've discovered that most folks don't realize what this means from a sonic volume standpoint.

You see, the volume level of a point source is proportional to the inverse square of the distance. That is, if you double the distance from a cone speaker, the volume level is reduced to one quarter of what it was (i.e., one over two squared). However, the volume level of a line source is proportional to the linear inverse of the distance. In other words, doubling the distance only reduces the volume level to one half (i.e., one over two).

This is the reason that all that clear, crisp, and detailed sound our speakers generate is so effortlessly transmitted throughout our listening rooms.

 

[JonFo]

... This is the reason that all that clear, crisp, and detailed sound our speakers generate is so effortlessly transmitted throughout our listening rooms.

kcl, agreed that one of the main attributes of an ML ESL is that they are indeed line sources, with their attendant dispersion characteristics.

As I posted in my center channel design thread:

Concept and Design

...
Line arrays allow the designer to achieve these benefits:
• Contours the vertical sound dispersion such that floor and ceiling reflections are minimized
• Maintains a wide listening area with room filling, nearly constant sound intensity
• Provides exceptional dynamic range and linear performance

All speakers produce sound in both the near field (close to the speaker) and the far field as distance is increased. Conventional point source speakers generate a spherical wavefront and they place the listener entirely within the far field while line arrays can locate the listener within either near or far fields.
For a line array the near field is where the radiated sound resembles a vertical cylindrical wavefront much like the one generated by the ESL panel. It is this match of polar radiation and power curves that make a line array of mid-basses the ideal companion for an ESL.
...

So while the ESL component of an ML does indeed provide that deep projection of sound into the room, most dynamic hybrids have challenges with getting mid-bass regions to match. Which is why the larger ML’s are generally better regarded, as their transition to point source mid-bass is lower.

As I’ve proven with my SL3XC, I believe that the ideal ESL is either one large enough to generate mid-bass cleanly at target SPLs (which is what a CLS gets close to), or to do what ML did on the Statement e2 and combine a line array of mid-bass to deliver the impact of those frequencies with a mached polar dispersion.


The line array projection of ML’s is one reason why they sound amazing from adjacent rooms. I’m constantly surprised by how well I can hear my HT from my office, which is 15 feet down the hall from the door to the HT. A pair of dynamic speakers (point source) under similar circumstances is nowhere near as clear (or loud).

In my book, ML’s are distinguished by the following main characteristics:
- Electrostatic panel – low distortion, highly accurate, no crossovers in critical regions
- Line array – benefits discussed above
- Dipole radiator – Pluses and minuses here. Plus: huge soundstage if well placed. Minus: combing artifacts, rear wave cancelation of mid-bass and below.

These are al things box speakers generally do not deliver. Only large line arrays of dynamic speakers come close (such as the big Infinity IRS V, Pipedreams, McIntosh XRT2K). See the 'super systems' thread for pics of these.


One reason DIY line arrays are popular is they deliver near ML quality sound for a fraction of the price. But without the ESL drive element, they really can’t provide that ultimate ‘je ne sais quoi’ aspect of ML sound