MartinLogan SL3 loudspeaker Manufacturer's Comment

Sidebar 6: Manufacturer's Comment

Editor: I know when the team of Wes Phillips and John Atkinson get hold of a speaker the manufacturer is going to learn even more about his product than he knew before the process began. We are Martin-Logan feel that the SL3 represents new levels of audio performance and it feels good "back here in the Midwest, that your observations are close to ours."

A few issues regarding the testing procedures. Yes, our products are different from point source products in the way that they launch information and, as a result, our testing procedures differ from the norm. I have taken the liberty to enclose a small explanation as to how we arrive at our testing measurements, and you can see that basically we move our testing position to the listener position, which we assume is about 3.2 meters from the speaker. As you can see, the frequency response evens out and the sensitivity scales much close to 90dB at that position.

With a point source it is easier to test at 1m, then certain things will occur at the listening position. With our product, we feel it important to test at, or close to, the listening position.

Also the waterfall can look slightly hashy as a result of a large line source launching information into the room as opposed to a point source. Information is arriving from the entirety of the panel to a single point on the microphone which is a partial contributor to a less-than-clean look. However, John is correct in his discussion as to how the ear handles this information making it less relevant than the test would imply.

And yes, Martin-Logan speaker products do benefit from better amplifiers. And yes, we are not the easiest load to but by far not the most difficult load to drive. As a result of that revealing nature, our electrostats most certainly benefit from better front ends and amplification.

Sometimes Martin-Logan products are easier to place in the room than point source products and, sometimes vice-versa depending on the nature of that room. The controlled frontal dispersion actually makes it easier to place a Martin-Logan in a long or narrow room, and therefore a better image and focus can immediately be achieved versus a wide dispersing product.

Again, thank you for your revealing work. We look forward to being sliced, diced, and dissected by Stereophile again in the future.

Martin-Logan on measuring panel speakers: Measuring panel speakers can be a challenge. Since we are no longer dealing with a point source, some care must be taken in making measurements. This always brings up the issue of near field and far field. The question is "are we taking measurements in the near field or the far field." An equation that gives the approximate distance of the transition point is:

transition_point = D-squared/lambda

Where D is the largest dimension of the transducer and lambda is the wavelength of the sound being produced. (This is just a rule of thumb equation, not an absolute mathematical definition.)

When we look at an electrostatic element with a D of 48", the transition point is shown in fig.1. At 10kHz, the transition point between near and far field is over 100' from the speaker! However, at 200Hz, the distance is only 3'. So some of our measurements are going to be in the near field. (By the way, for a conventional tweeter, the transition at 10kHz is 3/4".)

Fig.1 Transition point in feet plotted against frequency for a 48" diaphragm (note logarithmic vertical scale).