MartinLogan SL3 loudspeaker Manufacturer's Comment part 2
In the far field the dispersion pattern can be described in terms of angles and a constant (1/R) term. Meaning the radiation pattern is independent of the distance. In the near field, this is not the case. The radiation pattern is dependent on the distance.
What the hell does all this mean to us?
What it means is that a person sitting 3' away from the speaker will hear something different than a person sitting 10' away, even if they are at the same angle to the speaker. How then do we get a fair measurement of the speaker's frequency response? The way it is done at ML is to set the speaker up according to the owner's manual and measure the response. This is usually done at a distance to the speaker of 9-12'. The SL3's response curve at 10' is shown in fig.2. (Note: 8.9V at 3.2m is scaled such that a 90dB/2.8V/m point-source speaker would read 90dB on this graph.)
Fig.2 Martin-Logan SL3, response on-axis at 3.2m, 8.9V input level (5dB/vertical div.).
The speaker has been designed so that a person who takes these speakers home, reads through the owner's manual, and sets them up accordingly will achieve a response similar to the one shown above. The most critical part of the set-up is to get the speaker positioned so that when the listener looks at the curve of the ESL element they see the inside third of the panel.—Gayle M. Sanders, Martin-Logan Ltd.