The ICBM has a switch that allows the user to select between mono or stereo sub output from the L & R RCA sub terminals. In stereo mode, the Left Sub gets a full lowpass signal from the Front Left and Left Surround channels, and half the signal from the Center Front and Center Rear channels. This is explained in the ICBM Manual (Page 14, pdf file available @ this site).

I have tested the crossover response, and the ICBM does permit independent crossover settings for the following channel groups:
a) L & R Fronts (2 channels)
b) Center Front (1 channel)
c) L & R Surround (2 channels)
d) Center Rear (1 channel)

The crossover choices are 40Hz, 60Hz, 80Hz, 100Hz, 120Hz, and Bypass for each channel group.

The effect of flipping the switch from mono to stereo varies significantly on recordings with good bass content. I believe many recordings have mixed (summed) bass content to the L & R channels, and therefore have defeated the opportunity for stereo bass. I believe this underlines SH's point regarding the splitting of a specific musical instrument's sound signal, which can happen because:
a) the listener definable Sub/Main crossover setting (where the Subs are located distant from the mains), and...
b) the arbitrary mixing point chosen by the engineers in the studio (where low bass is summed equally to L & R, assuming the sonic characteristics of the listeners speakers and system are not up to reproducing full range stereo signals).

As SH states... "The closer the notes being played are to the bass crossover frequency [or low bass mixing point], the worse this disembodiment of the fundamental from it's harmonics will be, as the phase difference between the two will be greater due to the higher frequency".

One example... The Talking Heads and TomTom Club have very good stereo recordings of low bass frequencies, with lots of electric bass and all kinds of drums. The benefits of Stereo vs. Mono Sub-woofing are very evident. With stereo subs, the location, image and phase coherence of each instrument provides a sense of realism that is significantly better than with the ICBM switch in the mono position.

While I have not perceived a problem with the lack of a discrete LFE sub (or subs), I believe that Bossobase's quest for independent LFE signal is a good one. In my opinion, it is like chicken soup... will it help???... it couldn't hurt...
but it will cost you.

Best Regards

[This message has been edited by AGAssarsson (edited April 29, 2003).]