No. 2 [No. 1] • Jan/Feb 2004
ICBM (Integrated Controlled Bass Manager)
Inputs: All unbalanced, -10dBV; left, center, right, left surround, right surround, center surround, LFE
Outputs: as above plus left sub and right sub
Controls: Crossover frequency selectors for left/right front, center, left/right surround, center surround; pots for LFE mix and sub level; switches for L/R recombine, sub mono/stereo, low pass special/normal
Crossover frequencies: 40, 60, 80, 100, 120 Hz and bypass
Filter slopes: 2nd order Butterworth high-pass in normal and special modes
2nd order Butterworth low-pass in normal mode; 6th order Butterworth low-pass in special mode
Frequency response: From -3 dB at crossover point to -0.3 dB at 96 kHz
LFE mix range: unity gain to -10dB
Sub level range: Full attention to +9 dB
Signal-to-Noise: 105 dB
THD plus Noise: less than .015%
Relative phase shift channel-to-channel: less than 1 degree
Maximum output voltage: 9.5Vms
Power supply: 15VAC -300mA (wall-wart)
Dimensions: 1.76 H x 17.6 W x 7 D inches
Bass management, or rather the lack thereof, as been one of the major bugaboos about multichannel audio for some years now. This handy unit from online marketers Outlaw has been around for a few years now. It was created to solve most of the bass management problems, and one would think by this time the designers of hi-res players, preamps and receivers would have included proper bass management so that this unit was no longer needed. Well, they haven’t and it’s still needed.
Those few of you into multichannel with really full range speakers all the way around your listening room/home theater can move on to our next feature, but for the rest who haven’t grasped this problem, here’s the dope: Most speakers suitable for surround aren’t full range. They poop out somewhere below 100 Hz, yet many 5.1 DVD soundtracks and hi-res audio discs pump out lots of low energy in that part of the spectrum that can overload your speakers and cause distortion in the upper frequencies. Plus you are losing the lowest frequencies that add life to pipe organ, percussion, vehicle crashes in action movies, and so on. Even if you have one or two powered subwoofers and a crossover in operation, they are only getting the lowest frequencies that are fed to your left and right front speakers – not the ones sent to the center and surround speakers.
Sure, most preamps and receivers now have options for choosing between “large” and “small” speakers and often for setting the crossover point as well as delays for those speakers that must be closer to the listener than others in the system. But those options only work with Dolby Digital and DTS soundtrack material; when you play your multichannel SACD or DVD-A discs thru it that circuitry is bypassed and you just get a straight-thru analog feed of the six channels. Some hi-res players are beginning to have some bass management but most are still lacking in this regard. Why haven’t manufacturers copped to this serious oversight by now? What is really needed is a device to remove those booty-shaking frequencies from all four, five or six channels before they get to your “small” speakers that can’t handle them, and re-direct them to speakers that can – your subwoofer(s).
The ICBM is the only game in town to do just that. It is more versatile than any of the other controllers built into components – doing just about everything except speaker delay (that would require digital circuitry) and balance adjustment. (I’d also like a device that could re-direct any single channel to any amp and speaker – to accommodate the several alternative approaches to 5.1 for music. But few of us are playing around with that, so such is unlikely.)
You will need some quality patch cables – at least ten. The ICBM can be inserted into your system a few different ways. If your preamp or receiver controls bass management well enough for everything except your multichannel disc player (and if you don’t have separate players for the new formats), you can patch in the ICBM between the analog output of your player and the analog input of your preamp or receiver. If you only have a two-channel system with a separate preamp and amp plus a power subwoofer, you can use the ICBM as a very flexible crossover. You just feed the L & R out of your preamp into its L & R IN, then take the L & R OUT to your amp while feeding from the ICBM sub out to your subwoofer.
Even if you don’t have a multichannel SACD or DVD-A player and don’t plan on one, you might still find the ICBM useful since most preamps and receivers with some sort of bass management only give you one or two crossover points which may not be optimal for your speakers and subs. The ICBM has a wide choice of crossover points ranging from 40 up to 120 Hz so you can get the very best performance from your speakers and minimize any roughness in the transition from your main speakers to the sub(s).
Most users will probably hook up the ICBM the way I did in my system: Between the processor, preamp or receiver and separate amps. If you’re just doing 5.1, this means stereo cables from each of your five channel outputs to the ICBM inputs, then back into those channel inputs on your preamp from the ICBM outputs. The sub is connect to the left sub output; if there is a second sub connect it to the right output. If you have a 6.1 channel system you will also hook up the center rear surround channel, and for 7.1 systems (two rear surrounds) you will also need two Y adaptors to feed the single center rear signal to both rear speakers. I have a 7.3 setup, but instead of the center rear surrounds my additional pair of channels are side/height speakers plus three subwoofers. If the ICBM had stereo center channel outputs instead of mono I could use them for my side/height speakers (which are stereo). But since they don’t, I can’t; that’s unfortunate since the bass management in my preamp forces me to set the side/height speakers to Large if the front L & R are also set to Large, and of course they are.
In order to keep the Sub Level and LFE Mix knobs of the ICBM handy and to keep the connecting cables as short as possible, I installed the unit right on top of my Sunfire Theater Grand III preamp, using half-meter cables in and out. My triple-sub situation is a bit unusual. In consideration of the range of my Celestion SL-600si minimonitors, I use a crossover of 80 Hz. I have a powered sub directly behind my listening sofa normally fed directly from the LFE channel. Now I have it fed by the L sub output jack on the ICBM, but before the signal goes to the cable in the raceway under my floor and then to the cabinet with the rear sub, it encounters a Y connector which splits off the same signal which now goes to another Y connector at the amp input that powers the left Celestion subwoofer under my L front speaker. That way the sub receives both the below-80 Hz signal from the L channel of any two-channel material via the sophisticated Celestion crossover, plus the below-80 Hz signal from the L channel of the ICBM. For the R channel front sub I go directly from the R sub output on the ICBM to another Y-connector on the amp input for the Celestion sub – ignoring the single powered rear sub which is already getting the L channel sub signal.
I am still tweaking the various level pots on my amps, powered rear sub, and the front panel of the ICBM in order to arrive at a balance that will give a suitable low frequency support no matter what the source material – be it two channel or multi, action movie soundtracks, pipe organ, or quiet solo clavichord. I trust that when completed the Subwoofer Level pot on the ICBM will be all I will have to adjust occasionally. Which is luckily at hand while all the other pots are not.
Special Sub Controls
There are several controls affecting the subwoofer operation: the LFE Mix Control adjust the level of the LFE signal in relation to the signals to all the other speakers. It is normally left wide open, but if a particular movie has a really overwhelming LFE level, you can use it reduce the shattering of your Hummel figurines on the shelf. The Sub Level Control sets the output level going to the sub(s). It is unusual in not only being an attenuator but also in having a range up to +9dB increase in level. The normal zero point is marked with a white line on the panel. I can see turning down the level some when using my turntable since it can create extremely low thumps when setting down the stylus or moving about too energetically in the room. My Celestion sub drivers don’t cotton to that. Now there’s another item for the Outlaw ICBM Wish List: an adjustable – say 25 Hz on down – high pass filter to block out subsonics.
On the back of the ICBM are two small toggles. The one labeled Mode switches between a mono signal to all subs or a stereo one to separate left and right subs. It is suggested that the user try both options with different program material to see which is preferred. The other toggle switch is labeled Lowpass and has Special and Normal settings. The Normal setting is a 12dB per octave lowpass crossover point while Special is a 36dB crossover for those subs requiring a steeper filter curve. There is yet a third toggle over between the L & R main speaker Ins and Outs: This “L/R Recombine On/Off Switch” does not affect the subwoofer(s) at all but redirects into the L & R front channel speakers the bass in all of the channels not set to Bypass on the front of the ICBM.
One other consideration that the ICBM doesn’t address and you may want to consider is the phasing of your sub(s). The better powered subs now have a switch to change the phase, but my rear sub lacks that amenity. So I had to dig an old Switchcraft phase-reversal switch out of my audio junk box and wire it up. (They must still be made, I would think.) I was moved to do so after playing Chesky’s DVD-A test tones on their demo DVD, which includes one for subwoofer phase.
I found the insertion loss to be unnoticeable with the ICBM in the circuit, all the controls operated properly, and the owner’s manual is very clear and well-diagramed – unlike so many others. I am already hearing a richer low bass foundation to both music and film soundtracks. I didn’t realize how much low frequency information there was on the center and surround channels of some multichannel sources; my subs were missing out on this entirely! Also, many multichannel music discs don’t employ the LFE channel at all, so my powered rear sub wasn’t getting any signal. This is a unique and sophisticated multichannel bass management system which though coming in at a reasonable price still maintains high end standards.
– John Sunier