|Outlaw Audio ICBM-1 Integrated Controlled Bass Manager|
|Home Theater Accessories Accessories|
|Written by Richard Elen|
|Thursday, 01 August 2002|
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A look at Outlaw Audio's website makes it appear that the company's avowed specialty is audiophile quality at mass-market prices. If the ICBM-1 bass management system is anything to go by, they’re good at it. The unit costs a mere $249 and does a very important job very well for those who need bass management, as many readers are.
But before we get a look at the unit itself, let’s consider bass management and why you probably don’t have something like this unit already. Modern digital audio distribution systems like DVD-Audio and Super Audio CD offer six channels of audio, all of which are full range – they can go from DC to somewhere like half the sample rate. Even a regular DVD-Video disc can handle full range audio on five out of the six channels: the “.1” in a 5.1 system is the so-called “Low Frequency Effects” or LFE channel. In the case of Dolby Digital (and some DTS systems) the highest frequency the LFE can carry is limited to around 120 Hz.
You may be lucky enough to have a room full of full-range speakers, but most people aren’t, and as a result, we have to put up with at least a couple and quite often five smaller speakers, which can’t handle all the bass that might come along. Indeed, the other speakers might even be damaged by it, and you certainly would not hear the bass very well. The answer to this dilemma is to add a subwoofer – a special loudspeaker deliberately designed to handle bass frequencies alone.
So what do you do with the subwoofer? Hook it up to the LFE? No, you do not. That way leads to disaster, because the LFE is NOT the sub-woofer channel. What you do is hook your equipment up to a bass management system. In a nutshell, what a bass management system does is to insure that whatever channel bass information comes in on, the bass is fed to speakers that can handle it. This of course includes bass present on the LFE.
As an aside, it should be pointed out that the LFE is a holdover from the days of analog cinema surround systems, and it’s designed, as the name says, to handle extra-low bass effects, such as you might find in disaster and action movies. These really don’t exist in music, and even if they did, with a modern DVD-A or SACD capable of handling any bass signals that might exist on any channel, the LFE is a bit redundant. This is why record companies like Telarc and Chesky use it for something more fun, namely height channels, which are actually mastered for speakers positioned above your left and right main speakers.
Now, every Dolby or DTS decoder – whether it’s in your player or your receiver or preamp – includes bass management, It is mandatory. But if you have a six- or seven-channel analog input on your receiver or preamp for high-resolution players, these will bypass any bass management in your receiver or preamp. And if you have a six-channel analog output on your DVD-A or SACD player, this may bypass any bass management in the player, too – even if the player also handles DVD-V discs and has a bass management menu associated with any built-in surround decoder! This means that when you sit down to listen to an SACD or DVD-A, all your bass management might as well not be there.
Installation and Setup
This is where Outlaw’s ICBM-1 comes in. This long, thin (1.76 x 17.6 x seven-inch) unit goes between your DVD-Audio or SACD player’s analog outs and the special analog ins on your receiver or preamp – or, more usefully, between your preamp and power amp. It pulls the bass off channels that will be fed to speakers that can’t handle it and feeds it to channels with large speakers, or a subwoofer, or both – with more control than you could have dreamed of. This is a pretty vital function, basically consisting of a bunch of high-pass filters feeding your regular speakers, paired with an equivalent set of low-pass filters to drive the sub and/or other bass-capable drivers.
My existing setup has a Sony CE-775 SACD player and a Kenwood DV-5700 DVD-Audio player feeding their six respective analog outs into a homemade switch box and, from there, into the receiver. I inserted the ICBM between the switch box and the receiver ins with another six interconnects, and plugged its little 15v wall-wart into a socket switched by my receiver. This unit can also handle a seventh (center rear surround) channel. If you are using such a system and have a separate pre and power amp, you’d place the ICBM between the two; in my case, current hi-res audio players only output six channels.
The next thing you need to do is to insure that you aren’t doing bass management twice. The Kenwood doesn’t have bass management on DVD-A playback but it does when I play back DVD-V, and I am only using its analog outs (so I can’t ignore the bass management that’s involved when playing a DVD-V). The Sony SACD player, on the other hand, has quite a good bass management system.
What you do now is disable any bass management that might be present, so that the ICBM gets to do all the work. The CE-775 has a “direct multi-channel out” mode, disabling any bass management, which is exactly what’s required here. The Kenwood, however, does not offer such an option. If you have a Kenwood or other equipment lacking the multi-channel out, go into the speaker setup menu for the player and tell it that all the speakers are large (i.e., they can all handle bass). It doesn’t really matter whether this setting allows you to say that there is a subwoofer on the system or not, because the ICBM is going to pull low-end information from wherever it exists. So if your player doesn’t let you turn on the sub when the front speakers are large (some do, some don’t), don’t worry.
The ICBM is what would have been called in an earlier time a “multi-channel crossover,” meaning that it is able to redirect incoming signals below a certain frequency and send them somewhere else. Looking at the front panel of the ICBM, we see a set of four identical knobs, which determine the frequency at which this happens for each left/right front, center front, left/right surround and center surround (if you have one). There is a slight difference here: the left/right front control determines below what frequency sound is fed to the sub; for the others, the knob sets the frequency below which sound is sent to the sub or the left and right front speakers (more on this in a moment). There are two further controls: “LFE Mix,” which sets the level of the LFE (not the sub) relative to the other signals, and “Subwoofer Level,” which sets the level of subwoofer output feed (not the LFE).
On the rear panel, among the forest of gold-plated RCA connectors, are three switches. One determines whether you have mono or stereo subs. The common wisdom is that bass is not directional, but it sure behaves like it is sometimes. As a result, it is often helpful to use a pair of subs mounted left and right. If that’s to your taste, you switch this switch to stereo and plug the two subs into the L and R outputs. An adjacent switch determines the slope of the low-pass aspect of the crossover (the part that drives the sub), either normal (12dB per octave) or “special,” which is a sharp 36dB/octave low pass for some subwoofers that prefer a steeper crossover, notably THX-certified subs. Unless you have one of these subs, “normal” is fine.
The final switch, up at the other end, is confusing, but as the manual points out, the fact that it needs to be thought about a bit is completely outweighed by its usefulness. It’s called “left/right recombine” and, when it’s on, it redirects bass to the front left and right speakers. So if you don’t have a sub, you would set this switch to “on” and set the left/right front crossover frequency to “bypass”. If you do have a sub (I do), you try out listening to the system with the switch both on and off and see what works best. With this switch on, the front left/right crossover frequency determines what goes to the sub (set the frequency to “bypass” and this means nothing at all: it all goes to the front left and right instead).
As far as setting the crossover points is concerned, the optimum frequency will depend on the bass handling capability of your speakers. If you know the 3dB-down point of your speakers, the manual suggests that you add 10 Hz and set the crossover to the next value up from there, which is a pretty good rule of thumb. If, for example, you know your speaker’s response is –3dB at 55Hz, say, you add 10 (65Hz) and set the crossover frequency to the next setting up, namely 80Hz. If you don’t have access to that information, or if it’s not terribly meaningful, there is a handy chart that correlates speaker size to the optimum setting. Basically, the larger the speakers (i.e., the lower the bass they can handle), the lower the best crossover frequency setting, from 120Hz for little satellite speakers to bypass or 40Hz for tower speakers with massive drivers. In the final analysis, you listen and tweak. The main thing you’re listening for is a smooth transition from high to low frequencies, and the best possible bass definition – and, of course, no distortion.