John Kotches, Editor / PC Home Theater
Crossover Frequencies (Per Channel): 40, 60, 80, 100, 120 Hz and Bypass
Slope (Normal Curve):
Slope (Special Curve):
Signal to Noise Ratio (A-Weighted): 105 dB
THD + Noise: < 0.015%
Channel Groupings: Left/Right, Center, Left/Right Surround, Center Surround
Relative Phase Shift (Between Channels): < 1 Degree
Relative Phase Shift (Low-Pass vs. High-Pass): < 1 Degree
Bass, the final frontier
The first generation of DVD-Audio players hit the marketplace around mid-2000. While the sound quality to many was a big step up from its direct predecessor the Compact Disc, the players themselves lacked the features that customers have grown accustomed to for multi-channel sources, namely bass management and time alignment.
For Dolby Digital, DTS, and in some cases PCM, our preamp/processors or receivers can redirect bass as appropriate within the system so that speakers which might be lacking in the bass department can be helped out by the subwoofer. They can also add requisite delays across the speakers so that the relative times for coincident sonic events remain coincident (the sounds from all the drivers reach your ears at the same time). Both of these functions are usually performed in the digital domain, and the algorithms to perform the operations on the data are well established. But, DVD-Audio and multi-channel SACD don't have standardized digital outputs at the time of this writing, so for the most part, our processors or receivers cannot do bass management or time alignment on these sources.
There are also other issues with Bass Management and Time Alignment. The MLP (Meridian Lossless Packing) decoding algorithm is very intensive, and the generation of DSPs that exists in most processors is inadequate to the task of decoding MLP and applying bass management and time alignment algorithms simultaneously. Well, why not? It turns out that the typical multi-channel MLP encoded DVD-Audio data have an average data rate of about 6-7 Mb/sec. Peak data rates are literally at the maximum allowable for the DVD standard, in other words 9.6 Mb/sec. During these peaks, it is also possible that some data were encoded in advance of the current frames and buffered due to a momentary shortfall that occurs when MLP cannot compress the data stream adequately enough to fall under the maximum DVD data rate. Contrast these data rates with those for DD and DTS, which are fixed and, depending on encoding, can be anywhere from 192 kb/sec (DD 2.0) all the way out to 1.5 Mb/sec for DTS. So, at most, the DSP is having to perform operations on 1/4 of the data at any given moment, compared to DVD-A and SACD.
Thus, we've effectively run out of DSP horse power. Until the next generation of DSPs is available, most processors and receivers will rely on analog connections for DVD-Audio. There are other issues with the passing of a high-resolution digital data stream which also have yet to be addressed by DVD Working Group 4 (which governs DVD-Audio). These include copy protection to prevent unauthorized copying, and a defined interface. Current leanings are towards DVI (Digital Video Interface) or IEEE1394 (more commonly called FireWire)
SACD is actually more of a problem in handling with DSP. All of the algorithms in the commercial DSPs are built around a PCM data stream, which is not what DSD (Direct Stream Digital - SACD) presents. So, new algorithms for bass management and time alignment must be developed. DSD (the encoding scheme for SACD) represents a summation of the changes in the analog waveform input to the DSD encoder. Unfortunately this makes it very hard to determine spectral content within the signal, and as such, the algorithms are vastly more complicated.
At the time this review is being written, second generation DVD-Audio players are being released which include bass management - however it is not highly flexible, which is something we've grown accustomed to over the past few years as our processors have matured. Further, Sony's multi-channel SACD players also contain rudimentary bass management. In both cases, this amounts to a single crossover frequency available - and regardless of whether this is the right option for your system or not, that is all you get.
So, bass management is the ability to low-pass any speaker to the sub and have the remaining frequencies go to the speaker. With DVD-A and SACD players, no can do.
I'm fixing a hole where the rain gets in, and stops my mind from wandering.
Enter the people from Outlaw Audio and their cleverly named ICBM-1. The Integrated Controlled Bass Management device is designed to fill one of the holes that is missing for first generation and second generation DVD-Audio players, namely bass management. If your multi-channel DVD-A or SACD player has no bass management capability, or you find the options not palatable or compatible with your system, the ICBM-1 is designed to help you out.
Click on the pictures below to see larger versions.
The ICBM groups the available channels together in a highly logical arrangement. From left to right on the panel are the Left/Right mains (front speakers), Center Channel, Left/Right Surrounds, and finally the Center Surround input. Following the channel crossover controls are the LFE Mix and Subwoofer Level adjustments.
The back panel has fifteen (!) RCA jacks, and hopefully, you won't fill them all up. There are in/out jacks for each of the five main channels, plus the Center Surround. In addition, the LFE channel has an input, and can send out signals for two subwoofers (stereo). Between the Left and Right mains input is a toggle switch called L/R Recombine which will be discussed below. There are two toggle switches at the far left as you view this picture. Farthest left is the subwoofer output mode, which can be switched between Mono and Stereo and the Low Pass Special/Normal switch.
The L/R Recombine toggle switch has both On and Off (Duh). Factory default for this switch is Off. I'm not sure I like the labeling, but it's their product, so they can name it as they will. More importantly is its function; L/R Recombine is used as a method of augmenting the output of nearly full range mains with output from the subwoofer. When on, the crossover is engaged at the selected frequency with the appropriate low-pass output sent to the subwoofer. The left and right speakers themselves still receive the full range signal. You have to be careful and do a lot of listening to see if this is the correct solution for your system. A poor selection of crossover frequency with L/R recombine enabled could lead to bloated, peaked bass response, so if using this function make sure the selected frequency is fairly close to the speaker's -3 dB point, to minimize the overlap region.
The Stereo/Mono switch is used to set the LFE and derived subwoofer output to either mono or stereo mode. In Mono mode, it does not matter whether you connect the subwoofer to the left, right or both outputs - the same signal will be present. In Stereo mode, stereo subwoofer operation is utilized. In this mode, Left front and Surround low-pass output, half the Center Channel (and Center Surround if applicable) as well as half the LFE signal are passed through the left subwoofer output. The right subwoofer output gets the other half of the Center Channel, LFE, and the Right mains and surrounds. I did not have the ability to test stereo subwoofer outputs during this review period.
The Low-Pass Special/Normal switch sets the crossover slope for the subwoofer low-pass filter. In Normal mode, the high-pass and low-pass filters both have a 12 dB/octave slope. In Special mode, the low-pass filter uses a 36 dB/octave slope (high-pass remains 12 dB/octave). Special mode is recommended for subwoofers which are THX certified.
Each controllable channel grouping has selectable crossover frequencies of 40, 60, 80, 100 and 120 Hz as well as Bypass so that the speaker runs full range. These are discrete stops, not a variable crossover, so it should be of high precision.
The LFE mix control is used to adjust the level of the 0.1 LFE channel only and is able to provide attenuation to -10 dB. The normal position is marked by the white indicator at unity gain. This comes in handy if you find a soundtrack with a bit too much bass, or if your processor doesn't have a DTS music mode, you can back it down to -10 dB to make the LFE track a little more "musical" for lack of a better expression.
The Subwoofer output level control is akin to a master volume control. It is important to make the distinction between the LFE mix control, which is active only on the 0.1 channel, and this control, which controls the level of the summed low pass outputs of all channels with a crossover engaged AND LFE. It is a final point of fine tuning output level, and provides anywhere from +9 dB of gain down to infinite attenuation (no sound). As with the LFE mix control, a white indicator is on the chassis to indicate unity gain (unity gain means the output voltage is the same as the input voltage).
And I thought my wires were out of control before this piece was introduced
Perhaps the only real downside to the ICBM is that you have to introduce an additional three pairs of interconnects to your system. This gets very cumbersome if you already have a ton of gear requiring analog cabling. Outlaw is addressing this with their own brand of cables in a 0.5m length so that the ICBM-1 can sit directly atop of the source (or processor or receiver) where it is controlling bass management.
There are a variety of ways the ICBM can be hooked up, and I'll try to explain the most common uses and methods. The prevalent usage will be to perform bass management for a multi-channel SACD or DVD-A player.
It is also usable between a preamp/processor as an alternative to using the pre/pros internal crossover. The ICBM-1 is most appropriate in conjunction with a pre/pro or receiver that has global bass management points which are inappropriate for the system in which it is installed. The ICBM-1 actually has better bass management flexibility than my preamp/processor. While my pre/pro has more available crossover frequencies, it is a single frequency for all small speakers. This is a critical point if you're using the ICBM-1 between a pre/pro and an outboard amplifier, where you should set all speakers to large and subwoofer to on, which allows the ICBM-1 to do all bass management.
I don't have the space (or the amplifier channels) at this time to install a DTS-ES or THX-EX processing 6 or 7 channel configuration in my home theater. However the guys at Outlaw don't just design for me, they design for those that have more spacious setups that do have the 6th and 7th channels installed, via the Center Surround input. While THX-EX does allow for a pair of rear surrounds, the info is mono, not stereo, so only a single input for these formats are provided. On output to split off to dual channels, a Y adapter would be used between the Center Surround output and the power amplifier channels.
The other channels (Left/Right, Center, Surround Left/Right) are already familiar to our readership, so I will not discuss their usage.
All connection possibilities are fully discussed in the ICBM manual which shipped with my review sample.
She's almost Gothic in a natural way.
So, we know what all the controls are, and we know that the crossover points are as flexible as many receivers and processors. I touched on the reasoning for this product in the introduction, and at this point, I'm going to cut to the chase. The ICBM-1 works as advertised. For my system, I found the optimum crossover points to be 60 Hz for the Fronts and Surrounds, and 80 Hz on the Center Channel.
Let's start off with the basics. Taking a 5.0 track on DVD-A and derive a 0.1 track. Emerson, Lake and Palmer's Brain Salad Surgery has two tracks that are recorded as 5.0, "Benny the Bouncer" and "Still You Turn Me On". Why these two tracks were 5.0 with the rest of the disc being 5.1, I do not know. My reference amplifier, the Cinepro 3K6 Series III has a channel activity light which indicates when a certain voltage threshold is exceeded on any given channel. So I kept my eye open for activity on the subwoofer's allocated channel during these two tracks and sure enough, the amplifier indicated a signal was present. A physical check of the driver (one can never be too sure) indicated that it was indeed getting the crossed over signal. They shoot, they score! A 5.0 track now has a derived 0.1 track.
What about stereo DVD-A? Ok, no problem. I popped over to a disc that can serve multiple purposes. Steely Dan's Two Against Nature has both discrete stereo and 5.1 channel mixes. Most of the newer WEA label DVD-As are being shipped with both options. There are a couple of tracks with some really great bass on them, and it was these that I used to test the next features of the ICBM-1. Let's grab track one Gaslighting Abbey in stereo and 5.1. Once again, the Cinepro's visual indicator didn't let me down, and showed the presence of a derived 0.1 track from the stereo output. In the 5.1 mix, the bass guitar was mixed into all 5 main speakers, as well as the 0.1 channel.
There's really only one way to test this. Two times through, with just the subwoofer cables connected. It isn't all glamorous in the life of a reviewer! So I did just that. Pass 1 was with all crossover settings to bypass. Just a little bit of electric bass, and the impact portion of the kick drum were my constant companions. Once I put the crossovers into their normal positions, about half the electric bass popped into the subwoofer, indicating that some of the bass guitar (the B, E, and some of the A string) were now getting fed to the subwoofer. After that, I connected up the speakers and listened two more times. Once with the crossover disabled, which is my normal way to listen to this track. Bass guitar was everywhere. Nicely defined, and maybe just a bit looser than I'd like it to hear. When listening with the ICBM-1 engaged, and more of the bass guitar being covered by the subwoofer, the bass was tauter and more controlled. It was not a subtle difference because the bass guitar now popped in a newly authoritative way. So this was a wonderful enhancement to an already enjoyable listening experience.
I then hooked up the ICBM-1 to a stereo SACD player that is currently under review. Once again, the subwoofer started getting information below the crossover frequency, as it should. This applied to both SACD and Redbook CD played back through this player. I stuck on my 'boss bass' Redbook disc, the Irish Tune from County Derry. In my review of the SV Subwoofers, I demonstrated with a waterfall plot that portions of this track have 16 Hz information from the pipe organ, and will not play back this disc without bass management of some sort. I have clipped amplifiers and found excursion limitations in drivers with this relatively serene song. Once again, I was not disappointed.
Ok, this is all anecdotal, so how about doing some testing to make sure things are correctly implemented. Sure, subjective info is great, but how do you know that the crossover is actually implemented correctly, i.e., the labeled frequency is accurate, and levels are correct? A fair question to ask, since it would be easy to accept on faith that its functioning correctly. So,. I grabbed a test disc with the bass decade (200 Hz - 20 Hz, with 10 discrete tones at varying frequencies) and decided to attack the problem empirically. Does it really work as advertised?
Here are the results of the bass decade, left channel and subwoofer only connected, using the 200 Hz tone as my reference level. Crossover frequency was set to 60 Hz, and the crossover switch was at Normal, which implements a 12 dB high-pass and low-pass slope. My Radio Shack SPL meter was set to C-Weighted, slow, with the meter at 1m from the speaker or subwoofer. If you think the SPL meter is flat, nope! But all values have been corrected for known errors with the Radio Shack meter.
|Frequency (Hz)||Speaker with no Crossover (dB)||Speaker with 60Hz Crossover (dB)||Subwoofer output (dB)|
Ch, ch, ch, ch changes
So what haven't I talked about? Hmm. The changes brought about by including the ICBM-1 to perform bass management duties in areas that didn't previously have them. The biggest changes were apparent with DVD-A. These changes weren't subtle by any stretch of the imagination. On tracks with substantial bass content in the main speakers, I got a much tighter bass when utilizing the subwoofer as opposed to multiple lesser drivers in my other speakers. In addition, the bass was also more authoritative. It had weight, without losing nimbleness if you will.
In addition, if you're so inclined, you can use the ICBM-1 in a straight stereo system as a low cost external crossover for connection to a powered subwoofer. A high quality stereo analog crossover for US$250 is a bargain in and of itself.
If your DVD-A or SACD player provides adequate bass management for your system, you might be able to get away without this product. For the majority of our readership, who don't employ five full-range speakers in their system, it is my opinion you need this product to get the most out of DVD-Audio or Multi-channel SACD.
The ICBM-1 hits the target dead on and is well worth the asking price in even relatively modest systems. Outlaw is not getting this sample back, so I'm mailing them a check. As I add other multi-channel sources, they will get checks for additional ICBMs.
- John Kotches, Editor PC/Home Theater -
© Copyright 2001 Secrets of Home Theater & High Fidelity
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