The OEM Systems ICBM (Integrated Custom Bass Management) System might be the first subwoofer system to make it easy for average listening rooms to get great bass in every seat. Although it's a new system, first demoed at CES 2016, the ICBM's genesis dates back to the 2002 Audio Engineering Society convention.
The 2002 AES saw a true revolution in sound--or, at least, what should have been a revolution in sound. Previously, audio experts had been setting up subwoofers using a variety of methods and configurations, with adopters of various practices all proclaiming the correctness of their methods. In a paper authored and presented by Harman International researcher Todd Welti, titled "Subwoofers: Optimal Number and Locations," we finally learned how to do subwoofers right. Welti's paper proved that using four subwoofers, either with one in the center of each wall or one in each corner, delivered the flattest bass response across a large listening area.
This technique nearly eliminated the big problem with using a single subwoofer: if you optimize the bass for one seat, the bass won't be as smooth in the other seats. Some seats might see near-complete dropouts at certain bass frequencies. That's not a problem if you're the only one listening; however, if you're listening with family and/or friends, using a single subwoofer can't deliver a good experience for everyone.
The downside is that the method outlined in Welti's paper requires four subwoofers, which take up a lot of space and can be complicated to hook up and calibrate. Thus, manufacturers haven't done much to capitalize on Harman's findings. Harman released an automatic four-surround processor called the BassQ, but soon discontinued it. That's why I was enthusiastic when I heard a demo of the ICBM at CES. It's an attempt by an audio company to make using four subwoofers practical.
The $2,700 ICBM system combines four SE-80SWf eight-inch in-ceiling/in-wall subwoofers, four ENC-816LP in-wall enclosures, and one P-500XB subwoofer amplifier. You can also get a package with the same amp and just two subs for $1,600, and you can buy the package without the enclosures ($1,700 for four subs, $1,100 for two), which might get you somewhat deeper bass response (depending on your wall/ceiling configuration) at the expense of more drywall vibration and more leakage of bass into adjacent rooms.
This system makes the four-subwoofer configuration more practical primarily because of the slimness of the subs. Each one is just four inches thick with the driver and grille installed, making it practical not only to mount them in-wall, but also to simply slide them under or behind couches and other furniture. A dealer who stopped by my house to hear the system told me that the design's stealth is especially important. "We have very few jobs where we could install four subwoofers out on the floor," he said.
The system has two unusual and important features. First is the SE-80SWf itself, which uses a slimmed-down eight-inch, four-ohm driver that OEM Systems engineer Oliver Lieder told me is custom-designed for this sub. "The only stock component in it is the spider," he told me. (The spider is the part--usually a pleated yellow fabric--that connects the voice coil to the frame.)
Second is the P-500Xb, a Class D amplifier designed specifically to drive multiple subwoofers. It's a stereo amp rated at 90 watts per channel into eight ohms, and up to 500 watts RMS (700 watts peak) when bridged for mono into four ohms. It includes several subwoofer-friendly features, including a defeatable crossover that can be set for any frequency between 40 and 160 Hz; a subsonic filter adjustable from 10 to 50 Hz; a boost filter centered at 30 Hz and adjustable from flat to +9 dB; and a power range control for the internal limiter that adjusts the limiter's attenuation from 0 to -9 dB. It also offers the usual phase and level controls.
What the system doesn't offer is the ability to adjust the volume and EQ of each sub separately, which is recommended in the Harman paper. It occurred to me that you could connect two subs in series to each amp channel so that you could at least adjust volume and EQ in pairs, but this would require adding a couple of subwoofer EQ/control boxes and wouldn't give you the maximum output from the amplifier. At any rate, making all the subs independently adjustable would have greatly increased the cost of the system.
Lieder stopped by to show me the features of the P-500Xb and help with the setup. Not wanting to cut holes in my walls, I simply laid each sub on the floor in a different corner of the room, which yielded performance similar to what I'd have gotten by mounting the subs in the walls. We ran long in-wall speaker cables from the subs to the P-500Xb. To get the most out of the amp, Lieder put it in bridged mono mode, connected the two pairs of subs in series, then connected the pairs in parallel, giving a combined impedance of four ohms and allowing the amp to deliver all of its maximum rated 500 watts.
For Lieder's visit, we set up a 2.1-channel system using a Classé Audio CP-800 preamp and CA-2300 amplifier driving Revel Performa3 F206 tower speakers, using Wireworld Eclipse 7 interconnects and Mini Eclipse 7 speaker cables. Later, I switched to a 5.1 system using a Denon AVR-2809Ci AV receiver, an AudioControl Savoy seven-channel amp, and Sunfire CRM satellite speakers. With the Revels, I set the crossover point in the CP-800 to 80 Hz. With the tiny Sunfires, I set the AVR-2809Ci's crossover to 100 Hz.
Lieder showed me how the controls on the P-500Xb work and set them himself, but I almost immediately had to reset everything so that I could run measurements on the system. When I set it back up, I settled on a +3dB boost at 30 Hz, a subsonic filter setting at 20 Hz (because I intended to play ultra-low-frequency test material very loud and didn't want to damage the drivers), and a power range of zero to bypass the limiter. (Considering the CEA-2010 output figures I measured from the system, I thought it unlikely that the drivers really need a limiter--not for my short-term testing, anyway.)
When hearing Lieder's setup and the setup I did myself after the measurements, I was thrilled to hear how effortlessly the ICBM system blended with the Revels (and later with the Sunfires) with next to no effort from either of us. I think this occurred for a few reasons. First, I've found that subs with smaller eight- or 10-inch drivers seem to blend more readily with the main speakers when an 80-Hz or 100-Hz crossover point is used. (That's assuming we're talking about a fairly conventional, low-mass driver, not the high-mass, ultra-beefed-up small drivers found in typical mini-subs.) Second, the more even frequency and phase response of the four subs reduces that sense of boominess that makes the sub sound different than the main speakers and helps your ear tell there are subwoofers in the system. Third, with a subwoofer in each corner, the bass becomes impossible to localize, even if you're using a relatively high crossover frequency.
I expected the ICBM system would be more of a home-theater-oriented product, but its benefits for music reproduction are, to me, more impressive and important. I loved the evenness with which it reproduced the upright bass on my favorite jazz recordings. Singer Cécile McLorin Salvant's irresistible version of "Wives and Lovers" is packed with precisely played rhythmic accents from bassist Paul Sikivie. While a typical single-subwoofer setup would likely have made some notes in his bassline boom, the ICBM's four subs kept all the notes smooth and precise, which is especially important in a performance like this where timing is everything. In my listening chair, which I placed in a position where the bass tends to sound smoother in my room, the response sounded close to perfect. It wasn't as good in my room's "sour spot"--a place about six feet behind and four feet to the left of my listening chair where visitors often like to sit but where the bass usually sounds grossly uneven. Still, even in that compromised position, the response was about as flat as I'd get from a carefully set-up single subwoofer in my listening chair.
I loved the way the ICBM system allowed the lowest frequencies of the upright bass on Holly Cole's version of "Goodtime Charlie's Got the Blues" to blend perfectly with the upper notes, so the result sounded like a miked acoustic bass rather than a bass with a piezoelectric pickup. All the bottom-octave power of the bass was there, but not hyped--just the way a real bass sounds when you're a few feet from it.
When I put on Deadmau5's "A City in Florida," which like most EDM relies largely on a single, throbbing deep bass note, I was shocked and thrilled to hear how the ICBM system energized the whole room, making it feel like I was in a club with speakers surrounding a dance floor. The bass and the room seemed to be one, and I didn't get any sense that I was hearing a subwoofer. The system showed no sign of strain on this tune, even though my system was playing loud enough that it would have drowned out the noise of a pretty large dance party.
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