For a very long time my audiophile friends and I had a “nose-in-the-air” attitude toward subwoofers. In our minds, subs were meant for clubs, thunderous home theaters, and drivers who liked to annoy neighbors and passers-by with loud, thumping music coming from their cars. Subwoofers, for all intents and purposes, had no place in a dedicated high-end, two-channel audio systems. Awhile back, I’d experimented with several (single) subwoofers in my listening room, but each time I found that they produced nothing more than low-end filler—bass lines that were boomy and bloated, rather than taut and accurate.
Then I received two MartinLogan Balanced Force 210 subwoofers for audition, along with ML’s Perfect Bass Kit (PBK) for dial-in, and decided to give subs another go. Not only did these two subwoofers radically change my thinking, they've also become essential tools for achieving the kind of taut, controlled low end that would be impossible with most stand-alone speakers.
Setting up a subwoofer—much less two of them—is a long and involved process: To achieve optimal results you should expect to spend a minimum of ten hours, spread over a week or two, tweaking and listening. ML’s Perfect Bass Kit, sold separately ($100), helps immensely, but there’s no substitute for patient and careful tuning of your dual-subwoofer setup before employing PBK.
The classic method for discovering the optimal location for your subwoofer is to place the sub in your listening position, preferably in your chair, and then crawl around the room listening for the spots where the bass sounds best. While this method can be pretty accurate, it’s not very practical. What happens if the best locations are too far from your preamp, or in the middle of the room, or in some other unfeasible spot? Set-up challenges are further exacerbated when you use two subwoofers. I’m fortunate to have a very large listening space—33' x 10' x 27'. If you don’t have this kind of room and can only stick your subwoofers in corners, proceed with caution, as placing subwoofers there will reinforce room modes, and potentially cause your system to sound boomy.
I found the best placement for the Balanced Force 210s by using a kind of “balanced ratio” in between my speakers. Measuring from the tweeter, my speakers are set six feet from the rear wall, twelve feet apart, and toed-in 25 degrees. Measuring from the tweeter to the center of each subwoofer, I set each Balanced Force 210 three feet inside the main speakers and three feet behind each one. This means that the Balanced Force 210s are three feet from the rear walls, and roughly six feet apart.
I tested the Balanced Force 210s first with standard single-ended outputs and no bass management, then using PBK to measure the subwoofers’ outputs and optimize EQ, and finally with a preamp (the Classé CP-800) with bass-management capabilities. If you want to connect two Balanced Force 210s from a preamp or an integrated with subwoofer/auxiliary outputs, make sure the preamp has both left- and right-channel outputs—otherwise you will be running two mono subs. If you have only one subwoofer output, you can still “daisy chain” the two Balanced Force subs, and you can still use PBK to program one subwoofer, which will, in turn, control the second one. But far and away the best method for two subs is to have a preamp capable of dual-subwoofer bass management. The Classé CP-800 allows for this, permitting the use of two XLR outputs to run the Balanced Force 210s in a left-channel and right-channel setup.
The Perfect Bass Kit comprises a microphone, stand, two USB cables, and software that allows you to measure your MartinLogan subwoofers and automatically calibrate them to achieve the best sound in your room. Connect one USB cable from the Balanced Force 210 to your computer, and then connect the other USB cable from the computer to the microphone. Next, set the microphone at your listening position, then use the PBK software to run measurements in up to ten different positions around your room. The PBK software plays a series of test tones as you go through this process, and in the end automatically uploads the “correct” EQ into your subs.
One of the PBK software’s few pitfalls is that it’s a Windows-only program. This means that all of you Mac users will be out of luck, unless you use Boot Camp or Parallels to run Windows on your Mac. I had to borrow a PC in order to run PBK.
Another downside is that you will need a laptop or multiple USB extensions to complete your measurements. While the supplied USB cables are 12 feet long, they aren’t quite long enough to safely move the microphone around the room without potentially yanking a stationary computer off its rack. Invest in a ten-foot USB extender (about $6), or a USB-over-Ethernet extender (about $15), if you’re worried about the degradation that occurs with longer USB cable lengths.
The measurement process takes about ten minutes, and is fairly effective at performing final tweaks for you, but, as I said at the start, it is no substitute for proper subwoofer setup. Don’t expect to plop the subs down anywhere in the room and have PBK resolve all issues—correct placement is the first, and most important, step.