Subwoofers

Paradigm Reference Signature Sub 25 Subwoofer and Perfect Bass Kit Software (PBK-1)

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The Design

The Sub 25 is a sealed-enclosure with a 15" driver. The cone is made of mineral-filled co-polymer polypropylene with dual-spiders. The three-inch, eight layer voice coil uses a 37 pound ceramic/ferrite magnet motor structure (which goes a long way towards explaining why the beast weighs 114 pounds/51.7 kilograms). Paradigm explains that "due to the incredibly high power and tremendous output the SUB 25's grille is non-removable." At first I thought that was a forgivable piece of marketing fluff. However, while bench testing the Sub 25 I had to dampen two separate wall-hangings that started buzzing when I cranked the Paradigm that had never previously made a peep.

The Sub 25, like most high-powered subwoofers, is powered by a Class D amplifier that Paradigm describes as a patented Ultra-Class-D power isolation amplifier. The amp is rated at a monstrous 7,500 watts peak dynamic power, with 3,000 watts RMS sustained. The Sub 25 has a Universal Input power feature that allows it to operate at any voltage between 108 and 265 volts. Paradigm recommends that to achieve maximum performance the Sub 25 should be connected to a 240-volt line, or if a U.S. standard 120 volt line is used that the sub have its own dedicated 20-amp circuit. Unfortunately, my home has neither of those features, so the best I could do was connect it to a 15-amp circuit and keep all the other electrical devices on that circuit (except lighting) turned off. Even so, when I plugged in the Sub 25 the lights in the room noticeably dimmed.

The review sample came in gorgeous piano black, although the Sub 25 is also available in cherry or natural maple finish. As expected from a Paradigm Reference product, fit n' finish were superb. The Sub 25 is somewhat trapezoidal shaped, with tapered sides that eliminate any parallel surfaces that could create troublesome internal resonances.

Paradigm Reference Sub 25 powered subwoofer and Perfect Bass Kit (PBK-1)

The rear panel of the Sub 25 contains a volume knob (which I never dared turn more than halfway up); a defeatable low-pass filter variable between 35 and 150 Hz, and phase adjustment knob variable between 0 and 180 degrees. The Sub 25 has two RCA line-level inputs, as well as a balanced XLR input. Other than an on-auto switch and power cord connection, the only other connection on the back panel is a USB port.

This is where the Perfect Bass Kit comes in. As many audiophiles know, Paradigm is the sister company of Anthem, maker of high-end products like the Statement pre-pros. Anthem has its own proprietary room correction/EQ software called ARC. A version of ARC designed specifically for Paradigm subs is called the Perfect Bass Kit, the PBK-1. The PBK-1 includes a software based interface that installs on your computer, along with an individually calibrated microphone and a heavy-duty cast iron microphone stand that would feel at home on any nightclub stage.

I'm a big fan of room correction software for bass frequencies, since most serious problems involve standing waves that create nulls and peaks in the 20-100Hz range. However, most existing solutions have two limitations: They only measure and calibrate response at a single room position, and address only peaks by lowering offending frequencies (attempting to overcome a room null by boosting EQ is a good way to blow up a subwoofer). The PBK-1 addresses both of these problems.

Once the software was loaded into my laptop (fast and painless), I opened the program, connected the USB calibrated microphone to my computer, and connected the supplied USB cable between my laptop and the Sub 25. The program asks you to select at least five different measurement points in your listening room, and will measure up to ten different locations. One PBK-1 will adjust up to four Paradigm Reference subs. The ability to measure in multiple room locations is particularly important in bass response, because nulls and peaks can vary dramatically in various spots, often within a couple feet of each other. The PBK-1 takes into account the various nulls and peaks in the five (or more) listening positions, and creates a suggested correction to provide the best overall sound throughout the room.

FIG 3

Once the software has crunched the numbers from the test tones, it shows three frequency response curves. The red line (measured without any correction applied ) showed what I already knew, that my room had a serious null (the non-technical term for which is "suck-out") at about 50 Hz, and a boomy peak around 70 Hz. I have bass traps in my corners and acoustic treatments elsewhere, but could not do anything more with those two room modes short of knocking out and moving an entire wall.

The blue dotted line shows the target curve, what the PBK-1 would try to emulate through a series of EQ adjustments cutting and boosting targeted frequencies. Because the PBK-1 is designed to work with Paradigm Reference subs, it can boost frequencies up to certain limits to flatten out the room response without creating distortion or overdriving the amplifier. The blue line shows the frequency response after applying EQ, and the picture tells the story. The 50 Hz null and 70 Hz peak are essentially gone, with frequency response between 22 and 100Hz within 2 decibels. Most impressive!

Paradigm Reference Sub 25 powered subwoofer and Perfect Bass Kit (PBK-1)

Once the curve is set, you simply unplug the microphone and USB cables and are ready to rumble.