Build
Upon opening the attractive, multi-colored box, I was greeted with the backside of the 124.7w. The first thing I noticed was the wire connection terminal on one of the legs on the frame; right next to the hex-headed screw terminals, there's a switch labeled 2 ohm and 8 ohm. This switch allows the user to select the desired impedance to match the installation requirements. As you may have guessed, the Kappa 124.7w uses a dual voice coil and this switch is an awesome solution that simplifies the wiring. While there is no 4-ohm selection, a variation of this drive is available that is selectable between 1 and 4 ohms, the Kappa 122.7w. All the bases are covered - just be sure you're purchasing the correct sub for your application. Exclusive of the switch, there's really nothing too out of the ordinary about this woofer. Or is there?
The Infinity Kappa 124.7w looks well constructed. It uses a thick-gauge, bluish-gray, powder-coated stamped steel frame as a backbone. But something else about this driver led me to believe the engineers injected it with extra zest than a first glance would tell. Hanging off the rear is a functional piece more commonly found on an amplifier - a cool finned aluminum heatsink that engulfs the entire motor structure. This helps the metal motor components dissipate heat so that the sub can handle more power without premature heat-derived failure. However, what lurks beneath the heatsink is more interesting. The Kappa 124.7w uses no ordinary ferrite powered motor, but rather one driven by neodymium. This not only helps reduce the overall weight of the sub, but it also produces more power in a much smaller package. While impressive, what is spectacular is that there may not be another sub in this price range to use this relatively expensive magnetic material. Kudos to Infinity!
The driver employs a 3" voice coil that connects to a unique plastic collar/joint mechanism at the neck of the cone where it meets the spider. This injection-molded piece has two hang-offs that receive the incoming tinsel lead wires for both coils. Essentially this keeps the tinsel leads from hitting the backside of the cone by shortening the length between terminations - a nice idea that doesn't interfere with the integrity of the spider (like those tinsel leads sewn into the spider fabric). Speaking of spiders, the progressive unit on this sub appears to be a woven poly-cotton blend. It sits atop a translucent blue riser attached to the frame.
Out front, the extremely stiff, woven glass-fiber cone is justified at its leading edge by a rubber surround. The cone edge is turned down for additional strength while the hard black plastic Infinity logoed dust cap keeps debris from contaminating the voice coil gap. The Kappa 124.7w also uses a standard vented pole piece that, according to Infinity, reduces air compression under the dust cap, thereby minimizing mechanical noise and providing a more constant mechanical Q for reduced distortion. Interestingly, Infinity makes no claim that this helps vent heat from the voice coil.
Manual
The manual is printed on two separate sheets. The first sheet, listed as "Instructions," contains the gratuitous thank-you and information regarding sealed, vented and bandpass enclosures to assist you in your design decision. Three-quarters of the second page is dedicated to the connections - these are very important because, while the impedance selector switch does simplify it, connecting multiple subs and maintaining the proper impedance can be tricky. This section also includes a warning about loud music and your hearing and a small section on bass reproduction in your car.
The second sheet is a dedicated technical data page for the Kappa 124.7w. It contains mounting information, Theile-Small parameters, as well as enclosure recommendations for vented, sealed and bandpass enclosures. Power handling of this driver is listed as 350 watts RMS, 1,400 watts peak, with a sensitivity rating of 90dB.
Also included in the package is an Infinity decal, a gasket to seal the woofer with and a warranty registration card. These guys want to make sure you get the most out of your purchase!
Installation
After breaking this sub in at 15Hz for about 30 hours and adjusting my sealed box volume to an Infinity-recommended 1.3ft3, I installed it facing rearward in the right rear corner of the trunk of my BMW 3-series coupe. I then connected it to the bridged channels of my Genesis amp with the selector switch on the Infinity sub moved to 2 ohms. To provide an unobstructed output path into the passenger compartment, the rear seats backs were folded flat.
Rock
Robben Ford "Baby, I'm Your Man" Yeah, I know. Some of you are probably thinking, "Why does he always use the same tracks to test with?" Well, I'll answer your question. I use this particular track because it's one of the best ones I've found for ascertaining how seamlessly the sub-bass, usually coming from the rear of the vehicle, blends with the midbass being reproduced by the low-frequency drivers in the front of the car. The objective here, of course, is to have the subwoofer "disappear" from the equation and give the impression that all the bass is coming from one point in the front of the car. In addition, I know virtually every note of this song and can tell when something isn't quite right.
