To help you get the most out of the information and find just the right subwoofer for your system, we’ve put together explanations of some of the categories you’ll find in the spec charts.
Driver
This is the size and number of drivers (usually cones) in the subwoofer. A number in parenthesis indicates the number of drivers. Some entries include the legend “PR,” for passive radiator. A passive radiator is a cone or flat diaphragm, with no voice coil or magnet, that cannot produce sound on its own. The passive radiator isn’t driven by an amplifier, but rather moves in response to air-pressure variations inside the subwoofer enclosure caused by the active woofer’s motion. There’s just as much sound inside the cabinet as there is outside; the passive radiator channels some of that sound out into the room, extending bass response.
Loading
Loading refers to the enclosure design, which has a large effect on the woofer’s behavior. A sealed enclosure is just what the name suggests; the subwoofer enclosure is completely sealed. Sealed designs are also called “air suspension” or “acoustic suspension.” By contrast, reflex loading employs a hole in the enclosure (called a port or vent) that channels some of the sound inside the cabinet to the outside. Reflex loading has three main advantages. First, it increases a speaker’s maximum acoustic output level—it will play louder. Second, it can make a speaker more sensitive—it needs less amplifier power to achieve the same volume. Third, it can lower a speaker’s cutoff frequency—the bass goes deeper. On the downside, the bass from a reflex system rolls off more steeply than that of a sealed enclosure. Consequently, two subwoofers may have the same specified bass extension (say, 28Hz) but the reflex system will have less output at 20Hz compared with that of the sealed subwoofer with the same specified frequency response. Moreover, a reflex system’s transient performance (how quickly the cone can start and stop in reaction to the drive signal) isn’t as accurate as that of a subwoofer with sealed loading. There’s no definitive answer as to whether sealed or reflex loading is better; there are superb examples of each.
Amplifier Power
Most subwoofers include an integral power amplifier. Such subwoofers are sometimes called “active” or “powered.” A subwoofer with no internal amplification is called a passive subwoofer. When looking at the amplifier power ratings, keep in mind that manufacturers don’t always adhere to the same criteria for specifying the amplifier’s output power. For example, some manufacturers will provide the RMS rating, which you can think of as the power the amplifier can produce continuously. By contrast, the peak-power rating indicates the amplifier’s output power for very short bursts. Consequently, two subwoofers made by different manufacturers may both be rated at “1000W,” but one of those ratings is RMS, or continuous power, while the other can produce that 1000W only on peaks. The first subwoofer’s amplifier is in reality much more powerful than the second subwoofer’s amplifier even though they look identical “on paper.” The amplifier-power specs in this directory were provided by the respective manufacturers, and thus include a mix of RMS and peak-power ratings. When looking at subwoofer amplifier power ratings, read the fine print.
Frequency Response
This is the range of frequencies the subwoofer can reproduce. In full-range speakers (not subwoofers) we’re interested in how low the speaker goes in the bass and how high in the treble. But with subwoofers, it’s the first number—bass extension—that’s more important. Just as manufacturers don’t rate their amplifier power using the same criteria, subwoofer manufacturers don’t adhere to the same standards when specifying a subwoofer’s frequency response. For example, two subs may both have the same frequency response specification of 28Hz–300Hz, but the output from one sub may be attenuated (reduced in level) by 3dB at 28Hz, while the second sub’s output at 28Hz may be attenuated by 10dB. The first sub will produce deeper bass than the second sub even though they have identical frequency-response specs. When a manufacturer publishes a tolerance along with the frequency response, such as ±3dB, you can be sure that it’s an honest measurement.
DSP
Digital Signal Processing (DSP) is the manipulation of audio signals by performing mathematical computation. DSP can be used in subwoofers to achieve flatter frequency response, and to correct for driver misbehavior. Some subwoofers include integral DSP room-correction, a feature that measures the response of the subwoofer in your particular room and then creates a custom filter that removes the peaks and dips in the frequency response at your listening position.
Wireless
Some subwoofers can be connected wirelessly to your audio system. This is a convenient feature if you plan to position the subwoofer at the back of a room or if a cable would have crossed a doorway or hall.
App Control
A new breed of subwoofers can be controlled by a smartphone app. Such controls include level, phase, equalization, and DSP.
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