What is a Subwoofer?
A subwoofer is a type of loudspeaker that reproduces the lowest bass notes in the music. Basically, its a one-trick pony delivering bass with authority and nothing else. Doing that requires lots of power and a specially designed speaker with some key empirical measurements that should be maximized.
"What are some of those measurements that I should look out for?" you might ask. Well, let's see:
- Impedance: As we talked about in the previous article on speakers, impedance is the resistance to the flow of electric current. Higher impedances are easier for an amplifier to "drive," or power. Lower impedances or speakers wired in parallel are harder for your amplifier to handle.
- Materials: These are what your "drivers," or speakers are made of. The actual sound-producing cone can be made from any of a multitude of materials. The cone needs to be stiff, yet lightweight. Better materials are Kevlar or polypropylene. Metal cones are good but they tend to be more expensive to do correctly. Another area of concern is the "surround" material. This is the stuff that attaches your driver to the "bucket," or metal frame holding the speaker. Surrounds should be light and flexible, but strong. Good surround materials are rubber or composites, such as plastics.
- Free-Air or Boxed enclosure: This is how the sub is to be mounted. Free-Air enclosures have the sub speaker mounted to the back seat, or the rear shelf, using the trunk area as the enclosure. Free-air systems save space and have flat frequency response. The sub speaker needs to be designed for this purpose. For best performance, the trunk should be air-tight when closed. Boxed enclosures have the speaker mounted within a box with or without a "port" or a tuned bass opening. The port size and the box's volume (in cubic feet), needs to be matched to the speaker.
- Sensitivity: As with other speakers, this value tells you how efficiently a speaker converts electrical energy into sound. The higher the number, the louder the speakers will play at any given volume setting. Efficient speakers help you maximize the performance of your amp.
- Frequency Response: With subwoofers, you want the frequency response to go as low as possible. The human ear can hear approximately 20-20,000 hertz. Bass frequencies are usually considered 20-2000 hertz approximately. Look for subs that can extend frequency response down as close to 20 hertz as possible.
- RMS Power Range: As with other speakers, this is the range of continuous power the speaker requires to operate properly. Expressed in watts, RMS Power Handling refers to the amount of power a speaker can handle on a continuous basis. The RMS power range figure is a reliable way to rate and compare different speakers.
- Peak Power Output: Again, peak power handling refers to the amount of power a speaker can handle during a brief musical burst.
- Volume Acoustic Suspension: This is the volume of air having the same acoustic compliance ("stiffness") as the speaker's suspension, measured in cubic feet or liters. Lower numbers are better.
- Fs: The frequency at which a speaker naturally resonates in free air, measured in hertz, lower numbers are better.
- Xmax: This is the measure of a speaker cone's maximum excursion in one direction while maintaining a linear (non-distorting) behavior. This is measured in millimeters, and larger numbers are better.
