What Are Subwoofers?
A subwoofer speaker is simply a woofer, or a loudspeaker driver (a transducer), which is exclusively dedicated to high-fidelity reproduction of the lower frequencies in the frequency-spectrum. These usually encompass a range from 20Hz to 150Hz due to the type of technology and components, which only convert energy to low-frequencies.
As with any speaker, it uses an actuator which is a type of transducer or driver. Subwoofers are active or passive, again like any other type of loud speaker, which means they are either amplified internally or need a separate amplifier to work.
The first “subs” were developed during the 1960’s, but they have been greatly improved to be a stand-alone unit and part of a bigger audio system. Initially, they were just integrated with stereo systems but now they are also used in professional studios or, concerning our interest, in home-theater setups.
How it all Works
Any speaker works by translating electrical signals ultimately into sound waves, by fast vibrations of the diaphragm. If you open a speaker you will see the cone moving as it plays music.
The speaker contains a magnet and a voice coil, the latter with two wires attached feeding positive and negative current through. The components interact with each other depending on the polarity of the current. In simple terms, this up-and-down movement creates vibrations which ultimately create a wave of sound.
As briefly mentioned the type of driver for a woofer differs from that of normal speakers. The speaker size and circumference is much larger, for example, than that of mid-range or high-range drivers (tweeters) which need to vibrate considerably faster due to the frequencies they output.
Passive and Active
A passive sub is amplified by external means, which in a home-theater set up may also be provided by connecting to the receiver or similar. Some passive subs have built-in signal crossovers which will accept any kind of signal, filter out the bass frequencies and send anything else to another set of speakers.
Active speakers do not need to be provided with amplification and can be installed as a single unit, by plugging it in and connecting the wires to the inputs. This type of speaker has more options, such as crossover options which will allow you to control what kind of low-frequencies your speaker responds to.
In Summary
These are the basics of how a subwoofer is dedicated exclusively to low-frequency sounds. There are much more complicated aspects, such as the details concerning high-inductance voice coils and how these affect a subwoofer’s performance. If you are interested in the more technical aspects have a look at the following:
Related Brighthub articles:
How Does a Subwoofer Work?
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