Subwoofer

A subwoofer ( English pronunciation [ wu ː ˌ sʌb fə ( ɹ ) ] for a subwoofer ) is a special speaker that is designed by its design forth for the sole reproduction of low-frequency sound waves, the so-called bass or even just deep bass. A remote installation is possible because the source is not to localize low frequencies to the human ear.

Subwoofers are mainly used public address systems at large events in nightclubs, at the movies, in car audio systems and as components of hi-fi and home theater systems to use, especially for particularly compact main speakers, often referred to as satellite speakers.

General

Apart from the actual design, a distinction between active subwoofers, which are operated with a built-in power amplifier and passive subwoofers, which, as usual (passive ) speaker to be driven by an external, separate amplifier. The latter are more likely in Public Address and in the automotive hi-fi use. Hi -Fi and home cinema powered subwoofer are in use due to its compact design and easy handling.

Signal supply

The subwoofer can be powered in two ways with signals:

• About a crossover that filters the low-frequency components for the subwoofer from the signals for the remaining speaker and the other speakers forwards the remaining shares. Active subwoofers usually have a built-in crossover, in which adjust the crossover frequency can be made. A typical transition frequency in your home theater, here lies between 80 and 100 Hz, because frequencies below this limit are not localized.
• The subwoofer gets delivered a dedicated, already processed signal. To provide the current multi -channel sound systems such as Dolby Digital or DTS not only five or more surround-sound channels, but also a separate Low Frequency Effects channel called LFE, for the subwoofer.

Design principles and designs

What is colloquially referred to as the chassis of the subwoofer is actually the fixed part of the speaker. Through various - sometimes quite complex - housing principles sound completely different systems can be designed, although always the same loudspeaker is in use.

To create deep tones, the greatest possible amount of air has to be moved, what can be achieved in two ways:

• Insert a speaker with a large membrane surface that moves a lot of air because of the size, or
• Use a small speaker that can deflect as much as possible its membrane, which is also a lot of air ( called this property hub) is moved

Usually the speakers a subwoofer has a diameter of at least 16 cm, although this is already too little for normal rooms often to produce more usable level. The maximum playback volume is thus significantly influenced by the size and the stroke of the speaker.

Large market most speakers have diameters from 38 to 45 cm (15 to 18 inches). One of the biggest subwoofer speaker out of the Hi- Fi range is 80 cm speakers ( 31.5 ) FW800N by Fostex. Of course there are individual items that can be even greater, but it is sometimes very difficult to construct such large membranes, which have the necessary stability. Therefore, it is usually more practical to use multiple subwoofers to achieve a higher maximum level.

Designs

After construction principles, direct radiating subwoofer (also called Frontfire subwoofer ) and bottom radiator subwoofer (also down-firing subwoofer called ) distinguished.

Direct radiating subwoofers have the membrane on the front. Indicate the sound pressure primarily from the indoor air of the room. High-quality ( Frontfire ) or subwoofer tower speaker often have several ( bass ) chassis over each other to cause a more homogeneous excitation of the room. In Frontfire subwoofers with a single chassis that works close to the ground to find similar behavior as in down-firing subwoofers.

The housing types most commonly used are the sealed unit, bass -reflex enclosure. The bass reflex enclosure provides higher level in the bass range, while the closed housing having a better transient response.

There are passive subwoofer with two separate voice coils, which bring together the signal of two channels of a stereo signal only on the acoustic level to a mono signal. These can be operated with two passive satellite on a conventional stereo amplifier. Attention is drawn to the impedance of the coils when they parallel to be operated on a system with a separate ( individual ) power amplifier for the subwoofer. When two coils with 4 ohm example results in an impedance of 2 ohms, which would overload the amplifier so many 5.1 amp. As an alternative, in this case the two coils can be connected in series.

No subwoofer in the strict sense, but related, is the body of the transducer. It consists of one or more swinging weights mounted and one or more coils, which stimulate the weights vibrate. Structure-borne sound transducers are applied to, for example, in the cinema explosion scenes still alive ' to make by the seats are made ​​to vibrate. In home theater, the body sound transducers is not yet widespread. The usual response is from 5 to 45 Hz max in car tuning body transducers are mounted under the seat, to support existing subwoofer due to vibration.

List

Low-frequency sound waves below about 80 Hz are difficult to locate by the human ear. Because of this subwoofer can be placed theoretically independent of the speakers for higher frequencies ( the satellites). The most bulky subwoofer can theoretically be positioned anywhere in the listening room; yet the sensation harmonizes ideally with the action on the screen or the stage impression of the music. Furthermore, the satellites will be exempt from the transfer of the bass, so they can be designed smaller. Important for the auditory impression - - placement simplifies their will. Also due to the lack of localization ranges in principle from a subwoofer, even when played stereo or multichannel done.

Since subwoofer in practice depending on the slope (typically 6 to 24 dB / octave ), but the crossover used to radiate higher frequency components, a subwoofer between the front satellite speakers in about the same distance should like these are prepared for listening to an optimal to achieve sound.

In certain spatial conditions or the installation site is called standing waves can occur at discrete frequencies. In this case, for example, emerging from the subwoofer sound wave and the reflected from the back wall of the listening room sound wave at the meeting in certain zones of the space cancel each other out or reinforce each other places. This phenomenon is to be reduced somewhat by changing the location of the subwoofer. Current home theater amplifier therefore often use an automatic calibration, which analyzes the space by means of a microphone and problematic frequencies lowers, which - at least at the listening position - leads to a significantly better playback without affecting the low bass reproduction.

Blanket statements for installation can not meet, since the size and format of the space, equipment, and not least the design of the subwoofer affect the sound significantly. Bass reflex housing are often referred to as " Dröhnkisten ", although this is not true of course. If one were to impose the same frequency response as the bass reflex the closed case by means of an equalizer, the Dröhnverhalten would be identical.

Subwoofer in the composite

There are special composite several Constellations subwoofer to turn off annoying reflections in the listening room. Frequently -cited example is the single bass array (SBA ), the lateral and vertical modes in space bypasses through a special arrangement, but the longitudinal mode fully stimulates. The double bass array goes further and takes a second subwoofer assembly from an active extinction.