Loudspeaker

A loudspeaker, or simply speaker, is an electromechanical device which converts an electrical signal into sound. The term is used to refer to both the transducer, or driver itself, and a complete system consisting of one or more transducers in an enclosure. The loudspeaker is the most variable element in an audio system. The audible differences between speaker systems are considerable.

Woofers and tweeters

Because of effects such as resonance and various inertial effects, a single loudspeaker is not usually used to cover a wide range of frequencies; instead, a number of specialized drivers are employed. These drivers are often wired together using crossover circuits, which allocate different frequency bands to the different units. See subwoofer, woofer, mid-range, tweeter. Through the use of filters, only appropriate signals are applied to the various drivers. Passive crossover circuits take a full-frequency, full-power signal from an amplifier and send the appropriate frequencies to each driver. They are generally found within the loudspeaker enclosure. Active crossovers split the signal before amplification; once split, the signal is sent to several amplifiers. Each amplifier powers one or more loudspeakers for a specific frequency range.

Related Topics:
Resonance - Inertia - Crossover circuits - Subwoofer - Woofer - Mid-range - Tweeter - Filters - Amplifier

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Most manufacturers advertise their loudspeakers as "2-way","3-way", etc. This refers to the number of frequency bands into which the incoming source signal is split. For instance, a 2-way design splits the incoming signal into two bands with the tweeter handling sound above a certain frequency (known as the crossover point) and one or more combination woofer/mid-range speakers handling all frequencies below that. A 3-way design will have 2 crossover points with separate tweeter, mid-range, and woofer drivers. Low-priced speakers typically have a very minimal crossover design, consisting of a small capacitor in series with the tweeter in order to attenuate the lower frequencies, and simply relying on the woofer's inherent inability to reproduce high frequencies.

Related Topics:
Crossover point - Capacitor - Series

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The nature of speaker design is considered both an art and science. Adjusting a design is done with instruments and with the ear. Speaker designers will use an anechoic chamber (essentially a room with soundproofing that inhibits any reverberation or echo) to ensure the speaker will perform the way it is intended to. Some of the issues in speaker design are lobing, phase effects, off axis response and time coherence. In addition to the number of crossovers, another often advertised specification is the crossover order, also called the crossover slope. Essentially, no crossover stops frequencies exactly at a crossover point, rather the process is a gradual slope. The order of a crossover refers to how abrupt the slope is. Higher order crossover networks slope more sharply than lower order networks so therefore a first order network will have a more gradual split than a second order. A first order network filters at 6 dB per octave, a second order at 12 dB per octave, and a third order at 18 dB per octave.

Related Topics:
Anechoic chamber - Crossover order - Crossover slope - DB

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A less-expensive alternative is to use a single loudspeaker unit that contains two cones and a mechanical cross-over. This is usually done by placing a very small cone directly over the voice coil and coupling the larger cone to the voice coil with a mechanically-compliant material (or making the larger cone itself mechanically compliant). In this way, the small cone (usually referred to as a whizzer cone) is driven by all frequencies including the treble frequencies while the larger cone is only driven by the bass and midrange frequencies. In many modern speakers, a small piezoelectric tweeter (see below) is used instead of the whizzer cone.

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Subwoofers

Modern speaker systems often include a single speaker dedicated to reproducing the very lowest bass frequencies. This speaker is referred to as a subwoofer. A typical subwoofer only reproduces sounds below 100 Hz (although some subwoofers allow a choice of the cross-over frequency). Because the range of frequencies that must be reproduced is quite limited, the design of the subwoofer is usually quite simple, often consisting of a single, large, down-firing woofer enclosed in a cubical infinite baffle. Subwoofers often contain integrated power amplifiers that may incorporate sophisticated feedback mechanisms to assure the least distortion of the reproduced bass acoustic waveform.

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The very long wavelength of the very low frequency bass sounds reproduced by the subwoofer usually makes it impossible for the listener to localize the source of these sounds. Because of this phenomenon, it is usually satisfactory to provide just a single subwoofer no matter how many individual channels are being used for the full-spectrum sound. For the same reason, the subwoofer does not need a special placement in the sound field (for example, centered between the Left Front and Right Front speakers). It can instead be hidden out of sight. Placing it in the corner of a room may produce louder bass sounds. A subwoofer's powerful bass can often cause items in the room or even the structure of the room itself to vibrate or buzz. Extended periods of high volume bass can cause items throughout a room to "walk" on a flat surface until they fall off.

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Amplified subwoofers frequently accept both speaker-level and line-level audio signals. When teamed with a modern surround sound receiver and full range speakers, they are typically driven with the specific LFE (low frequency effects) output channel (the ".1" in 5.1, 6.1, or 7.1 specifications) provided by the receiver. This is because most full-range speakers are incapable of delivering the acoustic power required by the LFE in movies or in some cases, music. When used with speakers that do not reproduce low frequencies well, a subwoofer will often be configured to reproduce both the LFE channel and all other bass in the system, the latter being referred to as "bass management".

Related Topics:
Surround sound - LFE

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