Also known as Dolby Digital. This term usually refers to the connector found on a DVD decoder card, or DVD player that sends the 5.1 channel Dolby Digital has 6 discrete digital audio channels: 5 seperate full-bandwidth channels (for front left and right, center, and back left and right) and 1 "low frequency effects" subwoofer channel. Some receivers have Dolby Digital decoding built-in; others are simply Dolby Digital "ready" with inputs for hooking up an external Dolby Digital decoder.

A type of speaker enclosure which uses a sealed box to provide motr accurate bass response. Since it gives up some efficiency when providing a more accurate and controlled bass acoustic suspension requires more amplifier power to play at the same volume level as the more efficient bass reflex.

Refers to the range of frequencies a component can reproduce. For audio components like receivers, "full bandwidth" is generally considered to be the entire frequency range of human hearing -- 20-20,000 Hz.

An enclosure that comonly uses a round hole to increase and extend the bass response.

Bass reflex speakers must be carefully designed, or they distort the bass accuracy in exchange for the added output. One way to compensate for the loss of accuracy is to use passive radiator over the opening. This covering is designed to control air flow more than a standard port.

A speaker design which generates equal amounts of sound both forward and backward, with the two sounds being "in phase". See also Dipole.

A distortion in the character of a sound, such as the emphasis of certain frequencies (low high or mid tones), that reduce accuracy.

Since some people like high tones while others like low tones, the coloration of some speakers will falsly lead some people to choose speakers based on the speakers coloration, rather than choosing a speaker with a flat response

A circuit that acts as a filter dividing the frequency spectrum into two or more parts. It's the crossover's job to send only high frequencies to the tweeter and only low frequencies to the woofer, and midrange frequencies to the midrange driver.

The standard unit of measuring differnces in the expression of relative power or amplitude. One dB is the smallest change in loudness most people can detect. A 1 dB difference is barely noticeable, while 10 dB higher volume will sound twice as loud. Each 3 dB increase in volume level requires double the amplifier power.

The part of a speaker driver that moves, producing the sound. Each diaphragm is directly connected to a voice coil. The diaphragm for a woofer is a cone, while for a tweeter, it's often a dome.

The scattering of sound. Diffusion reduces the sense of direction of a sound source, a useful quality in surround speakers.

A special processor circuit that is designed to perform complex operations on audio waveforms. This specialization permits sophisticated sounds to be produced rapidly and efficiently. This architecture may be compared with video and graphic processor circuits that have been used to accelerate and improve video output. DSP is used in sound cards, or audio equipment to create soundfields which are electronic or digitally synthesized acoustical environments for audio enhancement, and to create time delays and for precise steering of multi-channel Dolby Pro Logic information.

A new format for storing audio and visual data. Comparable in size to a CD (compact disc), the DVD has significantly more storage capacity (enough space to store a 133 minute movie) and can hold both A/V information and data (like subtitles, and multi-language title abilities.) CDs may be played in a DVD player and DVD players are available for computers and for A/V component systems. DVD features multi-language capabilities, multiple image ratios, parental controls, multi camera angles, and superb frame control that can allow a clear still picture.

The A/V information found on DVD is MPEG2, and the digital output of a DVD player to a A/V receiver is AC3 (Dolby digital).

A speaker design which generates equal amounts of sound both forward and backward, with the two sounds being out of phase. Dipoles are often used as surround speakers. See also Bipole.

Discrete devices are real transistors, capacitors and resistors that make up an amplifier. An amplifier output section comprised of real transistors offers some big advantages over the commonly used (because it's less expensive) IC chip amplifier. Discrete outputs offer higher current capacity, handle more heat, work over a wider impedance range, react faster to sonic transients, and thus in general produce lower distortion, more dynamic and lifelike sound.

The degree to which a speaker's sound is spread over the listening area.

5.1 channel Dolby Digital has 6 discrete digital audio channels: 5 seperate full-bandwidth channels (for front left and right, center, and back left and right) and 1 "low frequency effects" subwoofer channel. Some receivers have Dolby Digital decoding built-in; others are simply Dolby Digital "ready" which requires hooking up an external Dolby Digital decoder.

A 4-channel surround sound system designed to be played back through 5 speakers: a center channel speaker for on-screen sound, front left and right speakers for sound that moves with the action, and left and right surround speakers (both surround speakers reproduce the time-delayed mono surround channel which provides ambience and sound effects).

Refers to the difference between loud and soft sounds. A speaker with wide dynamic range -- one that can reproduce the sudden and wide changes between loud and soft sounds in music and video soundtracks -- will sound more realistic.

Indicates how well a speaker system converts power into sound. This is measured by sending one watt of power and measuring the decibels at one meter distance. The higher the number the more efficient (i.e. louder) the speaker. Just to be clear: efficiency measures the quantity not the quality of the produced sound.

Flat is a good thing. It is the ability of the speaker to accurately reproduce a signal without adding colorations to the sound.

The human ear responds to frequencies from approximately 20 to 20,000 Hz. The frequency response indicates how much of the audible range can be accurately reproduced.

The unit of sound frequency; one Hz is equal to one cycle per second. The range of human hearing is 20-20,000 Hz. The lower the frequencies the lower the tones, for instance drums would typically send out frequencies lower than 100 Hz while the cymbols whould be in the 10-15 Khz range.

The flow of current through your speakers' voice coils creates the electromagnetic force that moves the cones and domes, creating sound. The dynamic qualities of music and movie soundtracks create short-term high-current demands. If current flow is limited, the sound will be, too. A high-current amplifier (or a receiver that uses one) may sound punchier and more powerful than other models with the same wattage rating.

The ability of a speaker to reproduce spatial information in a recording so that you can visualize the relative positioning of individual voices and instruments as you're listening.

The amount of resistance to the flow of current. Impedance will varies with the frequency of the input signal. Be carefull, low impedance speakers (4 ohms or less) can cause problems with receivers or amplifiers which are not designed to deliver large amounts of current.

The range of frequencies above bass and below treble that our ears are most sensitive to, which includes most vocal and instrumental sounds.

MPEG2 is a compression method used to store both audio and video information. It uses a complex algorithm to encode the information for storage and playback. MPEG2 compression is based on the use of "I frames" to create an initial video frame and then stores only the differences between the first I frame and the frames after it. When the image is completely different to the original I frame a new I frame will be created. Because of this method MPEG2 is ideal for storage and playback, but is terrible for video editing. The A/V information found on DVD is MPEG2, and the digital output of a DVD player (or a PC's DVD player card) to a A/V receiver is AC3 i.e. Dolby digital. MP3 is an audio format based on audio only MPEG2. MP3 allows you to encode an entire CD quality album (~70 minutes) to less than 100mb on your hard drive.

Some A/V receivers let you view component/system status on your TV screen. Some use a GUI (Graphical User Interface) for easy remote point-and-click control via on-screen menus and icons.

Refers to the timing relationship of two or more signals or soundwaves. In phase means that the speakers are moving in and out at the same time.

If your speakers are out of phase you'll hear significantly less bass, and the sounds will localize to the individual speakers.

The power amplifier takes the low-voltage signal supplied by the preamplifier and amplifies it to a sufficient level to drive speakers.

A measure of how much amplifier power, in watts, a speaker can take before it is damaged.

Also called a control amplifier or control center. A preamplifier (or preamplifier section of a receiver) handles the switching and selecting of signals, as well as amplifying them to the voltage level required for the input of a power amplifier.

Often included on mid- to high-priced A/V receivers, these connectors provide unamplified, low-voltage line-level signals for components like a powered subwoofer or a separate power amplifier.

An audio component that combines a preamplifier, amplifier, and radio in a single chassis.

The amount of continuous power, measured in watts, that an amplifier produces is called RMS power. The higher the RMS figure, the louder and cleaner your music sounds. When choosing an amplifier or receiver, the RMS rating is the power rating you should pay most attention to.

Stereo manufacturers often display peak power ratings on the face of their products. The peak power rating tells you the maximum wattage an amplifier can deliver as a brief burst during a musical peak, like a dramatic drum accent. The RMS figure is more significant.

Using a 4-pin connector, an S-video jack transmits the chrominance (color) and luminance (brightness) portions of a video signal separately, for improved color accuracy and reduced distortion.

A small speaker with limited bass response designed to be used with a matching subwoofer.

The ability to create a sense that the sounds are taking place within a physical space with definite width, height, and depth.

The intensity or level of sound (measured on the dB scale).

A speaker specially designed to reproduce a range of very low frequencies only usually in the range of 20-200 Hz.

Refers to the two speakers located beside or behind the listening/viewing position. They help create a three-dimensional soundstage by reproducing the surround information on video soundtracks and music recordings encoded with surround sound. Dolby Pro Logic uses a mono input to the surround speakers, while Dolby digital sends a stereo signal to give you that extra dimension.

A measurement of the accuracy of an amplifier (or the amplifier section of a receiver). THD refers to the amount of internally generated noise. The lower the number, the better.

Any device that converts information from one physical form to another. Examples: a phono cartridge (mechanical to electrical); a speaker (electrical to mechanical).

A short-lived aspect of a signal, such as the attack and decay of musical tones. A speaker that can react quickly to rapid changes in the music is said to have good "transient response."

A small, lightweight driver for reproducing the highest musical frequencies such as violins and cymbals, typical everything above 2,000 Hz.

Speakers that are voice matched have a similar timbre or tonal quality. Voice-matched speakers in a home theater system will result in more seamless wraparound sound.