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Knowledge Base

Acoustic Phase: The time alignment of sound waves. Phase is important at crossover points, where phase shift (time shift) occurs between the drivers. A difficult technical challenge with crossover design is precisely achieving the right amount of phase shift in each driver at the crossover point, so that the frequencies sum together properly.

Baffle: The front surface of a speaker, which affect sound radiation from the speaker drivers.

Balanced: Referring to wiring: Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling. Many higher quality home audio cables terminated with RCA jacks are balanced designs using two conductors and a shield instead of one conductor plus shield. See also XLR Connector.

Bass Reflex: A type of loudspeaker that uses a port or duct to augment the low-frequency response. Opinions vary widely over the "best" type of bass cabinet, but much has to do with how well a given design, such as a bass reflex is implemented.

Bi-Amplify: The use of two amplifiers, one for the lows, one for the highs in a speaker system. Could be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.

Bi-Wiring: The use of two pairs of speaker wire from the same amplifier to separate bass and treble inputs on the speaker.

Capacitors: A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an ac current.

Clipping: Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the "clipped" waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of "burned out" tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Coloration: Listening term. A visual analog. A "colored" sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

Coils: An electronic inductive component made of copper. Coils with a kernel should be avoided because they are creating distortion. Air coils and Foil coils are distortion free. Foil coils have a very low resistance and a large flat surface. Therefore the electrons can better "travel" to the driver unit when Foil coils are used in a crossover.

Cone Excursion: The distance that the driver cone can move (back and forth) without damage. Excursion is generally measured in millimeters (mm) or fractions of an inch.

Crossover: The circuit in the speaker that utilizes capacitors and coils to direct and control frequencies to the driver that can most accurately reproduce them. For example, the crossover sends low frequencies to the woofer or subwoofer, middle frequencies to the midrange driver, and high frequencies to the tweeter.

Crossover Slope: High and low pass filters used for speakers do not cut-off frequencies like brick walls. The rolloff occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Good designers use the filters required to get the optimum performance from the system.

Crossover Point: The frequency point at which sound is transferred from one driver to another. The loudness of the two drivers is the same at the crossover point.

Cross-talk: Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Damping (Damping factor, etc.): Refers to the ability of an audio component to "stop" after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is overdamped does not allow the initial energy to reach the full peak and cuts the decay short. "Boomy" or "muddy" sound is often the result of underdamped systems. "Lifeless" sound may be the result of an overdamped system.

D'Appolito: Joe D'Appolito is credited with popularizing the MTM (Midrange-Tweeter-Midrange) type of speaker.

Decibel (dB): Named after Alexander Graham Bell. We perceive differences in volume level in a logarithmic manner. Our ears become less sensitive to sound as its intensity increases. Decibels are a logarithmic scale of relative loudness. A difference of approx. 1 dB is the minimum perceptible change in volume, 3 dB is a moderate change in volume, and about 10 dB is an apparent doubling of volume. 0 dB is the threshold of hearing, 130 dB is the threshold of pain. Whisper: 15-25 dB, Quiet background: about 35 dB, Normal home or office background: 40-60 dB, Normal speaking voice: 65-70 dB , Orchestral climax: 105 dB, Live Rock music: 120 dB+, Jet aircraft: 140-180 dB

Diffraction: A change in the direction of a wave front that is caused by the wave moving past an obstacle.

Distortion: Occurs when a sound waveform is not produced accurately, and results in poor sonic performance.

Efficiency: The ability of a driver to convert electrical energy into sound energy without wasting too much electrical energy.

Frequency: An individual note or tone which is measured in cycles per second and usually notated as CPS or Hz. Fewer cycles per second produce lower notes which are typically reproduced by the woofer or subwoofer. More cycles per second produce higher notes which are typically reproduced by the midrange or tweeter. The human ear can hear frequency cycles from 20 to 20,000 per second.

Frequency Range: The range of frequencies over which a particular driver can operate effectively without creating significant distortion.

Frequency Response: The relative loudness of sound output over the entire range of frequencies. Frequency response is usually expressed as +/- dB (decibel) or as a graph.

Harmonics: Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic: second, fourth, sixth, etc.-is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand: third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality, execept first order loudspeaker crossovers, because they have an absolute minimum of phase shifts (the only type of phase linear speakers).

High-End Speaker: A speaker that utilizes high-performance drivers, a well-built enclosure incorporating quality materials and finish, and well-designed crossover circuitry with narrow tolerance components. High-end speakers reproduce sound with high accuracy.

Ideal Driver: A speaker driver that delivers excellent performance in terms of polar response, power handling, efficiency, frequency range and reliability.

Impedance and Electrical Phase: Electrical resistance of a driver and a complete loudspeaker in an alternating current environment; sound is delivered to the speaker in the form of an alternating current. The impedance of a driver and the loudspeaker is measured in Ohms and usually varies over its frequency range. When the impedance varies the electrical phase does it too. Electrical phase shifts requires the power amplifier is able to handle large variations in its the output. Therefore it is very important that the impedance shifts are soft and it is best when impedance of a speaker is linear.

Inductive Coupling: In a typical crossover, coils are not placed close to each other because of the inductive interaction between coils.

MDF: MDF is one of the best materials to loudspeaker cabinets. MDF is for example better than massive wood, aluminium, marble or other hard materials, because of its unique sound absorbing qualities.

Muddiness: Poor sonic performance in a speaker, resulting either from distortion or from a particular frequency being too predominant, thereby obscuring higher frequencies.

Polar Response: The measurement of how a speaker sounds when you are out of its "sonic sweet spot", also known as "off axis". However, a well designed speaker will have the same tonal characteristics regardless of where you are standing in relation to the speaker.

Power Handling: The wattage level that a driver can handle without sustaining damage due to over-heating the voice coil or over-extending the cone excursion.

RCA Connector: "Phono" plugs, used primarily as low-level connections between Phonographs/CD players/Tuners/Recievers/Amplifiers.

Resonant Frequency: Any system has a resonance at some particular frequency. At that frequency, even a slight amount of energy can cause the system to vibrate. A stretched piano string, when plucked, will vibrate for a while at a certain fundamental frequency. Plucked again, it will again vibrate at that same frequency. This is its natural or resonant frequency. While this is the basis of musical instruments, it is undesirable in music-reproducing instruments like audio equipment.

Slope: The rate at which the loudness of a particular driver decreases beyond the crossover point.

Soundstage: In listening to music or a movie soundtrack, the soundstage is the area where various sounds are dispersed from left to right and from front to back. The ideal soundstage creates a presence that gives the listener the feeling they are listening to a live performance.

Standing Wave: A buildup of sound level at a particular frequency that is dependent upon the dimensions of a resonant room, or enclosure. It occurs when the rate of energy loss equals the rate of energy input into the system. This is what you hear when you listen into a sea shell.

Tetrahedron Cabinet: A tetrahedron is an equilateral pyramid; it has only three sides and a triangle bottom, not four sides and a square bottom as a pyramid. As no standing waves occur in a tetrahedron it is a cabinet without preferences to resonance-frequencies. Inside the cabinet acoustic waves can never amplify one another in phase and are reflected by the inside walls under ever-changing angles.

Thiele/Small parameters: The numbers that specify the behaviour of drivers, as defined and analyzed by two engineers, Neville Thiele and Richard Small.

Transient Response: The ability of a component to respond quickly and accurately to transients. Transient response affects reproduction of the attack and decay characteristics of a sound.

Transparency: Listening term. An analog that can be best "pictured" in photography. The more "transparent" the sound, the clearer the auditory picture.

Transients: Instantaneous changes in dynamics, producing steep wave fronts.

Tuningfrequency: The helmholtz resonant frequency of a box. Also refers to the resonant frequency of other types of systems.

Tweeter: A speaker, (driver), used to reproduce the higher range of frequencies. To form a full-range system, a tweeter needs to be combined with a woofer, (2-way system), or a woofer and midrange, (3-way system).

Voice Coil: The coil of wire attached to a driver's cone that receives the electrical signal from the crossover circuit. The cone then moves in the magnetic field at the center of the magnet depending on the frequency and amount of current being delivered to the coil.

Wavelength: The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (Speed of sound at sea level is 331.4 meters/second or 1087.42 feet/second).

Woofer: A speaker, (driver), used for low-frequency reproduction. Usually larger and heavier than a midrange or tweeter.

XLR Connector: A type of connector used for balanced lines. Used for microphones, balanced audio components and the AES/EBU digital connection. The input to the Acoustic Reality Amplifiers are balanced XLR, but converter cables to RCA can be delivered. See also Balanced.