A test between two components.
For example, a test between two different pre-amplifiers. For the test to be
scientifically valid the levels should be matched.
See Dolby Digital
The acoustic characteristics of
a space with regard to reverberation. A room with a lot of reverb is said to
be "live"; one without much reverb is "dead."
A device which increases signal
level. Many types of amplifiers are used in audio systems. Amplifiers
typically increase voltage, current or both.
Before digital, the way all
sound was reproduced.
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.
The total frequency range of
any system. Usually specified as something like: 20-20,000Hz plus or minus 3
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.
1 & 2 Processing:
A signal processing circuit that provides improvements in imaging and
spatial realism by altering the frequency and phase characteristics of
portions of the input signal.
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
The use of two pairs of speaker
wire from the same amplifier to separate bass and treble inputs on the
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
A speaker type that utilizes a
tweeter mounted at the center of a woofer cone. The idea being to have the
sound source through the full frequency range become "coincident".
A frequency divider. Crossovers
are used in speakers to route the various frequency ranges to the
appropriate drivers. Additionally, many crossovers contain various filters
to stabilize the impedance load of the speaker and or shape the frequency
response. Some crossovers contain levels controls to attenuate various parts
of the signal. A passive crossover uses capacitors, coils and
resistors, usually at speaker level. A passive crossover is load dependent
(the transition may not be very smooth or accurate if a different speaker is
substituted for the one the crossover was designed for). An
active crossover is based on integrated circuits (ICs), discreet
transistors or tubes. An active crossover is impedance buffered and gives a
consistent and accurate transition regardless of load.
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. Salesmen and product literature will sometimes make claims
of clear superiority for the filter used in the product they are trying to
sell. Since the subject fills books, suffice it to say that there is no one
best filter, it depends on application and intended outcome. Good designers
use the filters required to get the optimum performance from the system.
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 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.
"Dry" or "lifeless" sound may be the result of an
Joe D'Appolito is credited with
popularizing the MTM (Midrange-Tweeter-Midrange) type of speaker.
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
dB is the threshold of hearing, 130 dB is the threshold of pain.
background: about 35 dB
home or office background: 40-60 dB
speaking voice: 65-70 dB
climax: 105 dB
Rock music: 120 dB+
aircraft: 140-180 dB
An open-back speaker that
radiates sound equally front and rear. The front and rear waves are out of
phase and cancellation will occur when the wavelengths are long enough to
"wrap around". The answer is a large, wide baffle or to enclose
the driver creating a monopole
Anything that alters the
musical signal. There are many forms of distortion, some of which are more
audible than others. Distortion specs are often given for electronic
equipment which are quite meaningless. As in all specifications, unless you
have a thorough understanding of the whole situation, you will not be able
to make conclusions about the sonic consequences.
Is a five-channel system consisting of left, center, right and left
rear, right rear channels. All processing is done in the digital domain.
Unlike Dolby Prologic in which the rear effects channels are frequency
limited to approx. 100-7000Hz, Dolby Digital rear channels are specified to
contain the full 20-20Khz frequency content. The AC3 standard also has a
separate subwoofer channel for the lowest frequencies.
Is a four-channel system
consisting of left, center, right and rear channel, (the single rear channel
is usually played through two speakers).
Digital Theater System. A
multi-channel encoding/decoding system. Used in some movie theaters. Also
now included in some home-theater processors. A competitor to Dolby Digital.
Digital Signal Processing. DSP
can be used to create equalization, compression, etc. of a digital signal.
Digital Video Disc or Digital
Versatile Disc. Standard that seeks to combine better-than-laser-disc
quality video with better-than-CD quality audio in a disc the size of a CD.
Requires special players. Seems to be a viable candidate to replace both
Laser Discs and CDs, but the jury is still out.
The range between the loudest
and the softest sounds that are in a piece of music, or that can be
reproduced by a piece of audio equipment without distortion (a ratio
expressed in decibels). In speech, the range rarely exceeds 40 dB; in music,
it is greatest in orchestral works, where the range may be as much as 75 dB.
A speaker that radiates sound
from a large diaphragm that is suspended between high-voltage grids.
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
High-Definition Compact Disc. A
proprietary system by Pacific Microsonics that requires special encoding
during the recording process. Some observers report HDCD discs as having
better sound. To gain the benefits requires having special HDCD in your CD
(Hz): A unit of measurement
denoting frequency, originally measured as C ycles P er S econd,
20 Hz = 20 CPS. Kilohertz (kHz) are hertz measured in multiples of 1,000.
A circuit that allows high
frequencies to pass but rolls off the low frequencies. When adding a
subwoofer it is often desirable to roll-off the low frequencies to the main
amplifiers and speakers. This will allow the main speakers to play louder
with less distortion. High-pass filters used at speaker level are usually
not very effective unless properly designed for a specific main speaker (see
Listening term. A good stereo
system can provide a stereo image that has width, depth and height. The best
imaging systems will define a nearly holographic re-creation of the original
Impedance is a measure of
electrical resistance specified in ohms. Speakers are commonly listed as 4
or 8 ohms but speakers are reactive devices and a nominal 8 ohm speaker
might measure from below 4 ohms to 60 or more ohms over its frequency range.
This varying impedance curve is different for each speaker model and makes
it impossible to design a really effective "generic" speaker level
high-pass filter. Active devices like amplifiers typically have an input
impedance between about 10,000-100,000 ohms and the impedance is the same
regardless of frequency.
A circuit that allows low
frequencies to pass but rolls off the high frequencies. Most subwoofers have
low-pass filters built in and many surround sound decoders have subwoofer
outputs that have been low-pass filtered.
Perceived volume. Loudness can
be deceiving. For example, adding distortion will make a given volume level
seem louder than it actually is.
A type of speaker that uses a
flat diaphragm with a voice coil etched or bonded to it to radiate sound. If
the magnets are both in front of and behind the diaphragm, it
becomes a push-pull magnetic-planar.
A speaker, (driver), used
to reproduce the middle range of frequencies. A midrange is combined
with a woofer for low frequencies and a tweeter for high frequencies to form
a complete, full-range system.
Any speaker that encloses the backwave of the speaker device even
though part of this backwave may be released via. a port or duct. The
primary radiation at most frequencies will be from the driver front. If the
driver is not enclosed it becomes a dipole.
Pulse Code Modulation. A means
of digital encoding.
A speaker, for example, has a
positive and a negative input terminal. Connecting a battery directly to the
speaker will result in the diaphragm moving outward. If you reverse the
battery leads, the diaphragm will move inward. Caution:
Too high of a voltage battery will also burn out the speaker!
Or Pre-amp is a device that
takes a source signal, such as from a turntable, tape-deck or CD player, and
passes this signal on to a power-amplifier(s). The pre-amp may have a number
of controls such as source selector switches, balance, volume and possibly
Radio-frequency sound waves can
be caused by many sources including; shortwave radio equipment, household
electrical line, computers and many other electronic devices. RFI sometimes
interferes with audio signals, causing noise and other distortions.
An audio component that
combines a pre-amplifier, amplifier(s) and tuner in one chassis. A Dolby
Prologic Receiver also contains a Dolby Prologic decoder for surround sound.
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.
A type of speaker that uses a
pleated conductor suspended between magnets. Most true ribbons are tweeters
only. Sometimes confused with mmagnetic-planar speakers.
A measurement of how much power
is required for a loudspeaker to achieve a certain output level. The general
standard used is on-axis SPL(Sound Pressure Level) at 1 watt input, 1 meter
The range or distance between
the noise floor (the noise level of the equipment itself) and the music
Pressure Level (Spl):
Given in decibels (DB) is an
expression of loudness or volume. A 10db increase in SPL represents a
doubling in volume. Live orchestral music reaches brief peaks in the 105db
range and live rock easily goes over 120db.
Sound waves can be thought of
like the waves in water. Frequency determines the length of the waves;
amplitude or volume determines the height of the waves. At 20Hz, the
wavelength is 56 feet long! These long waves give bass its penetrating
ability, (why you can hear car boomers blocks away).
From the Greek meaning solid.
The purpose of stereo is not to give you separate right and left
channels, but to provide the illusion of a three-dimensional, holographic
image between the speakers.
A speaker designed exclusively
for low-frequency reproduction. A true subwoofer should be able to at least
reach into the bottom octave (20-40Hz). There are many
"subwoofers" on the market that would be more accurately termed
Refers to a series of
specifications for surround sound systems. Professional THX is used in
commercial movie theaters. Home THX specifications are not published and
manufacturers must sign non-disclosure waivers before submitting their
products for THX certification. Manufacturers that receive certification for
their products must pay a royalty on units sold.
harmonic distortion (THD):
Refers to a device adding
harmonics that were not in the original signal. For example:
a device that is fed a 20Hz sine wave that is also putting out 40Hz, 80Hz
etc. Not usually a factor in most modern electronics, but still a
significant design problem in loudspeakers.
The use of three pairs of
speaker wire from the same amplifier to separate bass, midrange and treble
inputs on the speakers.
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).
Is the unit of power used to
rate the output of audio amplifiers. For a wattage number to have meaning
the distortion level and impedance must also be specified.
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).
A speaker, (driver), used for
low-frequency reproduction. Usually larger and heavier than a midrange