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32 Chapter 3: Glossary of Terms
Amplifi er Application Guide
Sound Pressure Level (SPL)
The acoustic volume or perceived loudness of sound, measured in
decibels. SPL is a function of a signal’s amplitude.
Speakon
®
A type (and brand) of multi-pin connector developed by Neutrik
®
which is now commonly found on speakers and amplifi ers intended
to be used in high power mobile applications. They have become
popular because they offer a very high quality reliable connection,
can handle extremely high power, are very durable, and are relatively
low in cost compared to other similar connectors. Standard Speakon
connectors come in four or eight conductor versions (though other
confi gurations are available). The Speakon 8 has the same footprint
as the EP8 connector and the Speakon 4 has the same footprint as
XLR “D” type connectors.
Stereo (Dual)
An operating mode of an amplifi er that allows channels of the
amplifi er to function independently.
Switching Power Supply
A power supply that fi rst converts AC mains power to a much higher
frequency by means of a switching circuit before making the power
available for use within the amplifi er. The primary benefi ts of a switch-
ing power supply are decreased overall unit weight and decreased
electro-mechanical emissions.
THD (Total Harmonic Distortion)
The ratio of the power of the fundamental frequency at the output of
a device versus the total power of all the harmonics in the frequency
band at the output of the device. All electronic audio devices intro-
duce some distortion to audio passed through them. The simplest
form of this distortion is the addition of harmonics to the output signal.
THD represents the sum of all the harmonics added by a device as a
percentage of the level of the signal being measured.
Thermal Dissipation
Energy not converted to the output of an amplifi er is instead dis-
sipated by the amplifi er as heat.
THX
®
Refers to a series of specifi cations for surround sound systems. Pro-
fessional THX is used in commercial movie theaters.
TLC
TLC (Thermal Limit Control) is a circuit developed by Crown which
provides amplifi er thermal protection. When a predetermined temper-
ature threshold is reached, the TLC indicator begins to glow to show
that the temperature sensing circuitry is starting to engage the input
compressor. By compressing the input, the amplifi er will not gener-
ate as much heat and will have a chance to cool down. The degree
of compression is directly proportional to the amount of overheating
experienced by the amplifi er.
Transformer
A transformer is a device consisting of two or more coils of wire
wound on a common core of magnetically permeable material. The
number of turns in one coil divided by the number of turns in the
other is called the turns ratio. An alternating voltage appearing across
one coil will be inducted into the other coil multiplied by the turns
ratio.
Transformers are used in power supplies, distributed speaker sys-
tems, and are often used to provide electrical isolation in circuits to
prevent ground loops because they pass AC voltages and block DC
voltages.
Transient
A non-repeating waveform, usually of much higher level than the
surrounding sounds or average level. Good examples of transients
include the attack of many percussion instruments, the “pluck” or
attack part of a guitar note, consonants in human speech (i.e. “T”),
and so on. Due to their higher-than-average level and fl eeting nature,
transients are diffi cult to record and reproduce, eating up precious
headroom, and often resulting in overload distortion. Careful use
of compression can help tame transients and raise average level,
although over-compression will result in a dull, squashed, fl at sound
to the signal.
Trim
Found on most mixers, trim controls provide the initial level setting
for each channel’s input gain. In most cases, trim adjusts gain of the
microphone preamp, but it may also apply to line level signals.
Unbalanced
In electronics, a condition where the two legs of the circuit are not
equal or opposite with respect to ground, usually because one leg
is kept at ground potential. In other words: An audio signal requires
two wires or conductors to function. In an unbalanced situation, one
of those conductors is used to carry both signal and ground (shield).
Unbalanced circuits are much more susceptible to induced noise
problems than their balanced counterparts. Because of this, unbal-
anced lines should be kept as short as possible (under 10-15 inches
(25- to 38-cm)) to minimize potential noise problems.
Unity Gain
A device or setting which does not change signal level (does not
amplify or attenuate a signal) is said to be at “unity gain.” Many
processors are set up for unity gain; that is, they can be plugged into
a system without changing its overall levels. In practice, unity gain is
often a desired setting for maintaining gain staging, and for optimizing
operating levels and signal to noise ratios.
Voltage
The electrical potential between two relative points in a circuit.
Voltage is measured in volts (V). Ohms law defi nes voltage as the
product of current (I) and Resistance (R) with the following expres-
sion: V=I*R.
VZ
®
VZ (Variable Impedance) is the name of Crown’s patented articulated
power supply technology. VZ technology enables Crown to pack
tremendous power into few rack spaces.
The VZ supply is divided into two parts. When the voltage demands
are not high, it operates in a parallel mode to supply less voltage and
more current. The power transistors stay cooler because they are
not forced to needlessly dissipate heat. This is the normal operating
mode of the VZ power supply. When the voltage requirements are
high VZ switches to a series mode to produce higher voltage and less
current. The amplifi ed output signal never misses a beat and gets full
voltage only when it requires it. Sensing circuitry observes the voltage
of the signal to determine when to switch VZ modes. The switching
circuitry is designed to prevent audible switching distortion to yield
the highest dynamic transfer function.
To learn more about VZ, download and read the VZ white paper at
www.crownaudio.com.
Watt
Power equates to the rate of energy transfer, or the rate of doing
work. Power is measured in Watts, and the watt has become a
common term in audio to describe the power handling capabilities
and/or requirements of speakers, and the power delivery capabilities
of amplifi ers. Watts law defi nes power (P) as voltage (V) times current
(I) with the following expression: P=V*I.
XLR (Cannon or Three-Pin Connector)
A three-pin professional audio connector used for balanced mic and
line level signals. The AES standard for wiring of XLR connectors
dictates that Pin 1 be soldered to the cable shield, pin 2 be soldered
to the signal hot lead, and pin 3 be soldered to the signal return lead.
The name XLR was trademarked by Cannon (now owned by ITT).
XLR has since evolved into a generic industry term, and many manu-
facturers now make this style connector.
Y-Adapter
A single cable that divides into two cables in parallel to feed one
signal to two destinations.
Z
The abbreviation for impedance.