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Online Guide Choosing a PA System
Loudspeakers

 

No matter how good the rest of the system may be, it can all fall apart at the loudspeakers. There's no
DigitalAll digital equipment, formats and systems represent audio in numerical code or form. Digital information is a precise way of expressing any of information that can be quantified in some way.
digital
or analogue debate in this area - it's here that the electrical signals have to be converted to waves of
AIRSome artists and producers believe that AIR - Always In Record - is a valuable technique, because it can capture moments of musical magic that may otherwise go unrecorded. It simply means that the tape or hard drive never stops running during a session.
air
and pushed out to the waiting audience. Because of this, the speaker
CabinetThe housing for a loudspeaker, often abbreviated to "cab".
cabinet
is as important as the ‘drivers’ themselves in the management and
DispersionDispersion defines how a speaker spreads its sound both horizontally and vertically and is an important element in speaker design. With low frequencies sound is dispersed over a wide angle as the wavelength is generally much larger than the speaker. As the frequency increases and the speaker becomes larger than the wavelength the opposite occurs and the dispersion becomes narrower.
diffusion
of the sound. You can get deeply immersed in speaker technology if it takes your fancy - our Online Guide to PA Speakers is a good place to start - but here we'll just consider the essential points.


The first issues concern compatibility with the
AmplifierA device for increasing the power of a signal by taking power from a supply and shaping the output to match the input signal.
amplifier
:

  • The
    ImpedanceThe term for electrical resistance when applied to AC current.
    impedance
    (a kind of electrical resistance, measured in Ohms) of the speakers must match the range of output
    ImpedanceThe term for electrical resistance when applied to AC current.
    impedances
    that the
    AmplifierA device for increasing the power of a signal by taking power from a supply and shaping the output to match the input signal.
    amplifier
    can handle. Each speaker will usually be rated at 4
    OhmsThe ohm is a unit used for measuring electrical resistance or impedance, named after the German physicist Georg Ohm. The rated impedance of a speaker (in ohms) tells us how much current it will draw when matching it with an amplifier.
    Ohms
    or 8
    OhmsThe ohm is a unit used for measuring electrical resistance or impedance, named after the German physicist Georg Ohm. The rated impedance of a speaker (in ohms) tells us how much current it will draw when matching it with an amplifier.
    Ohms
    . Resistance is a tricky principle, and much depends on exactly how you will connect everything together. The
    KeyAn additional input on a dynamics processor such as a compressor or noise gate, enabling the dynamics of one signal to control the level of another. This can be used for many functions, including ducking (compressing a music signal when a DJ or announcer speaks), synchronised gating, and (in conjunction with an equaliser) de-essing.
    key
    point is that an imbalance can damage speakers,
    AmplifierA device for increasing the power of a signal by taking power from a supply and shaping the output to match the input signal.
    amplifier
    , or both, so check the specifications of each element to ensure that they are compatible. Above all, make sure the total
    ImpedanceThe term for electrical resistance when applied to AC current.
    impedance
    of the speakers is within the operating range of the
    AmpereUnit of current; the amount of electricity flowing through a conductor. One Ampere is equal to the flow of 6.25x10^18 electrons through a conductor in one second.
    amp
    . See our Online Guide to PA Amplifiers for more on calculating this.

  • Remember the rule about Watts
    RMSRoot Mean Square: a way of calculating the average power over time to give a meaningful value representing the power of an audio signal. Generally thought to be the most meaningful way of measuring amplifier power output.
    RMS
    - match the speaker capacity to the output of the
    AmplifierA device for increasing the power of a signal by taking power from a supply and shaping the output to match the input signal.
    amplifier
    , allowing about 30% more power from the
    AmpereUnit of current; the amount of electricity flowing through a conductor. One Ampere is equal to the flow of 6.25x10^18 electrons through a conductor in one second.
    amp
    . The idea is that you don't run everything at full
    Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
    volume
    , but you have enough
    HeadroomA safety margin in the audio path over and above that required by a typical signal, the presence of which helps to avoid the possibility of distortion. Specifically in digital audio, the difference between Permitted Maximum Level (PML) and Digital Full Scale (FS, 0dB).
    headroom
    to cope with the highest
    PeakThe highest point of an audio waveform, or one of the highest points of an audio waveform.
    peaks
    .

speaker cabinet


A typical PA speaker

CabinetThe housing for a loudspeaker, often abbreviated to "cab".
cabinet, with low/mid-range and high frequency speakers


Frequency range

This is an important measure for musicians in particular, because it indicates the most suitable use for a speaker. Is it good for high, mid, or low-frequency sound? Most people can hear sound in the range between 20Hz and 20,000Hz (Hz = cycles per second). The ideal loudspeaker would be able to transmit effectively across the entire frequency range, although in practice this is virtually impossible.

So the
KeyAn additional input on a dynamics processor such as a compressor or noise gate, enabling the dynamics of one signal to control the level of another. This can be used for many functions, including ducking (compressing a music signal when a DJ or announcer speaks), synchronised gating, and (in conjunction with an equaliser) de-essing.
key
question is whether or not the loudspeaker can transmit consistently and with good quality, within its ideal frequency range. This is known as linear transmission. For the purposes of a general gigging PA, you will need a combination of speakers that offer a broad coverage of the frequency range.

The industry uses frequencies separated by a musical third, and the levels are expressed in decibels (dB). Typically, if a frequency response is shown as 40 - 20,000Hz, +/-3dB, you can assume that the
BassThe lowest part of the audio frequency range; in popular music, a (generally) rhythmic, low frequency melodic line emphasising the root notes of the chord progression.
bass
frequencies were raised at around the +3dB level, and that the higher frequencies were dampened at around -3dB. The usual warning about manufacturer data always applies - they will tend to use the figures that flatter their equipment, though most reputable companies will show fairly accurate frequency response data and
RMSRoot Mean Square: a way of calculating the average power over time to give a meaningful value representing the power of an audio signal. Generally thought to be the most meaningful way of measuring amplifier power output.
RMS
values.


Sound pressure

Sound pressure means
Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
volume
- the higher the pressure of the sound wave striking your ears, the louder it sounds. It’s measured, perhaps appropriately, in Pa (short for Pascals in this case - strength per unit area).

In fact, humans have a fairly limited audible range, from around 100Pa (the pain
ThresholdThe parameter in dynamics processing defining the level which an input signal must rise above (or fall below) to activate the circuit. A compressor is activated above the threshold, whereas an expander or gate is activated below the threshold.
threshold
for most of us) to about 20uPa. The ear detects these as logarithmic values, measured in deciBels. Zero dB roughly equates to 20uPa, and it usually starts to hurt for us at around 130dB. When considering speakers, the sound pressure level (SPL) is usually shown in decibels. For example a speaker may be shown as 400W
RMSRoot Mean Square: a way of calculating the average power over time to give a meaningful value representing the power of an audio signal. Generally thought to be the most meaningful way of measuring amplifier power output.
RMS
, 118dB
SPLSound Pressure Level: acoustic sound volume, measured in decibels (dB).
SPL
.

Not all manufacturers use the same measures, but what you are looking for is an indication of how much of the signal received is converted faithfully to moving
AIRSome artists and producers believe that AIR - Always In Record - is a valuable technique, because it can capture moments of musical magic that may otherwise go unrecorded. It simply means that the tape or hard drive never stops running during a session.
air
. The higher the number, the greater the
EfficiencyA specification, expressed as a percentage, measuring how efficiently a speaker converts an audio signal (watts) into sound waves (dB). As in any conversion process there is usually some kind of loss, which in this case is turned into heat.
efficiency
and/or sound pressure produced by the speaker. If, for example, you compare two speakers that have a difference of 3dB in their sound pressure ratings, then you can assume that you will need roughly twice the power to achieve the same
Volume1) In audio and music, the loudness or amplitude of a signal. 2) In computing, a fixed amount of storage space, addressed as a single entity ('C:', 'D:' etc). A physical drive may contain more than one volume, but a single volume may also span more than one drive!
volume
from the unit that is lower rated, and therefore less efficient.


ActiveDescribes an instrument or speaker system that has its own electronic functions built-in, as opposed to requiring external devices. Active speakers have their own amplifiers built-in, while an active instrument such as a guitar or bass will have electronic controls or a pre-amplifier.
Active
loudspeakers

For smaller venues,
ActiveDescribes an instrument or speaker system that has its own electronic functions built-in, as opposed to requiring external devices. Active speakers have their own amplifiers built-in, while an active instrument such as a guitar or bass will have electronic controls or a pre-amplifier.
active
loudspeakers are often a cost-effective option. These have amplifiers built-in – you simply connect them directly to a
ConsoleA device through which audio signals are routed for mixing, monitoring, processing and re-routed for either recording, amplification or both. A console contains a number of channel strips and a selection of auxiliary, monitoring and main outputs.
mixer
. Typically, the
ActiveDescribes an instrument or speaker system that has its own electronic functions built-in, as opposed to requiring external devices. Active speakers have their own amplifiers built-in, while an active instrument such as a guitar or bass will have electronic controls or a pre-amplifier.
active
loudspeaker
CabinetThe housing for a loudspeaker, often abbreviated to "cab".
cabinet
will contain mid-range and high frequency speakers. If you are connecting keyboards, or amplifying the
BassThe lowest part of the audio frequency range; in popular music, a (generally) rhythmic, low frequency melodic line emphasising the root notes of the chord progression.
bass
drum, it's worth adding at least one sub-woofer
CabinetThe housing for a loudspeaker, often abbreviated to "cab".
cabinet
to handle the
BassThe lowest part of the audio frequency range; in popular music, a (generally) rhythmic, low frequency melodic line emphasising the root notes of the chord progression.
bass
frequencies. In these configurations, the
BassThe lowest part of the audio frequency range; in popular music, a (generally) rhythmic, low frequency melodic line emphasising the root notes of the chord progression.
bass
CabinetThe housing for a loudspeaker, often abbreviated to "cab".
cabinet
will usually contain a
CrossoverA device that splits an audio signal into two or more frequency bands for more efficient amplification.
crossover
switch to distribute the frequencies between the appropriate speakers.

active loudspeaker cabinet system

 

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Contents:

[Contents] [Sound Sources & Signal Paths] [Microphones] [Cabling] [Mixers] [Amplifiers] [Loudspeakers] [Introduction to Acoustics] [Putting it all Together] [Examples] [Glossary] [Conclusion] [Hotdeals] [Feedback]