Commercial Audio Education
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What is a 70 Volt Sound System & what is it used for?
A 70 Volt Sound System is comprised of amplifiers, speakers with transformers, microphones, a telephone system
interface and an assortment of wires used as connections. It is generally used for commercial sound applications where
there is a necessity for electronically amplifying and distributing sound for the functions of paging, playing music and/or
pre-recorded messages to a commercial environment.
What are the components that make up a 70 Volt Sound System?
• Centralized Amplifier: The central unit of a 70 Volt System is the amplifier that amplifies the sound signal to be
distributed to pre-established speakers or paging horn loudspeakers.
There are power amplifiers, which are rack-mountable and have no external controls,
and packaged amplifiers, which have pre-amp features such as volume controls, bass
and treble controls, etc., that are built into the amplifier to make it a pre-amplifier
and amplifier all in one unit.
Amplifiers have many diverse features and many input and output connections. They
can feature XLR MIC Connectors or MIC terminal strip connections, auxiliary/RCA inputs for music sources, and 600 ohm
telephone inputs.
Most commercial amplifiers have speaker outputs for 4/8/16 ohm and 70V systems. Most Speco Technologies
amplifiers offer a ‘Music on Hold’ output feature to allow customers on hold to hear music or prerecorded advertising.
• Speakers: There are several different types of speakers including in-ceiling, in-wall, baffle and flush-mount cone
speakers or horn loudspeakers.
Optimal speaker selection for each installation can depend on what application the speaker is needed for. It can also
depend upon the area that is needed to be covered, the ambient noise level of the environment, whether the application
for the speaker will be foreground/background music or voice, and whether the speaker will be used indoor or outdoor.
For commercial applications in a 70 Volt System, the speaker must have a transformer mounted on it to be used.
• Transformers: The transformers that are used on 70 Volt System speakers are step-down transformers that convert
the high-voltage/low-current coming from the amplifier to the low-voltage/high-current signal that makes the
speaker work.
Each transformer usually has multiple wattage taps so that each speaker can be individually set as to how much
wattage will enter the speaker, and, because of this, how loud each speaker will be. The benefits of using transformers
are listed on the next page.
Transformers can be sold individually to be pre-mounted or already on a speaker.
• Phone System Interface Device: These systems are used to connect a phone system to the speaker system via the
amplifier for paging purposes.
• Microphones: Located in the front end of the system to receive the delivered sound, microphones are
low impedance devices that require a shielded cable so as to not to interfere with the amplifier or
speaker wires.
• Wires: Generally speaking, speaker wire is determined by the length of the run and wattage utilized:
For wire runs less than 50 ft. and 50 Watts of power or less use 16 gauge wire.
For wire runs more than or over 50 Watts of power use 14 gauge wire.
A lower gauge (thicker) wire can always be substituted for a higher gauge wire, but it is not permissible
to substitute a higher gauge wire when a lower gauge wire is needed.
Also 70 Volt systems must always use shielded wiring to protect from high voltage, high frequency
signals radiating into telecommunication and data circuits.
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