Buyers Guide for 70 Volts Distributed Outdoor Speaker Systems
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. Most commercial amplifiers have speaker outputs for 4/8/16 ohm and 70V systems.
• Speakers: There are several different types of speakers including in-ceiling, in-wall, baffle and flush-mount cone speakers or outdoor speakers. 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 next. 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.
What are the Benefits of Using a 70 Volt Sound System?
• A 70 Volt System uses a basis of high voltage to result in a lower current when distributing power to a sound system. Since Power equals Voltage times Current, a higher voltage will result in a lower current needed to arrive at a desired power load. This prevents long runs of wire from getting overheated by not having excessive, wasted current. This makes 70 Volt Systems very energy efficient. Many municipalities in America actually require the use of 25 Volt transformers because the municipalities’ electrical codes classify a 25 Volt system as low voltage, thus making it safer.
• Generally speaking, 70 Volt Systems are much more cost efficient than an 8 ohm speaker system when dealing with the volume installation of speakers.
• 70 Volt Systems are easier to design than 8 ohm speaker systems. The designer does not have to worry about keeping the impedance matched throughout their speaker system as they would on an 8 ohm based system. 70 Volt Systems can have their speakers daisy chained in parallel together without worry. Because 70 Volt speakers come with transformers, impedance is not an issue unless an extreme amount of speakers are installed together. This will make locating problems that occur easier to find by isolating it on individual small speaker runs where it can be quickly located. Also, it is an easy calculation in determining the amount of wattage needed in your amplifier. You will take the total wattage requirement of your 70 Volt speakers, or “load”, and include a 20% safety buffer to the upside arriving at the minimum RMS wattage your amplifier should have.
• 70 Volt Systems allow you to set the volume of each individual speaker by letting you customized the wattage taps on the speakers for the specific volume needed in your specific sound area. The higher the wattage taps are set on individual speakers, the more power the speaker consumes, the louder the speaker will be. The transformer on the speaker also serves as a safeguard to make sure individual speakers are not ruined by excessive wattage.
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