Need a sound system to play background music or make announcements in a restaurant, school, warehouse, or other institutional building? A high-voltage system often presents the most economical, practical, and safest solution.
To start, watch the following video
Commercial audio explained in less than two minutes.
A standard stereo receiver might not be the best solution
A standard home stereo receiver and a few pairs of speakers could provide a small business, such as a restaurant, with adequate background music — but that might not work well in a system with a lot of speakers and long wire runs.
Standard stereo amplifiers put out low-voltage, high-current signals that require thick (and relatively expensive) speaker wires to power distant speakers. The more speakers you add to a stereo system, the more difficult it becomes to safely connect them. You may find that you need multiple amplifiers, driving costs up considerably.
Benefits of a 70-volt system
Because the voltage is high, the current running through a 70-volt system is low. You can use thinner, less expensive speaker wires. The amplifiers in these systems don’t have "load impedance" issues. It doesn’t matter how many speakers you connect.
A 70-volt amplifier can drive as many speakers as it has power for, regardless of their impedance. Standard systems require multiple amplifiers driving speakers that need to impedance-match the amps' outputs.
Speakers with adjustable power levels
The speakers in a 70-volt system are like houses connected to an electric power transmission line. Each speaker incorporates a transformer that steps down the high voltage to a level that the speaker can handle. The transformer has multiple taps to achieve different wattage levels for the speaker. The higher the wattage tap, the louder the speaker will play.
It doesn’t matter how many speakers are connected as long as their total wattage rating doesn’t exceed the power capacity of the amplifier. System designers usually reserve 10% to 20% of an amplifier’s power as extra headroom available for those occasional moments of peak demand. This means that a single 500-watt amplifier could easily run 80 to 90 5-watt speakers, covering a considerable area for background music and announcements.
Crutchfield has put together a few commercial audio bundles that include the right components to cover the needs of a small retail store, restaurant, or classroom.
It only takes about one watt to produce clearly audible announcements or background music from a speaker about 10 feet away from the listener (two watts in a noisy environment like a restaurant or grocery store).
How do you determine how many speakers to put in each room? For ceiling-mounted speakers in open spaces, a rule of thumb says the distance between speakers should be twice the ceiling height. A room that measures 40 feet by 40 feet and has a 10-foot ceiling would be well covered by four ceiling-mounted speakers 20 feet apart each.