Stage and PA Amplifiers

Power amplifier or portable voice amplifier?

Two different products share this aisle. Power amplifiers take a line-level signal from a mixer and drive passive speakers; they come in two- and four-channel versions for stage rigs and building installs. Portable voice amplifiers are pocket-size or belt-worn units with a microphone and small speaker, used for lessons, tours and presentations. Check whether the listing includes a microphone, a charging cable and a lanyard, or whether it is the amplifier alone.

Matching watts and ohms to the speakers

Amplifier power is quoted per channel and at a given load, usually 4 or 8 ohms. A lower impedance draws more power, so an amplifier rated at 300 W into 8 ohms may deliver more into 4 ohms, but only if it is specified for that load. As a rule, choose an amplifier at or somewhat above the speaker's continuous (RMS) rating, never far below, because a clipping signal harms speakers. Install amplifiers may offer constant-voltage 70 V or 100 V outputs for ceiling speakers.

Questions about Stage and PA Amplifiers

How much amplifier power do I need for my speakers?

Pick an amplifier whose per-channel output at the speaker's impedance roughly matches the speaker's continuous rating, with a little headroom above it. A small amplifier pushed into clipping is more dangerous for speakers than a larger one running cleanly.

What happens if I connect a speaker with the wrong impedance?

A load below the amplifier's rating makes it work harder and may overheat it or shut it down. A load above the rating just reduces output. Read the minimum load on the amplifier, and remember that speakers wired in parallel lower the total: two 8-ohm speakers make 4 ohms.

Will a voice amplifier work with any headset microphone?

Not necessarily. Plug type, wiring and microphone power vary, so a headset can be silent or distorted. Use the microphone supplied with the unit, or one the maker lists as compatible.