Commercial Audio Buying Guide: Choosing a PA and Background Music System

Most shops, pubs, offices and schools need one thing: a 100V line mixer-amplifier with ceiling or wall speakers, plus a paging microphone if staff make announcements. This guide shows how to choose each part, how to size the amplifier, and when a ready-made package is the easier buy.

Everything below is from Adastra, the commercial audio range we stock in our Audio Systems department. We supply equipment; we do not install it. Your electrician or AV installer can fit it, and we can help them choose.

The four parts of a commercial sound system

Part	What it does	Where to start
Amplifier	Powers the speakers. A mixer-amplifier also has microphone and music inputs, often with Bluetooth, USB, FM or DAB+ built in, so it is the whole system in one box.	Amplifiers
Speakers	Ceiling speakers for suspended or plasterboard ceilings; wall speakers where there is no ceiling void; horns and column speakers for loud or outdoor areas.	Loudspeakers
Microphone	A paging microphone lets staff talk over the music. Models with a chime play a tone first.	Microphones
Cable and controls	Speaker cable to each speaker, and wall volume controls if some areas need to be quieter.	Volume controls

Step 1: 100V line or 8 ohm?

Choose 100V line if you have more than about four speakers, long cable runs or several rooms. Each 100V speaker has a power setting (a tapping), so one amplifier can run many speakers safely. Choose low impedance (4 or 8 ohm) for two to four speakers close to the amplifier, such as a bar, a meeting room or a home, where music quality matters most. Many Adastra mixer-amplifiers, such as the UM and UA series, have both 100V and 8 ohm outputs. Read more in 100V line speakers explained.

Step 2: count the speakers

As a starting point, allow one ceiling speaker for every 15 to 20 square metres in a shop or office with a normal ceiling height, and fewer, louder speakers in open warehouses or outdoors. It is better to have more speakers at a lower setting than a few very loud ones: the sound is more even and easier to understand.

Step 3: size the amplifier (worked example)

A 140 square metre shop floor needs about 8 ceiling speakers. The Adastra metal quick-fit 100V ceiling speaker has tappings of 1.5W, 3W and 6W.

8 speakers x 6W = 48W in total.
Add about 20% spare: 48W x 1.2 = about 58W.
So a 60W mixer-amplifier such as the Adastra UM60 is the right size. It has a microphone input, Bluetooth, USB and FM, and 100V or 8 ohm outputs.

If the shop later adds speakers, set some to 3W, or step up to a 90W or 120W amplifier. Never connect more speaker watts than the amplifier is rated for.

Step 4: add announcements and zones

One area: plug a paging microphone such as the COM41 or the COM60 with chime into the mixer-amplifier.
Different volumes in different areas: fit a 100V volume control in each area. Relay versions go to full volume for emergency announcements.
Different music in different areas: choose a multi-zone amplifier such as the V-122 dual zone or the RM244V with 4-zone paging.

Step 5: or buy a package

Adastra packages pair an amplifier with matched speakers and cable. For example, the 8-speaker ceiling PA package is the worked example above in one order: a UM-series 60W mixer-amplifier, eight metal-framed 100V ceiling speakers and a 25 m reel of speaker cable. There are also 4 and 12 speaker versions, Bluetooth in-wall packages for a single room, and outdoor horn and sound projector packages.

Common questions

What is the difference between a mixer-amplifier and an amplifier?

A mixer-amplifier has its own microphone and music inputs and volume controls, so it works on its own. A power amplifier (also called a slave amplifier) only makes a signal louder and needs a mixer or another amplifier in front of it. Most single-site systems only need a mixer-amplifier.

Can I play music from my phone?

Yes, on any mixer-amplifier with Bluetooth. Several Adastra models let you change the Bluetooth name and pairing code, which helps when there are several systems in one building.

Do I need a licence to play music in my business?

Usually yes. Playing recorded music or radio to staff or customers in the UK normally needs a TheMusicLicence from PPL PRS. Check with PPL PRS for your premises.

Can these speakers be used for a fire voice alarm?

Only speakers marked EN54-24 are approved for voice alarm use, and the whole system must be designed and commissioned by a competent installer. Use the EN54 Fire Rated filter in Loudspeakers to find them.