How to read a speaker spec sheet
Maximum SPL, sensitivity, coverage, frequency response: what each number on a loudspeaker data sheet tells you, what it doesn't, and how to compare two speakers fairly.
Two loudspeakers can look almost identical on paper and sound nothing alike in a room. That's partly because spec sheets measure speakers in ideal conditions, and partly because manufacturers don't always measure the same way. Here's what the main numbers mean, and what to ask about each.
Frequency response
What it says: the range of pitches the speaker reproduces, low to high, for example "55 Hz – 20 kHz".
What to look for: the tolerance next to it, such as "±3 dB". Without a tolerance, the range tells you very little: almost any speaker makes some sound at 40 Hz. A wide range with a tight tolerance is what you want. Also check whether the figure is for the speaker alone or with a recommended processor setting.
Sensitivity
What it says: how loud the speaker plays with a fixed amount of power, usually measured at one watt and one metre, for example "98 dB SPL (1 W / 1 m)".
What it means for you: a more sensitive speaker needs less amplifier power to reach the same level. Each 3 dB of sensitivity is the same as doubling the amplifier power. So a speaker rated at 98 dB needs roughly half the power of one rated at 95 dB to play as loud.
Maximum SPL
What it says: the loudest the speaker can play, in decibels of sound pressure level (SPL), at one metre.
What to ask: is it the peak (a brief burst) or the continuous level (music played for a sustained period)? Peak figures can be 6 dB or more above continuous, so a comparison of one maker's peak against another's continuous is meaningless. Remember too that level falls with distance: in open space, about 6 dB each time you double the distance. A speaker that's loud enough at one metre may not be at thirty.
Coverage (dispersion)
What it says: the angle the speaker covers, horizontally and vertically, for example "90° × 40°". It's usually measured to the point where the level has dropped by 6 dB from the centre.
What it means for you: this decides how many speakers you need and where they go. Too wide, and sound bounces off walls and ceilings and the room gets muddy. Too narrow, and the seats at the edges miss out. Look for how consistent the coverage is across frequencies: many speakers are wide at high frequencies and much wider, or narrower, lower down.
Power handling
What it says: how much amplifier power the speaker can take, often in several figures: continuous, programme and peak.
What to ask: to which standard was it measured? A figure measured to a recognised standard, such as AES2, can be compared with another measured the same way. Without that, the biggest number on the sheet is often the least useful. And power handling isn't loudness: sensitivity and maximum SPL tell you how loud it gets.
Impedance
What it says: the electrical load the speaker presents to the amplifier, usually 4, 8 or 16 ohms, or "100 V" for distributed systems in shops, hotels and offices.
What it means for you: it decides how many speakers an amplifier channel can drive. Get it wrong and the amplifier shuts down or fails. For distributed systems, look at the transformer taps (the power settings) instead.
What the sheet won't tell you
- How it sounds in your room. The room changes everything: its size, its surfaces, where people sit.
- How it sounds at the edges of its coverage, which is where many of your seats are.
- How it's supported, whether spares and service are available locally, and for how long.
That's why we model and listen in context before we specify. If you're comparing speakers for a project, send us the two data sheets and a description of the room, and we'll tell you what we'd look at and why.
