Reading a Speaker Spec Sheet: Watts, SPL, Dispersion and Frequency Response

In this guide:Watts · Sensitivity · Dispersion · Frequency response · Comparing · Picks · FAQ

Loudspeakers are sold on watts, which is the specification least connected to how loud the box goes. Two speakers with the same wattage can differ by 6 dB in output, which is a very large difference indeed.

The specification sheet does contain the answers. This guide covers which numbers matter and what they are telling you.

Why watts is not loudness

Wattage is power handling: how much electrical power the speaker can take without damage. It says nothing about how efficiently that power is converted into sound, and efficiency varies enormously between designs.

It is also quoted inconsistently. You will see continuous or RMS, program, and peak figures, and the same speaker can carry three very different numbers depending on which is printed.

• **Continuous or RMS** is the conservative, meaningful figure.
• **Program** is usually double the continuous figure.
• **Peak** is usually double again, and is close to meaningless for comparison.

When two boxes quote different measures, you are not comparing like with like. Find the continuous figure for both or ignore the number.

Sensitivity and maximum SPL: the useful pair

**Sensitivity** is how loud the speaker is for one watt at one metre, in decibels. It is the efficiency figure, and a difference of 3 dB means one box is twice as efficient as the other.

**Maximum SPL** is how loud it goes before it runs out, again at one metre. This is the number that answers “will it be loud enough”, and it is the one to compare between candidates.

Decibels are logarithmic, and the two rules worth memorising are these. Doubling the power gives you about 3 dB. Doubling the number of identical boxes gives you about 6 dB. That is why two modest speakers often beat one large one, and why buying an amplifier twice the size does far less than people expect.

Dispersion is the number that decides coverage

Dispersion, or coverage angle, is quoted as horizontal by vertical, for example 90 by 60 degrees. It tells you the shape of the area the box actually covers.

This matters more than output in most real rooms. A wide room needs wide horizontal dispersion or more boxes. A deep, narrow room wants a tighter pattern, because energy sprayed at the side walls comes back as reflections and muddies everything.

Vertical dispersion decides how much of the room front to back is covered evenly, and how much energy is thrown at the ceiling. Narrow vertical patterns are why column and line array systems work well in reverberant rooms such as churches.

Frequency response, and the tolerance

A frequency response of 50 Hz to 20 kHz means nothing without a tolerance figure. Quoted with a tolerance, for example plus or minus 3 dB, it is a real specification. Quoted without one, it may be describing the point at which the speaker is barely producing anything at all.

For a full range box, the low figure tells you whether you need a subwoofer. Most 12 inch tops are useful to around 60 Hz, which is fine for speech and thin for a band. Below that you are into subwoofer territory.

Comparing two boxes honestly

• Find maximum SPL for both. If only one publishes it, that tells you something.
• Compare continuous power, not peak, and only alongside sensitivity.
• Compare dispersion against the shape of the room you actually work in.
• Check the frequency response has a tolerance attached.
• Check the weight, the rigging points, the pole socket and the connectors, because those decide whether you can use it.

If you are choosing between an active and a passive version of the same thing, that decision is covered in active vs passive PA speakers.

Frequently asked questions

Is a 1000W speaker louder than a 500W one?

Not necessarily. Wattage is power handling, not output. A more efficient 500W box can be louder than an inefficient 1000W one. Compare maximum SPL and sensitivity instead.

What does 90 by 60 dispersion mean?

The box covers roughly 90 degrees horizontally and 60 degrees vertically. Match the horizontal figure to the width of your audience and the vertical to the depth.

Why do two speakers not sound twice as loud?

Because hearing is logarithmic. Doubling the number of boxes adds about 6 dB, which is clearly louder but not double the perceived loudness. Perceived doubling takes about 10 dB.

What frequency response do I need?

For speech, 100 Hz upwards is plenty. For a band without a sub, you want useful output to around 60 Hz. For anything with kick and bass guitar, add a subwoofer rather than chasing a low figure on the tops.