What Is Directivity?

Directivity describes how a speaker’s output changes with angle. On axis — straight at the tweeter — you hear the designed response. Ten, twenty, forty degrees off axis, the balance changes: high frequencies narrow first, crossovers lob, cabinet edges diffract.

Why the off-axis sound matters

In a normal room, most of the acoustic energy reaching your ears has bounced at least once. Walls, ceiling, desk — every reflection carries the speaker’s off-axis response into the listening seat, delayed by a few milliseconds.

So a speaker’s “sound” is really a weighted mix:

• Direct sound — timing, imaging, detail.
• First reflections (5–20 ms) — spaciousness, tonal character of the room.
• Late reverberation — the general “air” of the space.

The speaker decides the spectrum of all three, but it decides them differently, because each comes from a different angle.

The crossover problem

At low frequencies most speakers radiate equally in all directions. At high frequencies they beam like torches. The trouble sits in between — exactly where a two-way speaker crosses over. If the tweeter is narrow while the mid-bass is wide at the crossover frequency, the room receives a different tonal balance than the sweet spot does.

This is the problem a waveguide addresses: keeping the tweeter’s radiation wide enough at the crossover to match the mid-bass driver. We cover this in What a waveguide changes.

How to read directivity data

A directivity plot shows response at several angles, usually normalised to the on-axis curve. What you want to see is smooth, gradual narrowing as frequency rises — no sudden steps. Sudden steps at one frequency mean the two drivers are radiating differently at the handover, and the room hears it.

An example (sample data) is published in the Reference One archive.