What Is a Passive Radiator and How Is It Different From a Port? – Arendal Sound

Passive radiators and ports are both used to enhance bass performance in speaker systems. They serve a similar purpose, extending low-frequency output without needing a larger enclosure, but they do it in different ways.

What Is a Passive Radiator?

A passive radiator is a diaphragm that looks like a speaker cone but has no voice coil or magnet. It does not generate sound on its own. Instead, it reacts to the pressure changes inside the speaker enclosure caused by the active woofer.

When the woofer moves:

It compresses and decompresses air inside the cabinet
This air movement causes the passive radiator to move
That motion helps reinforce low-frequency output by tuning the system to a desired bass response

In effect, a passive radiator acts like a port.

What’s the Difference from a Port?

While both help extend bass, they behave differently:

Feature	Passive Radiator	Port (Bass Reflex)
Airflow	No airflow	Moves air in and out of the box
Physical design	Uses a cone or diaphragm	Uses a hollow tube
Wind noise (chuffing)	None	Can occur at high volumes
Space inside the cabinet	Takes up more space	More efficient use of internal air
Tuning flexibility	Adjustable with radiator mass	Adjustable by port length and width

Why Use a Passive Radiator?

Passive radiators are often chosen when:

The enclosure is too small to fit a long port
You want to eliminate port noise at high output

Summary

Passive radiators and ports both tune the bass response of a speaker, but a passive radiator uses motion instead of air flow. The result is deep, controlled bass without the drawbacks of air turbulence. While more complex and costly to implement, passive radiator systems offer impressive low-end performance in compact designs.