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.
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