I’m an audiophile and home theatre enthusiast. I keep hearing the term “passive radiator” and when I google it everything just goes over my head. Can someone explain like I’m 5?
In: Technology
I can’t offer an ELI5 explanation, but it is acoustically equivalent to a port. A port is a device which uses a resonating mass of air in a pipe to augment the sound coming out of the front of the speaker by using the out-of-phase radiation in the rear of the speaker. This resonance constructively combines with the sound in the bass frequencies. Ports tend to make noise if the speaker is playing very loud, low frequencies, and to solve this problem, you need to make the diameter of the port larger, but this then requires that the port be longer. It’s very easy to end up needing a port that is too long and too voluminous to practically fit in the box.
A passive radiator replaces that resonating mass of air in the port with a resonating speaker cone, very similar in construction to any other woofer, but generally having additional weights. These weights lower the frequency at which this cone resonates (the cone is attached to a ‘spring’ in the form of the spider and surround of the passive radiator).
It is relatively easy to make a passive radiator which can output more bass with less extraneous noise than a practically sized port could. It is probably the best way to augment bass in a high-end speaker, with the biggest downside being the cost compared to a plastic or cardboard tube.
High end passive radiators are engineered to perform like woofers, they just lack an electrical motor structure to generate movement on their own, but similar attention is paid to the stiffness of the cone, the excursion and output potential of the radiator, the stiffness of the chassis, and the resonances of all of these components.
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