Passive Radiator (Speaker,Enclosure)

 Passive radiator speaker design – Box calculation example

Passive Radiator (Speaker,Enclosure)

What is a passive radiator?

A passive radiator speaker design involves another speaker, but with no motor ass embly. The magnet and voice coil are gone, but the cone and everything you can passive bass radiator speaker designee from the front are all there. The passive radiator (Amazon affiliate paid link) subwoofer design is very similar to the bass reflex design, only instead of the vent or port, you have the passive bass radiator. Since they are very similar in design principles, they follow similar methodology and performance characteristics. However, certain differences do apply, some are good, and some are not so desirable.

Advantages over bass reflex:

No more vent non-linearities (resonant pipe sounds).

Air turbulence noise is no longer an issue when air rapidly escapes the pipe at high volumes.

No more high frequencies reflected out the port.

Space efficient. Sometimes large ports are demanded which will make the enclosure that much bigger.

Passive radiator speaker design is simpler and with fewer alignments.

Disadvantages over bass-reflex :

Steeper roll-off.

Less transient stability.

Slightly higher cut-off frequency (narrower frequency bandwidth).

Greater overall box losses (QL).

Passive radiators operate in conjunction with the active driver at low frequencies, sharing the acoustic load and reduce the excursion of the driver. Working similarly to a vent, the passive radiator will only add as much as they subtract. This means they will have the same advantages as the bass reflex port : higher power handling and lower distortion.

How does the passive bass radiator compare to the alternatives?

As we mentioned before, the response for the passive radiator speaker design is closely related to that of the bass reflex. The one thing that is unique to the passive radiator is the notch at the resonant frequency of the passive speaker. Usually, the resonance is located at the point where the response start to roll-off (f0), but for the passive bass radiator, this point is below the system’s cut-off frequency. This notch increases the slope of the driver low-frequency roll-off, and degrades the transient response

Which speaker is best for a passive radiator speaker design ?

If compared to the closely related bass-reflex design, the passive radiator (PR) design is more picky when it comes to choosing you speaker. When it comes to passive radiator alignments, they are fewer options, compared to the ported design. Please read the article regarding the bass reflex alignments before continuing. When it comes to PR, you are restricted to 3rd order Quasi Butterworth (QB3), 4th order Butterworth (B4) and 4th order Chebyshev (C4). This is because any driver with a Qts higher than 0.5 will produce a C4 response with a high amount of ripple (large peak near cut-off)

Conclusion on the passive radiator subwoofer design

The passive radiator is intended to be used as an alternative to the ported design. Pro’s and con’s have already been discussed and you should read them carefully to make a good decision if the passive radiator speaker design is for you. Also take note of the price. The passive speaker will be cheaper than the active one because they are similar in most aspects, but the passive one is missing the motor design. While this is true, there is no question that a passive speaker is more expensive than a piece of plastic pipe (a reference to bass reflex).