What Are Passive Radiators in Speakers?

Passive radiators are used in many modern speakers because they are a terrific way to get a whole lot of extra oomph out of a sound system without diverting valuable energy into creating that lovely bass effect that we all enjoy so much. They are common in smaller, modern, computer-driven speaker systems largely because they are designed to sound like a bigger speaker while remaining quite small. They are a relatively inexpensive way to deliver a full-throated, rich, and robust sound experience in a way that is mechanically efficient and ideal for the miniaturization that mobile sound systems require.

Now, we’ll explain more about what these speaker components are, how they work, and whether or not you should spend your hard-earned money on them.

What Are Passive Radiators in Speakers?

A passive radiator speaker is a clever way to get extra power and resonance out of a smaller speaker system. The reason they are called “passive” is that they are not powered by electricity, rather, they are powered by the air pressure created by the smaller speaker cones which receive all of the electrical power from the battery or AC source.

The reason passive speakers are so common is that they are ideal for the diminutive speakers you tend to get with BlueTooth capability. These are speakers that are meant to be easy to move around, carry, and that use low power from USB connections or a battery source.

As we will see, the limitations of mobile speakers make passive systems great design choices for these devices. But passive speakers are not necessarily ideal for traditional, full-sized speakers which enjoy the benefit of being plugged into an AC power outlet.

passive radiator schematics

Passive Radiator Speaker Design

A passive radiator is powered by the air pressure generated by the smaller powered speaker inside a modern sound system. They use a subtle and clever method to do a lot of work using very little power.

The way they work is by sealing the entire speaker unit so that all (or a significant amount of) of the vibration generated by the active speakers is forced to move through the delicate diaphragm inside the passive speaker. Because the air pressure inside the speaker cannot escape in any direction other than through the passive speakers, the effect of a big, powerful woofer is effectively simulated.

This principle is easy to test. Simply unscrew one of the active speakers from the speaker housing. Hold the active speaker in place and play your favourite music – preferably something with a lot of bass. Now, while the music is playing, pull the active speaker out of the unit.

What you’ll experience is the resonant sound generated by the passive speaker stopping. The beautiful, deep tones cease and you’re left with the ugly, tinny whining of the unaided passive speakers. To double-check your findings, simply replace the active speaker and you’ll hear those gorgeous, golden tones return.

We don’t recommend doing this test on any speaker that you don’t mind ruining, because there’s a chance that the seal will be permanently compromised. The seal should be easy to fix with a little bit of super glue, but again – don’t do this test if you’re not willing to take the risk.

heos 5 passive radiator speaker
A passive radiator help the HEOS 5 Wireless Speaker put out more bass then you think would be possible from such a small enclosure!

What are The Benefits of Passive Radiators?

A passive radiator makes it possible for woofers to generate deep, resonant tones that could normally only come from speakers with AC power contained in a large housing or box. Passive radiators use the principle that makes the diaphragms in your eardrums do what they do – respond to very low levels of energy for a great effect.

Depending on the tuning when passive radiators are built into a system, it will begin moving just as the drive woofer starts to create low frequencies. By engaging precisely at this point, passive radiators absorb energy from the active speaker. This reduces the motion of the drive woofer. The effect is called dampening. Because the drive woofer moves less, the risk of damage is also reduced.

In other words, passive speakers will not “blow out” as easily, like active speakers are prone to do. The power that drives passive speakers is much more gentle, in essence – making the speaker diaphragm much more likely to stay well within its mechanical tolerance. It really is an elegant solution to a longstanding problem.

This dampening effect is also conducive to the creation of smaller speakers that use less power and that are designed to be highly portable. The reduced range of motion of the woofer diaphragm, the absence of additional wires and power components, and the seal dependent design of the unit all contribute to the ability of these speakers to remain small and deliver satisfying levels of power.

Another important advantage of passive speakers is they are relatively inexpensive to produce. While the technology is still relatively new, you can expect to pay a premium for the novelty for a few more years to come. However, as these items lose the aura of newness, you can expect to be able to afford a heck of a lot of audio power at an increasingly lower price.

Passive Radiator Pros and Cons

So, we’ve talked about the reasons passive speakers are a wonderful innovation in the realm of audio reproduction. But there is still a place for traditional active woofers.

Passive radiators give you great output in a small package while consuming very little energy – and they are far less likely to blow out, as active speakers are prone to do.

Pros

  • Passive radiators work great in portable systems
  • They deliver richer sounds at lower octaves
  • Transient responses are smoother since no mechanical change has to occur to produce different response levels
  • Passive speakers are much less vulnerable to environmental conditions like temperature and humidity

Cons

Passive speakers are not as loud as ported woofers

While they can work well at lower energy levels, they do not use the available power as efficiently since the power has to be shared between the main speakers and the woofers
example of ported speaker

Passive Radiator vs Port Speakers

Traditional ported subwoofers are anything but obsolete. When it comes to delivering high-quality audio to a large audience, over long distances, and making a big impression, port speakers are still the king. They are the big guns of the audio world. So the question is, “Should I buy passive radiator speakers or port?”

The answer depends on how and where you intend to use them.

Pros & Cons of Ported Speakers

Pros

  • Ported speakers are powerful
  • They are more efficient with the power they use
  • High-end models tend to produce less distortion

Cons

  • The vent tends to let sound escape, making directional sound harder to produce
  • More vulnerable to heat, cold, and humidity
  • Ported speakers will not function without solid and precise construction
  • Much more likely to “blow out” due to lower vibration tolerances

With that in mind, it’s not hard to see where ported speakers are best and where passive speakers will give you the most bang for your buck.

When to Buy Ported Speakers

When you place a particular penchant on power, ported speakers are probably ideal. You can still get a lot of power out of passive woofers, but not as much. Home sound systems that are going to be protected from the elements can benefit from using ported models.

The one caveat is that you should know how loud you are likely to play your system. If the answer is “very,” then you’ll want to make sure that the speakers you buy have vibrational tolerances approaching the higher end. Otherwise, you’ll just end up replacing them and spending the money you tried to save in the first place.

Of course, if you’re in a heavy metal band, ported speakers are non-negotiable – and you probably already know that.

sonos beam
The Sonos Beam soundbar uses 3 passive radiators to put out an impressive amount of bass!

When to Buy Passive Speakers

Passive speakers are great for everyday use, when you’re not trying to wake up the neighbours, but still want to get a decent amount of power out of your sound system.

If you’re setting up a home stereo system for the first time, passive speakers can be a great choice. This is due to the fact that BlueTooth models don’t force you to fool around with complex wiring schemes. You’ll be able to reposition the units easily. Also, because passive speakers produce more easily directed sound, it’s easier to pinpoint the centre of the stereo effect that you want to create- especially for a home theatre entertainment system.

Finally, passive speakers are great on the overall cost to own. Because they are less likely to break and less vulnerable to the elements, they tend to last longer than ported speakers. You can get a decent amount of power for less money, passive speakers draw less electrical energy, and they are more durable. All in all, you will spend less money over time on these systems.


Do you have any questions about passive radiators in speakers? Or are unsure of what would work best for your home? Ask in the comments below or contact us and we would be happy to help.

Passive Radiators in Speakers originally published on avu.ca

Leave a comment