Passive Radiator

[bad03ranger 10+ year member]

what is it for and how does it work

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[WhoSayWho? 5,000+ posts]

It is to give you more deebeez. My understanding is that it is basically the soft parts of a sub -- no motor. It works off of the movement of the air caused by the sub -- or at least that is my understanding I have never seen one. Either that or magic.

 

[DidUHearThat? 10+ year member]

As he said, they work off the air pressure developed inside the cabinet to produce more sound. The sound pressure alone moves the cone back and forth and this produces sound.

They can add more low end to the powered speaker/sub, but they also effect the impedence of the powered speaker because it acts as another suspension. That energy isn't free and it puts more effort on the main driver and amp. It also isn't a huge gain in low end.

Usually this is done with small drivers and small boxes, like 4" drivers to give them a little more bass. It's usually not worth the cost and hassle. Back in the day when high power drivers and amplifier watts were expensive and labor was cheap this was more common. Now high power drivers and amps are cheap but the labor to install and build them is not, making them less practical.

For the hassle of calculating the effect and extra cost you can just get a higher power driver or add a second regular driver.

 

[WhoSayWho? 5,000+ posts]

As he said, they work off the air pressure developed inside the cabinet to produce more sound. The sound pressure alone moves the cone back and forth and this produces sound.They can add more low end to the powered speaker/sub, but they also effect the impedence of the powered speaker because it acts as another suspension. That energy isn't free and it puts more effort on the main driver and amp. It also isn't a huge gain in low end.

Usually this is done with small drivers and small boxes, like 4" drivers to give them a little more bass. It's usually not worth the cost and hassle. Back in the day when high power drivers and amplifier watts were expensive and labor was cheap this was more common. Now high power drivers and amps are cheap but the labor to install and build them is not, making them less practical.

For the hassle of calculating the effect and extra cost you can just get a higher power driver or add a second regular driver.

Ah, some real insight. Good info because I had always wondered about them. The only time I see them now is in connection with BA subs. The PR seems to be about $110 and a second G5 would only be another $100 (210 total). But if space is a primary issue then it might be still be worth it.

 

[DidUHearThat? 10+ year member]

Many computer speakers have passive radiators and some large headphones use a passive radiator.

For high power subwoofer designs they are not practical.

 

[MBrock4u 10+ year member]

A manager friend of mine has one for his Boston G5 in his trunk. He run a car audion shop I frequent. Very impressiive. Sugjested I get one for my G5. After hearing my G5 in my SUV for about a month, I decided that I wasn't interested and didn't need it. My G5 sounds fabulous as is. No need to mess with it or spend more money. G5's are simply fantastic at every level.

 

[bad03ranger 10+ year member]

Many computer speakers have passive radiators and some large headphones use a passive radiator.
For high power subwoofer designs they are not practical.

i was just wondering how this would work in a reg cab mini truck

http://www.infinitysystems.com/car/products/product_detail.aspx?prod=BASSLINK%20T&cat=BSL&ser=BSL&Language=ENG&Country=US&Region=USA

 

[DidUHearThat? 10+ year member]

i was just wondering how this would work in a reg cab mini truck
http://www.infinitysystems.com/car/products/product_detail.aspx?prod=BASSLINK%20T&cat=BSL&ser=BSL&Language=ENG&Country=US&Region=USA

It will certainly work, and the basslink seems to get good reviews, for wha it is... a small/low power, all-in-one sub. The only question is can you do better for the price? If you built your own box with a pair of 8" or a low profile 10" you can probably get more "bang" for you buck.

 

[helotaxi 5,000+ posts]

A passive radiator system doesn't stress the powered driver any more than a ported setup does. It has the same effect and works in a similar manner to a port. The suspension and mass of the PR creates a delay in the PR movement that brings it into phase with the primary driver. It allows you to tune a small box low without needing the space taken up by the long port that would ordinarily be required for a low tuning. The main drawback is that you usually need about 2x the cone area/swept volume of the driver in passive radiators, so, for example a 10" sub might require 2x10" radiators or 1x15" radiator.

 

[DaPinballWizard 10+ year member]

I have a G512 with the passive radiator in a 1cu ft box and it works really well. It doesn't take up much room and is really easy to tune. It can be changed from 30, 35, 40, and 45hz very easily. For a small package it has pretty good output.

 

[thch 10+ year member]

the simple delay explanation is mostly inaccurate. for instance, it doesn't really explain why excursion is reduced, nor why the system would be able to output +10dB over a sealed box.

But otherwise the passive radiator does act as a resonator that does get excited by the woofer, in much the same manner as a ported box.

a passive radiator, unlike a port, must move to make sound. while a port has issues with turbulance, a passive radiator has issues with overexcursion.

 

[Kyle_Keating 10+ year member]

what is it for and how does it work

it does the same thing as a port, its a moving mass with a resonance.

for example, a 6" port reaches its compression limit at about 14-15" peak to peak. This is when the air velocity reaches a high level and eddy current/turbulence forms as well as excessive drag on the sides of the port. Drag is not a linear function, it has a squared term.

that means the AIR in the port is moving 7-8 " each direction back and fourth with good linearity and will produce lots of SPL (much more than the active driver). It is the air inside a port that is like the cone of the woofer. Its reaches its maximum spl at resonance which depends on the mass of the air in the port and the volume of the box too. Think of a spring mass-system. At resonance is when the most air comes out of the port. This is also why when people say xmax doest mean anything, they don't understand that xmax is shifting from the active woofer to the port during resonance, and if you're port can't displacement air... you're out of luck for high SPL numbers. its all about displacement one way or another.

The PR does the exact same thing, expect its much larger but can't move as much so here is a quick comparison.

A 6" port moving 14" peak to peak is about the same as a 15" passive radiator that can move 2.5 to 3" peak to peak before compression. When they both reach compression, you're in for distortion and SPL losses, but hte advantage of the PR is you can tune it deep in any box volume, and you can re-tune it later one. Its more dynamic in tha regard.

 

[bk12321 10+ year member]

a PR, as others have said, is simply a subwoofer minus the motor/electrical parts, just a suspended cone pretty much.

it enables you to have a "ported enclosure" without the port, and with a much smaller box. you can change the frequency of the enclosure by changing the "moving mass" of the PR. to change the moving mass, you just add or remove a number of weights attached to the PR.

 

[helotaxi 5,000+ posts]

the simple delay explanation is mostly inaccurate. for instance, it doesn't really explain why excursion is reduced, nor why the system would be able to output +10dB over a sealed box.
But otherwise the passive radiator does act as a resonator that does get excited by the woofer, in much the same manner as a ported box.

a passive radiator, unlike a port, must move to make sound. while a port has issues with turbulance, a passive radiator has issues with overexcursion.

Actually the "simple delay explanation" and how it replicates a port explains all of that when you consider that the PR has inertia just like the air in the port and the inertia of the PR moving in phase with the primary driver increases the pressure in the box and mass loads it, reducing excursion. Also because the PR is moving, its swept volume couples with the primary driver creating a coupled output that increases SPL compared to just the primary driver in a sealed box.

 

[crod504 10+ year member]

I have 2 G5 10's w/ GTR's (PR's) and they are LOUD for being 2 sq 10's... I'm pretty sure I would be close to 140 with my US amps MD2D if I got metered... this is a trunk car.