vosschs
Passive Radiator
Harry Olson first described passive radiators (PRs) in his patent Loudspeaker and Method of Propagating Sound that was issued back in 1935. Except for an article by Olson in 1954, very little was published about PRs until Nomura and Kitamura in their IEEE paper in October 1973, and Small's JAES paper in October 1974. Since then, passive radiator systems have had a relatively mild impact in the home audio market, while the car audio market failed to embrace it. However, two car audio manufacturers, Boston Acoustics and Earthquake, have recently initiated a movement towards the use of PRs in the automotive industry, taking from their experience in home audio.
So what are passive radiators, what do they do, how do they work, and what are the positive and negatives?
Passive radiators are often deceiving as they commonly look like a conventional subwoofer. However, these certainly are not subwoofers. While they look like and even appear to move like a normal subwoofer from the outside of a speaker system, what is behind them tells a different story. Passive radiators lack a key ingredient that assures they are not a woofer: the motor structure. In other words, they have no voice coil, magnet, top plate, t-yoke, tinsel leads or terminals. PR's are essentially an unpowered driver, therefore they must be mated with a powered woofer in an otherwise sealed enclosure.
Passive radiators systems are referred as a variation of a ported enclosure. While they are mathematically identical, PR's use a diaphragm to take the place of the port.
A PR is essentially made of two parts: a "weighted diaphragm" and a "spring". The weight of the diaphragm is a critical element the design and must be correct for the part to function properly. By changing the weight of the diaphragm, the resonance frequency will change, thus effecting the tuning of the enclosure. The spring is a combination of the stiffness of the suspension materials, and the air trapped within the cabinet. This too can change the tuning of the enclosure, much the same as the enclosure volume of a vented box changes its response.
PRs are tuned, by the mass loading, to resonate at a frequency below the active woofer's linear response range. A passive radiator has a useful range about a 1/4 octave above and below its resonance. However, the typical roll off is a fairly steep 18 dB/octave. The combined response of the woofer and passive radiator should produce about a half an octave bass extension at low frequencies that add up to the level produced by the woofer on its own at higher frequencies, if the PR is tuned properly. In other words, a small amount of low frequency bass that the system would normally have difficulty reproducing now exists.
In a passive radiator system, both the cone of the active woofer and PR could move in phase with each other, or any combination of opposite motions, up to 180 degrees out of phase. Keeping both cones exactly in phase would be ideal in order to reinforce the output of the woofer, but as physics would have it, this sort of resonant system is not exactly possible.
One of the advantages of this type of system is that as the frequency being reproduced nears the resonance frequency of the PR, the excursion of the woofer decreases, thus taking the burden away from the woofer when producing the lower octaves. This is why it is common to see passive radiators larger in diameter than the active woofer in the system, as the woofer does not need to have the low frequency extension it would need in other enclosure designs. Also, this occurrence can allow the smaller diameter woofer to better its response at the upper and mid bass regions.
As with the good, always comes the bad, for passive radiators are not perfect. As mentioned prior, passive radiators can reproduce tones up to 180 degrees out of phase of the woofer. Depending on the frequency generated and the positioning of the passive to that of the active woofer, the frequency response could have small amounts of cancellation. So long as the overall phase response does not contain any sudden changes or discontinuities, the human ear/brain should not detect this. However, when the phase response changes rapidly over a small range, it can be noticeable, as some people are more sensitive to this than others.
Another inherent problem is the fairly sharp roll off of the PR. The frequencies below the passive radiator's tuning will roll off very rapidly. In addition, the air in the speaker box no longer acts like a spring to control and restore the motion of the PR and especially the woofer below the resonance of the PR. Much like a woofer in a vented enclosure, power handling of the woofer can be limited below the tuning frequency. This, in effect, could damage both the active woofer and the passive radiator.
Passive radiators can be challenging to design. Most radiators now days have adjustable weight setups on the cone that make for easier tuning to the enclosure. However, picking the correct woofer, one with a low QTS (0.2 to 0.4), and designing a suitable enclosure are equally important.
From-
http://www.caraudiomag.com/technical/0206cae_boxbasics/
Harry Olson first described passive radiators (PRs) in his patent Loudspeaker and Method of Propagating Sound that was issued back in 1935. Except for an article by Olson in 1954, very little was published about PRs until Nomura and Kitamura in their IEEE paper in October 1973, and Small's JAES paper in October 1974. Since then, passive radiator systems have had a relatively mild impact in the home audio market, while the car audio market failed to embrace it. However, two car audio manufacturers, Boston Acoustics and Earthquake, have recently initiated a movement towards the use of PRs in the automotive industry, taking from their experience in home audio.
So what are passive radiators, what do they do, how do they work, and what are the positive and negatives?
Passive radiators are often deceiving as they commonly look like a conventional subwoofer. However, these certainly are not subwoofers. While they look like and even appear to move like a normal subwoofer from the outside of a speaker system, what is behind them tells a different story. Passive radiators lack a key ingredient that assures they are not a woofer: the motor structure. In other words, they have no voice coil, magnet, top plate, t-yoke, tinsel leads or terminals. PR's are essentially an unpowered driver, therefore they must be mated with a powered woofer in an otherwise sealed enclosure.
Passive radiators systems are referred as a variation of a ported enclosure. While they are mathematically identical, PR's use a diaphragm to take the place of the port.
A PR is essentially made of two parts: a "weighted diaphragm" and a "spring". The weight of the diaphragm is a critical element the design and must be correct for the part to function properly. By changing the weight of the diaphragm, the resonance frequency will change, thus effecting the tuning of the enclosure. The spring is a combination of the stiffness of the suspension materials, and the air trapped within the cabinet. This too can change the tuning of the enclosure, much the same as the enclosure volume of a vented box changes its response.
PRs are tuned, by the mass loading, to resonate at a frequency below the active woofer's linear response range. A passive radiator has a useful range about a 1/4 octave above and below its resonance. However, the typical roll off is a fairly steep 18 dB/octave. The combined response of the woofer and passive radiator should produce about a half an octave bass extension at low frequencies that add up to the level produced by the woofer on its own at higher frequencies, if the PR is tuned properly. In other words, a small amount of low frequency bass that the system would normally have difficulty reproducing now exists.
In a passive radiator system, both the cone of the active woofer and PR could move in phase with each other, or any combination of opposite motions, up to 180 degrees out of phase. Keeping both cones exactly in phase would be ideal in order to reinforce the output of the woofer, but as physics would have it, this sort of resonant system is not exactly possible.
One of the advantages of this type of system is that as the frequency being reproduced nears the resonance frequency of the PR, the excursion of the woofer decreases, thus taking the burden away from the woofer when producing the lower octaves. This is why it is common to see passive radiators larger in diameter than the active woofer in the system, as the woofer does not need to have the low frequency extension it would need in other enclosure designs. Also, this occurrence can allow the smaller diameter woofer to better its response at the upper and mid bass regions.
As with the good, always comes the bad, for passive radiators are not perfect. As mentioned prior, passive radiators can reproduce tones up to 180 degrees out of phase of the woofer. Depending on the frequency generated and the positioning of the passive to that of the active woofer, the frequency response could have small amounts of cancellation. So long as the overall phase response does not contain any sudden changes or discontinuities, the human ear/brain should not detect this. However, when the phase response changes rapidly over a small range, it can be noticeable, as some people are more sensitive to this than others.
Another inherent problem is the fairly sharp roll off of the PR. The frequencies below the passive radiator's tuning will roll off very rapidly. In addition, the air in the speaker box no longer acts like a spring to control and restore the motion of the PR and especially the woofer below the resonance of the PR. Much like a woofer in a vented enclosure, power handling of the woofer can be limited below the tuning frequency. This, in effect, could damage both the active woofer and the passive radiator.
Passive radiators can be challenging to design. Most radiators now days have adjustable weight setups on the cone that make for easier tuning to the enclosure. However, picking the correct woofer, one with a low QTS (0.2 to 0.4), and designing a suitable enclosure are equally important.
From-
http://www.caraudiomag.com/technical/0206cae_boxbasics/
If you remember anything out of that article, remember these two sentences.
bonesninja
5,000+ posts
CarAudio.com Veteran
never seen one before...very interesting
Stones I think it fair to say ya no ur stuff,alot of history in your knowledge, I'd be proud to know ya!!!!!!Sqeak if ya know more sayit! If not quit waistin space...Hence remember this phrase( Those who knows will show!~Those who dont rely on sarcasim or lies!)
Do they still make the passive radiators tunable i.e. add weight to the cone ? I haven't played around with them in a while. I have noticed the manufacturers have started producing them allot more lately. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
You fucking idiot, he copy-n-pasted that from a magazine article.
What in the fucking hell are you talking about //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif
Whether or not those BA PR's are easily tunable or not, I couldn't tell you. But most of them (from other companies) are I believe. Really, they'd almost have to be as that's the only way to tune a PR
johnson
10+ year member
CarAudio.com Elite
Cool, I thought that was the only tuning method for them. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
VOA_NIGHTMARE
10+ year member
CarAudio.com Veteran
Eathquake had some that I tried i think they were called slaps cant remember its been about 8 yrs or so They did make a diffrence, but I would rather just port abox instead of making a large sealed box thats single chamber.
//content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif
//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
rocky 59
5,000+ posts
CarAudio.com Veteran
squeak hes calling you out. take him down!
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