I have had the pleasure of hearing a few older klipsche (spell?) speakers that used rear facing passive radiators and smallish drivers on the front of the enclosure. This was quite a while ago tho, before I was interested in DIY audio, so I have forgotten what the low end really sounded like. I understand that you can model an enclosure using a ported design and tune the radiator to the port frequency, but I want to know how the sound differes between a passive radiator and an adegquately sized port with no wind turbulance. Does it sound any different? How about below the tuning frequency where the driver is unloaded in a ported enclosure, is it unloaded in a passive radiator application as well??
you really don't get much midbass and midrange leakage at all. Distortion is nice and low, and you don't have to worry about port wind noise. Passive radiators also facilitate smaller-than-optimum boxes because they can, in many cases, represent super-long ports if necessary.
There is a penalty to be paid for the passive radiator design.
Everything you said was true about tuning the passive radiator to the port frequency. However, the passive radiator itself has a frequency of resonance an octave or so beneath the port tuning frequency, which causes a sharper cutoff due to interference. Where a ported box would have a cutoff of 24 dB per octave, a similar passive radiator design would have a cutoff slope of 30 dB per octave.
Since transient response is related to cutoff slope, the higher the cutoff slope, the worse the transient response. Slightly more "boom" or "overhang". It should be noted that to Closed Box fans, even the ported designs have too much "hangover" already, since a Closed Box has a cutoff slope of 12 dB per octave and a ported normally has a cutoff slope of 24 dB per octave.
One member here, Thomas W, built a 6 cu ft enclosure with a Blueprint 15 incher based on a passive radiator design. In Thomas' design, he replaced the passive radiator of the previous design with a flared 6" flared port and reported an audible improvement in the transient response.
For these reasons, passive radiators generally are used where ports are inconventient-eg; very small boxes where prots would take up a huge percentage of the internal box volume.
I think they sound pretty good myself, but they do have that slightly steeper cutoff slope. They would be used more often but a port is generally cheaper and more convenient. If you are willing to pay a little extra for the passive radiator, you can build a good design.
Everything you said was true about tuning the passive radiator to the port frequency. However, the passive radiator itself has a frequency of resonance an octave or so beneath the port tuning frequency, which causes a sharper cutoff due to interference. Where a ported box would have a cutoff of 24 dB per octave, a similar passive radiator design would have a cutoff slope of 30 dB per octave.
Since transient response is related to cutoff slope, the higher the cutoff slope, the worse the transient response. Slightly more "boom" or "overhang". It should be noted that to Closed Box fans, even the ported designs have too much "hangover" already, since a Closed Box has a cutoff slope of 12 dB per octave and a ported normally has a cutoff slope of 24 dB per octave.
One member here, Thomas W, built a 6 cu ft enclosure with a Blueprint 15 incher based on a passive radiator design. In Thomas' design, he replaced the passive radiator of the previous design with a flared 6" flared port and reported an audible improvement in the transient response.
For these reasons, passive radiators generally are used where ports are inconventient-eg; very small boxes where prots would take up a huge percentage of the internal box volume.
I think they sound pretty good myself, but they do have that slightly steeper cutoff slope. They would be used more often but a port is generally cheaper and more convenient. If you are willing to pay a little extra for the passive radiator, you can build a good design.
/agree
I associate LARGE PR designs with low end "boom", shake the house, rattle, etc.
Trying to reproduce delicated bass guitar solos just don't seem to cut it
for me, I pefer sealed or ported over
PR for normal "bass"...
For subwoofer duty with a low
crossover point, perhaps 60-70hz,
it's not bad at all, but I wouldn't run
PR systems above 100hz......
If you are working with 6-8" PR's,
then you can cheat more........heh
I associate LARGE PR designs with low end "boom", shake the house, rattle, etc.
Trying to reproduce delicated bass guitar solos just don't seem to cut it
for me, I pefer sealed or ported over
PR for normal "bass"...
For subwoofer duty with a low
crossover point, perhaps 60-70hz,
it's not bad at all, but I wouldn't run
PR systems above 100hz......
If you are working with 6-8" PR's,
then you can cheat more........heh
Jared said:
Just had a pr of klipsch heresys thru here -- the entire back panel acted as a PR -- didn't work too well.
With a PR there is another resonance you have to worry about -- perhaps someone with better knowledge of PRs than i can fill in on that.
dave
Current PR makers...
I've never heard the Klipshe PRs, but you can go to a pro/roadie shop and test out the Mackie 624 active studio monitors or the larger 824 model. They use a PR hidden behind the rear-mounted amplifiers.
Way too expensive for my DIY wallet, but relatively cheap when you consider that you get 4 good drivers, 4 clean amplifiers and 2 well-designed enclosures.
🙂ensen.
I've never heard the Klipshe PRs, but you can go to a pro/roadie shop and test out the Mackie 624 active studio monitors or the larger 824 model. They use a PR hidden behind the rear-mounted amplifiers.
Way too expensive for my DIY wallet, but relatively cheap when you consider that you get 4 good drivers, 4 clean amplifiers and 2 well-designed enclosures.
🙂ensen.
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