I am going to be tuning my sub which has 2 15" PR's in it, can i tune them each with a different weight to extend the LF response? I know that it wouldn't work with a port but PR's are different right? or would the combined air resistance find a spot in the middle of the 2 tunings to resonate? 
I have yet to even put it together, but soon i will be testing it out. thanks for the help.
Mike
I have yet to even put it together, but soon i will be testing it out. thanks for the help.Mike
Intersting to read a post involving two Passive Radiators that is not involving the Peerless XLS, lol. 
Not that there is anything wrong with that driver-it's just that all the two PR threads seem to be about it.
My guess is that the two PR's will act like two ports tuned to different frequencies. That is, the tuning will be a lot closer to the higher tuned Passive Radiator than the lower tuned Passive Radiator. The higher tuned Passive Radiator, (or port), probably will "short circuit" the lower tuned one.
Not that there is anything wrong with that driver-it's just that all the two PR threads seem to be about it.My guess is that the two PR's will act like two ports tuned to different frequencies. That is, the tuning will be a lot closer to the higher tuned Passive Radiator than the lower tuned Passive Radiator. The higher tuned Passive Radiator, (or port), probably will "short circuit" the lower tuned one.
you think if done properly it could provide a slower roll-off below Fb? I assume that a PR box rolls off similar to a ported box at 18db per octave. ***-u-me..... memory could be failing though. so tuning one at the "proper" freq for the box size, then tuning the second a quarter octave or a half an octave lower is what i was thinking. You are right about the one tuned higher "short circuiting" the other, it would be lighter, therefore louder, again, i am assuming. but that second lower tuned PR would pick up where the other left off, albeit with lower spl. I wonder how the two PR's would interact if tuned different? hhhmmmmm interesting. a little experimentation is in order. By the way the PR's are stryke audio PR's, they were only 45 bucks, quite a steal. the sub is a well broke it Dayton 15 DVC I bought a few years ago. It has been so long i don't even remember what i was tuning the box to! 
ah well, it'll all come back to me.
ah well, it'll all come back to me.Ported subs generally roll off at 24 dB/octave. In cases where the Qts of the driver is much less than 0.38, the volume of the box is much less than the Vas and where the box tuning frequency is much higher than the Fs, they might roll off at 18 dB/octave.
However, when you substitute a Passive Radiator for a port, generally you add 6 dB/octave rolloff. This is because the Passive Radiator itself has a resonance frequency, lower than the box tuning frequency but still enough to cause problems. Ports do not have the situation.
So a ported box which rolls of at 24 dB/octave, when a Passive Radiator is substituted for a port, rolls off at 30 dB/octave. A ported box which rolls off at 18 dB/octave, when a Passive Radiator is substituted, rolls off at 24 dB/octave.
With one port or Passive Radiator, the bass reflex box, (yes, Passive Radiator boxes are bass reflexes, even though we normally use the term as a synonym for "ported") "goes dipole". That is, once you hit the tuning frequency the cone motion increases drastically to the point it would be as if you took a board and just mounted the speaker on it with no enclosure. Put another way, once the tuning frequency is reached, the enclosure begins to disappear, acoustically.
With two Passive Radiators, this process is likely to commence with the higher tuning frequency. The lower tuned frequency Passive Radiator is unlikely to affect much at all.
There might be some effect if the lower tuned Passive Radiator is tuned to within a quarter octave or so of the higher. There, the two Passive Radiators are likely to interract together-might be interesting. Worth a try-you can always tune them identically if you don't like what you get.
Once there is a difference of much more than a quarter octave or so, though, I would think the higher tuned Passive Radiator would begin to start "short circuiting" the lower tuned one.
However, when you substitute a Passive Radiator for a port, generally you add 6 dB/octave rolloff. This is because the Passive Radiator itself has a resonance frequency, lower than the box tuning frequency but still enough to cause problems. Ports do not have the situation.
So a ported box which rolls of at 24 dB/octave, when a Passive Radiator is substituted for a port, rolls off at 30 dB/octave. A ported box which rolls off at 18 dB/octave, when a Passive Radiator is substituted, rolls off at 24 dB/octave.
With one port or Passive Radiator, the bass reflex box, (yes, Passive Radiator boxes are bass reflexes, even though we normally use the term as a synonym for "ported") "goes dipole". That is, once you hit the tuning frequency the cone motion increases drastically to the point it would be as if you took a board and just mounted the speaker on it with no enclosure. Put another way, once the tuning frequency is reached, the enclosure begins to disappear, acoustically.
With two Passive Radiators, this process is likely to commence with the higher tuning frequency. The lower tuned frequency Passive Radiator is unlikely to affect much at all.
There might be some effect if the lower tuned Passive Radiator is tuned to within a quarter octave or so of the higher. There, the two Passive Radiators are likely to interract together-might be interesting. Worth a try-you can always tune them identically if you don't like what you get.
Once there is a difference of much more than a quarter octave or so, though, I would think the higher tuned Passive Radiator would begin to start "short circuiting" the lower tuned one.
The two PRs will act as two ports with a very tiny difference below fh (there is a zero there for the PR). Having two ports or PRs, it makes no sense at all to make them different from each other. Together with the box, they will act as one resonator with one helmholtz frequency. The only thing that will happen if they are given different masses/areas/lengths is that one will move more than the other, but always proportional to one another.
Wide frequency spacing of the ports is fairly pointless, and
note the shorter port will work towards towards the total
box volume, the shorter port will work, the longer port will
be next to totally ineffective bieng "shorted" by the other
port.
If the ports are closely tuned due to the phase reversal
at resonance the effect is to add damping to the Q of
the port resonance, so again fairly pointless, there are
other ways of adding this damping if required.
That this is PR's rather than ports makes no difference.
sreten.
note the shorter port will work towards towards the total
box volume, the shorter port will work, the longer port will
be next to totally ineffective bieng "shorted" by the other
port.
If the ports are closely tuned due to the phase reversal
at resonance the effect is to add damping to the Q of
the port resonance, so again fairly pointless, there are
other ways of adding this damping if required.
That this is PR's rather than ports makes no difference.
sreten.- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.