Not sure if this should go in subwoofer or multi-way forum...
Is there any reason why a passive radiator would be a bad choice for a pro-style (high sensitivity, low excursion, low displacement) woofer? Like JBL or Eminence?
Furthermore, I've read that the displacement of the PR should be at least 2-3 times the displacement of the woofer. I've also read that the diameter of the PR should be greater than or equal to that of the woofer. Since many new PR's have large displacements (and large excursions) and many pro-style woofers have comparatively low displacement (and low excursion) is it okay to use a 12" passive for a 15" woofer as long as the displacement is sufficiently large. Also, is it a bad thing to use the same size woofer with a displacement that > 6x the woofer's displacement. What happens if the PR's displacement is too high?
One of the reasons I am asking this is because I am interested in the CSS APR's. They are priced very well and have some pretty huge excursion and displacement which I imagine is a good thing.
Thanks
Is there any reason why a passive radiator would be a bad choice for a pro-style (high sensitivity, low excursion, low displacement) woofer? Like JBL or Eminence?
Furthermore, I've read that the displacement of the PR should be at least 2-3 times the displacement of the woofer. I've also read that the diameter of the PR should be greater than or equal to that of the woofer. Since many new PR's have large displacements (and large excursions) and many pro-style woofers have comparatively low displacement (and low excursion) is it okay to use a 12" passive for a 15" woofer as long as the displacement is sufficiently large. Also, is it a bad thing to use the same size woofer with a displacement that > 6x the woofer's displacement. What happens if the PR's displacement is too high?
One of the reasons I am asking this is because I am interested in the CSS APR's. They are priced very well and have some pretty huge excursion and displacement which I imagine is a good thing.
Thanks
No. It is not ok to use a 12" PR on a 15" driver.
If the displacement is "too high"? By this I think you mean the Xmax, linear travel?
If the Xmax is very high, there is no problem, the PR is just more linear at higher excursions. If you don't use the full excursion, no problem.
Best to use an 18" PR with a 15" driver... even that may be insufficient IF the tuning is low enough and the level is high enough.
_-_-bear
If the displacement is "too high"? By this I think you mean the Xmax, linear travel?
If the Xmax is very high, there is no problem, the PR is just more linear at higher excursions. If you don't use the full excursion, no problem.
Best to use an 18" PR with a 15" driver... even that may be insufficient IF the tuning is low enough and the level is high enough.
_-_-bear
It might be OK depends on the specifics, IE 1) the box tuning, 2) both the driver and PR Sd & Xmax, 3) max SPLs. I dont see much fault in yer reasoning. Like everything else in engineering it depends. use freeware to model this
BTW Most importantly Pro drivers dont go so low that longish tuning vents are not a problem requiring a PR solution. Lastly to get the most SPLs, steep highpass filters are usually specified in Pro applications to prevent over excursion.
BTW Most importantly Pro drivers dont go so low that longish tuning vents are not a problem requiring a PR solution. Lastly to get the most SPLs, steep highpass filters are usually specified in Pro applications to prevent over excursion.
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I am somewhat aware of the pro-drivers not going quite so low but thanks for the warning.
Another related question about low excursion woofers & PR's. I've read that, especially when then cabinet is close to Vas that woofers can bottom out easily with low base even at low volumes. Does a PR help protect the active woofer from bottoming out in that case?
No, a PR is not really different than a vent at low frequencies near its primary and the drivers resonances ( two bumps). Under non linear overdrive IE Xmax it may take more of a beating than the driver which could offer itself up first thus saving the bass driver. Lol but again it depends whose limits Xmax comes 1st.
Box tunings near Vas indicate unsuitable Qts damping and reasonable tuning and/ or box sizes. I suggest modeling your example yourself to decide why a PR is needed and explore the tuning tradeoffs. DL a freeware program.
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Box tunings near Vas indicate unsuitable Qts damping and reasonable tuning and/ or box sizes. I suggest modeling your example yourself to decide why a PR is needed and explore the tuning tradeoffs. DL a freeware program.
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nah... the relationship between the excursion of the PR and the excursion of the main driver is not 1:1 at all. In fact there is almost no motion in the main driver when the excursion of the PR is max'd... so if ur F3 is around 40Hz. probably the maximum excursion of your PR may not be so great to begin with. Drop it to 35, 32, and down and all of a sudden you are moving a LOT of air with it.
Also you have to look out for excursions below the desired F3 point... and, within reason the smaller the PR, the greater the velocity and higher the excursion required for the identical output compared to a larger PR. The higher the velocity, the harder it is to stop the PR cone.
As you go lower in freq the mass loading that is added to bring the resonant freq down increases dramatically. At lower velocities it is easier to control and stop that mass loaded cone.
Otoh, Bob Carver used a 1:1 driver/PR diameter in his Sunfire subs, but I do not know if they were electronically corrected.
Nobody I know of has ever used a larger main driver and a smaller PR with any success.
Oh, yeah, an early PR system was done by EV, iirc with two 8" drivers, and again a 1:1 ratio between drivers.
There is a difference between a vent/port and PR, assuming a larger PR to driver ratio. That comes in the form of a different velocity of air at resonance due to the larger area (presumably, most ports are not that large), making for a better acoustic match to the air...
The PR will act well below F3 as a box that is not quite all the way open, so there is some loading, this may or may not prevent woofers from "bottoming out". I'd not count on that, to protect the woofers, especially if you like rather high SPLs. Use a HP filter in that case.
_-_-bear
Also you have to look out for excursions below the desired F3 point... and, within reason the smaller the PR, the greater the velocity and higher the excursion required for the identical output compared to a larger PR. The higher the velocity, the harder it is to stop the PR cone.
As you go lower in freq the mass loading that is added to bring the resonant freq down increases dramatically. At lower velocities it is easier to control and stop that mass loaded cone.
Otoh, Bob Carver used a 1:1 driver/PR diameter in his Sunfire subs, but I do not know if they were electronically corrected.
Nobody I know of has ever used a larger main driver and a smaller PR with any success.
Oh, yeah, an early PR system was done by EV, iirc with two 8" drivers, and again a 1:1 ratio between drivers.
There is a difference between a vent/port and PR, assuming a larger PR to driver ratio. That comes in the form of a different velocity of air at resonance due to the larger area (presumably, most ports are not that large), making for a better acoustic match to the air...
The PR will act well below F3 as a box that is not quite all the way open, so there is some loading, this may or may not prevent woofers from "bottoming out". I'd not count on that, to protect the woofers, especially if you like rather high SPLs. Use a HP filter in that case.
_-_-bear
sorry there is NO difference in a correctly designed vent ( at low air velocity ) and a passive radiator at small signal for the purposes of calculating low freq response ie driver resonance and box tuning. but there might be very slight differnces in outputs, lower for the PR due to mech losses. but they are negligble IMO for reasonable designs. high SPLs the non-linear effects of either the driver changes due heating mostly and to the port due to high velocity or a PR at its linear limits, then this is much harder to analyze.
My guess the OP has the wrong driver for his purpose and feels ( is searching) a PR is going to help somehow.
My guess the OP has the wrong driver for his purpose and feels ( is searching) a PR is going to help somehow.
hi,
Nominally PR excursion for equal driver areas needs to be x2.
If its not, use two PR's. Due to PR excursion linearity hardly
ever can you use a smaller PR with a bigger driver. The way
drivers are made a typical driver sans magnet suits a driver
one size down, e.g. 8" PR with a 6.5" bass, or 6.5" and 5".
rgds, sreten.
Nominally PR excursion for equal driver areas needs to be x2.
If its not, use two PR's. Due to PR excursion linearity hardly
ever can you use a smaller PR with a bigger driver. The way
drivers are made a typical driver sans magnet suits a driver
one size down, e.g. 8" PR with a 6.5" bass, or 6.5" and 5".
rgds, sreten.
infinia, sure no difference in calculating at all. In practice they are not the same at all. They don't sound the same, and you can do things with the PR that a port just doesn't really want to do. And, how are you defining "small signal"? I am more interested in the way it works at normal listening levels and up.
As far as what the OP is going for, he will have to say more about it.
sreten, my experience building PR speakers says that the "x2" criterion is from a JAES design and does not accurately reflect what the real world requirements are. In my experience a mere x2 is insufficient unless your tuning frequency is no lower than 40Hz, then maybe and only maybe ur ok.
Tune down to and below the ~30Hz region and suddenly you want a boatload of linear excursion.
_-_-bear
As far as what the OP is going for, he will have to say more about it.
sreten, my experience building PR speakers says that the "x2" criterion is from a JAES design and does not accurately reflect what the real world requirements are. In my experience a mere x2 is insufficient unless your tuning frequency is no lower than 40Hz, then maybe and only maybe ur ok.
Tune down to and below the ~30Hz region and suddenly you want a boatload of linear excursion.
_-_-bear
Calculating and measuring is all we have to predict frequency response. Small signal is about <5% Xmax. Software modeling is still useful in showing linear excursion of drivers due to box tuning regarding driver / PR ratios, if absolute accuracy is not true trends still can be analyzed. Everything else is empirical or rule of thumb guess work.
I don't actually have a design in mind per se or even a current project, let alone an obstacle. I just started reading about PR's lately and wondered if/how the low excursion and low displacement of a pro-style woofer effects the performance - assuming the woofer has a low enough Fs and can be tuned low enough to warrant a PR in the first place.
I appreciate the responses but as far as advancing the thread, I don't really have a direction I'm going in, I was just trying to glean some knowledge from you all.
I appreciate the responses but as far as advancing the thread, I don't really have a direction I'm going in, I was just trying to glean some knowledge from you all.
Hi goody75,
I think you have raised an interesting idea. It should be possible to use a PR with a smaller piston area than the active driver, as long as the PR has adequate excursion.
If you enter your driver and PR data into Bagby's Woofer Box and Circuit Designer: Loudspeaker Design Software ; you can evaluate the interactions, and also add electronic filters. Highly recommended.
After that you'll have to build something.
Regards,
I think you have raised an interesting idea. It should be possible to use a PR with a smaller piston area than the active driver, as long as the PR has adequate excursion.
If you enter your driver and PR data into Bagby's Woofer Box and Circuit Designer: Loudspeaker Design Software ; you can evaluate the interactions, and also add electronic filters. Highly recommended.
After that you'll have to build something.
Regards,
it works i use a jbl 2226 from 20-80hz +/-2db f3 of 17hz in a 1.7cf box with a 18'' ae pr. thd measured at .4% at 95db, then spikes at 30-40hz to 5% at 105db , while 17-30 sits at under 1% at 105db. also measured the excursion to be at 7mm/105db.
it wasnt a planed project just had the pr and had forgotten what i had bought them for so i used them, winisd was very close but the ae pr tune higher then winisd models them too.
it wasnt a planed project just had the pr and had forgotten what i had bought them for so i used them, winisd was very close but the ae pr tune higher then winisd models them too.
Whats the VAS of the 2226 and the Fs?
My seat of the pants reaction is no way.
You can tune the PR down to 17Hz, but the response is non flat below the rolloff of the driver WRT the Vb vs. VAS, wherever that works out to be - usually considerably higher than Fs.
_-_-bear
My seat of the pants reaction is no way.
You can tune the PR down to 17Hz, but the response is non flat below the rolloff of the driver WRT the Vb vs. VAS, wherever that works out to be - usually considerably higher than Fs.
_-_-bear
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