Passive Radiator for Low Excursion, Low Displacement & High Sens Woofer? - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th May 2012, 05:51 PM   #1
goody75 is offline goody75  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Motown (area)
Default Passive Radiator for Low Excursion, Low Displacement & High Sens Woofer?

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
  Reply With Quote
Old 4th May 2012, 06:41 PM   #2
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
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
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 4th May 2012, 07:05 PM   #3
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
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.
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust

Last edited by infinia; 4th May 2012 at 07:32 PM.
  Reply With Quote
Old 4th May 2012, 08:02 PM   #4
goody75 is offline goody75  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Motown (area)
Quote:
Originally Posted by infinia View Post
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.
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?
  Reply With Quote
Old 4th May 2012, 08:24 PM   #5
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
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.
.
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote
Old 4th May 2012, 09:29 PM   #6
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
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
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 4th May 2012, 09:54 PM   #7
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
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.
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote
Old 4th May 2012, 11:23 PM   #8
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
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.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 5th May 2012, 12:46 AM   #9
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
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
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 5th May 2012, 03:43 AM   #10
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
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.
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low Q Woofer in OB with High Zo Amp CLS Multi-Way 24 4th May 2011 05:14 AM
passive radiator excursion jaybee Subwoofers 24 23rd August 2010 04:48 AM
Passive Radiator Excursion HTRookie Subwoofers 13 17th December 2008 09:05 PM
Karlson for high impact low excursion applications freddi Multi-Way 1 31st March 2007 04:51 AM
Any drawbacks to using ferrofluid in a low-excursion woofer? 454Casull Multi-Way 7 9th December 2006 03:40 PM


New To Site? Need Help?

All times are GMT. The time now is 12:37 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2