User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 4th September 2016, 03:44 PM #1 bcodemz   diyAudio Member   Join Date: Feb 2014 Passive radiator vs port theory So my previous understanding was that passive radiator and ported enclosures were very similar. I thought the diameter of the PR is the equivalent as the diameter of the port. The mass of the passive radiator is equivalent of the mass of air within the port. Therefore, changing the mass of the PR changes the tuning. However, it turns out the tuning of the PR actually affected by the Fs of the driver and not just the Sd and Mms. Therefore, this means the tuning is affected by the Cms of the PR since Fs is determined by Cms and Mms. So, there are 3 major things that determine the tuning of a ported enclosure: enclosure volume, port diameter, and port length. But it seems like there are 4 major things that determine the tuning of a passive radiator enclosure: enclosure volume, Sd, Mms, and Cms. So what is the equivalent of Cms in a ported enclosure? Or is either port diameter or port length a combination of 2 passive radiator parameters? Last edited by bcodemz; 4th September 2016 at 05:17 PM.
 4th September 2016, 04:57 PM #2 Arty diyAudio Member   Join Date: Feb 2011 both of them are defined by a tuned volume. and from then on nothing is common in between the 2. __________________ V*A=VA V*A*PowerFactor = WATT
 4th September 2016, 05:01 PM #3 djn   diyAudio Member     Join Date: Oct 2004 Location: Albuquerque, New Mexico I use use at least twice the cone area of the woof as the only measure. It's always work for me. I just built a pair od small speakers with a 5" driver and used two 5" PRs. It sounds great.
 4th September 2016, 05:53 PM #5 chris661   diyAudio Member     Join Date: Feb 2008 Location: Sheffield A PR has its own inherent springiness. When you put it into a cabinet, this lumps with the air compliance, to give a new resonance for the PR. In a ported box, the air inside the box is the only spring acting. Chris
 4th September 2016, 06:11 PM #6 Charles Darwin   diyAudio Member   Join Date: Nov 2009 Location: Birmingham, UK They are similar in the principle on which they work: In both cases the bass driver is coupled to a mass via the internal air within the box. Tuned correctly both will resonate in sympathy with the bass driver. The main difference is that with a port the mass in question is a few grams while with a PR it is a few hundred grams. Tight bass is not a PRs strength.
 4th September 2016, 06:51 PM #7 TBTL   diyAudio Member   Join Date: Oct 2013 When you ignore the suspension compliance and losses (of the PR), PR and ported are identical. Therefore bass tightness is also identical, even tough a PR has a mass of a few hundred grams.
 4th September 2016, 06:51 PM #8 Arty diyAudio Member   Join Date: Feb 2011 but we can get rid of port rezonance. in exchange we get more cone rezonance errors, and as the PR moves we have a less linear spring load on the woofer. bracing is yet a nother problem for some cases, as the passive radiators take away space needed for bracing. accoustic coupling between the woofer and a port may be better in some cases, we can choose the port exit loaction better in many cases than the passive radiator, summing of the 2 might happen better with ports. i don't dislike PR sound, and it does have advantages in a few areas, but for me the drawbacks outweight the gains. __________________ V*A=VA V*A*PowerFactor = WATT
Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by bcodemz However, it turns out the tuning of the PR actually affected by the Fs of the driver and not just the Sd and Mms. Therefore, this means the tuning is affected by the Cms of the PR since Fs is determined by Cms and Mms. So what is the equivalent of Cms in a ported enclosure? Or is either port diameter or port length a combination of 2 passive radiator parameters?
You seem to confuse your terminology here. You say that PR tuning depends on the Fs of the driver - that is false.

Here is a picture of a 12" driver in a 150Lbox tuned to 20Hz, ported and with a loose and stiff 15" PR. The loose PR has a Vap of 2200L, the stiff one 225L.
Total mass is 434grams for the 15" diameter port (for comparison), 464 grams for the loose PR and 723g for the stiff PR.

You can see the loose PR has a response very similar to the ported box. I actually changed the leakage losses so you could see it better near cutoff. The main effect of PR compliance is to make a null at the PR's free air resonance frequency. Basically you want to keep the PR resonance as far away from the passband as possible.

Woofers don't make good PR's generally because their compliance is too low and the resultant notch will mess up your curves....

Ports don't have a compliance...it's a really funny question
Attached Images
 passive.png (47.0 KB, 808 views)
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley

bcodemz
diyAudio Member

Join Date: Feb 2014
Quote:
 Originally Posted by Ron E You seem to confuse your terminology here. You say that PR tuning depends on the Fs of the driver - that is false. Here is a picture of a 12" driver in a 150Lbox tuned to 20Hz, ported and with a loose and stiff 15" PR. The loose PR has a Vap of 2200L, the stiff one 225L. Total mass is 434grams for the 15" diameter port (for comparison), 464 grams for the loose PR and 723g for the stiff PR. You can see the loose PR has a response very similar to the ported box. I actually changed the leakage losses so you could see it better near cutoff. The main effect of PR compliance is to make a null at the PR's free air resonance frequency. Basically you want to keep the PR resonance as far away from the passband as possible. Woofers don't make good PR's generally because their compliance is too low and the resultant notch will mess up your curves.... Ports don't have a compliance...it's a really funny question
Thank you for the insightful post.

Haha yeah I was really confused because I couldn't imagine ports having compliance.

What program are you using to get those models? WinISD is not accurate for PR modelling and Jeff Bagby's excel sheet does not account for parameters that cause PR losses. I'd be very interested to work with a program like that.

Even in your example, the stiff PR needed almost twice the mass to achieve the same tuning. Wouldn't that imply that it's not just mass and surface area that determine's a passive radiator's tuning?

I agree most woofers don't make good PRs for the reason. Unfortunately the number of 5.25'' passive radiators on the market is exactly one, not exactly a lot of choices, hence my attempts at making a DIY PR.

Last edited by bcodemz; 5th September 2016 at 07:45 PM.

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post danielgap Full Range 6 26th March 2016 01:25 PM Ro11 Multi-Way 11 2nd November 2013 11:12 AM focal7C Multi-Way 3 30th January 2008 11:44 PM jamikl Subwoofers 1 3rd June 2006 10:23 AM DeonC Multi-Way 6 5th August 2005 08:52 AM

 New To Site? Need Help?

All times are GMT. The time now is 02:00 PM.