# Passive radiator



## loupy31 (Apr 26, 2006)

Hi Guys,

I have a sub consisting of a 12" peerless driver and a matching passive.

As it stands at the moment, the passive faces down to the floor and the driver faces into the room, If I was to swap the Two around, would that make a difference in the performance.

Peter:scratch:


----------



## Jack Gilvey (May 8, 2006)

PR's typically aren't meant to be used in a horizontal orientation, it pulls their mass off-center. I'd swap them, even if just for longevity of the PR surround. This is a DIY I guess?


----------



## bobgpsr (Apr 20, 2006)

Not a performance issue but I understand from John J of AE Speakers that you should never mount a PR face down or up. The suspension of a PR can not handle the sag. IIRC there is a formula that you can use, given a driver's parameters, that can tell you if it is ok to mount a driver face down or up. Is your sub a DIY design?

Bob


----------



## loupy31 (Apr 26, 2006)

Hi Guys,
Firstly let me say thanks for replying to my question, This sub was a kit from a local retailer, I did some mods to it to make the box a lot more rigid, and replaced some of the power amps wiring to something a bit more substantial, 
So place the drive underneath facing down and the PR facing into the room, Ok I had a feeling that how it goes but you guys confirmed it, Ok first thing in the morning , the soldering iron comes out.

Thanks again guys....................Looking forward to getting my BFD 1124P

Peter


----------



## Dundas (May 16, 2006)

Hmmm....VMPS have been mounting their passive radiators horizontally for years.
http://www.vmpsaudio.com/technical.htm#07bassys


----------



## Jack Gilvey (May 8, 2006)

Apparently they've been designed for that. They claim a "very low moving mass". On the whole, PR's shouldn't be down-firing.


----------



## Sonnie (Apr 11, 2006)

Yes... very low moving mass on the VMPS PR's. They further use dough to weigh them... which can be pinched. I don't rightly understand all of it and I've pinched mine according to the instructions, but can't tell a difference. It still seems like I'm missing some of that mid-bass. Maybe the replacements will be different.


----------



## Dundas (May 16, 2006)

I would take that "very low moving mass" stuff as marketing talk. I had a VMPS Smaller Subwoofer (now known as a Dedicated Subwoofer) and its PR was a normal pulp cone with a spider and a foam surround (which eventually failed). Where do you reduce moving mass on a PR? Cone, surround, spider or dust cap? That's all there is. I would think that a PR has as much need for a stiff cone as an actvive woofer but, relatively speaking, all PRs have "very low moving mass" when compared to a comparable actve driver. VMPS's whole approach is to add moving mass to tune the subwoofer so I gotta question this orientation info.
Also, I do not recall anything in Peerless's information regarding orientation of their PRs.


----------



## bobgpsr (Apr 20, 2006)

Dundas said:


> ...all PRs have "very low moving mass" when compared to a comparable actve driver...


Not really. The two 18" AE PRs that I used in my DIY sub each have 2.5 kg of moving mass (mms). The sub uses a 200 liter internal volume enclosure with a 15" Adire Tumult driver. Resulting bass reflex tune is 15 Hz.










Close mike'd the driver to find out its tune:










the TrueRTA freq response with normal 1/24th octave and also 1/6 octave smoothed (shifted up by 10 dB)








Note that the SPL levels are not calibrated in the plot above. Just doing a relative freq response measurement there. 

Got up to 110 dB in room SPL before my circuit breaker popped. Mackie M1400 pro amp driving sub at 30 Hz sine in a 7000 ft^3 room. 

Finally measured harmonic distortion at 2% @ 13 Hz 102 dB SPL using a LinearX M31 calibration mike.










Bob


----------



## Jack Gilvey (May 8, 2006)

> VMPS's whole approach is to add moving mass to tune the subwoofer so I gotta question this orientation info.


 That's the way all PR's are tuned, the Mms. Ones with substantial Mms,and a nice loose suspension, like my 1400g Lambdas, sag noticeably when horizontal. Their "cone" is a 15" diameter, 3/4" thick piece of MDF. PR suspension should be pretty loose to work well, not stiff enough to center the mass vertically.


----------



## loupy31 (Apr 26, 2006)

Hi Guys,

Later today I will swap the drivers around............ I think my next step in this "Hobby" is to get a calibrated mike to use with my software, That should help to realy tune my sub.

BTW. Thanks to all for posting replies to my questions.........for some one like me ( not quite up to speed ) it is a huge help.

Peter :T


----------



## Dundas (May 16, 2006)

This design may be similar to what you have:
http://www.vikash.info/audio/xls10/
The Peerless PRs have exactly the same moving components as their comparable active drivers with mass added to acheive desired tuning:
http://www.speakercity.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=SC&Product_Code=830548
Application notes from the Peerless site:
http://www.tymphany.com/papers/appxls12b.htm

Lots of information available about these drivers by Googling “Peerless passive radiator” but can not see anything about PR orientation. Let us know if swaping makes a difference.


----------



## Jack Gilvey (May 8, 2006)

> Later today I will swap the drivers around............ I think my next step in this "Hobby" is to get a calibrated mike to use with my software, That should help to realy tune my sub.


 Yup.


----------

