Passive Radiators?

[MatrixDweller]

I'm thinking about making a sub and like the sealed designs that incorporate a passive radiator.

Does Fi make passive radiators to match their woofers? Or would I just need buy two and remove the magnet from one?

Would I really benefit from designing a sub that way or do ported subs do the job. I don't have the space, nor the WAF, to make an infinite baffle sub (although that would be waaaay cool). Primarily I'd be looking to build something that could go low but not sacrifice too much accuracy.

[mrstampe]

I'm certainly no speaker engineer, but I don't think you can rip off the driver magnet to make it a PR. The radiator lacks a motor unit and coil -- which I would think would decrease friction and mechanical resistance. Its tuning comes from specific weighting of the radiator. The driver is significantly lighter without the option of adjusting the weight.

If Fi makes a PR, I'd be interested. If not, then there are other options that can be paired with a Fi subwoofer driver.

[Mike P.]

Taking the magnet off a driver and adding weight to the cone to increase the mass is the "old school" way of making a passive radiator. Today there are better options with manufactured PR's. Creative Sounds sells them, although a sub needs to incorporate the specifics of the PR with the driver.
http://www.creativesound.ca/

[imbeaujp]

You should buy a real passive radiator. It will be cheaper and well calibrated.

Here is my building thread with Peerless components

[bobgpsr]

MatrixDweller wrote:

I'm thinking about making a sub and like the sealed designs that incorporate a passive radiator.

As a point of fact they are not really sealed but instead model as a bass reflex (ported). Please look for real passive radiators. I got my two (PR2500's) from Acoustic Elegance (John Janowitz) and they work very well with a CSS SDX15. Looks like John now has some 1600 gram MMS 18" PR's available.

[Mike P.]

bobgpsr wrote:

As a point of fact they are not really sealed but instead model as a bass reflex (ported). Please look for real passive radiators. I got my two (PR2500's) from Acoustic Elegance (John Janowitz) and they work very well with a CSS SDX15. Looks like John now has some 1600 gram MMS 18" PR's available.

Yes, those are the same ones Creative Sounds sells.

[Fi Audio]

I have done custom PRs for people as well as production PRs for a couple of companies, but PRs have seemed to have lost favor in the DIY market in the past couple of years so I havent thought much about them. Ive got everything Id need to make them... although aesthetically I would get a different surround done that would cover over the whole cone (although I have done some bubinga, purple heart, and curly top maple "cones" for customers about a decade ago).

I could easily do some matching PRs as well. I would simply machine a centralized mass that the soft parts would attach to and thread it so that the mass could be adjusted. If there is a decent interest Ill make a proto and post it.

Thanks,
Scott

[Mike P.]

This is good news! I was unaware that Fi made custom PR's. Hopefully this will turn into another option for the DIYers.

[mike c]

how do you know how many PR's you need?

for example, I want to tune to 15hz ... how many PR's for that?

[Fi Audio]

The drivers volumetric displacement sets how "much" PR you need. Rule of thumb is usually twice the displacement of the driver. So for a single 15" that can move 2.5" p-p you would need a single 15" PR that could move 5" (well thats not too feasible) so a pair that have the same 2.5" p-p ability will work. Going up in size never seems to hurt as the larger radiating area couples better with the environment its in.

As for tuning a PR, in theory if the suspension of the PR is the same as that of air, you are simply taking the port volume (area of port= area of PR X the length of the port) and finding the mass of air inside. This mass would be the equivalent mass of the PR. Now that is in theory as you cant have a PR with the same compliance of air. So... its easiest at that point to find a program to design things mass wise based off of the Vas and Sd of the PR.

Thanks,
Scott

[mrstampe]

I'm definitely interested to see what you can offer, design- and price-wise. I'm considering coupling 2 PRs to either the CSS SDX15 I own and/or a Fi Q I'm considering.

[MatrixDweller]

That's a pretty good thread on your PR construction imbeaujp. I'll be looking back at that when I decide to build. Is a PR the way to go though? It would be my first time building a sub so would I be best to make a traditional ported design?

[imbeaujp]

MatrixDweller wrote:

That's a pretty good thread on your PR construction imbeaujp. I'll be looking back at that when I decide to build. Is a PR the way to go though? It would be my first time building a sub so would I be best to make a traditional ported design?

If you use the same drivers and the same dimensions as me (40 - 43 liters), you will have the same result.

Here are the first mesurements in my room with 2 subs : First calibration with 2 peerless XXLS

[imbeaujp]

Here are some kit and design you can use with Peerless products:

http://www.solen.ca/v1/sxxls.htm

My configuration is with one passive radiator, but I use an external amp (Rotel RB-1080) :

SUB XXLS12
Frequency response 18Hz to 40-160Hz (adjustable).
Capable of an astonishing 122dB at 25Hz.
The amp is the SUB-250R 360 watts/4 ohms, with remote control,
THD 0.08%, S/N ratio 100db.
Adjustable gain.
The crossover is a 2nd order low pass adjustable from 40Hz to 160Hz.
The subwoofer is the Peerless 308SWR51XXLS (830844).
The box volume is 1.5 cubic feet (43L) using a matching passive radiator the Peerless 308PAS425G (830548).

[Mike P.]

imbeaujp wrote:

Here are some kit and design you can use with Peerless products:

http://www.solen.ca/v1/sxxls.htm

My configuration is with one passive radiator, but I use an external amp (Rotel RB-1080) :

SUB XXLS12
Frequency response 18Hz to 40-160Hz (adjustable).
Capable of an astonishing 122dB at 25Hz.
The amp is the SUB-250R 360 watts/4 ohms, with remote control,
THD 0.08%, S/N ratio 100db.
Adjustable gain.
The crossover is a 2nd order low pass adjustable from 40Hz to 160Hz.
The subwoofer is the Peerless 308SWR51XXLS (830844).
The box volume is 1.5 cubic feet (43L) using a matching passive radiator the Peerless 308PAS425G (830548).

Since you're discussing your sub here, maybe you could tell us what it is tuned to. I can't find it in your thread.

[mrstampe]

MatrixDweller wrote:

That's a pretty good thread on your PR construction imbeaujp. I'll be looking back at that when I decide to build. Is a PR the way to go though? It would be my first time building a sub so would I be best to make a traditional ported design?

Hey MatrixDweller,

Do you have a timeframe you're considering for this build. Just selfishly watching your thread to see if you decide on the PR route before I would try it for myself. I'm also scouting around for other examples of this design. What PR sub designs are you looking at for inspiration? Links?

[MatrixDweller]

I just set up all my stuff in my dedicated HT room (pictures to follow soon). I'd be thinking once I can get the money together I would start building an impressive sub. It would probably be late spring if it can pass the WAF. I could definitely build one for a fraction of the price I could buy a pre-made one. I'm thinking the wife will probably quash it though.

I've looked at a few sites:
http://www.hardwareanalysis.com/cont...nch-subwoofer/
http://www.subwoofer-builder.com/passive.htm