Passive Radiator

[Suicide Bobb 5,000+ posts]

You don't need double the cone area if the Xmax of the pr is the same or more than the driver. Doubling the cone area is done to prevent over excursion of the pr. But if u have the same xmax or more xmax this is unessesary as u shouldnt exceed the limitations of the pr. Reason why Boston recommends using a 12 pr with a 12 sub.

Are you sure about this? It contradicts what I've heard from multiple sources...

 

[Imtjnotu 5,000+ posts]

All these things are true.
I'm not sure that you get better output vs. a ported box though. Otherwise, we would be seeing tons of PR's in comps. And the Xmax needs to be around half that of the sub from my experience.

The biggest concern is doubling the cone area. That's why I suggested two 12" PR's with my two 10" subs. I may also do both GTR's with my 12" Eclipse TI. Oddly enough though, Boston recommends the 12" GTR with the 12" G5...not sure what their reasoning is there but I trust them lol.

Btw...Boston sure doesn't cheap out on anything. They sent me an allen wrench to change the weights inside the GTR (to tune it to either 30, 35, or 45hz), but they didn't just send me a standard cheap-o allen wrench. It was a bull-head allen wrench, which generally cost more. I know, we are talking pennies here, but it's the details that count. I was happily surprised to see that they sent a bull-head allen wrench instead of the standard kind.

Ah ur right it is only half

 

[audioholic 5,000+ posts]

"To design a passive radiator alignment, start with a simple ported alignment using that driver that provides the desired box size and frequency response. Then, use the diameter of your chosen passive radiator as the "port diameter", and use this to calculate the required port length. Work out the volume occupied by this port and then use this to calculate the mass of air occupied by this port. The result is the required mass of the passive radiator. If it is too small, use a larger passive radiator and repeat the calculations." - The Subwoofer DIY Page - Passive Radiator Systems

Some good, basic info on pr's in that link.