Augmented passive radiator

[Emiel]

I'm thinking of building a subwoofer for home theater use.
I'd like a low f3 (about 25Hz or less) in a small cabinet (about 50 to 60 liters). (but that's probably what everbody wants in a HT sub)

I've done some research and I came across the Augmented Passive Radiator (APR) in Dickason.
An APR is a system with two passive radiators with different size and two chambers. The f3 is half an octave lower than a normal passive radiator with a slightly more volume (20%) of the cabinet.
There's not much info on this forum or the internet about DIY APR's.

Is there anybody out there with some expirience on building an APR?
Or does someone have some more info/examples on DIY APRs?

[planet10]

Is that the Earl Geddes design? If so, he wrote a paper for the AES Journal which covers the basics. It is also in his book....

The other way to get low bass in a small box is do a sealed box with a Linkwitz transform -- lots of power required & a driver with a big xMax.

dave

[Dave Jones]

Originally posted by Emiel
I'm thinking of building a subwoofer for home theater use.
I'd like a low f3 (about 25Hz or less) in a small cabinet (about 50 to 60 liters).

Peerless XLS or XXLS with a passive radiator will get you there.

[Raoul]

Did you find the design in, The Loudspeaker Cookbook? That's the only place I have seen it. I've been thinking about building one of those for a while, but haven't found very much information on the design. I may be wrong, but I think Adire Audio's free version of LspCAD had an option to model APR boxes. The option of drivers is limited with Adire LspCAD, though.

I really like the isobaric version Dickason mentions

[planet10]

Originally posted by Raoul
Did you find the design in, The Loudspeaker Cookbook?

It must be in the newer edition, it isn't in the LDC is i have.

dave

[Raoul]

I think it is the the edition before the current one (red cover edition). I think it is described in a few brief paragraphs at the end of the chapter on vented design. Almost written in as an afterthought.

[Emiel]

Originally posted by planet10
Is that the Earl Geddes design?

The design is by Thomas Clarke

Originally posted by Raoul
Did you find the design in, The Loudspeaker Cookbook? That's the only place I have seen it. I've been thinking about building one of those for a while, but haven't found very much information on the design. I may be wrong, but I think Adire Audio's free version of LspCAD had an option to model APR boxes. The option of drivers is limited with Adire LspCAD, though.

I really like the isobaric version Dickason mentions

I indeed found the design in The Loudspeaker Cookbook. (2nd edition). It's a the end of the chapter about passive radiators.
I've tried LspCAD, but there's only the possibility to simulate normal PRs not APRs.

Anybody ever build one?

[Raoul]

Yes, your right. The description is longer than I remembered at two and a half pages. Also, Clarke published articles in JAES, so there may be some more information there. Looks like another article appeared in Speaker Builder (1984, I think). Maybe someone has a collection of S.B. backissues.

[BassAwdyO]

Why would you want a multichamber enclosure with passive radiators used to create resonances? It would get awefully costly to put two passive radiators in a box to do only a bit more than one passive radiator could do, or dare I say a port or two! Vent noise really isnt an issue if it is properly sized and flanged. Even using a vent between the two chambers instead of a passive radiator would cut costs with the elimiation of a "hole" in the speakerbox.

So what does the FR of one of these look like?

[Raoul]

Well, the cost is less of an issue as it doesn't use standard PRs. The PR surround is connected directly to the enclosure, and the PR baskets are linked together. V1/P1 function as an airspring. Excuse my artistry, but I think I captured the idea...