Augmented passive radiator

[Raoul]

My thought was to cut scrap masonite or MDF disks to the appropriate size, and link them to one another using sturdy dowels. The cost would be reduced to the price of the surrounds.

[xstephanx]

mdf is too heavy, not stiff enough porbably, and wouldnt work very well for that, maybe try plexiglass with something for reiforement? maaybe an x of vertical ribs across the back of the pr? btu once again it gets pricey

maybe you could use 1/4 ply if the prs were small

[Raoul]

I think 1/4" or less MDF might be okay. My thoughts had primarily been with thin HDF like Adire uses on their PR15. Maybe give HDF or foam core board a thin coating of fiberglass. Plexiglass could look pretty cool, but I'm not sure it would be much lighter than thin HDF. The moving mass of the PRs is not as critical as with conventional ported design as the compliance of the PR is dictated by the V1/ P1 airspring.

Note that the 2 PRs have different dimensions. P1 is smaller than P2.

[Raoul]

Also, I thought about putting two surrounds on each PR -- on on the inside and one on the outside of the box wall. Might help support the "cone" and make for more linear movement. Earthquake uses this design, but I first saw it on a diy site somewhere on the net. One problem I have had is finding the big surrounds I want. Something big and mean like Adire's Brahma or Tumult surround.

[BassAwdyO]

Ahh! I totally thought you were talking about some passive radiator version of a dual chamber multi-resonant enclosure. Very interesting to use the airspring to make the PR's spring more linear.

I think the airspring will bring up PR resonance requiring more mass however, and some efficiency will also be lost.

Try it out, post results!

[Raoul]

Well, I have a couple projects going right now, including my token weird project (Hegeman subwoofer), so it will probably be awhile before I get around to building one. I have been occasionally browsing eBay for another Brahma 12 or 15 so I can build an isobaric version someday. A couple of Tempests might be neat, as the response could reach very low.

Maybe this will help with some of the confusion. Here is Vance Dickason description of the Augmented Passive Radiator from The Loudspeaker Cookbook, Fifth Edition:

The augmented passive-radiator (APR),is a twin cavity variation of the normal drone cone concept. It is capable of most of the vented and PR systems' alignment variations For a given driver (Qts), the APR will have a higher output rating, and a 15% - 25% lower cutoff (up to a half octave extension). The tradeoff for this substantial increase in low frequency range is about a 20% increase in total enclosure volume. Compared with normal PRs, the APR has better transient performance and lowercutoff frequencies. This occurs because the notch frequency is lowered to an out-of-band location.

For you patent surfers there are also a couple of patents on the design. The first patent was received November 1973 by E. Hossbach. The other was granted to Thomas Clarke in February, 1978.

Apparently a design is featured in the February, 1986 Speaker Builder magazine.

[simon5]

The APR is a very interesting concept if everything is true.

20% larger box for one half octave lower tuning, better transient response, higher output... very good !

[Raoul]

Normal size box if you go isobarik...