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?
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?
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
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
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 really like the isobaric version Dickason mentions
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.
planet10 said:
The design is by Thomas Clarke
Raoul said: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?
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.
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?
So what does the FR of one of these look like?
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.
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
maybe you could use 1/4 ply if the prs were small
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.
Note that the 2 PRs have different dimensions. P1 is smaller than P2.
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.
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!
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!
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.
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.
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 !
20% larger box for one half octave lower tuning, better transient response, higher output... very good !
This is the next box design I would like to complete for an AE Speakers TD15H-8 that I have. I want to use an SBB4 alignment, but the design tables in Speaker Design Cookbook don't include that alignment. I'd really like to find the info I need.
My thoughts are if I design and build the enclosure for a single woofer, I should be able to do two pairs in isobaric loading later with the same enclosure as long as I factor in the extra room for mounting and displacement of the isobaric loading and the second internal enclosure for the second APR.
Here is a link to a Patent description with some good explanations of theory for this design. However not much help in specifics for designing it.
My thoughts are if I design and build the enclosure for a single woofer, I should be able to do two pairs in isobaric loading later with the same enclosure as long as I factor in the extra room for mounting and displacement of the isobaric loading and the second internal enclosure for the second APR.
Here is a link to a Patent description with some good explanations of theory for this design. However not much help in specifics for designing it.