Official Rythmik Audio DIY Subwoofer Kit thread - Page 13 - AVS Forum | Home Theater Discussions And Reviews
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post #361 of 370 Unread 06-17-2015, 10:06 AM
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Originally Posted by johnrclark View Post
It appears there's a Rythmik DIY kit that provides for two 12-inch aluminum-cone drivers in one enclosure: on Rythmik's website, it's under the "Custom Installation > DS1200 Custom Install" tab. According to Rythmik, "With HX800XLR3 amplifier, one can drive two drivers with one single amp. It has two Hypex 400WRMS power amplifier modules in one heat sink so that each module independently drives one driver with servo control."

This would seem to circumvent the "no 8-ohm Al-cone 12" issue.

(PS--Sorry for lack of links... as a newbie, board software won't yet allow me to include 'em.)
Excellent! I had forgotten about that new Rythmik amp, made for exactly your desire of a dual woofer per enclosure sub. That will make a great sub!
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post #362 of 370 Unread 06-18-2015, 06:38 AM
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I'm leaning towards putting two 12-inch Rythmik drivers in my old Velodyne ULD-15 enclosure, in a sealed push-push configuration.

Given that the ~ 2.5 cubic foot enclosure is about the right volume for a single 12-inch driver, I reckon that it is also about right (to first approximation) for 2 drivers in a push-push configuration. Each driver would "see" an enclosed volume of ~ 2.5 cubic feet, more-or-less independent of the other driver.

In other words, the Velo box should work as well with two 12-inch drivers, as with one.

Am I correct in this line of thinking?
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post #363 of 370 Unread 06-18-2015, 06:55 AM
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As long as the 2.5 volume is the required volume for the Rythmik, any 2.5 cubic foot enclosure would work...
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post #364 of 370 Unread 06-18-2015, 11:33 PM
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As long as the 2.5 volume is the required volume for the Rythmik, any 2.5 cubic foot enclosure would work...

The Rythmik aluminum-cone woofer is spec'd as needing a 2.0 cu.ft. box, so the OP will have a half a cu.ft. for added bracing, a very good idea. As for two woofers needing the same volume as one, that I don't know. But two opposing drivers can't be a bad thing (as Mark Seaton will tell you. Bill Fitzmaurice, on the other hand, disputes the claim of force-cancellation resulting from the dual-opposed woofer design).
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post #365 of 370 Unread Yesterday, 07:15 AM
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Originally Posted by johnrclark View Post
Given that the ~ 2.5 cubic foot enclosure is about the right volume for a single 12-inch driver, I reckon that it is also about right (to first approximation) for 2 drivers in a push-push configuration. Each driver would "see" an enclosed volume of ~ 2.5 cubic feet, more-or-less independent of the other driver.

In other words, the Velo box should work as well with two 12-inch drivers, as with one.
Now I'm doubting my own logic.

Presumably, the optimal volume for a sealed box is proportional to the subwoofer driver area. Bigger driver area requires bigger box volume.

Two like-size drivers in the same box, driven in phase, should be essentially equivalent to a single driver of twice the area. I would expect this to be true no matter where in the box the two drivers are mounted: opposite sides, or same side.

Therefore, by this logic, a box optimally sized for one driver, would be much too small for two like drivers.

(Parenthetically, I note that Rythmik's F25 sub, which uses a pair of 15-inch drivers, appears to be of roughly twice the internal volume of a Rythmik single 15-inch driver sub.)

So now, in light of this, I plan to refit my Velo ULD-15 box with a single down-firing driver. Only question is whether to go with a 15-inch DS1501 or a 12-inch DS1200. The box's gross internal volume is 2.54 cubic feet, which falls right between what Rythmik recommends for the 15-inch driver (3 cubic feet) and the 12-inch (2 cubic feet). The 15-inch would be slightly under-boxed... the consequences of which I am unsure. The 12-inch would leave a bit of extra volume for bracing (of which the very stiff Velo box currently has none). I've always thought bigger is better, but in this case I'm not sure.

I listen mostly to music, with only the occasional movie, so accuracy is more important to me than house-thumping power.

Any recommendations about which driver to put in my Velo box?
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post #366 of 370 Unread Today, 02:57 AM
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I definitely know what I would do: Put in 1/2 cu.ft of bracing and a 12" woofer. The Rythmik F15 factory box is already undersized at 3 cu.ft.---4 cu.ft. is the optimum volume for the 15" woofer; anything smaller decreases the output of the sub, the only reason for going with a 15 over a 12. Plus, the cross-bracing (1" to1-1/2" dowels running from panel to panel, as many as you can fit in the enclosure to arrive at 1/2 cu.ft. Run them front-to-back, left-to-right, and top-to-bottom, four per wall if you can) with improve the sound QUALITY of the sub more than the marginally greater output of a 15" woofer over a 12 (especially in the undersized enclosure). Maybe Brian will chime in here.
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post #367 of 370 Unread Today, 03:27 AM
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Would this dual 12" sub be a servo sub? Are you able to have 2 subs acting in a servo set-up since the accelerometer is on the voice coil of the driver(s)?
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post #368 of 370 Unread Today, 10:11 AM
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I definitely know what I would do: Put in 1/2 cu.ft of bracing and a 12" woofer.
That's exactly what I intend to do.

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Originally Posted by BDP24 View Post
Maybe Brian will chime in here.
In a reply to an email, Brian did confirm that the 12" driver is the better choice for this enclosure.

Thanks for all the help!
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post #369 of 370 Unread Today, 11:41 AM
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Would this dual 12" sub be a servo sub? Are you able to have 2 subs acting in a servo set-up since the accelerometer is on the voice coil of the driver(s)?
In this particular case, the enclosure is too small for dual 12's (each needs it's own 2 cu.ft. of volume). But in principle, yes, you can use the Servo woofers in dual-opposed operation in a single cabinet.The Servo-Feedback operation of the Rythmik woofers does not preclude that---why would it? The accelerometer on the voice coil of each woofer is for that woofer only---it doesn't know or care what another woofer is doing.
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post #370 of 370 Unread Today, 11:53 AM
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That's exactly what I intend to do.



In a reply to an email, Brian did confirm that the 12" driver is the better choice for this enclosure.

Thanks for all the help!

Cut the braces just long enough that they fit between two opposing panels snugly. Then apply wood glue to the two ends of each brace, tapping them into place with a hammer or mallet. Let the glue dry (and the glue fumes to evaporate) for 24 hours, re-install the enclosure's internal stuffing, and enjoy your new sub! If you want, while you have the enclosure emptied out install panel-damping material to the interior side of each panel of the box (except the baffle, of course) before putting everything back in. Brian's partner at GR Research, Danny Richie, sells just such a product---NoRez, designed for that exact purpose, damping the MDF panels of speaker enclosures.
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