New Passive Radiators from Creative Sound - Page 2 - Home Theater Forum and Systems -

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post #11 of 35 Old 09-09-07, 07:05 PM
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Re: New 15” Driver - CSS SDX15

I'd venture to say you may even need to go larger, as two 18" PRs may displace more volume than a 6" diameter port - the volume of the enclosure won't change whether you use a port or PRs.
That'd be an incorrect guess. The port would require what, 12 liters? And going off say two 18" LMS-5400s (not PRs, mind you), they take up 9liters total.

The real benefit of PRs is for drivers that are more optimal in smaller enclosures, so one can tune them low without being restricted by the port length. This obviously doesn't apply to the SDX-15, or quite a few other drivers.

If you model a 300 liter ported LLT, you'd still need to make a 300 liter PRed sub to match the performance.
Well that actually depends on the roll off one is looking for. If you moved the sim that I did to 300 liters, it actually drops the Fb to 12.9. Move it back to 250 liters for 14Hz, and the LLT vs the PR FRs look practically the same. Both have an F3 of about 25-26Hz, and an Fb of 14, but the LLT is 50liters bigger. In the scheme of things, obviously not worth it.

As I mentioned in the post before you, since I knew what you were thinking before you posted it, with the SDX it makes sense to go big and forget PRs. There may be one case somewhere where a guy wants a lot of performance in just 200 liters and a 15.5Hz tune...this may be a route he wants to go. Then again, one could just roll with two sealed SDX-15s in 200 liters, opposed firing and all that.
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post #12 of 35 Old 09-09-07, 08:42 PM
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Re: New 15 Driver - CSS SDX15

Hmm. Thinking out loud.

6" diameter port volume = (6.5"/2)^2 x 3.14 x 27" = 895"^3

Dual 18" driver volume, assuming it's roughly half a sphere = 2 x (18"/2)^3 x 3.14 x (4/3) = ~6100"^2

Now sure, a driver or PR isn't a perfect half sphere, as the driver structure is more of a skeleton, so I'll be nice and only use 1/5 of that calculated volume, giving me ~1220"^2. What I am missing here?
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post #13 of 35 Old 09-09-07, 10:02 PM
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Re: New 15 Driver - CSS SDX15

The volume of 6100"^3 that you've calculated is for two 18" spheres.

TC Sounds had the displacement of their PR at about 2.25 L each (0.08 cu ft). This probably makes sense since a typical large 15" driver is in the 5 L range and has that big motor on the back. The CSS PRs are essentially flat discs (no additional displacement) with a basket around it. The basket is the only think that contributes to the internal volume displacement.
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post #14 of 35 Old 09-09-07, 10:49 PM
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Re: New 15” Driver - CSS SDX15

What I am missing here?
What Geoff said.
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post #15 of 35 Old 09-09-07, 11:56 PM
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Re: New Passive Radiators from Creative Sound

These posts were moved to their own thread since they are off topic to the other thread.

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post #16 of 35 Old 09-10-07, 05:09 AM
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Re: New Passive Radiators from Creative Sound

one more good feature of a passive radiator is that onw can lower the size of the box keep a low tuning and add some eq in the bottom (it won't require as much as a small closed box)
post #17 of 35 Old 09-10-07, 09:23 AM
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Re: New 15 Driver - CSS SDX15

vinculum wrote: View Post
Anyone know if those PRs use foam surrounds? I've emailed CSS this question, but nobody got back to me. They almost do look like foam, but it is hard to tell.

Dr V
Dear Sir,

Apologies for not getting back to you. The surrounds are foam.

Bob Reimer
Creative Sound Solutions

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post #18 of 35 Old 09-10-07, 09:55 AM
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Re: New Passive Radiators from Creative Sound

nowadays there are practically no problems with foam surrounds...they last almost as long as a rubber dito
post #19 of 35 Old 09-10-07, 10:17 AM Thread Starter
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Re: New Passive Radiators from Creative Sound

While I understand people around here, most from the US, all you guys thinking big. In Finland people think a bit differently. All big is not so important as to you guys here(speaking of subwoofers now). All I am saying is that not everyone is willing to go for the more bigger enclosure. In Finland people are just to about use to the idea of an 300l enclosure, which is quite big. Mostly people are happy with their chorus vertigos and such small subs.

So when you come to think about it 225l isn't small, but its considerably smaller than 300l. Takes even more less space when you double the subs(also the price sky rocket ). Still 225l enclosure is way too big for most people around here and only a handful would thinking of taking that thing to their home. But the nature of the PRs and some of you have a good point there, it's not practical to build one big box with way more money, because LLT takes less floor space even thought it's bigger. I guess you understand what I'm saying, right?
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post #20 of 35 Old 09-10-07, 04:40 PM
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Re: New 15 Driver - CSS SDX15

WillyD wrote: View Post
Might want to check your math there Ilkka.

The 2:1 doesn't just apply to a simple ratio of # of PR vs active driver. So lets see...

Two 18" PRs with 38.1mm xmax. Yeah, thats 18.28800 liters of displacement from the PRs alone.

One 15" driver with 30mm xmax, 4.8 liters of displacement.

3.81:1 ratio. Would it still have a touch of compression? Quite possibly at full tilt, sure. A lot less than the LLT? I'd guess so.

Now with the 5400 and the TC PRs you have, you will practically have a 2:1 ratio. Thats another story.
Yeah, you got me there, sort of... While I naturally meant that they would have the same Sd, I sort of forgot that the SDX was a 15", and those PRs were 18". An Unibox simulation shows very little compression for that combination. But IF we have a true 2:1 ratio, then some compression below the tuning frequency will be present. Probably very similar to what a 15" driver has with a 6" port.
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