# 2 PR CSS SDX15 System



## steven2583

I just built a sub with SDX15 with two passive radiators. The box is 10 CF and change. The amp is 250 watts. I just finished putting it together yesterday for testing. So far it sounds good. I just wondered how much do the passive raditors tend to move. I turned it up quite loud.  The recommendation was two PR. I have Vandersteen sub with a only 1 PR and 3 8" drivers in a box about 3.75. The vandersteen box the PR moves a lot more then my new box and seems to be stronger. Everything seemed to model good under WinISD. In WinISD it said that it was going to go down to 22hz. Testing it out it seems to be dropping off at 25hz which it is close enough. I have 350 grams on the PRs. Should I lighten the weight and hear what happens? 

It also seems I have a big suck out at 30hz 10db. I think it's the room. Any ideas what I can do about that?


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## ec114

steven2583 said:


> Testing it out it seems to be dropping off at 25hz which it is close enough. I have 350 grams on the PRs. Should I lighten the weight and hear what happens?
> 
> It also seems I have a big suck out at 30hz 10db. I think it's the room. Any ideas what I can do about that?


Not convinced that 25Hz peak is bandwidth. Might be a 20Hz (or lower) room-related dip, like below. EDIT: Nevermind, just looked at the (small!) graph more carefully. That peak is actually very close to 22Hz. It's a log scale; halfway between 20 and 30 is 23...

The 30Hz dip would most obviously be an 18ft room dimension. Is the sub in the corner? If so, moving it out along that 18ft wall 1/4 the way from the corner should help. Or adding another sub in the opposite corner...


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## steven2583

My room is 12 ft wide by about 45 feet long with 8 foot ceilings. The back 50% of the room opens up to 16 ft wide. Den opens up to the dining area and then the kitchen. Home entertainment unit is in the front 57" rear project television 2 ft wide. Heading away along the walls on each side of the room a subwoofers(8 ft). Total subwoofers 2. 15 feet further back is the main listening seat. That is where I had the mic. for the measurements.


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## bobgpsr

I also built a 2 PR (18") sub a few years ago that now uses a CSS SDX15 driver. The system is tuned to ~13.5 Hz and the PR's only really start moving with low bass that has below 25 Hz content.

For example early Santana recordings don't move the PRs much but the more recent ones do.


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## Mike P.

> I have 350 grams on the PRs.


Are these the CSS APR15 passive radiators?

Are you using a 250 watt plate amp, if so what make and model?


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## steven2583

I haven't tried a movie yet. I just ran some music and it I'm guessing went to 30hz at least. Tonight or tomorrow I will be trying out some movies. I'm sure I can find information below 25hz.

It's a Parts Express Amp. It a discontinued parts express plate amp that is rated for 250 watts (272). 19hz hpf.


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## Mike P.

> It a discontinued parts express plate amp that is rated for 250 watts (272). 19hz hpf.


The non boost model?


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## steven2583

By default it's non-boost. If I want to boost it I will have to get a soldering iron out with a resistor or two. From the graph it looks like it is going to 20hz already with correction. I figured with a HPF at 19hz the boost isn't going to do anything for me. Am I correct?


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## Mike P.

No, you don't need any boost. Orange is what you have, 8 washers per PR. Also shown is 10 and 12 washers per PR. It's easy to change tunings with these externally adjustable PR's.


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## steven2583

Here are some photos.


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## steven2583

I finally finished the sub. The looks of it came out quite well. I have a question about performance. I measured the sub again the the frequency response seems to be a little different now. Quite a steep drop off starting around 35Khz. I'm not sure what changed but it seems to model a little differently. It's in the same location as previously within a few inches. I was hoping it would go lower. I tried changing the weight for the passive woofer but the spike around 35Khz didn't seem to change. Any ideas what I can do to get a flatter response. I'm just wondering do I have a leak now. How do you tell if you are leaking?


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## Mike P.

That is a gorgeous sub! Did you use weather striping to seal the components to the cabinet? What program and equipment are you measuring with?


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## steven2583

Thanks, I though the looks came out better planned.
I used WinISD. I use silicon cement. I made a gasket and let it dry so the fumes wouldn't rot the rubber. It was probably 1 to 2 mm thick. Then I cranked down the nuts so that it would be about 1/2 mm think.

Playing around with it a litte more decreasing the weight to 200 grams the bump by 20hz came up to 86 db. Which seems quite different that what WinISD told me.


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## Mike P.

What program is the graph from in post #11?


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## steven2583

I have an Anthem Statement D2v. I used the mic in my main listening position. I didn't bother moving the mic around the room.


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## Mike P.

Do you have a SPL meter? Being able to measure the SPL of test tones would go a long way in determining where the problem is. I think the Anthem Statement D2v is faulty.


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## steven2583

So I should I need test tones at different Hz. So if I take three test tones. One at 30 another at 40 and one at 20. If the dbs between the point roughly match what the anthen measures then the D2v is correct?


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## Mike P.

Single test tones from 30 to 10 hz would give you more accurate information on what your sub is doing. Use a SPL meter that has a correction file for added accuracy.


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## steven2583

I just have a radio shack sound meter. Other then that I have the mic that came with the anthem.


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## Mike P.

Perfect, that's what you need. Here is where to find the correction values for your specific meter. 

http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html


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## steven2583

This is the finished sub.


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## mdrake

Nice work, looks very professional. :T

Matt


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