Passive Radiator CSS SDX10 Design and Build

[EngineerNate]

They make a larger square Neutrik jack.

lol noted for if I ever pay attention to this after I get these running.

 

[EngineerNate]

It was also entirely intentionally that the SpeakOn jack is mirrored between the two

 

[mwmkravchenko]

At least you use proper loudspeaker connectors.

 

[EngineerNate]

Got the speakOn connector mounting done.

Moved on to fitting the drivers prior to final finish work.

Ran into a snag. These two things are not the same!

Fortunately a difference I could accommodate with some hacking. It’s not pretty and it’s a little upsetting after spending this much time on the cabs, but these things happen. Cutting a perfectly straight cut through a driver hole wasn’t gonna happen. I may do some additional clean up with the kutzall. I may not.

I did clean up the second one a bit after taking that pic.

Drivers fit nice now.

Also found out my assumption the CSS PRs were the same diameter as the drivers was incorrect. Eventually I’ll need to 3D print some filler strips. The website didn’t list a diameter. I should have asked.

All things I can address in the 3D model for if I want to build another set or if anyone else would like to build a copy.

Cheers,
Nathan

PS-I always joke that it’s not a real project until you bleed on it. Well. I was cleaning up the inside edge of the driver cutout with some sandpaper and caught a splinter and got it a solid 3/8” up under my nail. That did the trick! Fortunately came out cleanly.

 

[mwmkravchenko]

Got the speakOn connector mounting done.

View attachment 522675

Moved on to fitting the drivers prior to final finish work.

Ran into a snag. These two things are not the same!
View attachment 522677
View attachment 522678

Fortunately a difference I could accommodate with some hacking. It’s not pretty and it’s a little upsetting after spending this much time on the cabs, but these things happen. Cutting a perfectly straight cut through a driver hole wasn’t gonna happen. I may do some additional clean up with the kutzall. I may not.

View attachment 522681
View attachment 522682

I did clean up the second one a bit after taking that pic.

Drivers fit nice now.
View attachment 522684
View attachment 522685

Also found out my assumption the CSS PRs were the same diameter as the drivers was incorrect. Eventually I’ll need to 3D print some filler strips. The website didn’t list a diameter. I should have asked.

View attachment 522686

All things I can address in the 3D model for if I want to build another set or if anyone else would like to build a copy.

Cheers,
Nathan

PS-I always joke that it’s not a real project until you bleed on it. Well. I was cleaning up the inside edge of the driver cutout with some sandpaper and caught a splinter and got it a solid 3/8” up under my nail. That did the trick! Fortunately came out cleanly.

If you seal the box first, you can mask and paint the area black around the PR's it will not look that bad.

Mark

 

[EngineerNate]

Cleaned up with a die grinder and wheel/drum sander attachments. Much better.

I got the pilots drilled for the woofer mounting bolts and the holes soaked with CA glue to harden the wood. They’ll get wood tapped to 10-32.

I wiped CA glue into the face of the mating surface as well to harden it up and make it a better surface for the seal to press against.

 

[mwmkravchenko]

I used to make jigs out of Baltic Birch and tap to 100% thread depth. Never had a failure with untreated threaded holes. CA on top!! Aye Chihuahua!

Mark

 

[EngineerNate]

Finished the driver and PR attachment holes today and spent the evening prepping for finish, filling any voids/tearout in the plywood with some resin and sanding flush. I also put a tiny chamfer on the driver openings as a finishing touch.

Going to give them one more once over with 240 on the orbital then apply the first coat. Hopefully tomorrow evening.

 

[EngineerNate]

Popped the grain and did a final 220 grit pass then applied the first coat of finish on the top and sides last night. Unfortunately don't have an antigravity paint booth to get all six sides in one go. Fortunately hard wax oil is easy to blend. I applied a coat on the bottom this afternoon.

 

[EngineerNate]

First coat cured. I’ll knock the grain and dust nibs down with 320 or 400 before the next coat.

 

[EngineerNate]

Second coat on. Raised them higher so I could get past the bottom radii on the main coat.

 

[EngineerNate]

 

[kemmler3D]

These are looking pretty phenomenal, thanks for all the updates!

 

[EngineerNate]

@Keith_W hope you don’t mind the tag. As someone who I know has measured a whole bunch of setups, any thoughts on whether to orient these woofers high or woofers low? My original intent was to get the woofer as close to the mid on my bookshelves (sitting on top of them) as possible, but I’ve read a bunch more about floor bounce since then that’s muddied the waters.

 

[Keith_W]

Are you asking me whether you think the box should be upside down (woofers closer to the floor)? Without reading the whole thread, I don't know what the bandpass is. But I would have thought that the wavelengths are so long that it does not matter, all it's going to do is shift the reinforcement by maybe 5-10Hz up or down. One of these orientations is going to be better for you. Or ask someone who actually knows ... like @sigbergaudio or @Duke.

 

[EngineerNate]

Are you asking me whether you think the box should be upside down (woofers closer to the floor)? Without reading the whole thread, I don't know what the bandpass is. But I would have thought that the wavelengths are so long that it does not matter, all it's going to do is shift the reinforcement by maybe 5-10Hz up or down. One of these orientations is going to be better for you. Or ask someone who actually knows ... like @sigbergaudio or @Duke.

Yes, it’s a sub, though the driver is flat to 1khz so long term I planned to experiment with crossing it at 200-300hz.

 

[sigbergaudio]

@EngineerNate Can you summarize the question / alternatives you are pondering so I don't have to read the entire thread?

 

[mwmkravchenko]

Floor bounce is about 1.2 kilohertz to 1.5 kilohertz. It's height from the floor to the driver in that reproduction range. And then the distance to you. Ceiling bounce is usually a little lower in frequency. Keeping these acoustic additions in mind is important when you are relying on gated measurements. The gating will remove the fill in effect created by the bounce to the mic, or a slightly different bounce to your listening position.

For a subwoofer your position within the room is more critical. You can actually simulate the dominant modal points in your room in REW.

Next you see the same loudspeaker measured via ground plane method. Notice the notch between 1 kilohertz and 2.7 kilphertz. The room acoustics fill this in. Outside there is no reflection path for this effect.

 

[mwmkravchenko]

REW Beta Release - REW API beta releases

This thread is for V5.40 beta releases, which include the REW API. Here are the download links (updated 9th May 2026): Windows builds from beta 125 are signed with a new certificate. Windows SmartScreen will warn that the app is not recognised until it has seen sufficient downloads, click...

www.avnirvana.com

Room simulator is 3rd from the top right.

Rather intuitive to a guy like you I am guessing.

Mark

 

[EngineerNate]

@EngineerNate Can you summarize the question / alternatives you are pondering so I don't have to read the entire thread?

Basically, I’m trying to optimize between keeping the subwoofer as close to the floor as possible and as close to the midwoofer it’s crossing to as possible. I’m guessing there are a lot of variables and my best bet is to try both and measure, but I was curious if there was any knowledge to be gained froM folks here.

Cheers,
Nathan