# Dual SDX15 Project



## Geoff St. Germain

I received my two CSS SDX15 from Bob a couple of weeks ago. I think that I've finally settled on a design for them. At first I was strongly contemplating a sealed design, but I think that the additional extension of an LLT better suits what I want out of this setup. The plan is for this to replace the lower section of my TV stand. Hopefully the opposed drivers will sufficiently reduce vibration for this purpose.

The enclosure is about 450 L tuned to 16 Hz, which is a little smaller than the enclosure recommended by CSS (they recommend about 240 L per driver, so 480 L). The external dimensions of the enclosure are 44" L x 34" H x 26.5" D.

Some pictures:




























Any input?

Hopefully I'll get started on this sometime next week.


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## Exocer

Looking awesome! It models really well in that size enclosure.


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## Bent

Geoff, I think I'd try to tie the front and rear panels together too.
To me, it seems like these are pretty large un-supported panels, they might be subject to a bit of vibration.

Opinions?


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## Geoff St. Germain

Bent,
My initial thought on that was that the drivers are mounted perpendicular to that axis and those are also two smallest faces.

Anyone have any thoughts on this?


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## Geoff St. Germain

Alright, I picked up all of my plywood today and have begun building. Here is the finalized design:










It's 420 L tuned to 16 Hz with a 3" x 23" slot port that is 42" long. The external dimensions are 44" (L) x 24.5" (D) x 33.5" (H).

I'll have some progress pictures up tomorrow.


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## WillyD

I dig it. Very functional as a TV stand while performing very well. Good call on that slot port. Air speed looks to stay low enough and 1st port resonance isn't too low. Sweet. Are you gonna power this one with the Crown XTI amp you already have?


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## Warpdrv

Sweet.... Im really looking forward to seeing your photos, and build progress.... 

That box is really close to the size I would like to do... if not a bit over sized.....


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## Geoff St. Germain

WillyD, 
Yeah, I'll be using the XTI-2000 for now. It doesn't really have enough power to drive these things to their limits in this enclosure. From my modeling, it should be able to take 2500 W or so, which is about 1000 W more than I'll get to them out of the XTI-2000. 

The slot port provides a lot more ability to fine tune to port area compared with round ports. I also like the way it acts as bracing.


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## Geoff St. Germain

Well, I have all of the pieces cut, now it's just a matter of piecing it all together. 

Here's the start:


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## Bent

good lookin' roundover there on the bottom of the port :tup


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## Exocer

Really nice wood! I'm envious/ :bigsmile:


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## Geoff St. Germain

Thanks guys. Here's the rest of the work from the day. Built and installed the rear wall of the port. The small cut you can see is a 1/8" recess so that the quarter section of sonotube I'm using to make the curve in the port will sit flush.


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## Warpdrv

Wow... Looks great... is that the Birch Ply..? 
I didn't realize that you were putting both drivers in the same box...
I was looking for 2 seperate boxes, single driver in each...

I was wondering how you were going to make those gradual curves... great idea with the 1/4 sonotube...

keep posting those awesome pics...


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## Geoff St. Germain

Yeah, dual opposed drivers in the same box. I want to have as little vibration as possible for my TV.

Yeah, it's birch ply, it is called Lion King Birch 3/4" Cabinet grade. I need about 3.5 sheets of plywood for this enclosure, and at about 90 lbs per sheet for MDF there it was going to make for a finished enclosure pushing 400 lbs. I'm not entirely sure how much weight saving there will be, but a sheet of this plywood sure seems a **** of a lot lighter than a sheet of 3/4" MDF. I'd built my last two subwoofers with MDF so I figured I'd try plywood. So far the main thing I'm noticing is none of that MDF dust that gets inside and over everything when you shape MDF. That alone is almost worth the difference in cost.

Here's today's work.










Mock fitting the top of the port:


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## WillyD

Great work so far, Geoff.That birch-ply looks nice.


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## Geoff St. Germain

Well, the port roof and front/back are on. Now I have to get all the bracing in before attaching the top.


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## Geoff St. Germain

Well, the box is all sealed up now. It's just a matter of sanding, painting and installing a few odds and ends (feet, handles, binding posts, drivers ).


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## andersonbc

Looking killer ... I have been thinking about a very similar design for a few weeks now (box design with slot port). I'm very interested to hear how it sounds!


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## brucek

Looks like a great job.

You're using magnet supports. Do the drivers touch at the back once they're installed or is there a gap?

Can you tell us a bit of the basic theory why the opposing drivers help to reduce box vibration?

brucek


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## Ilkka

brucek said:


> Can you tell us a bit of the basic theory why the opposing drivers help to reduce box vibration?
> 
> brucek


It's the Newton's third law: To every action there is an equal and opposite reaction.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

When there are two drivers, net forces are cancelled out, leaving no forces at all. That means the drivers won't transmit any vibrations to the box.

I can say that it works great!


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## Geoff St. Germain

brucek said:


> Looks like a great job.
> 
> You're using magnet supports. Do the drivers touch at the back once they're installed or is there a gap?
> 
> Can you tell us a bit of the basic theory why the opposing drivers help to reduce box vibration?
> 
> brucek


Thanks Bruce.

There's a 3 7/8" gap between the drivers. That isn't a special number, but there should be at least enough of a gap to allow proper venting of the pole piece vents.

Ilkka covered the other part.


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## andersonbc

Pardon me if this is a dumb question :coocoo::

So, one of the subs *isn't* wired out of phase for a push/pull configuration? It seems to me that a push/pull would not cancel out forces. If they are not push/pull is there any loss because the drivers push against each other?

Thanks in advance for the explanation.


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## Ilkka

andersonbc said:


> Pardon me if this is a dumb question :coocoo::
> 
> So, one of the subs *isn't* wired out of phase for a push/pull configuration? It seems to me that a push/pull would not cancel out forces. If they are not push/pull is there any loss because the drivers push against each other?
> 
> Thanks in advance for the explanation.


They have to be in-phase, push-push configuration. But they are not pushing against each other per se. They are only working in the same air volume.


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## andersonbc

Thanks Ilkka.


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## Sonnie

Awesome Geoff... and you ain't even finished... :T


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## Jason Schultz

Hi Geoff 
sorry to interrupt your construction work (looks great and very practical approach to venting.) Can I please ask where you got your slot vent calculations from. 
thanks

Jason


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## Geoff St. Germain

WinISD can calculate square/slot ports in addition to round ports.


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## Warpdrv

Hey there Geoff.... where are our updates...?


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## Geoff St. Germain

I've been pretty busy flying lately.

Anyway, the enclosure is painted, the drivers installed and wiring finished. Now I just have to get to switching it out with the current TV stand.

Here are some pictures.


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## Warpdrv

That really looks great buddy.... kinda industrial looking... 

Can't wait to hear the report of your first impressions...


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## bobgpsr

Very impressive. :unbelievable: A no compromise for quality and output implementation. :T 

It has to weigh a lot -- hence the handles? 

Two man lift -- just barely?


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## planet10

Cool. Nice to see you are taking advantage of push-push. How are you planning on coupling the driver magnets (and at the same time keeping the pole-piece vents clear)?

This is the kick i needed to get the push-push SDX15 TL done. (looking at it, i am quite impressed at how small you have managed to keep your box)

dave


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## Geoff St. Germain

Thanks for the replies. It's not too terribly heavy, it's easily a two man lift.

Hopefully I'll get it in place tomorrow, I got home too late from my flight.

dave,
I wasn't planning on putting anything between the two magnets. I figure the magnet supports, double thick baffle and internal bracing should be sufficient.


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## planet10

Geoff St. Germain said:


> Thanks for the replies. It's not too terribly heavy, it's easily a two man lift.
> I wasn't planning on putting anything between the two magnets. I figure the magnet supports, double thick baffle and internal bracing should be sufficient.


I stongly suspect that you will get better downward dydnamic range if you do. You certainly would if the box wasn't a sub. MDF is pretty "mushy" as far as stiffness goes. A solid chunk of aluminum or hardwood -- even ply -- directly wedged between the magnets will give you a much more direct, stiffer, and efficient coupling path. One of the beauties of push-push is that it can actively cancel vibration so that it doesn't load the box. Without direct coupling you would be depending on the box to transfer the coupling energy instead of never letting that energy get into the box defeating some of the inherent goodness of push-push.

dave


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## Sonnie

Lookin' really good Geoff... :T


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## Geoff St. Germain

planet10 said:


> I stongly suspect that you will get better downward dydnamic range if you do. You certainly would if the box wasn't a sub. MDF is pretty "mushy" as far as stiffness goes. A solid chunk of aluminum or hardwood -- even ply -- directly wedged between the magnets will give you a much more direct, stiffer, and efficient coupling path. One of the beauties of push-push is that it can actively cancel vibration so that it doesn't load the box. Without direct coupling you would be depending on the box to transfer the coupling energy instead of never letting that energy get into the box defeating some of the inherent goodness of push-push.
> 
> dave


There's no MDF in the box. The drivers are also built into a sort of cage within the box and the wider parts of the magnet are fit directly against the magnet brace, which are mounted to a cross brace and the top of the box and top of the port. You can see it best in the model picture and sort of in the closeup of the driver cutout in the assembled box.


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## planet10

Oops my bad (been a long day and the build photos of another dual SDX15 were in mind), indeed that is plywood. That will mitigate things somewhat. Everything else is still valid. 

They should dramatically outperform that other build which was MDF and do not take advantage of push-push.

http://www.avsforum.com/avs-vb/showthread.php?t=874265?

dave


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## Exocer

Geoff, you probably can't wait to hear what this sub can do :bigsmile: Excellent job overall.

I anxiously await your impressions of the sub...probably because I haven't built a DIY ported sub myself _yet_


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## WillyD

Great looking sub Geoff.:clap: 

I too await your thoughts.


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## Guest

Very nice Geoff...and great to see another Winnipeger into DIY


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## SleeperSupra

Any updates???


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## F1 fan

Very nice:TI like the textured finish,is that a spray paint or bed liner?


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## SleeperSupra

How does it sound?


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## Geoff St. Germain

I haven't had any time to take any measurements or do any EQ to the subwoofer. I have been much to busy with a course I'm on as well as other projects that require what time I do have, such as the end tables I'm building for my wife which will take the place previously taken up by my two sonosubs. The sub sounds great though. The one issue I've run into on one frequency response sweep I did is that the back panel of my LCD seems to have a resonance at around 40 Hz and it vibrates against something in the TV that it isn't rigidly attached to. I haven't had any issues with it watching any movies or playing video games, but it's something I want to take care of.

Anyway, I'm really happy with these drivers and the slot port has enough area that I can notice much less air flow compared with the 6" ports in the sonosubs I had.


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## Oscillate

Happy to resurrect this thread 

I also have two SDX-15s that have been sitting, new in their boxes, for the last two years.
During that interim, I have gone around and around on the various alignments that I could/should build.
Of the different enclosures I have read about or modeled, this seems like one of the best!
Could you please post your updated thoughts and impressions after living with this sbwoofer for 2 years...
Many thanks.


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## Mika75

I'd love to see this as 2 separate enclosures, with a single front firing driver :cunning:


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## planet10

Do not underestimate how much you would lose by not having push-push woofers.

dave


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