# Dual CSS SDX-15 enclosure



## fergi

Can anyone direct me to the Dual CSS SDX-15 subwoofer build referenced by item number 6 in this subwoofer ranking list.

I would like to build one of these but can't find the plans. If the plans don't exist perhaps I could get some help in the design of one just like it?

Thanks,

John


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## Mike P.

Without a link to the sub I can't say. Hopefully someone knows what build this is.


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## GranteedEV

Since I have no idea what that sub was like, let's just start from scratch! 

What we know is

- 2000+ w of power - EP2500
- Dual CSS SDX-15

what I'm going to assume is

This will be a sealed design
The two speakers will be push-push opposite with each other
because you're going with a slight emphasis on HT performance over music (57-48 score) that lower extension is desired by you.

what I need to know is

- Are there room space constraints?

what you need to know is

-CSS doesn't have these in stock, I think not until the Mach 2 version is released.
-To get the _most_ out of an EP2500 level amp, theoretically want a 20 ampere circuit.


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## fergi

GranteedEV said:


> Since I have no idea what that sub was like, let's just start from scratch!
> 
> What we know is
> 
> - 2000+ w of power - EP2500
> - Dual CSS SDX-15
> 
> what I'm going to assume is
> 
> This will be a sealed design
> The two speakers will be push-push opposite with each other
> because you're going with a slight emphasis on HT performance over music (57-48 score) that lower extension is desired by you.
> 
> what I need to know is
> 
> - Are there room space constraints?
> 
> what you need to know is
> 
> -CSS doesn't have these in stock, I think not until the Mach 2 version is released.
> -To get the _most_ out of an EP2500 level amp, theoretically want a 20 ampere circuit.


I have a pair of CSS SDX-15 that need a home and I already have a QSC RMX 5050 AMP in place with a 20 amp circuit.

Space should not be a problem.

Thanks for your response.

John


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## Mike P.

Is this for music, HT, or both?


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## fergi

Mike P. said:


> Is this for music, HT, or both?


This will be for music.


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## GranteedEV

-Okay now that I know it's for music I'm starting with 

-a Qtc of .6 - the box size is *365L*
-2 SDX-15s in a sealed enclosure 
-1800 w of raw power (one channel of the QSC is overkill!)

i'll start by reducing some of the excursion until we find a reasonable power level... if we just turn the SPL down by 3db and instead pump 900 watts into it we shouldn't run into too much excursion... and mind you 120 db is probably more than you'll ever use! Just never run it too much louder than that and excursion won't be too much an issue IMO!

Next I add 3db of gain at 20hz, Q = 1 we can smooth out the SPL a bit. Any other EQ will just be CUTS for room response, not gain. If you've got a dedicated 20a circuit, power necessary (double the wattage) for that 3db gain shouldn't be an issue! We can easily hit 1800 watts with the QSC!

And this is certainly enough headroom for us to work with! It'll have to get REALLY loud before you run into an excursion issues! THX reference level _peaks_ are considered to be 115db, and this sub can do that with less than even 900W, so as long as you stay at zero on your receiver after calibration, there shouldn't be any problems! Sweet, right? Well as long as we don't hit any compression, which I don't know how to model to be honest. The EQ gives us enough extension to really make movies blast even with a sealed design... If our +3db point is 120db, then our -3db point of 114 db will arrive at 20hz! You'll definitely get some subsonics as a bonus!


More importantly with a with a Qtc of .6, this should be a very musical sub!

(will post winISD screenshots later, must go somewhere right now)


The purple line is just for reference - it is a single SDX-15 with a Qtc = .707 Qtc fed 1100w with no EQ or high pass filter. A pair of these would have more output and definitely sound really good. You can go lower on the Qtc to get more musical if you want. Enclosure volume for this one is at 104L

The green line is the sub we just modeled. 

One final consideration is to scrap all of that and go with a pair of transmission lines  Really, a pair of subs will cleanly outperform a single sub with two drivers in room response!

So if the dual SDX15, .6 qtc sub sounds good to you, we can get to making a google sketchup model. what'd ya think?


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## fergi

GranteedEV said:


> -Okay now that I know it's for music I'm starting with
> 
> -a Qtc of .6 - the box size is *365L*
> -2 SDX-15s in a sealed enclosure
> -1800 w of raw power (one channel of the QSC is overkill!)
> 
> i'll start by reducing some of the excursion until we find a reasonable power level... if we just turn the SPL down by 3db and instead pump 900 watts into it we shouldn't run into too much excursion... and mind you 120 db is probably more than you'll ever use! Just never run it too much louder than that and excursion won't be too much an issue IMO!
> 
> Next I add 3db of gain at 20hz, Q = 1 we can smooth out the SPL a bit. Any other EQ will just be CUTS for room response, not gain. If you've got a dedicated 20a circuit, power necessary (double the wattage) for that 3db gain shouldn't be an issue! We can easily hit 1800 watts with the QSC!
> 
> And this is certainly enough headroom for us to work with! It'll have to get REALLY loud before you run into an excursion issues! THX reference level _peaks_ are considered to be 115db, and this sub can do that with less than even 900W, so as long as you stay at zero on your receiver after calibration, there shouldn't be any problems! Sweet, right? Well as long as we don't hit any compression, which I don't know how to model to be honest. The EQ gives us enough extension to really make movies blast even with a sealed design... If our +3db point is 120db, then our -3db point of 114 db will arrive at 20hz! You'll definitely get some subsonics as a bonus!
> 
> 
> More importantly with a with a Qtc of .6, this should be a very musical sub!
> 
> (will post winISD screenshots later, must go somewhere right now)
> 
> 
> The purple line is just for reference - it is a single SDX-15 with a Qtc = .707 Qtc fed 1100w with no EQ or high pass filter. A pair of these would have more output and definitely sound really good. You can go lower on the Qtc to get more musical if you want. Enclosure volume for this one is at 104L
> 
> The green line is the sub we just modeled.
> 
> One final consideration is to scrap all of that and go with a pair of transmission lines  Really, a pair of subs will cleanly outperform a single sub with two drivers in room response!
> 
> So if the dual SDX15, .6 qtc sub sounds good to you, we can get to making a google sketchup model. what'd ya think?


I'm not seeing the graphs you are describing but if you think a pair of subs would be better than a single enclosure with dual drivers then by all means let's go that route. I have been looking at the SDX-15 sub enclosure designs on the CSS web site. They offer 3 designs, one 2.5 ft^3, one 3.4 ft^3, and one 6.5 ft^3. Are any of those close to what you had in mind?


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## Mike P.

2 subs is better than one as you can even out the in room response with different sub placements. 3.7 cu.ft. each would give a Q of .7 for music. The subs would handle 1000 watts each and still be within Xmax.


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## bassman_soundking

The SDX is a great sub, enjoy and good luck with the build!


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## GranteedEV

IMHO a Q of .6 is better, although it would handle less power


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## fergi

Mike P. said:


> 2 subs is better than one as you can even out the in room response with different sub placements. 3.7 cu.ft. each would give a Q of .7 for music. The subs would handle 1000 watts each and still be within Xmax.
> 
> View attachment 24196


Thanks Mike,

I will modify the 3.4 ft^3 design to give 3.7 ft^3. I will probably increase the height dimension to obtain the volume increase. 

John


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## Mike P.

GranteedEV said:


> IMHO a Q of .6 is better, although it would handle less power


.6 requires a 6.3 cu.ft. box for less output in the 40 to 80 hz range. Why would that be better?


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## GranteedEV

the .6 qtc will give less distortion and a tighter sound, not to mention slightly deeper extension. SPL is the tradeoff, but IMO it's worth it. Especially since we've got two subs, not just one.


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## Mike P.

The deeper extension is so minimal it would be unnoticeable, not worth the extra box size but that's just my opinion.


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## GranteedEV

The cleaner sound from less air spring distortion would be the biggest advantage IMO, not the slight bass extension.


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## Mike P.

If it was measurable would it be noticeable in a comparison?


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## bassman_soundking

Fergi have you considered going with a ported design? My box might be larger than you are willing to go, but it is about all that I could expect from a 15" driver. I use a dual 6"ports, and I block one port for music and unblock it for movies. This gives me 19 hz tune for movies and 28 hz for music.

**EDIT** My boxes have a footprint of only 18" wide by 22" deep while being 49" tall.


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## bassman_soundking

fergi said:


> I'm not seeing the graphs you are describing but if you think a pair of subs would be better than a single enclosure with dual drivers then by all means let's go that route. I have been looking at the SDX-15 sub enclosure designs on the CSS web site. They offer 3 designs, one 2.5 ft^3, one 3.4 ft^3, and one 6.5 ft^3. Are any of those close to what you had in mind?


I also definitely recommend 2 separate boxes when at all possible


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## scotthulbs

I believe it or not have the box that was used in that test. I bought 2 SDX 15's, an EP2500, and the box all from Craigsub a couple years back. I still have the box in my garage. The box is not DIY it was made by Elemental Designs. Its a real nice box all 1" mdf tons of bracing very solid, with the ED truck bed liner coating. Too bad you aren't closer I would say you could just have it if you could pick it up. I never used the box because I put the subs in PR boxes. They are nice subs I'm sure you will be pleased with a pair of them.


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## bassman_soundking

scotthulbs said:


> I believe it or not have the box that was used in that test. I bought 2 SDX 15's, an EP2500, and the box all from Craigsub a couple years back. I still have the box in my garage. The box is not DIY it was made by Elemental Designs. Its a real nice box all 1" mdf tons of bracing very solid, with the ED truck bed liner coating. Too bad you aren't closer I would say you could just have it if you could pick it up. I never used the box because I put the subs in PR boxes. They are nice subs I'm sure you will be pleased with a pair of them.


Is that box a push-pull type or some other arrangement?


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## fergi

scotthulbs said:


> I believe it or not have the box that was used in that test. I bought 2 SDX 15's, an EP2500, and the box all from Craigsub a couple years back. I still have the box in my garage. The box is not DIY it was made by Elemental Designs. Its a real nice box all 1" mdf tons of bracing very solid, with the ED truck bed liner coating. Too bad you aren't closer I would say you could just have it if you could pick it up. I never used the box because I put the subs in PR boxes. They are nice subs I'm sure you will be pleased with a pair of them.


I too wish that we lived closer as I would love to have the enclosure you describe.


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## fergi

bassman_soundking said:


> Fergi have you considered going with a ported design? My box might be larger than you are willing to go, but it is about all that I could expect from a 15" driver. I use a dual 6"ports, and I block one port for music and unblock it for movies. This gives me 19 hz tune for movies and 28 hz for music.
> 
> **EDIT** My boxes have a footprint of only 18" wide by 22" deep while being 49" tall.


My apologies for taking so long to respond bassman. I just finished building two Maelstrom-X Sonotubes so I already have the low frequencies covered. The reason that I have the two CSS SDX-15 drivers is because I purchased them used at a good price and was going to use them in my Sonotube build. After listening to the Maelstrom subs for a while I find myself wanting more mid base. Don't get me wrong, when the Maelstroms really kick in they are positively amazing. I just want to hear more in the 30 to 80 Hz range. Ultimately, I'd love to be able to use the Maelstrom and the CSS subs at the same time with some kind of a crossover. For now I'd just like to build a sub with great mid-base.

Thanks for your response.

John


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## bassman_soundking

I find that I switch things often. I also noticed with LLt's you can have a lack of good rock bass.


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## GranteedEV

fergi said:


> After listening to the Maelstrom subs for a while I find myself wanting more mid base. Don't get me wrong, when the Maelstroms really kick in they are positively amazing. I just want to hear more in the 30 to 80 Hz range. Ultimately, I'd love to be able to use the Maelstrom and the CSS subs at the same time with some kind of a crossover. For now I'd just like to build a sub with great mid-base.John


While i think you should make the SDXs for the sake of making em, why not turn the gain / trims up on the maelstroms? If you're getting flat frequency response, then the only issue is just that the mid-deep-bass isn't loud enough. your maelstroms should definitely be giving you 30 to 80hz... it may be a poorly implimented crossover on your receiver or something, because it's not like they're more quiet at 50hz than at 20hz, and it's certainly not like they can't go loud.


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## fergi

GranteedEV said:


> While i think you should make the SDXs for the sake of making em, why not turn the gain / trims up on the maelstroms? If you're getting flat frequency response, then the only issue is just that the mid-deep-bass isn't loud enough. your maelstroms should definitely be giving you 30 to 80hz... it may be a poorly implimented crossover on your receiver or something, because it's not like they're more quiet at 50hz than at 20hz, and it's certainly not like they can't go loud.


I have experimented with the crossover frequency on my AV amp and adjusted the SW output level of the AV amp and I would still like more output in the 30 to 80 Hz range. It has been suggested that I plug the port on the Maelstroms to obtain more of the upper frequencies and I will try that as soon as I can come up with a suitable plug. Perhaps my expectations have been too high for the Maelstroms.

From the time that I first visited this site I have been trying to decide which design would best satisfy my particular listening style. I'm sure that I was making a nuisance of myself by asking so many questions about the different designs so I decided to build the Maelstrom design just to see what it sounded like. Now I'm going to build a sealed design and listen to them side by side and see for myself what the differences are.


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## Mike P.

> I'm sure that I was making a nuisance of myself by asking so many questions about the different designs


No such a thing. You ask, we answer, it's what we're here for. :T


​


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## fergi

Mike P. said:


> No such a thing. You ask, we answer, it's what we're here for. :T
> 
> 
> ​


Mike,

You have always been more than accommodating, I couldn't have done it without your help.

Thanks.

John


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## fergi

Mike P. said:


> No such a thing. You ask, we answer, it's what we're here for. :T
> ​


Mike,

Would a properly designed sealed sonotube enclosure work just as well as the box designs on the CSS web site?

John


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## Mike P.

Yes.


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## Binary

a properly designed sonotube will outperform the "cookie-cutter" designs that are listed on the CSS website. Those are just there to give people an idea of how big of a box its happy in, as most people can't tell that from the T/S params. the CSS drivers are a great example of how technology can help you oust even the most expensive competitors (XBL2 much). The build qualitys are awesome! and i own quite a bit of CSS products.

I personally own,

6x CSS SDX 7 - various projects
4x CSS el70 - center channel
1x CSS SDX 15. - sub (obviously)

and then i have seen/heard/used the TRIO8 and TRIO12.

As far as im concerned, Bob has some of the best built products for the dollar available.


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## fergi

Binary said:


> a properly designed sonotube will outperform the "cookie-cutter" designs that are listed on the CSS website. Those are just there to give people an idea of how big of a box its happy in, as most people can't tell that from the T/S params. the CSS drivers are a great example of how technology can help you oust even the most expensive competitors (XBL2 much). The build qualitys are awesome! and i own quite a bit of CSS products.
> 
> I personally own,
> 
> 6x CSS SDX 7 - various projects
> 4x CSS el70 - center channel
> 1x CSS SDX 15. - sub (obviously)
> 
> and then i have seen/heard/used the TRIO8 and TRIO12.
> 
> As far as im concerned, Bob has some of the best built products for the dollar available.


Thanks Adam,

I've had a pair of small ADS bookshelf speakers for over 20 years now and I've been looking for a suitable replacement for them. I feel that I should be able to build a great pair of bookshelves to accompany my SDX-15s. Do you have any experience with any CSS products that would make a good bookshelf project?


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## Binary

depending on whether you're adding a subwoofer to it or not, i'd recommend the EL70's, they are nice and simple, as you need no crossover, and in the right sized of sealed box, it creates an acoustical high-pass so you litterally need no other components to have a decent sounding bookshelf.

Now as far as i'd do it, i'd make room for two of the EL70's, as one is only about 86db sensitive. They extend cleanly into the 45hz range, and all the way up to about 18k, that being said, i cant hear higher than 16k, and almost no one i know can hear much higher than that as well. sealed will work okay, but i still recommend ported and to high-pass around 40~45. My center is tuned just above 50hz. Its a decent sized box, and amazing sound.

Now if you wanted to spend a few more $$ and have an even sweeter sounding bookshelf that doesnt need a subwoofer, i'd say an SDX 7 crossed to something like a Bohlender Grabener Neo8, around 650hz with a 2nd order to the neo8 would sound fantastic, although it would need an L-Pad for the tweeter, adding to costs.

So yeah, money no object with CSS, i'd definitely do the SDX7's. I've got a pair of SDX 7's in roughly 1.5 cubes heavily stuffed with fiber-fill, and it gets solid extension, as well as having plenty of room to eq down low, and play plenty loud. The hardest part is crossing over in a two way around 700-800hz, the SDX's tend to ring around 800-1000.

If you want the simplest design that will sound fantastic, i'd go with the EL-70s, theres something nice about those full range drivers. I've tricked people into thinking my mains with 15" woofers were on when i was only running my center.


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## fergi

Binary said:


> depending on whether you're adding a subwoofer to it or not, i'd recommend the EL70's, they are nice and simple, as you need no crossover, and in the right sized of sealed box, it creates an acoustical high-pass so you litterally need no other components to have a decent sounding bookshelf.
> 
> Now as far as i'd do it, i'd make room for two of the EL70's, as one is only about 86db sensitive. They extend cleanly into the 45hz range, and all the way up to about 18k, that being said, i cant hear higher than 16k, and almost no one i know can hear much higher than that as well. sealed will work okay, but i still recommend ported and to high-pass around 40~45. My center is tuned just above 50hz. Its a decent sized box, and amazing sound.
> 
> Now if you wanted to spend a few more $$ and have an even sweeter sounding bookshelf that doesnt need a subwoofer, i'd say an SDX 7 crossed to something like a Bohlender Grabener Neo8, around 650hz with a 2nd order to the neo8 would sound fantastic, although it would need an L-Pad for the tweeter, adding to costs.
> 
> So yeah, money no object with CSS, i'd definitely do the SDX7's. I've got a pair of SDX 7's in roughly 1.5 cubes heavily stuffed with fiber-fill, and it gets solid extension, as well as having plenty of room to eq down low, and play plenty loud. The hardest part is crossing over in a two way around 700-800hz, the SDX's tend to ring around 800-1000.
> 
> If you want the simplest design that will sound fantastic, i'd go with the EL-70s, theres something nice about those full range drivers. I've tricked people into thinking my mains with 15" woofers were on when i was only running my center.


Thanks Adam,

As mentioned earlier, I'm looking for a bookshelf that will compliment a sealed subwoofer design using my CSS SDX-15 drivers. I did some research on the Bohlender Grabener Neo8s and one reviewer on Parts Express advised not to take them below 1k hz because he had damaged one doing that. Is the Neo8 a tweeter?

John


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## Binary

The neo8 is a mid/tweeter of the planar variety. Its a bit of an exotic part so to speak. The thing about them is yes, you can definitely cook them under 1khz, but not if you are running them properly. A 2nd order highpass at around 800 is do-able as long as youre not looking for 100+dbs, which you said you aren't.

The Neo8 is different, its harder to work with than a conventional cone, but the results it can produce are dramatic, as well as very behaved.

This project was suggested based on your build requirements, but if you've got the dual sdx 15, just run the EL70's, its cheaper/smaller/easier, and will sound just as good, the difference is the extension you'd get, but the sub will offset that from the get-go. Hope this helps.


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## fergi

Binary said:


> The neo8 is a mid/tweeter of the planar variety. Its a bit of an exotic part so to speak. The thing about them is yes, you can definitely cook them under 1khz, but not if you are running them properly. A 2nd order highpass at around 800 is do-able as long as youre not looking for 100+dbs, which you said you aren't.
> 
> The Neo8 is different, its harder to work with than a conventional cone, but the results it can produce are dramatic, as well as very behaved.
> 
> This project was suggested based on your build requirements, but if you've got the dual sdx 15, just run the EL70's, its cheaper/smaller/easier, and will sound just as good, the difference is the extension you'd get, but the sub will offset that from the get-go. Hope this helps.


Thanks again Adam


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