# SDX15 Sealed 100 Litres



## Dasher (Jul 25, 2011)

Hi All,

I am in the planning stages of a sealed box for my brand new SD15, which will be used primarily for music.
Due to my lounge room I need to keep the box as small as possible, (another reason I chose a sealed box).
I have two questions I'm hoping someone out there can help me with.

1) If I use polyfill or similar how small can I go with a sealed box before I sacrifice performance?
2) What figure do you use for the volume the driver iteself will take up inside the box?

Any help will be appreciate.:huh:


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## Mike P. (Apr 6, 2007)

The SDX15 would need a 21" cube (external measurement) for a Q of .7. Is that too big of a cabinet?


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## RodK (Mar 30, 2011)

The external dimentions of my box are 20" X 20" X 22.5" with a double front plate and it is stuffed with 2 poyfill pillows.

Bob from css says the sdx15 takes up 7 litres.


P.S. Where on earth did you get a brand new SDX15? 

P.S.S I love my sealed SDX15. I had an amp issue with mine but just got a replacement and couldn't be happier.


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## Dasher (Jul 25, 2011)

Sorry guys I should have given more detail in my question. I was at work and a little pushed for time.

My new house is small I am very limited on placement. So my idea is to have the sub between my mains and under my TV. To do this I need to make it wider and shorter than normal. I'm looking at about 40 inches wide by 14 inches deep by whatever high, (I haven't settled on exact dimensions yet). To get a Q of 0.7 it looks like I need 103 litres but I also understand that polyfill can make the box appear larger than it actually is. Although I can live with 103 litres I would like to make the box as small as possible (in volume) using polyfill. How much smaller can I actually make it without affecting performance?

_Bob from css says the sdx15 takes up 7 litres_
Thanks. I hadn't measured it but I wouldn't have thought it was that large.

_P.S. Where on earth did you get a brand new SDX15? _
http://darcheraudio.com.au . This guy is located in Tasmania, Australia and has them in stock.

_P.S.S I love my sealed SDX15. I had an amp issue with mine but just got a replacement and couldn't be happier_.
Thats good to hear. I have never heard one in action but it certainly looks impressive.


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## nc535 (Aug 6, 2010)

A linkwitz transform can give you the sound/performance of a big box in a small box for the cost of a few db of SPL at the top end. Lots of references on the web. You probably need to travel a ways on the learning curve to do it but it would be worth the trip if space is that critical. You can simulate a sealed box with Linkwitz Transform in WinISD and then implement the crossover with a MiniDSP for abt $125.


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## RodK (Mar 30, 2011)

40 x 14 x 18 will give you plenty of room for lots of bracing and still give the q you want. If you want to go smaller than this, the only dimention I would change would be the 40" width.


http://www.hometheatershack.com/forums/enclosure-volume-calculator/


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## Dasher (Jul 25, 2011)

_40 x 14 x 18 will give you plenty of room for lots of bracing and still give the q you want. If you want to go smaller than this, the only dimention I would change would be the 40" width._
Thanks Rod, those dimensions are possible. Also thanks for the link thats a great page, sure to come in handy.

_A linkwitz transform can give you the sound/performance of a big box in a small box for the cost of a few db of SPL at the top end._
Hmmm I like the sound of that, (no pun intended). Are the only sacrifices for this the loss of db? Will it affect the sound quality at all? I can easily afford to loose some db as not only is my room small but my house is joined on both sides and I am not looking for loud.

_You can simulate a sealed box with Linkwitz Transform in WinISD_
I had a play around with that this morning and it looks good.

_and then implement the crossover with a MiniDSP for abt $125_
I just received my miniDSP about a week ago. I wanted to use it as a crossover and EQ. Looks like it might come in more handy than I thought.


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## nc535 (Aug 6, 2010)

check out Siegfried Linkwitz's web page for the theory. He uses it in very high end, very well regarded systems. I like it because you can tune how the box sounds electronically by moving the target F3 and damping factor around with the transform. To see how many db of SPL you give up, look at the Transfer Function Magnitude (EQ/Filter) screen in WinISD. If you are just changing damping factor and not trying to reduce F3 it won't be much. Add 6 db to the SPL at 20 Hz to what WinISD shows for room gain and boundary reinforcement. More than that I can't say because I'm still working on my first sub using it!
Jack


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## Dasher (Jul 25, 2011)

_I like it because you can tune how the box sounds electronically by moving the target F3 and damping factor around with the transform._
Yep it sounds almost to good to be true. I haven't been able to determine how many db's I will loose as winLSD doesn't always co-operate with me. I thought it was because I had a BETA version but maybe I need to try and download it again.


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## nc535 (Aug 6, 2010)

Dasher said:


> _I like it because you can tune how the box sounds electronically by moving the target F3 and damping factor around with the transform._
> Yep it sounds almost to good to be true. I haven't been able to determine how many db's I will loose as winLSD doesn't always co-operate with me. I thought it was because I had a BETA version but maybe I need to try and download it again.


Let me give you a couple more tips:

Don't worry about the error when you try to close it. That's just the way it is. Use Windows task manager to end task when you are done.

One thing it is fussy about is the order in which you enter parameters when creating a new driver model. That could definitely throw you. Here is a link for help on this site:
WinISD Pro Tutorial and Download (A detailed guide on how to use WinISD Pro) - Home Theater Forum and Systems - HomeTheaterShack.com
http://www.hometheatershack.com/for...d-guide-how-use-winisd-pro.html#ixzz1K5NeBgy6

Once you get the driver model accepted, then choose an alignment. If sealed start with QTC = .707 and see what box size results. If too large, the progressively try higher QTC and then use the Linkwitz Transform to bring the QTC and optionally also the F3 down to where you want it.

Once you get past that its a matter of interpreting results. On the loss of SPL. Just get to the equalizer response screen and see find the max db of boost its putting in - that much comes off the top. Simple as that.

Another thing you need to watch is maximum cone excursion. Go the the "Signal" screen on your project menu and enter the maximum "System Input Power" you plan to use. Then go to the Driver Cone excursion screen on the main results graph window. Is this within the Xmax of the driver? If not, either reduce power or, if its happening below 20 hz, try adding a high pass (subsonic) filter via the EQ/filter screen of the project window.

At this point you could build the box and use the EQU capability of MiniDSP to tune it to how you like it. One more thing you can do in design is estimate how much low frequency you will get from being close to the wall and floor and from room gain. That is done with Jeff Bagby's "Diffraction and Boundary Simulator". You can google for the download and I think find tutorial for it on the Parts Express site. Using this will help you avoid overdesigning for low end extension. You don't need to do as much EQing as the WinISD plot makes you think because of boundary reinforcement. 

Jack


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## Dasher (Jul 25, 2011)

Wow thanks for taking the time to give me the tips its greatly appreciated. :wave:
I haven't heard of Jeff Bagby's "Diffraction and Boundary Simulator. I will have to have a look at it over the next day or two.
I will also have to have a look at the SPL like you suggested. I couldn't figure out how to judge the drop so thanks.
I was also considering buidling the box and then using REW and the minidsp to adjust accordingly. I dont have an SPL meter or a decent soundcard though so it would depend on costs.:dontknow:


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## nc535 (Aug 6, 2010)

eventually you will want to spend the money for the mic and sound card but you can get started without it you are on a budget and just doing a sub. Set the MiniDSP to the parameters you get from WinISD and then tweak from there by ear. If you've got a smart phone, try the RTA PRO app. It will give play test tones thru ur spkrs and capture and display a spectrogram. For $5 you can't beat it.


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## Dasher (Jul 25, 2011)

I just got RTA lite for free on the iPhone. It looks to be a handy little gadget, thanks.


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## Dasher (Jul 25, 2011)

Ok well I have had a play with a smaller box with the Linkwitz transform and it all looks good except for the cone excursion. 
From my little knowledge it doesn't seem worth while as the excursion is excessive starting around 28hz. Now I'm not sure what range is practical for music but I would assume 28hz is too high a cut off for a sub.
It looks like I will need to go the suggested 103litres and try adding a small boost at the bottom if needed.

Any thoughts?


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## RodK (Mar 30, 2011)

Thats why I am happy with my setup. 500 watts is enough for me and the Oaudio plate amp has adjustable high pass with boost built in. I am running mine at the 16 hz setting right now. the bass is tight and full.


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## Dasher (Jul 25, 2011)

RodK, I just realised the other thread is yours, the sub looks great. The dimensions might be different but volume etc is pretty much exactly what I will probably be looking at.

_500 watts is enough for me_
My last one was an 18 inch driver in 420 litres ran with 500 watts and I never got close to pushing hard, 500 watts was plenty.


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## RodK (Mar 30, 2011)

Thanks. I did alot of research and was flopping back and forth between sealed and ported, but I am extremely happy with the end result. Especially with music it sounds amazingly good, but still has lots of thump for movies.


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## Dasher (Jul 25, 2011)

RodK said:


> Thanks. I did alot of research and was flopping back and forth between sealed and ported, but I am extremely happy with the end result. Especially with music it sounds amazingly good, but still has lots of thump for movies.


I understand completely, I was in the same boat being undecided between sealed and ported. The performance of the ported looks so good in WinISD that its hard to resist. I just cant afford to go to 200 litres and being Im looking at music I will go sealed.

Just out of curiosity, your internal brace, does the round cut out actually support the magnet on the driver or is there clearance?


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## RodK (Mar 30, 2011)

there is clearance. I did not want to add any resonance problems. I also used pl premium to seal the box and it appears that I have no leaks. Bite the bullet, build it sealed and don't look back. I am so happy that I did.


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## Dasher (Jul 25, 2011)

Ok so after looking at my options I have decided to stay at around the 103 litres as suggestd and not use the Linkwitz transform due to cone excursion issues.
This brings me back to my original question.

If I stuff the box with polyfill how much smaller can I make to box, assuming that I want the performance of 103 litres, Q 0.7?


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## RodK (Mar 30, 2011)

If you are ok with 103 litre size then build it that big and still stuff it.


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## Dasher (Jul 25, 2011)

RodK said:


> If you are ok with 103 litre size then build it that big and still stuff it.


Sounds reasonable.....


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