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Discussion Starter · #1 ·

I'm in the process of building my first sub.  I was originally sold on the Marty cube design, but I've been reading more and more and came across a sub in the archives that got my curiosity going.  It's got a higher WAF, the drivers are protected from my kids, and the footprint works better in my room.  I also like the look, for what that's worth.

 

Here is the thread.  http://www.avsforum.com/t/1428124/ssd-15-dual-opposed-vertical-sub-build    

 

My initial question revolves around volume requirements for this sort of design.  He's running two 15" drivers in a box that is 3.23 cubic feet.  Do dual drivers in a sealed box see the volume independently?  AKA does each driver see the total 3+ cubic feet, or does each see 1.5 cubic feet?  I've googled for the answer, but not successfully.  I've seen several other similar builds like this which use about the same volume, so it seems like each may see the full 3 cubic feet. 

 

I'd be looking at putting two SI HT 15" speakers in this build.  I've tried to model this in WinISD, but this is the first model I've ever built so I have no confidence in my results.  From what I see, I've got a pretty sharp dropoff with this design once I cross under 50.  If I make the enclosure 6 cubic foot, it drops off more slowly.  But as I said, I've got no idea if that's correct or not.

 

I'd appreciate any thoughts on the topic of appropriately sizing a cabinet in this configuration.  I would have thought google would have given me a quick answer, but my search mojo doesn't seem to be working this AM.  
 

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Quote:
Originally Posted by G-Money1572  /t/1521712/dual-oppossed-vertical-subwoofer/0_50#post_24459250


I also like the look, for what that's worth.


Here is the thread.  http://www.avsforum.com/t/1428124/ssd-15-dual-opposed-vertical-sub-build    
That's similar to my midwall subs but I use 12" drivers.
Quote:
Originally Posted by G-Money1572  /t/1521712/dual-oppossed-vertical-subwoofer/0_50#post_24459250


My initial question revolves around volume requirements for this sort of design.  He's running two 15" drivers in a box that is 3.23 cubic feet.  Do dual drivers in a sealed box see the volume independently?  AKA does each driver see the total 3+ cubic feet, or does each see 1.5 cubic feet?  I've googled for the answer, but not successfully.  I've seen several other similar builds like this which use about the same volume, so it seems like each may see the full 3 cubic feet.
If you built 2 1.5cf enclsures with a single driver in each, and sat them on top of each other, you'd get the response as the single 3cf with a pair of drivers.
 

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I too have subs like that but 12". It does work very nicely for protecting from kids and also getting the driver closer to the boundary. I get a very smooth response this way.
 

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Discussion Starter · #4 ·
So said another way. If the 15" drivers I'm looking at spec 3 cubic feet for a sealed enclosure, I need 6 cubic foot of volume for this setup to get comparable performance?
 

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If you put 2 drivers in a single space, the each "see" half the space.


From what I've picked up around here that roll off around 50 sounds right to me. I'd model if for you but chances are you are doing it right (and I'm pretty new to WinISD as well. If you look at the first post of the marty cube build the single sealed 18" rolls off around 40Hz - so two of the smaller drivers in a smaller space probably does roll off. With that being said, depending on your receiver (one with audio calibration and more specifically sub calibration capabilities) or if you get a miniDSP or DSP in the amp (such as inuke) and a mic you should be able to compensate for the quick roll off and get a great sounding sub.


I too saw this build and was impress with the WAF - ended up going marty cube though
 

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I drooled over nube's build myself but I have no idea how is getting the posted FR with a couple of sealed 15s. Unless there is some kind of "slot loading" magic or something else that I don't understand going on there? I do get that he is using a minidsp and may be applying a linkwitz transform, but still that seems crazy good.


Not to imply it didn't happen, just that I don't understand and wouldn't want to expect results that good in my room if I tried to duplicate the build..
 

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Discussion Starter · #8 ·

I've been playing with WinISD most of the afternoon, and feel a bit more comfortable with it.  I've modeled the dual build, the Marty Cube, and a sealed 15"er.  I'm hopeful they are close but no guarantees.   I got most of the Martycube info from a thread on here.

 

I have a Yamaha receiver, so will probably be getting a iNuke 3000DSP so I can equalize the sub.  The Qtc on the original linked build seems to be around .84, which is high but it sounds like I can adjust for that with the iNuke. I do see the drivers he used spec a 1.5 - 2.5 cuft box - which is less than the SI HTs.  I should have modeled them but didn't yet.

 

I've attached my graphs below.  I'm not sure if I've got any meaningful conclusions yet.  I used 600 watts per driver as a starting point for each.   

 

Red = Sealed 15" SI HT with 3 cubic feet volume

Yellow = Marty Cube with 18" SI HT.  I put a high pass filter in at 15hz, per the recommendation on the thread.

Blue = Dual Opposed build with 15" SI HT using the cubic volume from the original thread.

Green = Dual Opposed build with 15" SI HT with volume necessary to get to .70 Qtc.  That worked out to be 5.3 cubic feet.

 

I'd be curious if anyone has any thoughts, or has any tips on things I should have done differently. Or conclusions that I should be drawing from this graph.  I'm about as green as they come when it comes to building speakers.

 

 
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