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Discussion Starter · #1 ·
I posted this question in my build thread in the "Other Audio" section. But I needed to ask it here to get some real answers.

I have built a very nice home theater sub for a friend utilizing a DIYMA sub and an LT550 plate amp. The sub is VERY accurate and sweet. But, as others have said, it just doesn't have the impact that some other subs have. Make not mistake, this would make the PERFECT (and I mean that) home audio sub; but it wont quite cut it as a home theater sub. It gets down and dirty, no lie, but we actually bottomed it out quite hard in one scene and I was forced to turn it down. There was a fight scene that had some extreme low end content and all of a sudden there was * POP POP POP * and I was scrambling for the volume on the remote. His room is a decent size and we need to experiment with placement first. We were limited on placement because he didn't have an LFE cable and we were using a short RCA as a temporary set up. Once we get a longer LFE we can corner load the sub and see how it does there.

My initial plan, if corner loading doesn't give us enough low end, is to swap out the driver for a different 12. I didn't come to this conclusion easily though. I like the sound of the DIYMA R12 and it's basket looks like a million bucks in that enclosure. But, my friend is careful but not quite as careful as I am when it comes to cranking the system. So I think that needs a solution. My idea, if corner loading doesn't work, is to switch out the driver with a....wait for it......Shiva X that I have in my room. The Shiva X is close to the same size. The Shiva needs 1/8" larger cutout than the DIYMA but I always make cutouts a touch larger than needed in case manufacturers lie about cutout measurements. And before anyone asks, it's because it's happened to me before in the past. So, I think it might fit in the box. The only thing that might be a gamble is if the bolt holes will line up properly to mount the sub. The Shiva X has an enclosure recommendation on their site that says it will work in a 1.25 cubic foot enclosure. The enclosure that I've built is 1 cube. It's close but I think it models fine in Unibox. It actually models better (response wise) than the DIYMA. The big thing though, is that (according to Unibox) the Shiva wont even touch it's Xmax with the 550RMS I have to throw at it in that size of a box. But, the kicker is, Unibox says that the DIYMA shouldn't either...wtf? :confused:

What do you guys think?
 

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Discussion Starter · #3 ·
I've never heard of anyone porting theirs. Can you link me to a thread that has one ported with some results?


Either way, I think you're missing the point. The graph I have in Unibox says that even with 550RMS the peak cone excursion shouldn't exceed 18mm even at 10hz. So that leads me to believe that I've modeled something wrong or the ts specs are wrong. What gives?
 

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Needs to be ported for HT use otherwise you won't get enough low end gain. With a lot of movies there is strong low frequency content, sometimes even subsonic (explosions etc.) that can be very demanding on a sub.

What I don't understand is your modeling? IIRC, most drivers will bottom quite easily with 550 watts.
 

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Discussion Starter · #5 ·
What I don't understand is your modeling? IIRC, most drivers will bottom quite easily with 550 watts.
I know. I don't understand it. I had this thing at about 1/3 gain if even that much, and it bottomed out so hard that it tripped the amp into turning itself off. I had to walk over there an flip the switch off and then on again for it to work again.

I'm using Unibox to model the sub with the following TS parameters posted by Zach.

Fs 25.21
Re 3.60
Qms 4.75
Qes 0.38
Sd 491.0
Vas 41.7
Xmax 23.00
(Le) 1.32
(Le2) 0.00
(Re2) 0.00

I'm putting in Nominal Power as 550.0 and the graphs for a 1cube box say that it shouldn't reach Xmax at any frequency above 10hz. Did I do something wrong or are the specs wrong?
 

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Where you set the gain doesn't mean anything though. You can still reach peak power with the gain set all the way down if your source is powerful enough. If the amp is tripping, that's completely separate from the sub bottoming out and probably means you're exceeding the safe operating limits of your amp.

I'm not sure what to make of it myself. I do know that the solution is to port it though... I'm actually kind of surprised you're getting any kind of low end output in a sealed box. I have a pretty small room myself... probably 15x15 and I definitely need to port to get flat response to 20hz. Output is pretty satisfying though... but if I had a larger room I'd probably even use 2 12's for some movies so you can really feel it. HT is just a completely different beast... you might even be better served by one of those mach 5 18's for dirt cheap. Those things are ungodly loud, and you don't even need more than a few hundred watts to get them moving.
 

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Discussion Starter · #7 ·
I think what I might do is build a small simple test enclosure that is 1 cube. Then I can test out the Shiva in the room and see if it would get the job done in that same sealed 1cube box I built him. If it doesn't work out I'll just take back the sub and get him something ported. His room is bigger than I thought it would be anyways.
 
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