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Discussion Starter #1 (Edited)
Hello all,

I am a lurker/newbie and I am appealing to your good nature for some opinions & advice. I always try to contribute positively to every forum I frequent and HTS will be no different.

For whatever reason, I have been dealt the good fortunate that MY WIFE asked me to build her a “small HT” centered around a 50” LG plasma, Pioneer VSX-1014, and other misc. gear I have lying around. I’ll let the fact that my wife is asking for this sink in for a minute. :)

OK, my first two thoughts are:
1) I finally get to put together some Murphyblaster CAOW1’s for L/C/R & Madisound “Recession Busters” for surround/back and
2) what kind of sub should I go with?

To maintain the WAF, I plan to install all drivers—including the subwoofer—in a “hidden” manner (in-wall covered with magnetic grills & picture framing). This means the sub & port will “peek out” between two studs, which mandates a sub no larger than 12” (gap between studs is somewhere around 13-1/2”)…the dual-18” RL-p18 LLT I have designed will have to wait for the “big HT” that I will build in the near future. The bulk of the enclosure will reside in the garage which shares a wall with the soon-to-be “small HT”. So I began a search for a single, HT-capable, 12” sub and the Shiva-X sure looks like a winner!

I ran the Shiva-X thru WinISD given the following limitations & goals and this is what I found:

Limits/Goals:
1) Achieve maximum extension with a LLT-type alignment,
2) Use a slot port (the enclosure will be a little shallow so bending a big, round port around in it would be a hassle),
3) Limit power to 500W (per comments in THIS POST) from an EP-2500,
4) Limit excursion to 20mm (per comments in THIS POST) to maintain linearity,
5) Limit port velocity to 18 m/s (recommendation from “Flare It” program), and
6) Room dimensions are 13x15 with the rear "wall" opening into the rest of the house.

Results:
1) 5.36 cubic foot enclosure tuned to 21 Hz (box will be roughly 13-1/2"W x 20"D x 54"L),
2) 12.0”x3.0” slot port, 35.9” long (both ends will be flared with either ½” or 1” radius),
3) Excursion max is 19.7mm at 30Hz & roughly 500W (ignoring subsonics),
4) Port velocity max is 17.7 m/s at 19Hz & roughly 500W
5) Port resonance is 188Hz (a little low, but should be OK for a THX crossover)

Please let me know if I’ve missed anything or fell for any “gotcha’s”. This isn’t my first sub build, but it IS my first HT sub.

Here are the WinISD plots:






Questions:
1) Although this is intended to be a HT sub, my wife likes to throw on XM and listen to music while she moves thru the house. Is this sub alignment a good choice for 50/50 music & movies/TV????
2) Am I an idiot for planning to tie the enclosure to the studs it will partially sit between? Will this rattle the hell out of the drywall & cause noise issues?
3) Would it be better to let the enclosure sit between the studs and not actually touch them?

Here's a quick sketch of what the enclosure will look like. Note how I've allowed for port tuning by reaching thru the speaker hole and attaching "shims" made of 1/2" MDF with the same cross-section as the port itself.

 

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I think what you have looks great. I'd offer one alternative.

Since you are putting the box in the garage, is an Infinite Baffle setup an option? You could have 2 18s or 4 15s in manifold with the opening in your wall being basically the same size as the shiva box you have planned. That would help with the "musical" ability of the sub if you are of the camp that says ported subs don't sound as good as sealed for music.
 

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Discussion Starter #3
Thanks for the insightful comment. I did think about an IB setup (sealed too for that matter) and it was appealing. Ultimately, I want to experiment with a ported setup this time around...and REALLY want to play with an LLT-type of alignment. The ported alignment will give me the bottom octave I want...then again, an IB with some EQ would probably do the same...with a less-complex enclosure. I am concerned about manifold sizing though! Hmm, decisions, decisions. LOL
 

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You have done your homework! Good to have you on board here at the Shack.

I see no problem with your approach. The IB suggestion is another valid approach if it fits your application. A single ported Shiva has great output for the "Small HT". :yes: The box design looks fine, and you can often get by with smaller ports with higher peak velocities at maximum output if you find yourself having issues with the port length or size. The dual 4" flared port never seems to have audible chuffing problems and it is significantly less area than your planned 36 in^2 port area. I think anything over about 28 in^2 would be sufficient as long as you are putting a roundover on the exit/entry of the port. Also consider that you will be using a subsonic filter, which will greatly decrease the port velocity @ 19hz.

I see nothing at all wrong with how you have it designed. If it where for me, I'd make the port smaller & shorter but that is the only change I'd make. Excellent first post!

Kevin Haskins
Exodus Audio
 

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I was thinking something like this sounded like it would work great for you.


Put 4 of Kevin's DPL-15s in, 2 in each manifold. Trust me I've modeled the out of it and drooled over the results. Sadly the wife is still not sold on the idea of a big hole in the ceiling and is scared of the back waves making the rest of the house "boomy" since I have to use an attic not a garage.

On the topic of your box though, the second bend in your port may not be a good idea. Is the box tall enough to run it straight up and have enough clearance? I've been under the impression that keeping the opening of your port as far away from the driver is the best way (but not 100% necessary).
 

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Here is the spl from 1 ported shiva in the box you describe (with a high pass filter) vs 4 dpl-15s in an IB setup, dpl in yellow:

 

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Discussion Starter #8
Someone mentioned in another discussion that the wall will act as a large baffle...what effect might that have on my model? Will it cause frequency response problems?!?
 

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Discussion Starter #9 (Edited)
As Kevin pointed out, you'll need a subsonic filter to protect the sub from over excursion. Consider the Reckhorn B1 for an add on unit since the EP2500 doesn't have a subsonic filter.
I bought a Elemental Designs EQ.2 on Monday afternoon and I just got an e-mail saying it was delivered this morning. It has the SSF plus 2 eq filters.

The sub is on its way too, so I might be cutting wood yet this weekend. :yay2:

EDIT: First case of bad news...it looks like the EQ.2 was a bad choice. My Pioneer VSX-1014TX receiver isn't capable of driving the EP2500 to 1.2V and the EQ.2 doesn't provide any gain. The manual says the Pioneer is only good for ~330mV (WOW that sucks!) and the EP2500 wants to see upwards of 1.2V. I guess I should have gone with the B1 as suggested above...make that WILL go with the B1 as suggested above.
 

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Hey guys! I am happy to discover this area. I really like the IB using 4 DPL 15's. I'm currently using a pair of Shiva-X in a U-channel OB and am really loving the performance.
 
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