Is it possible to build this sub - w/picture (1 Viewer)

[ClarkZ]

After much searching I have come to the conclusion that there aren't premade plans to build the sub I want. I guess that means I am going to have to design it myself. I am hoping to use the sub in my HT and I want it to fill up the space under the screen (in between two columns). I am hoping that this will help to frame in the screen. This is why the measurement seem so stange. I want it to be 7 feet horizontal by 15 inches wide by 18 inches tall (all of these measurements are approximents). I would prefer that it is bottom firing and ported.
Here is the picture of what I want
Can anybody tell me if this is even close to being feasible, and what problems I might run into. I'm open to any suggestions.

 

[Cam S]

It's totally possible, but you may run into the same negatives effects by the sub being enclosed like that. I know a lot of guys say to not pace speakers inside wall units that enclose it cuz it effects the sound severly, but it may be different for you and your design. I'm sure one of the more knowledgable guys will clear this up.

 

[Joe Meissner]

looks like a great box to do dual shiva's or something? im sure the guru's will give you a few tips. I'm working on my first DIY sub right now. and these guys are awesome that help us newby's out.

good luck

 

[ClarkZ]

I was concerned about have a "speaker in a box" effect. I hope that having the speake 3 feet from either edge will cut down on this problem. Thanks for the encouragement so far. At least I don't feel like an idiot for suggesting it, at least yet

 

[jeff lam]

I am hoping to use the sub in my HT and I want it to fill up the space under the screen (in between two columns).

Does this mean you have a projector?

If not, you may want to try it in a normal box first to make sure you won't get "green screen" from the magnet of the driver(s).

Looks like a great design. If it's down firing I think you will need at least 3-4 inches clearance from the ground. And if you're limited to 15" wide, 12" subs are the biggest you can go.

 

[ClarkZ]

Actually I just getting started with the theater construction, and I will be getting a projector. The size can be changed a bit. How wide would I need to make it in order to fit a Tempest into it.

 

[jeff lam]

I would say 17" min so you will have at least 1 inch on each side to play (the outer measurement is 15" or 15 1/16" or something like that). I would strongly suggest this route, then you could even go dual tempests if you wish. The tempest has much more displacement than the shiva.

 

[Dustin B]

Another issue would be that to tune in the 16-18hz range a 6" port would have to be longer than your specified height dimension. It might fit if you tuned in the 20-22hz range though.

 

[ClarkZ]

I don't have a lot of room to add on the height (maybe a couple of inches). Would this be enough to tune it down to the sub 20hz range? Could I put a 90 degree bend in the port or would that totally mess things up? Does anybody have a link to show me what software I need to use to model the sub and possibly some sort of HOWTO to get me started. Thanks for all of the encouragement!

One really stupid idea... but is it possible two have to ports to make up the difference

 

[jeff lam]

Depend's on what design you use as to how big/long your port needs to be. My tempest only uses a single 4" flared port and is only 14" in length overall. Dan Wiggins came up with this design so it's more than OK by me to use the 4" port with the tempest.

You could go with smaller dual ports to try to get them to fit right. I'm sure you could work it out to fit in your required height.

 

[ClarkZ]

How does port length affect tuning. I know there's a relationship, but I'm not sure what it is.

 

[Dustin B]

Edit: Deleted, belonged in a different thread.

 

[Mike Lazalier]

Clark, this program has helped me out more times than I can recall.
It's a speaker modeling program that uses either the AV8, Shiva, Tempest, or Maelstrom. It's called LspCAD for Adire, and you can get it at:
http://www.adireaudio.com/Files/Adire.zip
Mike

 

[Jeff Rosz]

hi clark,
a single tempest, in that box looks pretty good. 20hz tuning can use a 6"x14" port.
18" is to the bottom of the screen? flip the box over 90 degrees, or can you go 18"^2 x 84"?

How does port length affect tuning.

longer the port the lower the tune. think of pipe organs, flutes and piccolos(sp.) and such. play with lspcad and you will learn the relationships, they become second nature to you real fast.
one thing i noticed in your drawing was a backside 7' long "leg". i dunno if i would do that. also, an 84" wavelength has a freq. of ~160hz, thats above the crossover but there may be some harmonics to think about. maybe an expert can clear up these two points and i can learn something too
lates
edit, how big is the room?

 

[Chris Tsutsui]

When I designed my box I thought the idea of making it a trapezoid/pyramid shape would help reduce internal standing waves.
But I heard people say shape doesn't mean anything so I guess I'm doing it for looks.
I just got my tempest, I have a few pics of it on my site now.
You sure u don't want to try a different shape other than a box? Those measurements make a box that's 13 cubic feet which is a lot to work with. Jeeze, you could fit two EBS alignment tempests in an enclosure that size.

 

[Jeff Rosz]

hi chris,
as i understand it, shape doesnt matter, but 2 opposing parallel sides do. maybe some angled braces would break it up. but like i said, me no expert on the subject, just sponging knowledge in hopes of such ...and its good discussion

 

[ClarkZ]

I come up with a few more questions.

The first is what does 18"^2 x 84" mean. I get the 18" and 84" but I'm lost on the other part (I'm really new to this).

The second is, What is the benifit of having dual tempests? If I went for two would the run off the same amp (I've ordered the pe 250 watt one thats on sale)

The third is, Does the sound a sub makes come out of the port or is it so that the air can be expelled when the driver moves in and out?

The forth is, With a sub this big would I need to line the interior with foam?

The room that this is going to go into is 14'x11' with the primary seating being 10' from the screen. I am going back and forth about whether I should make the GR AV1+ or the Audax HT. I will probably end up the the AV1+ since I can make them front ported.

Thanks to everybody who has helped so far. Being a newbie isn't that much fun and its great to move through this stage as quickly as I can.

 

[jeff lam]

18"^2 means 18"x18". The ^2 just means "squared". Also when you see ^3 that means "cubed". The arrow just means move it up just as you would write it on paper but it doesn't allow that kind of text on post's.

 

[Jeff Rosz]

hi clark,
ya it just means 18"x18"x84". im lazy. but now i did get off my keester and plotted some graphs...
one of the benefits(among others) of having 2 drivers can be seen
here with the same box, same amp. the red line represents 2 tempests, the blue shows 1 tempest.
for the 3rd question, yes you get some output from the port but look at plot2...cone displacement. the box is tuned to 20hz by the port, follow the movement of the cone. can you figure out whats going on here?
4th...generally, ported subs should be lined. ymmv.
14' by 11'...one should do the trick. heck, one shiva would do the trick. you wont be disappointed. you could build now for 1 driver, and plan(build) ahead to install a second later if its not enough. keep this in mind....trade-offs and compromises are everywhere. get this, give that. btw, there are other drivers out there too, check em out. lates

 

[Pete Mazz]

How about just making it a sealed alignment. Drop in two Tempests and that thing will put out tremendous amounts of very clean bass.

Pete