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Discussion Starter #1
I recently got a second row couch for our modest HT, and read quite a bit about THIS Danley "couch" sub. Basically, 2 of them would make a good couch riser. I don't have (nor would I spend) $4500 for 2 of them, but since i have to build a riser, it doesn't seem like *that* much more work to make it into a decent sub enclosure.. I'd have to skin the bottom, and try to seal the top as best as could be done.

Danley uses 8" subs in their tapped horn config, but if my riser is to be 12-15" high, I think I can go bigger, especially if we put the subs in the top..

I already have a pair of 18's as the main subs, I think these would be a neat near-field setup, that could play from ~25-30hz up to ~80hz. I have an eq.2 that can handle the phase adjustment and the 25-30hz high-pass duties, and was thinking of a modest amp, like a Behringer A500 to power them.

The dimensions of the riser would be approx 6' deep, 7' wide, and 12-15" high. (Needs to be at least 12" high, but I can go a little higher, it's not a big deal) - that's PLENTY of air space, but money is tight for this, so I can't use high $$ speakers.

I'm open to suggestions for drivers that might work well, and also any opinions on this..
 

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Discussion Starter #2
Crud, this probably should have gone in the more general DIY subwoofer section... mods please move it if you feel it's appropriate! :)
 

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I'd like to try and keep the total driver cost under 300, which will put amp & subs at 500.

BUT, if there's a very compelling reason to go with more (or more expensive) drivers, I'm willing to hear it - would then just construct the riser to spec, and have some empty holes for the time being.
 

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Discussion Starter #6
What 18 inch subs do you have now?
I have Fi IB18's in a small-ish IB with the Ep2500 running them... Which led me to a thought.

I could wire the Fi's as a single 2 ohm load, and run that from the left channel of the EP2500. Then that would leave the right channel for the other subs, which frees me up from needing another amp, and would give 800watts into 2 ohm, or 635 into 4 ohm. Frees up a little cash while lowering overall cost..

Doing a little messing around with WinISD - Here's a few variations on your idea, using the full 35cubes. All of these are modeled with 800 watts, high-pass filters to keep xmax in check, and with 8" ports, enough of which keep the port velocity below 25ft/sec.
Yellow is my IB with 800 watts (for reference)
Blue is Mike's idea
Red and that purplish color are my 2 other ideas...


Going into this, I really wasn't thinking of a setup that would be as loud as my IB, but I'm all for it!
 

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2 Fi IB18's in a 2 ohm load on one channel and 2 MJ-18M's in a 2 ohm load on the other channel would work. The MJ-18M's in 35.cu.ft tuned to 21 hz is too high a tuning, 15 hz is much better. With 800 watts input power you'd get over 118 db at 16 hz and you wouldn't need at SSF. Porting would require two 8 inch ports 28 inches long. Sitting on a couch with that setup underneath would be an experience!
 

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Discussion Starter #8
After receiving advice from a few sources and doing some more modeling, in order to best blend with my IB, I'll be doing 2 Fi IB3 15's "sealed" - the size of the enclosure gives me a .7 Qtc and a nice flat FR curve, both of which match my plotted IB curve. This should work and blend well, while adding a little more total SPL (not that it's lacking now), and help smooth out room response... not to mention adding some nice near-field "kick"..

I think the difference in the driver tonality and the enclosure type might cause "issues" if they weren't close..
 

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Why not?

Making your drivers fire upwards will cause distortion from non-linear motion and also cause them to bottom out way sooner. Manufacturers that sell down-firing subs are compensating for the force of gravity in the suspension. It should be noted that it is still difficult to make this compensation stay linear with excursion. I would make every effort possible to make the drivers fire sideways like they were designed for.

A manifold alignment should be rather straightforward, and you're gonna want your riser to be a height that is conducive to the natural height of steps...I think it's 7.5" per step??? I could be mistaken, but if you're gonna do anything over half a foot, then I think you should end up around 15", which is more than enough room for a pair of twelves.

Another problem you'll run into is the time alignment between your riser sub and whatever other subs / mains you've got running in the room. You can actually end up with less bass if you don't add a time delay to the riser subwoofer to ensure that its pressure wave arrives at the same time as everything else.

For $200, I don't think you're gonna find what you need. A Crown XTi would have the processing you need built-in, but I hear they don't make the best subwoofer amps...though it might be acceptable for your application since you won't be cranking these subs very hard (since they're so close).

In fact, since you want to budget less for the drivers themselves, why don't you build yourself a tapped horn or even a full sized horn? With that kind of cubic feet available, there's all sorts of horn loading you can do....and make it go real deep too. , I got a pair of 12" AA Assassins to do 130dB down to around 20Hz with only 200W in a tapped horn. And those drivers were $100 each.
 

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Discussion Starter #11 (Edited)
Another problem you'll run into is the time alignment between your riser sub and whatever other subs / mains you've got running in the room. You can actually end up with less bass if you don't add a time delay to the riser subwoofer to ensure that its pressure wave arrives at the same time as everything else.
I have been considering selling my 2 eq's (Rane PE17 and unused Elemental eq.2), and could probably come close to buying a DEQ2496 with the proceeds, (within $75 or so.) The DEQ has a channel-specific delay setting, so I should be good to go there..

In fact, since you want to budget less for the drivers themselves, why don't you build yourself a tapped horn or even a full sized horn? With that kind of cubic feet available, there's all sorts of horn loading you can do....and make it go real deep too. , I got a pair of 12" AA Assassins to do 130dB down to around 20Hz with only 200W in a tapped horn. And those drivers were $100 each.
Since I had the millisecond of genius and realized I have a free amp channel, I could budget more for the drivers/enclosure...
My enclosure choice was to better "blend" with the sound from my IB.. I would think a tapped horn would have phase issues with a sealed (IB) sub that a fixed delay could not eliminate?

The idea of the horn intrigues me, but I've had a hard time finding "horns for dummies", but I'm still researching... Don't think it's something I'd want to undertake on my first enclosure-building project though!
 
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