New DIY project - big sub, small box (passive radiator?)

[solid7]

I am looking, looking, and looking again, at all the different types of subs out there. I have started learning WinISD, and trying to make educated decisions. I have to admit, I'm still too new and unfamiliar to have much of an idea of what I'm doing.

Here is the question - I am looking to do another DIY project, this time, a box sub. LLT is definitely out of the question. (it will not be considered under any circumstances) I have an RL-P15 sitting around, doing absolutely nothing. I would like to build a box somewhere in the neighborhood of 2 ft sq. x ? tall. (preferrably 3 ft or under) From what I see, my only 2 options are sealed, or PR.

I don't mind spending the money on the PRs. I am currently looking at 2 18" PRs from Acoustic Elegance. However, building, tweaking, and interpreting data in box building software is my weak point right now.

Anyone care to chime in on where I might start? Which would most likely be a better build? (budget is not a question)

Finally, if a PR is a good option, is it feasible/possible to make a down firing driver, with PRs on adjacent corners? The reason would be to be able to fit the box in a corner with the PRs pointing parallel to the walls. (corner loading) I have a wall to the right of my listening position, but not the left.

Thank you.

[Mike P.]

Although I don't have access to WinISD at the moment, I do recall modelling the RL-p15 in 5 cubic feet with 2 15 inch passive radiators from Parts Express. I forget what the tuning frequency was, I'll look it up as soon as I get home.

[solid7]

I tried modelling with 2 18" radiators, and I have to admit, either I have no idea what I'm doing, or I've missed something in the parameters, because the output doesn't make any sense to me.

What about the down firing issue? Can anybody provide guidance on that?

[mayhem13]

In 100L with 2 1600 PR's opposing with 1000w flat output of 118db to around 30hz with an f3 of 26.73hz with walls covered. This driver is excellent for downfiring with a sag factor of only .98. You can add some weight to the PR's to get lower in that volume for the driver reaches xmax around 20hz or simply buy the 2100g PR's. Either way this will be an awesome small box sub paired with a PE 1000 watt plae amp. Keep us posted if you decide to build it!

[SQBubble]

I'm in the same boat as you, expect me it's for a different sub. Your best bet is going with the PRs, it'll give you some great SPL improvements down low(depending on tuning) compared to sealed... And firing the driver down with the PRs parrarel to the walls like you said is what I would personally do, sounds like the most logical thing to do, plus it'll look very nifty! Keep us posted, Good luck!!

[solid7]

mayhem13 wrote:

In 100L with 2 1600 PR's opposing with 1000w flat output of 118db to around 30hz with an f3 of 26.73hz with walls covered. This driver is excellent for downfiring with a sag factor of only .98. You can add some weight to the PR's to get lower in that volume for the driver reaches xmax around 20hz or simply buy the 2100g PR's. Either way this will be an awesome small box sub paired with a PE 1000 watt plae amp. Keep us posted if you decide to build it!

This sounds good, but just a few questions...

1) must the PRs oppose? (I would prefer adjacent for corner loading)
2) What are the 1600 PRs? (I was looking at using 2 of these)
3) What do my box parameters look like if I want the tune frequency to be somewhere around 17-20 Hz? (sorry, I am still learning WinISD)
4) I know nothing of plate amps. Would an external amp + BFD be acceptable? (I already have an extra of each)

I will definitely keep you posted on this build. I've been chomping at the bit to build another sub.

Thanks for your help!

[mayhem13]

The lowest practical tune i could achieve in model at that box size(100L) was 18.7 hz by increasing the mass of the PR's to 2750 grams each. The 1600 i mentioned was the mass of the PR's as yo will recieve them. I believe AE makes two versions, one with 1600 grams and another with 2100 grams. By increasing the MMg of the passive, you effectively lower the tune but as in ported, without increasing box volume, low end rolls off sharply. If you increase the box to 150L (5.3cuft) then low end output will increase significantly but that's a pretty big box and you eluded to wanting something smaller. As to opposing PR's, the moving mass of the PR's stabilizes the box which may rock at extreme output. You should be fine at 90 degrees from eachother with the sub downfiring though. If it was me building this. I would build a pentagon shaped cab with the driver forward loaded on center and the 2 PR's on either side with the remaining two sides against the wall. I'm planning a tall version of this for behind a chair in my room as an accent table. Since it's behind the chair, all that will be seen is the top for lamp or something if i velcro it down. LOL.

[solid7]

mayhem13 wrote:

The lowest practical tune i could achieve in model at that box size(100L) was 18.7 hz by increasing the mass of the PR's to 2750 grams each.

I'm pretty certain that the max allowable weight is 2500 grams.

mayhem13 wrote:

By increasing the MMg of the passive, you effectively lower the tune but as in ported, without increasing box volume, low end rolls off sharply. If you increase the box to 150L (5.3cuft) then low end output will increase significantly but that's a pretty big box and you eluded to wanting something smaller.

I want something smaller, but I'll go up to 150L. That's the absolute biggest.

I'm wondering if 18" passives is the way to go, or if this design would be better suited to 15". I'm going to try modelling in Unibox, and see what I get. (wish there was a database entry for the RL-P15)

[mayhem13]

At 1000watts with 2 AE PRs 18" and factory set to 2100 grams in 150 liters you will have an effective tune of 18hz with 114db output at 20hz. In other words a monster. BUT as with ported, cone excursion goes off the board around 15 hz so a subsonic filter is essential. The PRs on the other hand are nowhere near xmax. I think a Pro Amp and BFD is going to be essential here but the Dayton 1000watt plate may have a built in high pass- i think i read that somewhere ?? 20Hz ?? Anyone....Bueller.....?

[mayhem13]

Yep-after looking at Freq response graphs, non selectable 20hz high pass at about 12db per octave. Very usefull in this application. Actually may not be steep enough but you can cut with the PeQ as well up to -14.5db with a very low q, sort of like a notch. Hopefully you won't need the Peq elsewhere for it only has one channel available. But for $349 on sale, seems like a god deal to me.

[solid7]

I will probably stick with the EP2500, and use a Reckhorn B-1, as recommended in another thread.

Yeah, it sounds like a monster, though...

[eyekode]

Note that as for box size, if you are putting 2 18's then you will be hard pressed to get a box < 4.5 ft^3 (127l?). This is roughly a 20" cube. Might as well go up to the 150l box to really reach low!

[bobgpsr]

Opposing the 2100 gram PR's is good for canceling out the effect on the box of the reaction to the thrust of the heavy moving PR masses. Keeps the whole thing from walking.

I like my 195 litre internal volume DIY with a CSS SDX-15 driver and two 18" AE 2500 gram PRs. Tuning came out to be 15 Hz as desired. The Mackie M1400 pro amp that drives it has a freq adjustable high pass filter -- mine is set to ~15Hz.

If you can get Excel then the free UniBox download is very good for modeling PR subwoofers.