Please help me design a PR subwoofer

[mike c]

thanks Mike P!

[Warmon]

Wow! 59lbs. that thing reminds me of Angelina Jolie's lips. it's

[mike c]

c'mon ... this guy needs your help!

[Mike P.]

Right on, Mike. Teach him when he's young!

[mayhem13]

Ok given your driver and i beleive you said TWO Pr's, 100 liter box is ideal with 1500 watts and 2500g load each PR gives totally flat response down to 17.7hz at 115db with room to spare if you have more power to feed and i mean without high THD's so a pro amp is the only way to get there. You will need to roll of below 18hz with a steep slope. The driver will bottom at 16.4 hz without it. Overall a really nice set up in only 100 Liters. Hope this helps and lets see some pix when you're done. I'm waiting on 2 JLaudio 13w7's refurbished for a similiar project with 2 18 PR's 2100grams to 3.6hz in 170liters. This system will do 121db flat to 16.8hz with 2200 watts.

[WmAx]

mayhem13 wrote:

With the pr extension you're gonna have at extreme levels, you will have to put the PR's on opposing sides or the cabinet is gonna rock with the weighted movements. Your eD driver is capable of full extension of those PRs at 18 hz.

Assuming soft rubber feet on a wood floor, or spikes on a carpeted floor, and factoring the weight of this finished cabinet with drivers and PRs is going to weigh in the range of 200 lbs. assuming a moderately braced cabinet; it will be stable with the drivers and both PRs on the same side. Also, even if it was substantially lower in weight, there would not be an issue in practical use - in real music or movie use - one would use but a small fraction of the maximum output potential possible with this proposed design.

-Chris

[mike c]

mayhem13 wrote:

Ok given your driver and i beleive you said TWO Pr's, 100 liter box is ideal with 1500 watts and 2500g load each PR gives totally flat response down to 17.7hz at 115db with room to spare if you have more power to feed and i mean without high THD's so a pro amp is the only way to get there. You will need to roll of below 18hz with a steep slope. The driver will bottom at 16.4 hz without it. Overall a really nice set up in only 100 Liters. Hope this helps and lets see some pix when you're done. I'm waiting on 2 JLaudio 13w7's refurbished for a similiar project with 2 18 PR's 2100grams to 3.6hz in 170liters. This system will do 121db flat to 16.8hz with 2200 watts.

i only managed to snag one PR ... what numbers are we looking at for just one ...

this subwoofer won't be working alone so i wouldnt need it go ultra loud.

[mayhem13]

1 PR would be at about 114db 30hz and 110 db to 18 hz-still very respectable. Roll off below 20hz for safety but without rolloff this sub will play to 16hz with the PR maxing out. I suggested the Funky 18 PRs for the 72mm of xmax. Using that PR would be devastating.

[mike c]

found this:
http://answers.yahoo.com/question/in...2113651AAYB8gZ

all i need now is the effective diameter of the PR or to solve this:
R = (Sd/PI)^0.5

Sd is .110m^2

im kinda rusty with raising by half exponent, how does that work?

[mike c]

wild guess: im looking at 3 cf box with just 300g of weight? hmm doesnt sound right, or if it does, I can make a smaller box since the PR can handle more weight

[Mike P.]

mayhem13 wrote:

1 PR would be at about 114db 30hz and 110 db to 18 hz-still very respectable. Roll off below 20hz for safety but without rolloff this sub will play to 16hz with the PR maxing out. I suggested the Funky 18 PRs for the 72mm of xmax. Using that PR would be devastating.

Anthony, are you modelling the TC Sounds passive?

[mayhem13]

Yes thats the tc passive at 2240grams weighted. Modeling PR's specs isn't that difficult if you know the weight at a given Fs-Like a port-check out DIYsubwoofers.com for the math and all the other great info. A little dated but math is math. Most sub designers like PR's at 2 to 1 ratio to maximize efficiency. The whole point of these systems is reduced box size and no port resonance but at a cost over ported that being the PR's themselves. While PR systems generally cannot match the efficiency of large ported systems, they get pretty close without the size/port res. tradeoffs. And PR systems do like drivers with big motors and lots of power which does cost. Either way your project sounds like a success in the making. Just keep the box net volume at or slightly above 3.5 cubes. I would down fire the driver and front fire the PR.

[mike c]

thanks! 3.5 cubes.

but i would kinda like to do a front firing sub (e.g. 13av.2 at the bottom (because its heavier), and the PR above - kinda like a reverse Velodyne 1812)

was there a specific reason i should down fire the 13av.2? or was it just to keep the box size small?

[mayhem13]

You can pick up a few db downfiring and it will mask driver excursion noises assuming your floor is carpeted. I'm sure that driver at maximum xmax is flapping away. I'm afraid that much moving mass on top from the PR may make it a little unstable. You could front fire the driver and rear fire the PR instead-you'll just need 6" clearance to the wall behind.

[mike c]

by going with a bigger enclosure size, it will give me better performance right? i cant seem to limit myself to 3.5 cubes if i wanted a front firing setup ...

i prefer front firing subs

[mayhem13]

Much bigger than that and there won't be a spring of air inside the box substantial enough to control cone excursion-very important in a PR design. Anything wrong with the rear firing passive?-only very low freq from the passive and definately not something you ears can locate. No sonic advantage to both firing forward-may even result in some cancellations and phase issues.

[mike c]

i just like looking at the front firing drivers

hmm, ok, so 3.5 cubes max. ill maybe stuff the box with tons of bracing to keep the box volume small and heavy down low.

option 2:
maybe one forward firing, the other side firing?

[mike c]

general idea til i actually receive the PR:

23 x 15 x 38.5 (if possible, i'll go 22 x 15 x 38 or smallest i can go)

1"



black things are supposed to be air pockets inside put there to kill enclosure volume and keep the weight heavy at the bottom and back ... i can fill up those pockets with "bracing" to add more weight.

and i will also add bracing around the drivers to kill some more volume.

[mayhem13]

Looks good if you have to use only 1 PR. You could fill those voids with concrete cheap and easy or plaster-cheaper and easier. This should help stabilize it against rocking. At the base i would contruct a nice platform roughly 1.5x the actual cabinet footprint and use spikes if on carpet and rubber feet if on hardwood/tile. Looking forward to seeing it finished-good luck and keep us posted.

[Warmon]

From everything I read on PR's [ain't no expert]; aren't you are going to have serious issues with vibration and possibly even tap dancing unless you locate that single PR directly behind the sub? I would definitely get it below center of gravity.

[Mike P.]

I'd suggest filling the voids with sand in platic bags. Much easier and cleaner.

[mike c]

my business is steel, so adding steel weights should be no problem. i guess ill have to build it and play with it before i do any "finishing"

i wish i could go deeper to keep the footprint balanced, but that would add a LOT of enclosure volume i will have to kill again ...

id up fire the passive if i could, but read that pr's shouldnt be up firing or down firing (but why are they boxed as up-firing during shipping)

[Mike P.]

Adding steel to the bottom sides should resolve any tipping issues.

[mike c]

how much power do i need for this thing?

i can get a 1000w class d amp for about twice the price of a behringer EP2500 (b&o 1000ASP module at d-sonic.net)

if 1000w can get me through (vs. behringer's 1600w), i'm willing to pay the price difference.

[mike c]

dry fit