Dual 18" P-Audio sub opinions on a budget, limited options due to the wood I have.

[Sastusbulbas]

Dual 18" P-Audio sub opinions on a budget, limited options due to the wood I have.

Hello,

Some time back I had thought about making a pair of subs, dual 18, similar to the JBL 4642A but on a budget.
I had a lot of free wood, but I never got the drivers, and this got put away for a few years.
I had cut the wood, but I had nothing suitable for the internal bracing, just a load of 45mm + 45mm square lengths of timber. The wood I have.

4 panels of 46"+28" 1" chipboard.
4 panels of 48"+24" 1" chipboard.
4 panels of 28"+24" 1" chipboard.
Lots of long lengths of 45mm+45mm.
a few good lengths of 1cm thick sonotube 76mm internal diameter.

I must have calculated a pair of 48" wide, 30" high, 24" deep, ported cabinets for twin 18" subs with that. |Not even sure what volume that equates to. The PC that had the info is gone, as are the files. I cannot get WinISD to work on this PC for some reason?

Not sure how I was planning to brace and frame the inside of that with the 45+45 though.

I am thinking of four P-Audio E18 400S 18" drivers? Unsure of port length. Thinking of a 25Hz tune? Would this work for a budget large cinema style sub?

This is to compliment a budget cinema set up in a large room, it is either 60ft+60ft or 80ft+80ft.
There are eight Cerwin Vega V152, two for center channel in a 7.1 set up. An AV amp drives them, with a Yamaha PS3500 doing sub duties with it's 25hz filter on. Currently two JBL 15" car subs in 116ltr cabs are not doing too well, sort of getting lost in the mix due to the 103db sensitivity of the Cerwin vega's in that size of room I guess? A lack of slam and weight.

Any ideas or opinions would be welcome, I have a rather tight budget, hence the P-Audio drivers.
I have tools, the above wood, plenty of wood glue and screws, and a few nights left this week to get the work done.

 

[Inductor]

4 panels of 46"+28" 1" chipboard - Front baffle 48"+30"
4 panels of 48"+24" 1" chipboard - Top, bottom
4 panels of 28"+24" 1" chipboard - Sides
Cinema Sound LF & Subs
http://www.jblpro.com/pages/pub/cinema/4642a.pdf
http://www.jblpro.com/pages/pub/components/2241.pdf
(clone)
http://www.p-audio.co.uk/pdf/E18_400S_.pdf

If you are using 1" chipboard this will give 464.6L for the enclosure plus vent (6-8L) and drivers 2x each (Volume Displaced by
Driver: 8.5L),

8.5L v. displaced by driver 1
8.5L v. displaced by driver 1
7L +/- port volume
------
24L

464.6L - 24L = 440.6L

Totaling 440.6L (net volume), not counting with bracing, away from the 506L announced by JBL.
I modeled a 506L (net) enclosure what was acceptable for a clone (yours) and a 440L what is not so much so for your clone sub speaker (see below). These drivers not being a replacement for the JBL 2241H 18" require a much bigger enclosure. If you need to know the ports please post if you will make them round or square (and in this case the thickness of the ply).

 

[Inductor]

In the case of a rectangular port (inside dimensions) you have:
40cm x 10cm with port length 15,5cm
or 3 round ports (internal):
11.8cm diameter x 12.3cm for the port length.

That was for the JBL with 506L net. In your case with ~440L enclosure, ports will be longer, with 16cm for the round port lengths and 19.5cm length for the rectangular ports (internal).

 

[Sastusbulbas]

Thank you very much.

I can use either 18mm MDF, 1" chipboard, or tube, 96mm outer diameter, 76mm internal diameter for ports. I don't mind if it is a slot from top to bottom either. whatever takes the least volume but aids bracing I guess.

I guess recessing the front baffle an inch or so would lose too much internal volume also.

I can use a mixture of 45mm+45mm baton and 2"+4" timber for bracing, but guess I would want to try and minimize the amount I use? Do I need to try and keep the resonance of the cabinet high when tapped though? Would 45mm baton along all the internal edges and as a couple of figure 8 braces be overkill?

Edit, Though would 1" chipboard need such extensive bracing, or would bracing and a port arrangement along the lines of a G-Sub be better? Would that be better using the 24" as height? If I need a grill n recess I could always add baton later.

 

[Sastusbulbas]

After thinking of this a little,

I am wondering if I could use the P-Audio E18 400S 18" drivers as dual 18" in the following enclosure?

I will stick with the materials I have, and use either 18mm or 25mm material for bracing the rear of the cab, as is seen in the G-Sub, but with the added lengths for the internal dimensions of 46" + 28". I seen some spare chipboard at work so will measure it up, not sure if it is 18mm or 25mm.

The cabinet external dimensions will be 48" wide, 30" high, 24" deep, but the front baffle recessed. I am unsure if it should be 1" or 1 1/2". As I would like a full grill at some point if it is not too costly.

If I have 1" internal bracing as is done in the G-Sub, with an internal size of 46"+28"+22 1/2", what width and depth of 28" high slot port would be needed?

I would not want to go below 25Hz, and would like to maintain decent LF performance for a budget cinema sub without compromising the drivers too much. What sort of port tuning would be best suited to this cabinet and driver?

 

[Shadydave]

Brace well, brace often

2 x 18" subs.
You better brace that box well.
Do a search on bracing.
Panel braces with most of the material cut out are usually the strongest, but if you need to save wood you can go all the way around the box, every 6" and put 3 or 4" wide "studs" made from the 3/4 or 1" material that the panels are made from.
Put them against the exterior panels with glue and screws
Think of what the framing in a stud and drywall house looks like, you would just want the studs around the entire perimeter of the box.
You want it to look like a house with the siding on but no drywall inside.
Then running several 1" dowels across the box from side to side and front to back will also help.
Do a search on bracing, there are many pictures.
If you do not brace it well, you will be sorry later on when the box makes a bunch of obnoxious noises.
I have burned subwoofer boxes that I built before I understood bracing.

Dave

 

[Inductor]

Let's consider the initial dimensions:
48" x 30" x 24" = 464.6L (- 24L) ~ 440L (net)
(440L = 15.538ft³)
let's consider your new dimensions,
48" x 30" x 22 1/2" = 432.6L (- 24L) ~ 408L (net) w. baffle recessed 1 1/2" from 24"
(408L = 14.408ft³)

P AUDIO E18-400S, 408.0 L@28.0 Hz
"What width and depth of 28" high slot port would be needed?"
With a port surface area of 28" x 2 1/2" (S: 313.95 cm2 or 71.12 cm x 6.35 cm) you need a length of 8 35⁄64" (21.69cm), internal dimensions of port.
Let's check the volume of the port (1" chipboard), now for the new squeezed dimensions of the BR enclosure:
30" x 4 1/2" x 7 1/2" = 0.586ft³ = ~17L
Let's recalculate the sub and port with the new data, for 398.0 L@28.0 Hz;
28" x 2 1/2" port area and 8 53⁄64" length (22.43cm).

P AUDIO E18-400S, VB = 390.0 L, FB = 29.0 Hz
(Note, this inside volume required for precise calculations, as you may notice is faraway from the stated net volume by JBL of 506L)
Now let's consider the situation you are in, with this driver (2x) and box, if you keep squeezing it with added bracing and all. Let's consider the new volume taken by the 1" wood port and a new port dimension of a slot port, with a surface area of 28" x 3". This will give you a final port length of 10 17⁄32" (26.75cm).

Your intention of not having very low extension is good for the protection of the woofers. Have fun.

I would not want to go below 25Hz, and would like to maintain decent LF performance for a budget cinema sub without compromising the drivers too much. What sort of port tuning would be best suited to this cabinet and driver?