Custom 8" Enclosures
 

Well, after mulling it over for a few months, I decided to bite the bullet and fab up some custom fiberglass enclosures. I was planning on using my older 10W3D4's because I love how they sound, but after some measurements and mock ups I didn't want to sacrifice the room they'd require. Instead, I researched 8" subs and found favorable reviews from the SQ crowd for the JL 8W3V3. I was very skeptical that two 8's would produce the rich lows below 60Hz with the same ease the two 10's do, but after finishing these enclosures (approx 0.35 ft³). Since I wasn't going for ground shaking thunderous power, I had reasonable expectations that the two 8's would do the job just fine.

I didn't take any photos of the first layer and first steps, but I pulled the two interior panels and the trunk mat and placed them on a work table. I then coated the layup area with blue painters tape to cover every little nook and cranny, and then everything else with trash bags to prevent spills. I cut a small block of wood and taped it in place over the trunk security button so the fiberglass wouldn't rest against it. In total I used a bit over 1.5 gallons of 3M all-purpose polyester resin from Home Depot, two sq yards of fiberglass mat, and about 3 sq yards of other fiberglass fabrics (some medium weight, some heavy). Polyester resin REALLY stinks and uses MEKP (Methyl Ethyl Keytone Peroxide) as an activator, and it's nasty stuff. I work with various resins, hardeners, catalysts, and activators at work, so this stuff isn't exactly foreign to me.

Anyways, after the first several layers had cured to an appreciable thickness (about 1/4"), I trimmed them to a shape that was expected to provide about 0.35 cubic feet, and that would place the subs where I wanted. I cut some small blocks of MDF to support the rings in three places, and as you can see, I also used a sheet of MDF for the bottoms. I ordered some MDF rings from ebay, they are machine cut from a single block of 1" thick MDF and the fitment was spot on with the JL 8W3V3's. I drilled them and used metric nut plates. These turned out to cause me some headaches later because a couple got cross threaded and spun in the MDF, chewing it up. In hindsight, I'd either skip these or glue them in place. But, in the end, these nut plates allowed me to use black hex head bolts that looked really slick. Build thread for the rest of the audio system is here.

It's not shown but you can sort of see it in the later pictures, I added a rectangular plate for the terminal cups. It was positioned before the fabric was stretched over to ensure I had a place to mount my wiring.

http://i11.photobucket.com/albums/a1...closures01.jpg

http://i11.photobucket.com/albums/a1...closures02.jpg

http://i11.photobucket.com/albums/a1...closures03.jpg

After the rings were mounted, I stretched on some t-shirt material from the local fabric store. This was temporarily glued in place around the back side with a hot glue gun. More of the same polyester resin was brushed on and allowed to cure. This created a firm formed shell for more material to be laid onto. Once the resin was cured, I ground away the fabric where the hot glue was used. It ground away easily as it was soaked with resin. I didn't want too much wrap, only an inch or two, and I also didn't want the hot glue residue in my bond line when the outer layers are laid up.

http://i11.photobucket.com/albums/a1...closures04.jpg

http://i11.photobucket.com/albums/a1...closures05.jpg

More fiberglass and resin, and eventually dark gray felt was applied with spray adhesive and more stretching. It was trimmed around the edges for a clean look. The wiring was installed, and then they were wired up. I wanted the connection point to be accessible so they can be removed easily for track days, so it's tucked right up at the top edge, out of sight but still easy to reach.

http://i11.photobucket.com/albums/a1...closures06.jpg

http://i11.photobucket.com/albums/a1...closures07.jpg

The end result? I am VERY happy with them! I mentioned I was skeptical of the 8's, but sweet Jesus do they sound good. Very accurate, tight, clean, and rich bass.

http://i11.photobucket.com/albums/a1.../JL8W3V301.jpg

http://i11.photobucket.com/albums/a1.../JL8W3V303.jpg

http://i11.photobucket.com/albums/a1...4100160001.jpg

edit: updated the amp rack, click here for the rest of the audio build.

http://i11.photobucket.com/albums/a1...ti/PDXV915.jpg

Overall I'm extremely happy with the results, and they sound fantastic! If they sound this good brand new, I wonder what they'll sound like a month from now once they're broken in... :D:D:D

I'll upload a few more pics this week, I was running out of daylight.

Those look great. I wish I knew how to do fiberglass work. Well done!

How deep is the box? The reason I ask is I have 2 8's I'm installing in a few month, and I'm tying to decide on my design. My subs are 5.75" deep, of reference.

Got pics of the amp rack? And how its installed?

This!


I-Tapatalk

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misssed that line in the OP :sigh:

Nice build and I dig the amp rack. I want to try to glass something up but im not nuts on breathing all those fumes

These JL's are 4.63" deep (from surface mounting), and the magnet diameter is 4.75". Since these 8W3V3's were the focus of the design and the most compact shape was the mission, the enclosures were designed around them. That's kind of why the face of the enclosure is sort of flat, it's almost as if the corner of the trunk was held at an angle and filled like a puddle. The ring's placement brought them almost as close as possible at the angle I wanted without physical interference with the back of the shell. The magnets have about 3/16" clearance, IIRC... I was also looking at the JBL GTO804 which is slightly more shallow, but the basket is a huge wraparound type that made the backside really wide, they likely won't fit. If I were designing another enclosure, it wouldn't be difficult to get them to fit, it's all decided by where the ring is located, angle, height, positioning... It could be that a slightly more laid-back angle would be all that's necessary to get your subs to fit a similar shape.
Me either, of all the resins and epoxy systems I use at work, polyester stuff is the worst! We can smell it clear across the hangar. Home Depot sells good half-face respirators for about $25-30. You'll want one with replaceable organic vapor cartridges. A box if 100 nitrile gloves is about $10-12. Keep a large bottle of isopropyl alchohol and paper towels/shop towels around to clean up!

Bout to do this exact build. Was debating doing 1 10 inch but after seeing this couldnt resist two 8 inch. Thanks so much for all the input. I might need to hit you up for some more details.

How did you position the rectangular plate before putting on the cloth? What did you use? Something of similar size? How did you mount it?

And do you need two amps? Can one amp suffice? What are the advantages of having two?

Good catch, I forgot to mention those! I used two rectangles of 1/4" MDF, mounted much the same way as the speaker rings. The terminal cups are from radio shack. The rectangle was cut to shape and glued in. I had to carve out an area of glass at the top to ensure the fabric would stretch smooth over it and still give me some clearance to get to the connectors while they're installed in the car.

The two amps are different, one is a PDX 4.100 for the front mids and tweets on individual channels, the second amp is a PDX 1.600 for the subs. It's a mono block amp and both subs are 4ohm, wired in parallel so they are 2 ohm. Normally this would increase THD a bit and increase power, but with this amp it doesn't make much difference between 2ohm and 4ohm. Anyways, the amp has recently replaced with a single PDX V9, which has 4 100 watt channels and a single 500 watt channel for the subs, with this setup it's plenty of power. Ill post more pics soon, I'm in the process of making a smaller rack now that I only have one amp.

Edit-
To answer your question, two amps are not necessary, but could certainly be used. If you have two 4 ohm subs, you could power them via a two channel amp to maintain 4 ohms each, which is easier on the amp and produces very slightly less THD, but for subs it's really not audible. I chose a mono block for simplicity and they're designed for subs anyways. The V9 sub channel is the same.

Thanks! Also if I'm planning on just putting in an amp and two 8 inch subs should I leave the stock amp how it is controlling the rest of the speakers and just the amp that I get to power the subs?

Sure, that would work just fine. The only thing you need to figure out is how you're going to get the signal to the sub amp. Are you keeping the factory head unit or upgrading it as well? If your factory head unit doesn't have any preouts, I think you could tap into the line-level signal input at the OEM amp.