DIY JBL 4645C

mantha3

Member
2010-10-18 6:20 pm
I had an opportunity to hear a JBL 4645C and loved it. I have a pair of Wayne Parhams 4PI speakers and thought the 4645C would be nice to check out. I was thinking the 18" 2242H would sound nice with the 2226H 15" in the 4PI. So I got a lot of work done on the sub this weekend.

The build is using marine grade okoume 3/4" ply. Much like Baltic Birch but has a veneer I can stain. A mahogany looking veneer. Pretty nice and I suck at veneer work.

Baffle started a week ago. I have two layers of 3/4" so the face should be pretty stiff.. Full bottle of wood glue between the two layers -
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mantha3

Member
2010-10-18 6:20 pm
I had a little trouble finding a port with the 7-1/4 to 7-1/2" inside diameter port. I measured the port on a 4645C I saw at about right between 7-1/4 to 7-1/2" inside diameter and about 12" long in port.

I found 8" Schedule 80 PVC. This stuff is thick walled and heavy. A 12" section of this stuff is a hair shy of 10lbs. the pipe is about 3/4" thick... Nice as you can round the inner edge on the port side inside the subwoofer. I didn't want to use cardboard for the port...

I cut the opening of the Port using a smaller hole... So I can flush cut the port opening to the port. I use 4 "L" brackets and some worm gear fasterners used for home heating. I used a 6" and 3" worm gear and connected them together.. Cut a recess hole for the port to go in and PL glued it in.. Then used the fasteners and covered them and all with more PL adhesive

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mantha3

Member
2010-10-18 6:20 pm
man I sure hope it sounds good when all is said and done... I put another coat of varnish on it.

I thought some bracing would be a good idea... On brace spanning the rear wall behind the woofer and then another cross brace spanning the ceiling... LOTS of wood glue.

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mantha3

Member
2010-10-18 6:20 pm
Notes on this - I was looking at the JBL 4645C (Stage/THX stadium movie) and S1S (Nicer looking home theater marketed) subs... I liked S1S for being a bit shorter, narrower and deeper... So my sub is a bit more like the S1S but has the 10 cubic feet of the 4645C and the same single port

4645c H1010 x W67.4 x D45 = 225 liter (internal)
S1S ex H87.6 x W53.3 x D55.9 = 185 liter (internal)

My sub is 22" Wide X 22" Deep X 36" tall.

I'll add the cut plans and cut plans later.

I thought I'd post all this in case someone down the road thought to build a 4645C. I realize none of this is new... Just a big old ported JBL design with some minor tweaks.
 

mantha3

Member
2010-10-18 6:20 pm
More notes -

I found in another forum post the dimensions for a standard JBL 4645C. I saw a 4645C in person and the dimensions I could verify were good. I could not open up the 4645C

JBL 4645C cabinet dimensions

25 ½” W x 39” H x 17 ½” D

Front and rear baffle are made from 1” MDF

Top, bottom and sides are made from ¾” MDF

Internal brace is ¾” MDF 37 ½” H x 24”W with cutouts and centered front to back

The cutouts are 4” x 17 ¼” and 25” x 17 ½”

This leaves a 3 5/16” thick border around the inside of the box and 2” behind the driver

1” fiberglass behind the driver, on the bottom and lower sides

Above the driver area there is nothing except paint behind the port opening

Front to back stiffener at the top center of the driver cutout is 5 ¼” x 16”

Port ID is 7 1/4”, OD is 7 ½”, tube is 1/8” thick paperboard material

Port length is 12 ½” from front of baffle to end of tube

Tube is rabbeted into baffle 5/8” overall length of paper tube is 12 1/8”

The front and rear baffle boards are set in ½” from the edge of the side boards.
 

mantha3

Member
2010-10-18 6:20 pm
Thinking more for doing the FR measurement. I may..

What I've built thus far for speakers I built from tested/verified designs from Wayne Parham and Troels Gravesen. Given that I didn't buy the measurement gear/software. I didn’t want to learn the hard way that what I built was off… Can get expensive learning from mistakes with good wood, parts, measurement gear, time spent etc. Oh, that and I’m kina lazy. I talk of doing this sort of FR measurement stuff but end up in a chair with a beer in my hand liking what I hear and the motivation is gone. Or my wife tells me to stop playing with the audio toys for a while.

I was originally thinking of just building a 4645C exact... Same port and box... I deviated some so this sub would fit better where I wanted to place it. From what I understand with sub woofers the dimensions changing are not such a big deal.. Just make sure you have the cubic feet you need and the port size right generally for a big old ported sub.

Port size is the same inside diameter and length as a stock 4645C (At least the one I saw and listened to in person.)

Overall box size in cubic feet is about the same
Stock 4645C - 25 ½” W x 39” H x 17 ½” D - 10.072 cubic feet or 8.333 cubic feet with a 3/4" thickness
My DIY 4645C - 22"W X 36" H X 22" D - 10.083 cubic feet or 8.39 cubic feet with a 3/4" wood thickness

Same JBL 2242H driver used in both

So… For a subwoofer I don’t feel this is too custom from a stock 4645C.

One down side… With all the wood, fat and heavy port and the 2242h… This damn thing weighs in around 200 lbs if I had to guess
 

mantha3

Member
2010-10-18 6:20 pm
I did see some write up on that "They have less resonance from same wavelength modes and harmonics" with the bracing sticking out of the rear wall and the ceiling this should address that. I have a four inch brace extending down from the ceiling and a 5 inch brace extending inward from the rear wall. this was the type of solution to this that I've seen used and verified with success else where. With some luck I'll be good.
 

mantha3

Member
2010-10-18 6:20 pm
Inducer,

I don't have the woofer installed as of yet. Do you have thought on how to avoid issue without scrapping the box? I understand the concern you have brought up... I see many ported subs marketed that are basically square boxes with rear ported ports...
 

mantha3

Member
2010-10-18 6:20 pm
One other note.. the interior is not square.. The Face wall is 1-1/2" thick so it is extending in more than the side walls.. I read more and the detail you are mentioning is more true when top to bottom and side to side is uniform.

So the interior has the face extending in.. With the perpendicular bracing.. So I don't see the wave issue quite so much.