[slim2fattycake]

Okay, so this sub is going to be used 80% for movies and 20% for music. This sub is going to be in a basement that has an open plan and is fairly big. the room is 41ft by 13.5ft roughly. here are some pictures of the area.

here is the entertainment system:

 

[slim2fattycake]

my goals for the MJ-18M are to be tuned at 20hz, subsonic filter at 17hz with 660 watts of input power. I am going for a 11ft cubed internal volume. The gross volume will be 12.66ft cubed. the box will be 23.5 width X 40.5 height X 27 depth. the port will be 22 width X 2.75 height X 31.51 length.
here are some more pictures

 

[slim2fattycake]

these are my graphs using WinISD.

 

[slim2fattycake]

Here is the rest of my set-up.

50" diagonal hitachi about 10 years old. i really want a projector but i dont have the money yet. i am looking forward to it though. o and the sub box will be on the right side of the entertainment center besides the wall. everything will have to be moved over 3 inches to fit the box in there.
2 Acoustech HT-75 towers
1 sony center channel (about 12 years old)

2 venturi DV32 for the rear surround

2 front sony towers (old about 12 years) for the side surround
I want to switch them with another set i have laying around that are more modern but I have to fix one problem with them first. then these sony towers are going into the bathroom.

The sitting area: there is a single couch on the right and a 2 seater couch on the left.

You have seen the new sub addition already.

and then these are the rest of the equipment. I may have to build a stand alone rack for these because i cannot see them without having the cabnet door open. it is kind of in the way especially when its dark.
Top to bottom:
yamaha RX-V663 receiver, philips dvp-5960, wireless microphone system, eQ.2 processor, california dvd player for karaoke midi music with over 500 songs, mostly vietnamese. ( i dont know why asians like to sing karaoke so much., and then the behringer ep1500

ps. the halloween stuff is my girlfriend's idea. she thinks it makes the basement have a more homey feel.

 

[slim2fattycake]

okay now onto the build.

i started cutting some mdf today and this is all i have done in 4 hours, thats with cutting all the panels and port for the box. i still have to cut the braces though.

this is the port

the box

it was $75 worth of mdf and it was heavy. i completely forgot how heavy one sheet of 3/4 inch mdf was. but most of the 4 hours was wasted on trying to use cut things to save on not having to buy more wood.

 

[slim2fattycake]

I will paint the outside of the box a high glossy black color called midnight black. I am debating on using polyfill in the box or egg crate foam. I already have a bit of the egg crate foam in the garage i can use. i may go for that unless someone wants to persuade me not to.

I am tired now after all the posting. . but ill try to do some more tomorrow after work.

 

[Mike P.]

There are lots of builds with egg crate foam and other damping materials. I've always recommended it and have used it in all my subs as that is what I've been taught and have read from a book on speaker building back in the 1970's. Recently the use of egg crate foam has been debated. Some say it has no effect on damping the back wave of the sub, which is what it's supposed to do. I have personally tested 2 identical subs, one with and one without and I can hear a difference. But as was pointed out, that's not very scientific way to test.

 

[slim2fattycake]

will the egg crate foam take up volume of the box?

 

[Mike P.]

Not if it's open cell foam.

 

[slim2fattycake]

can you give me an image of the open cell egg crate foam?

 

[Mike P.]

Sorry, I'm away at work for a week. It's the same foam WalMart and Sears sell as mattress pads. If you look at it closely it has tiny holes in it like a sponge.

 

[Ricci]

Hey Slim...How's the build goin?

 

[slim2fattycake]

im doing more now. i had tests in a lot of classes and was swamped during the week.

 

[Guest]

I will paint the outside of the box a high glossy black color called midnight black. I am debating on using polyfill in the box or egg crate foam. I already have a bit of the egg crate foam in the garage i can use. i may go for that unless someone wants to persuade me not to.

I am tired now after all the posting. . but ill try to do some more tomorrow after work.

This has been beaten to death on other forums with tests to back it up so i feel fairly confident saying this...

Poly isn't as good as fiberglass, but both are better suited for a sealed cabinets to slow down the waves and make the box appear larger than it really is. You can do the same with a ported cab, but making it 'larger' will affect the tuning and lower the total Q iirc. In other words, you want to line ported cabs instead of stuffing them, unless you built a small box on purpose and predicted the stuffing as part of your tune. Lining can be done with anything, including the fiberglass (rolls of 3-4 inch thick) but it's likely the stuff will make it outside the cab through the port with use, so people usually stay with egg crate foam and other more user friendly materials when it comes to ported configs. 1.25 inches of foam won't stop a 20 meter wave in it's tracks, but it does make the box a bit less resonant even if you used a 'dead' material to build it such as MDF. I would go with several layers loosely bonded together and to the walls with spray adhesive. Make sure none of it touches the port entry or gets inside it. I've also lined a pair of speakers with poly that came in sheet form, about 1.5 inches thick non-flufffed. It worked well for dampening the midrange, which isn't really applicable to a sub unless it's a Bose unit :rofl2:

 

[slim2fattycake]

wait, are you saying to just spray adhesive on the walls instead of egg crate foam? i know you said fiberglass is better but i have no experience with fiberglass so i will not try to venture that way yet.

 

[Mike P.]

He's saying to use a spray adhesive to glue the egg crate foam or fibreglass insulation to the cabinet walls.

 

[slim2fattycake]

okay so i had cut some more today and had one of the front panels done. when i went to cut the circle out for the 2nd front panel (2nd baffle) i needed to have a diameter of 18.125 inches but its only 18 inches exact. I used a circle jig i rigged up to cut it. i was guessing it was going to be off so i could get that .125 but it came out to be exact 18 inches. what can i do to make the circle bigger without messing up the perfect circle look? the 2nd panel was going to make the sub flush with the box and was going to be .75 inches in the length of the port as well. so what can i do to fix this problem?

 

[tenzip]

Put the circle you cut out back in with a board or two screwed to the back to hold it in place, and try again. I assume you're using a router. As long as you're careful about keeping the cutout centered in the hole, you should be fine.

Or get out the sandpaper and elbow grease.

 

[slim2fattycake]

sandpaper and elbow grease doesn't sound too pretty. . i'll try the board thing but i have no idea what you're talking about the two screws.

 

[Mike P.]

He's talking about the piece removed from the sub cutout. If you put it back, it's loose and needs to be attached firmly. This can only be done by centering the cutout piece in the hole, use a strip of wood long enough to attach the cutout piece to the baffle. After the cutout piece is attached you can use your router with the circle giude to trim a liitle more off the baffle. Here's a bad pic in Paint to give you an idea.