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Need Help: JBL 2242h with a slotted port

post #1 of 37
Thread Starter 
Backstory: I used to have (> 15 years ago) a Peavy Black Widow 18" in a DIY enclosure that I used in conjunction with a DIY 12" sub. This was done on the cheap while I was going through college.

I've since moved on to a pair of SVS subs that I've been mostly happy with. However, I start finding myself wanting for that massive mid-bass impact that sound reinforcement speakers can deliver for movie soundtracks. So, I've gone out and picked up a JBL 2242h... but now realize that I've no idea what to do with it.

It seems in looking around the net, that internal volume of the enclosure should be between 9 and 12 cubic feet and it should be ported and tuned to 22 - 25 hz, EQ'd with a boost @ 25hz, and have a subsonic filter around 22hz to prevent excessive excursion under the tuning frequency.

I've got a false wall up front in my theater that sits 18" from the actual wall...so I'm limited in the depth of the enclosure. The rest of the enclosure can be as tall/wide as it needs to be.

I was thinking of stacking the SVS subs side-by-side on top of where the 18" driver is in the corner of the room so it may be advantageous for the enclosure to be low to the ground as well?

I need help in designing the overall dimensions of the enclosure and validation of what I've read online so far. I'm also wanting to have a slotted port, as it seems that an adequate round port would be enourmous.
post #2 of 37
Thread Starter 
Just incase the environment isn't clear, here are some pictures:
Behind the fake wall... Blackout cloth over the window on the "real" wall on the left, fake wall on the right. It's framed, and then wrapped with black speaker cloth.


This is the view from the front of the room
post #3 of 37
One is tuned to 25hz with 400w and the other is tuned to 35hz with 700w. Both with a 4th order high pass.
LL
post #4 of 37
I don't know about slot porting it, But I know that about eight feet with an 8 inch port (the sonotube usually runs a little smaller, like 7.70) like 17 inches long gets you about 22hz and mine was flat in room to about 18-19 hz.
Dont worry about a boost, you room should do that, and you'll be fine with a hi pass at 20, just wanna make sure its steep. If you use Crown XTI 2000 or 4000 you'll get your power and hipass/eq in one package.

I can dig through my old notes/sims if you need. Youll get your mid bass slam believe me. I actually have two more to build just NO time.
post #5 of 37
chromy, you are not alone and absolutely on the right track.

that is the driver used in jbl's top of the line, cost no object, reference system.

this is the enclosure:
http://www.jblpro.com/catalog/Genera...?PId=206&MId=1

i would shoot for 8 cubic feet and tune it to around 25hz, since you have other subs for below that.

don't skimp on the amp. 2kw is a reasonable amp for that driver. that should get you up into the upper 120 db range, which is what you are looking for for peaks. my only concern would be if your mains can keep up.

3rd order highpass at 22hz would be a good protective measure.
post #6 of 37
in 8 cubic feet, an 18" wide by 2.5" high and 17" deep slot port tunes the cab to around 25hz. anybody with winisd or similar can tell you similar information in two seconds. if your slot port ends right at the back wall, the tuning will be a bit lower than the model.
post #7 of 37
Quote:
Originally Posted by Tack View Post

Youll get your mid bass slam believe me. I actually have two more to build just NO time.

Tack, where do you set your crossover point?
post #8 of 37
Thread Starter 
Thanks guys! I'll be building this out starting in a few weeks. I'll be sure to take some pics and let post them!
post #9 of 37
Quote:
Originally Posted by Erich H View Post
Tack, where do you set your crossover point?
At the time, I experimented with 40 up to 120 with good results. I didn't get a bunch of time with it until I dropped it in the garage and killed it. My Td18 build was originally scheduled for a 2242 and the TD was a drop in replacement.

When I get time Ill exchange one of the new 2242s and check out any differences sine I don't see firing up the table saw for some time yet.

http://www.avsforum.com/avs-vb/showthread.php?t=1141754


Chromy, keep in mind this driver has 54 mm of XMECH so its pretty hard to hurt. I believe if the XMAX was rated similar to the way some of these ID mfgrs do, it would be a larger number that what JBL lists. No offense to any ID cos, I just think they're a little more optimistic.

XMAX is more of a selling point on boards like these than it is to pro system designers for theaters.

If you want to use your SVS's to fill in the bottom, the Mini-Dsp http://www.minidsp.com/ would be really handy for that. I plan someday to do something similar with an Exodus 21 but I honestly haven't missed the sub 20hz stuff.
post #10 of 37
Quote:
Originally Posted by Mrkazador View Post
One is tuned to 25hz with 400w and the other is tuned to 35hz with 700w. Both with a 4th order high pass.
Could you please post/link to where to download the WinISD file for the 2242H?
post #11 of 37
post #12 of 37
Thank you.
post #13 of 37
Thread Starter 
Wow Tack, that Mini DSP seems very slick. I'm going to have to look into that (also, very affordable).
post #14 of 37
If you have subs doing the lifting down low, I'm not sure I'd even bother to port it. I have a friend with a system (2ch) using a pair of PHL 7030 sealed which are similar to the 2242 and even with a huge amount of EQ to 35Hz barely move even at really extreme levels.

If you really want to port it, Vb=90L,Fb=37hz with a Q=2 HPF at 37Hz to make a 6th order system.

Below are the curves for this with 800W input.
LL
LL
post #15 of 37
Thread Starter 
Ok, last question(s) before I build this thing over the weekend... For targeting a port with the dimensions of 18 x 2.5 x 17...

Questions are all based on how I need to get this box to fit into my room and some of the "funky" dimensions that I'll be working with (47" wide, 24" tall, 17" deep... external dimensions) Driver will be mounted to one of the 47" wide x 24" tall sides and facing into the room.

First question: Does it matter where the port exits? Should it be in the front or back, or can I port it out of a side?

Second question: If front or back porting I'll have to put a bend in the port. Am I concerned with the overall volume? Length of the port in the middle? What do I need to be thinking about with this? If it's with volume, am I better off using something like a 10" PVC pipe that's 9.75" long and figguring out how to flare it? Is the flare part of the overall length of the port?

Thanks guys! I'll be sure to take construction pics and post them!
post #16 of 37
if you have at least a port diameter, a little more would be better, from the exit to a wall, you will be okay. it just needs enough room to 'breathe'. given your form factor, a 16" x 3" x 20" long port will also tune a 8 cubic foot cabinet to 25hz.
post #17 of 37
Where are those construction pics, Mister!
post #18 of 37
And sound impressions!
post #19 of 37
I'm going up there to visit this weekend. I'll hound him about this while I'm up there.
post #20 of 37
Quote:
Originally Posted by taxi View Post

i'm going up there to visit this weekend. I'll hound him about this while i'm up there.

woohoo!
post #21 of 37
Thread Starter 
Evidently it worked so well Taxi is going to build one himself. I totally forgot to take construction pics, but I'm sure I'll get enlisted to help Taxi with his, so we'll take pics then.
post #22 of 37
awesome...did you build just one or multiples?
post #23 of 37
I just got done testing a 4645C JBL cab for DB 2 weekends back so I should have the measurements up soon.
post #24 of 37
He built one, and I'm going to build one to go along with my current sub, an SVS PB-13Ultra.
post #25 of 37
My speaker for this project shipped today.

Build weekend is April 21st.
post #26 of 37
"I just got done testing a 4645C JBL cab for DB 2 weekends back so I should have the measurements up soon."

what did you think of it?
post #27 of 37
Yea, what are your thoughts on the JBLs? I have two of the older 4645s i bought a month or so ago on craigslist that i sadly haven't gotten to test out. My AVR randomly died a day or two after I got them, so I've been system less for a bit here.
post #28 of 37
Just so you know, the measurements are up at Data-Bass...

Thanks Josh!

http://www.data-bass.com/data?page=system&id=68&mset=73
post #29 of 37
Thanks for linking that Mike...


Yeah the 2242H is really strong in a few areas like efficiency, top end extension well into the lower midrange, etc. It's a great sounding driver. It is not as rugged either mechanically or thermally as some of the big drivers out nowadays and it wont do as well with the sub 30Hz bass because it just doesn't have the stroke available (only 9mm xmax). I tend to think of it as a well engineered extra strength woofer rather than an ultra low frequency subwoofer. Follow JBL's recipe with it and it will reward you with great bass just don't try to make it extend much below 25 or 30Hz as it really isn't the right tool for that.
post #30 of 37
I have 4x2242 in 4645 cabinets and love them. They are more or less flat down to 22hz and that's good enough for me. I previously had a pair of LMS5400 but prefer 2242 in every way except of the 15-25 hz region
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