Rear port requirements for line array

[rnrgagne]

Hi,
I have to move my HT to a new room and the only way I'll be able to do an IB there will be to vent through a wall with 2"x6" studs. Ideally I'd like to mount a line array of two 15" drivers on either side of my screen between the studs. The other room is a functioning family room / kitchen so I'd like the vents for the IB to be low and as small as possible using some kind of painted grate.

So with that in mind what's the smallest opening I could get away with?

[norpus]

My understanding is the best sound for smallest opening is for opening to be at least same as combined area (Sd) of the drivers

[ThomasW]

The idea is no resistance behind the drivers, so an open wooden frame (as big as both drivers) covered with grill cloth is the only acceptable cover.

In addition the kitchen/family room will have pounding bass in them when the sub is operating.

Given these issues it sounds like an IB is not in your future.

[rnrgagne]

Thanks Thomas,

Having an IB in my current HT I can't live without one. (I Have to move the HT because some neighbor complained to the city that I was building a basement suite and to make a long story short I have to restore it to a crawlspace.)

I've got to figure out a way to make it work. I'm not concerned about the bass in the family room. But I certainly don't want two 16" X 30" holes mid wall there either. Which is why I was thinking the back vents would be lower - and not that big. (Kind of like a periscope tube.)

So if I read you correctly the most important factor is the lack of restriction on the back of the drivers, so when I see IB's with eight drivers firing into one opening the reverse doesn't apply?
I thought I saw a picture where a guy had four drivers in a box firing outwards and the backs venting into a basement through that box. I could be wrong but I din't think the opening was the equivalant of the SD of the four drivers.

The biggest openings I would want into the family room would be about two 16"X16" openings and they would have to be close to floor level so I could put a couch in front or other furniture to make the less obvious. (With a reasonable gap to not restrict the airflow)

I could also build boxes for the drivers as a stage but that would likely need to vent into the family room as well.

[ThomasW]

I guess I'm confused you don't want 16"X30" but 2-16"X16" are okay?

Don't build anything with a jog in it (periscope). The opening needs to be directly behind the drivers.

Why not use standard round perf-metal 15" driver grill covers, directly behind each driver? Well I guess that's pretty much the same as 16"X16" grate.

BTW the 8-18"s fire into an opening larger than their combined Sd. The 4-15"'s in a small cube 'outie' are the best compromise he could create.

[twisterz]

What about putting your Line Array across the bottom of the screen and and opening the wall all the way across behind the couch, mabey a sofa table between the wall and couch to help hide the opening and give it better clearence.
If you put anything on that table you might need earthquake putty to hold it in place.

[rnrgagne]

Thanks guys,

Yeah a bit confusing, I don't wan't two 16 x 30 openings or one 16 X 60 I know that wouldn't have a hope in hell of passing the WAF.
I think a couple of 16 X 16 openings symetrically spaced & down low is the best I could hope to get away with..

What if I did build a stage/box that was 7' wide by 2' or 3' deep and vented through the two 16 x 16 openings? Would that be a reasonable compromise worth doing?

[ayreonaut]

Better yet, build a box on the floor under the screen about 37" wide, 19" high and 19" deep.

Mount two 15" drivers facing forward and one on each end like this: >OO<

Vent almost the whole back through two 16"x 16" openings.

[lhreeves]

Since you have to convert the basement area back to a crawl space, why can't you use that space for a floor mounted manifold IB like this:






Then you don't have to go into that other room at all.

[rnrgagne]

Thanks,

Believe me - I would if I could - but I've got concrete floors with in-floor heating. So no can do.

I'm really choked, I love my IB and it will be tough to live without.

[rnrgagne]

"Better yet, build a box on the floor under the screen about 37" wide, 19" high and 19" deep.
Mount two 15" drivers facing forward and one on each end like this: >OO<
Vent almost the whole back through two 16"x 16" openings."

I think I'd rather work with the "stage" idea - something the width of the screen for aesthetics.

So with four IB15's, if I did something like 18" H x 87" W X 30" D with two 16" x 16" vents, would it behave more like a ported sub or an IB? Would it be worth the effort?

[ThomasW]

rnrgagne said:

"Better yet, build a box on the floor under the screen about 37" wide, 19" high and 19" deep.
Mount two 15" drivers facing forward and one on each end like this: >OO<
Vent almost the whole back through two 16"x 16" openings."

I think I'd rather work with the "stage" idea - something the width of the screen for aesthetics.

So with four IB15's, if I did something like 18" H x 87" W X 30" D with two 16" x 16" vents, would it behave more like a ported sub or an IB?

It would be a bandpass.

Would it be worth the effort?

Work on the wife to let you make an appropiately sized opening. Give her a choice an opening appropriate to what's needed, or live with a BIG ugly box sub in the room....

[rnrgagne]

Hmm, I wouldn't make it ugly - but she doesn't have to know that.....
Love the idea.......make it seem like it's her choice.

BTW what's a bandpass?

[ThomasW]

rnrgagne said:

BTW what's a bandpass?

It's a subwoofer where the output is boosted at a specific frequency by having the driver fire through a slot.

Google is your friend for things like this..