Bass bin/subwoofer questions

[jcpahman77]

There has been quite a lot of discussion lately about the 8" buyout sub from PE. I'm sold enough on them that I want to use one each in bass bins under my main speakers (Tritrix TL's to be built yet). Each one will be powered by a Foster plate amp (scroll about 1/3 of the way down the page) and modified for proper sound (see this thread on how to modify the Foster amps).

The real question is, what kind of box should I put it in. There is a bit of an argument going as to whether a ported box is going to make this sub too boomy in my room. Thekorvers has been nice enough to give me some box design info for a ported enclosure.

2 cu ft. tuned to 26 Hz has an f3 of 22 Hz.

With 100 W: cone excursion = + 7 mm SPL = + 106 dB
Round port 4” diameter (= 12.5 sq. inches), length 22”: port air velocity = 67 ft. /sec
Slot port 15 sq. inches, length 27”: port air velocity = 55 ft. /sec

With 150 W: cone excursion = + 9 mm SPL = + 108 dB
Round port: port air velocity = 82 ft. /sec
Slot port: port air velocity = 68 ft. /sec

I would go with the 15 sq. inches slot port.

MSaturn believes a ported enclosure in my living room is going to be far to boomy. I've attached photos of my living room as well as a sketch of what I think the enclosure should look like. I'm looking for more opinions on this. My AVR is going to be an Onkyo TX-SR608 with Audessey 2EQ.

Please provide constructive criticisms and why you think what you think so that I can learn and build the proper enclosure.

Thanks in advance.

Jesse P.

The photos are too large to attach so here they are. The first two are of my living room and how it walks into my dining room and the third is what I've come up with for a box design. It's roughly to scale where 1 square = 1 inch. The top 2 inches is a "pocket" for the Tritrix TL's to set into. The square hashed in is where the plate amp will mount opposite the sub. I'm not real sure how to design bracing so I've just drawn some in there.

[arlis_1957@yahoo.com]

he gave you advise based on your room being small. that room is not. what are the actual dementions?

[jcpahman77]

12' across and 15' to the back of the couch. My wife misplaced my tape measure so I'm not sure how much farther back it is to the end of the dining room.

[Sydney]

FWIW: I had much less problems with "boomy" and room influences in areas that are open ( no doors ) and can't be pressurized.

[Erich H]

12' across and 15' to the back of the couch.

You might want to figure the entire room, not just to the back of the couch.

That's a big room.

[jcpahman77]

Problem is, I don't know how to do room corrections on paper. I usually sit behind a sound board with headphones, that's how I do my room corrections. Can I count on Audessey to be adequate?

[philiparcario]

that room will need a third sub. I suggest 2 sealed ones as bass bins to start. then in a few months add a third sub.

[jcpahman77]

I have 2 fairly crappy ones now and they get loud enough, they're just muddy and undefined and lack punch. I doubt three is going to be required for my taste.

[jcpahman77]

he gave you advise based on your room being small. that room is not. what are the actual dementions?

You might want to figure the entire room, not just to the back of the couch.

That's a big room.

that room will need a third sub. I suggest 2 sealed ones as bass bins to start. then in a few months add a third sub.

So basically it seems that I shouldn't have to worry too much about it being boomy. I know my drawing is a bit hard to see, but does anyone see anything wrong with the design? Keep in mind 3/4" MDF for the construction, I didn't draw the thickness into the diagram, but I hope you get the idea. If I built that the way I have it drawn is there anything wrong, or perhaps anything I should do better?

External dimensions will be 9" wide by 15" deep and 26" tall and use a slot port 15 sq. inches by 27" long.

[thekorvers]

So basically it seems that I shouldn't have to worry too much about it being boomy. I know my drawing is a bit hard to see, but does anyone see anything wrong with the design? Keep in mind 3/4" MDF for the construction, I didn't draw the thickness into the diagram, but I hope you get the idea. If I built that the way I have it drawn is there anything wrong, or perhaps anything I should do better?

External dimensions will be 9" wide by 15" deep and 26" tall and use a slot port 15 sq. inches by 27" long.

The gross volume of your enclosure is only 1.44 cu ft. From this you have to subtract the volume of the port, driver and bracing. For a net volume of 2 cu ft, your enclosure will end up much larger than this. You will have to tweak this. If the enclosure ends up being too large to your liking, we can always model a smaller enclosure. Everything is a trade off and nothing is set in stone.

[jcpahman77]

Ya, somehow that's right. Don't take that wrong I'm agreeing, I can't seem to figure out how I buggered the math on that. Let's take the internal width to 10", that puts it within a cubic inch of two cubic feet -- again, that is if my math is right. Naturally that is going to require an adjustment to the dimensions of the slot port, but I'll adjust that to equal 15 sq. in.

[Erich H]

Ya, somehow that's right. Don't take that wrong I'm agreeing, I can't seem to figure out how I buggered the math on that. Let's take the internal width to 10", that puts it within a cubic inch of two cubic feet -- again, that is if my math is right. Naturally that is going to require an adjustment to the dimensions of the slot port, but I'll adjust that to equal 15 sq. in.

http://www.the12volt.com/caraudio/boxcalcs.asp#por

[edlafontaine]

I/We all want to get it "right the first time". Don't overlook the possibility of stuffing (by degrees) ports IF they do sound too "boomy". The stuffing, by reducing port output, will reduce the "boom".

2) 8" woof's in that room are not too much.

Just my 2cents...trying to ease the analysis paralysis...options are good

[millertime]

here is a box calculator that mite help you... you can play with it to see how it changes things...http://www.reaudio.com/speaker_box/LPort_Box_Calc.html