2245H box/vent help

[elshout]

I am about to build a box for a 2245H sub. I am using the 1983 article: http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm

I am going to build the 12 cu ft - 25 hz unassisted box. If I read the article right, the port will be 9 inches? Is this correct? If it is correct it will be 20 inches in lenght.

I am not able to find any 9 inch PVC. I can find 6 inch, so can anyone tell me what the equivilant for a 9 inch x 20 inch port be if I use 2 - 6 inch ports? What would be the length of each of the 6 inch ports?

Any reliable help would be greatly appreciated.

Thanks
Scott

[loach71]

I am about to build a box for a 2245H sub. I am using the 1983 article: http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm

I am going to build the 12 cu ft - 25 hz unassisted box. If I read the article right, the port will be 9 inches? Is this correct? If it is correct it will be 20 inches in lenght.

I am not able to find any 9 inch PVC. I can find 6 inch, so can anyone tell me what the equivilant for a 9 inch x 20 inch port be if I use 2 - 6 inch ports? What would be the length of each of the 6 inch ports?

Any reliable help would be greatly appreciated.
You can get some "concrete form" (Sonotube) tubing at your building supply store. It is available in the size you need. The PVC tube - if available would be horribly expensive.

[grumpy]

reliable help? :) I get 12ft3/23Hz w/ 9"dia x 20" long port, using WinISD....
two 6" ports is nearly the same (19.25" each), just using plain, non-flared tubes
(slightly smaller cross area using 2 - 6" ports).

[johnaec]

You could also make square or rectangular ports. A 9" diameter circular port is 63.62 square inches, while an 8" square port is almost equal to that at 64 square inches.

John

[just4kinks]

This link is for car-audio, but the equation is the same and the information is very useful.

http://mobile.jlaudio.com/support_pages.php?page_id=165

[elshout]

Thanks for the responses. You all answered my questions perfectly. Sorry Grumpy, I did not mean to be offensive, I just did not want anyone guessing. I wanted an educated answer because I am new at this. You all gave some excellent advice.

Thanks again.
Scott

[grumpy]

I did not mean to be offensive, I just did not want anyone guessing. I wanted an educated answer because I am new at this. You all gave some excellent advice.

Hah. :D
Well, certainly none was taken by me.

Smiley :) wasn't intended as defensive, just as a caution to weigh what
you might get in response.

Glad you got what you came for.

Welcome aboard. -grumpy

[lgvenable]

Scott,
My sub will be complete in about 2 weeks, and I'll start port tuning. Do a search for my threads, and check out the responses. Zilch did some calculations using bass box 6 for me, which are more accurate than WinISD.

Like you I'm building a 12 ft3box using the same article. I've already purchased a woofer tester off the Bay for 43.00 to do the final port testing, by sweeping the sub with a frequency generator, and then using the impedance plots of the woofer with and without the port plugged to calculate the exact port tuning. After you determine this; you fine tune the length of the port to yield the desired 25HZ (same target as I've got). I should be able to tell you what I had to do.

You should be aware that the fill can add virtual volume to your box, so in the end, it is necessary to do the painful job of port tuning the box. I'll be using fill from Lowe's or Menard's, so in the end, I should be able to give you excellent values on your port lengths; provided you use the same type I'm using. I'll be happy to ship you a pair of 7" cores at no charge , but you'd need to pay shipping.

I should have pictures I can post sometime next week. As we put the box to gather, it has been planned that all pieces will fit like a puzzle, interlocking with the other pieces via dado's;lap joints or rabbeted joints; with liberal use of biscuits as well .

The sides will be tied together with bracing cut just barely short of the other side, and then drawn in slightly (1/16 or 3/64); so that the box will have no resonance and be tightly built.

The advice I got from the forum was there can hardly ever be enough bracing. Thats why I went the double box route. I plan on building a sub to last the rest of my audio career; so I spent the extra 225 in materials to do the double box route with veneer to boot. Thank God my wife understands! (Barely)

PM me if any questions and I'll shoot you my cell, as perhaps the leg work I've already one will help you

By the way, if you know anyone with access to converting equipment, I'm using 7" OD 6" ID cardboard cores as my ports, as thats a standard size core widely available. Of course as someone already mentioned, you can use sonotubes as well.

I'm using a Crown PS400 bridged mono at 660 w; but making sure I stay below 550 to keep well below 0.05% THD and have an absolutely pristine signal to the sub.

I'm also using a parametric EQ to put in 5.0 db boost at 30HZ, and 0.5 at 40, 50 and 60 HZ to get a flat response.

I've got an excel file with all the drawing, you'll need to double check the dimensions, as I got a professional cabinet maker to build mine. I have used 3/4" mdf for the inner box, 12 (or is it 13) ply 3/4" Baltic birch, and walnut veneer, with fir 2 x 4 bracing. After everything is said and done, its 12 ft3 internally, and 17 + externally. Estimated weight = 180+ lbs, so it'll have handles on its sides.

I've been working on it for 2 months, so I have some pretty mature plans. The design is going to replicate the look of my L100T's right down to the grill which will be help on via dowels going into rubber plugs; lust like on the L100T's.

Heres's what Zilch told me in PM's:

BB6P today says 12.3ft3 tuned to 25 Hz:

1 x 7" @ 7.05"
2 x 6" @ 14.91"
3 x 6" @ 26.76"
1 x 8" @ 10.6"

BB6P suggests one 7" vent 7.43" long for 2245H in 12 cuft with normal fill.

Alternatively, it's 2 x 6" at 14.67" or 1 x 8" at 11"

2 x 8" @ 34.52"


Final size = ~ 47 x 30 x 23 (seems like its slightly under that by 0.25" in height).

I had the MDF box built, and then layered it with the Baltic birch to get a very tight fit.

Larry