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View Full Version : (2) 05' Alpine R Common chamber box check



MattSWE
05-16-2005, 03:21 AM
The box I am wanting is 3.5 cubic feet 35 Hz tuning

External dimensions using 3/4 MDF :

14.5" High 32"Wide and 17" Deep = 3.557Cubic Feet. Even after the sub(s) and port displacement there will still be 3.5cuft right? Now all I need help with is the port dimensions. I would really apperiate it.

Alpine says the max ported specs per sub is 1.75 I am going for optimum sub preformance. Each sub will have 750watts (hifonics BX1500D) @ 1 ohm

jimmyjames1700
05-16-2005, 10:05 AM
The box I am wanting is 3.5 cubic feet 35 Hz tuning

External dimensions using 3/4 MDF :

14.5" High 32"Wide and 17" Deep = 3.557Cubic Feet. Even after the sub(s) and port displacement there will still be 3.5cuft right? Now all I need help with is the port dimensions. I would really apperiate it.

Alpine says the max ported specs per sub is 1.75 I am going for optimum sub preformance. Each sub will have 750watts (hifonics BX1500D) @ 1 ohm



http://img77.echo.cx/img77/5200/untitled7rt.png

Those demensions will work. I suggest a single 2.5" x 13" port on either side of the front baffle that is 24" down the center. You'll just have to make it into a "L" shape. Wang away.

Final volume works out to 2.752 cuft net after all displacemnet, 1.375cuft per sub. Tuning is exactly 35Hz, -3dB point is 30.16Hz. You will need a Subsonic Filter set around 20-25Hz to prevent overexcursion.

I did also model a 3.5 cuft net box with the same tuning but the was virtually no advantage to going any bigger than the box you are planning.

MattSWE
05-16-2005, 04:44 PM
so this is the final box, is everything right?
http://img129.echo.cx/img129/6822/finalboxdesign6sq.th.jpg (http://img129.echo.cx/my.php?image=finalboxdesign6sq.jpg)

jimmyjames1700
05-17-2005, 08:48 AM
Port should be the same "width" its entire lenght. The 2.5" should remain constant throughout the bending of the port also. So it should be 2.5" at both openings.

And the 24" length should be measured dead center down the middel of the port.
Otherwise everything else looks good. Check out JL's website and their Port Tutorial for some good Port construction info.

MattSWE
05-17-2005, 06:08 PM
http://img265.echo.cx/img265/4804/finalboxdesign3pw.th.jpg (http://img265.echo.cx/my.php?image=finalboxdesign3pw.jpg)

there, everything is corrected

jimmyjames1700
05-17-2005, 10:53 PM
close, but the last piece of the port isn't 24". if you could draw a line down the middle of the port, from opening to the end, it should be 24" long. go to jl's website and look at the data sheet for any w7 woofer and look at the vented box drawing to get what i mean.

here

http://www.jlaudio.com/subwoofers/pdfs/12W7_MAN.pdf

trust me, you don't want to guess at this at all. slot ports can't be adjusted after the box is finished.

Moe Lester
05-18-2005, 12:40 AM
you havent accounted for port displacement, and that isnt enough for sub displacement. the box needs to be larger.

MattSWE
05-18-2005, 12:40 AM
i think I got it, 14.5 deep and 9.5 long aginst the back wall equals 24"

jimmyjames1700
05-18-2005, 08:57 AM
you havent accounted for port displacement, and that isnt enough for sub displacement. the box needs to be larger.

It's fine. like I said above, after port and sub displacement it works out to 1.375 cuft per sub and tuning at 35 hz. Going to 1.75 cuft per sub, same tuning, results in only 0.6 dB gain @38 Hz with 0.5 Hz lower F3. No practicle reason in going any bigger.

jimmyjames1700
05-18-2005, 09:13 AM
i think I got it, 14.5 deep and 9.5 long aginst the back wall equals 24"

I dont now exactly what you mean here. It's this easy.

Look at drawing that shows your box from the top view. Look at the port and draw an "L" in your port. One tip of the L should be at the beginning, the other tip at the end. Again the "L" is down the center of the whole port, not touching either port wall. That "L" should be 24". So then one side of the port, the box side ( from the side the subs are on to the end of the port) would be 25.25" in total length. And the inside of the port wall ( the 2 pieces that make up the inside of the port )would be 22.75" in total length.

Keep in mind that in real world application, the sub box while probably tune about 3 hz lower in reality. Most boxes always end up tuned a couple Hz lower than designed.

If you want to compensate, design the box tuned a couple Hz higher than your target (35Hz) say like 38Hz. I would do a 19" port.

This would give you 1.43 cu ft per sub ( AFTER ALL DISPLACEMENT ) and tuning @ 37.7 Hz. In the real world this box would end up just at 35 Hz.

MattSWE
05-18-2005, 04:52 PM
ya know what, i think Ill use roundports instead. Screw taking the chance of F#$#%#%^ up the slot, could you tell me what diameter tube and legenth should be used? oh, and should I use 1 or 2 of them?

thx