posted
i just designed my box for 2 re xxx 15's. im starting to think i may not have enough port area. i dont want to have port noise. this is my first ported box also. the volume is 8cu feet with a port 14x3x13" long, which should tune it to 28. is 42sq inches enough? if not how big should i go? i dont mind redesigning the whole thing if i have to. thanks
posted
42 is ok 50 -60 would be nice 140 is too large for your low of tuning and not needed.
a 3" dia port is only 7sq inches you have over 6 times that much port area.
worried about it do 50sqin X 16" long
140 sqin would need to be 50" long which is stupid long and take up 4 cubic feet (not including the wood the port walls would displace).
-------------------- ---Member of Team Gates--- Don't knock it, if you know nothing about it. Posts: 3074 | From: Okla USA | Registered: May 1999
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use the floor of the box as one wall of the port that will help on port area and lower panel strength.
redo that brace two braces runing up and down and side to side should fit the bill and two front center to the back pannel
-------------------- ---Member of Team Gates--- Don't knock it, if you know nothing about it. Posts: 3074 | From: Okla USA | Registered: May 1999
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quote:Originally posted by Iboomalot: 140 is too large for your low of tuning and not needed.
It isn't too large, and is needed. If he is tuning to 28hz, that port is going to be an L, and a long one at that
My present daily box is 4.15net, tuned to 27hz, with 70sq" of port. It's an L and there is slight turbulance, that's why I'd recommend it as a minimum. I would go with 80sq" if I was to redo my present box. It'll depend on power too, I got it wired to 1ohm on my 2500d If I had a 1200-1500wrms amp, 70sq" would probably be enough.
posted
he could run a 30 sq in port and not run into "port noise"
he is fine just redo the port slightly and bracing location.
if you want to up your box size by 40% or more you can go a larger port but its not needed. I think after nearly 20 yrs in this sport I have an idea on what a simple ported box can and can't do.
going off your pic and assuming 3/4" wood you should be close to 8.1 cf without taking into account sub displacement which should drop your net volume to around 7.6cf
***edit****
50" long 140sqin port would need to go from one wall to the other and then travel back the entire depth of the the box 20" + another 11" added to the depth of the box for needed airspace, the the port would have to travel UP the back of the box and then take a slight bend or another U turn so the port isn't facing the back of the subs (for loading purposes).
lets see port displacement assuming 4" tall by 35.5 wide and 3/4" wood
port displacement = 4.88 cf sub displacement = .5 cf needed net volume = 8.0 cf
total needed = 13.38 cf interior volume
width = 35.5" same ht = 21.0" same depth = 31.1" increased 11.1"
-------------------- ---Member of Team Gates--- Don't knock it, if you know nothing about it. Posts: 3074 | From: Okla USA | Registered: May 1999
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posted
thanks for all the help. i was hoping to have the woofers and port firing to the rear, but it looks like im going to have the woofers firing up and maybe the port firing to the rear. im going to be running a power t30001bd to the 2 subs with either a 1.4ohm load or a .7 if it will handle it. a friend of mine tells me it will. i will post up a new pic once i get it redesigned.
thanks again
JB
Posts: 21 | From: Brockton, MA | Registered: May 2004
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posted
i'll agree with iboomalot..... using box walls as port walls is definitely a good idea. it benefits the port, aswell as the integrity of the box....
-------------------- - Wes Sowers - Discount Car Stereo L.L.C. Kent, Wa 98032 (206)824-5875
posted
this is ot from my post, but would having the woofers high enough so that half of them were firing right at the rear window of the blazer make me loose any db's? i originally wanted them lower than the window because you cant deaden the window and im sure it would loosen up alot after having 2 15's bang on it all day. im still trying to find a way to have the woofers and port facing to the rear.
thanks again.
JB
Posts: 21 | From: Brockton, MA | Registered: May 2004
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I think after nearly 20 yrs in this sport I have an idea on what a simple ported box can and can't do.
Certainly you do Randy, you helped me double check my math on my box. However, high displacement drivers aren't NEARLY as old as you are , and I doubt you've had any experiece with them(don't take it as a slant ) In my experience with the XXX, which is a high linear displacement driver, it does require a more port area than "conventional" subs, simply because it moves more air. The fact I have a decent amount of power on tap allows me to reach the linear limits, and at that point, the extra port area is a nice thing to have, that's all I'm saying.
posted
i agree but with people using larger ports than in the past. many 15s in the past only used one 4" or two 3" ports per 15 that is only 12-14 sqin per driver.
So I agree to a point but he doesn't NEED 140sqin of port but if he can fit that then great.
40-60 sqin is more than enough to keep port noise low even on a XXX or other large X-max sub. once port noise becames a factor SPL levels would be high enough to mask any noise.
I guess if you listen to 10hz at full volume it could become a factor too but I feel in a normal install and normal high power useage he is fine.
IMO putting in a 140sqin port for SPL then plugging 2/3 of that to 50sqin for SQ would be a better choice. This would keep box volume lower and still give him the SPL when desired.
-------------------- ---Member of Team Gates--- Don't knock it, if you know nothing about it. Posts: 3074 | From: Okla USA | Registered: May 1999
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posted
here is another design. slightly more port area. i think im gonna try this one and if port noise is a problem, ill redsign it with the woofers on top and the port on the back. here are the images:
The air speed is pretty high. But it's ok. There's a little port noise, but i think it's caused by my "L" bend, even if it's rounded.
Often a straight port with less area, is better than a bended port with higher area. If we talk turbulences, air compression/dB loss is another thing. That's what i've experienced.
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