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kushy_dreams
06-03-2011, 05:53 PM
I've got some extra wood and 4in pvc pipe laying around that I plan on throwing together for 2 MTX 7500 12s that I got real cheap on craigslist.

My question is should I use 2 or 3 port tubes? They have an xmax of 16.5 and sd is about 522cm^2 iirc. The box will be about 4-4.25 tuned around 38hz. I'm just trying to make something that will sound good so I can resell it quickly.

The vent match for 2 is .03 and the vent match is .01 for 3 in win-isd. I don't really understand the vent match, just that it has to do with port noise. All help is greatly appreciated.

kushy_dreams
06-03-2011, 11:03 PM
Really no one can offer any help?

RAM_Designs
06-04-2011, 09:12 PM
What exactly do you mean by "port tubes"?

kushy_dreams
06-05-2011, 04:26 PM
4 inch pvc pipe. I have used it before on other boxes and its worked fine, I file and sand the edges down so theres no hard edges.

Buck
06-05-2011, 04:31 PM
You would be fine with either imo, but 3 is more than likely going to be louder, although you may lose some ability to play lower than your tuning frequency vs. 2.

kushy_dreams
06-05-2011, 04:34 PM
I would have thought that 3 would have helped the low end due to moving more air but I guess not. What does the vent match feature in win-isd do? All I know is that you want it under about .1 to keep port noise to a minimum.

Buck
06-05-2011, 04:41 PM
Vent mach is just that, the speed of the air in the port. Mach= 580 miles/hour.

.1 or .05 or .01 = whatever of 580 miles/hour.

---------- Post added at 02:41 PM ---------- Previous post was at 02:40 PM ----------

And I question the accuracy of multiple ports in winisd.

kushy_dreams
06-05-2011, 04:56 PM
So a lower port velocity will get louder than a higher port velocity? Is this why you see such huge ports with spl boxes?

RAM_Designs
06-05-2011, 05:09 PM
I'd do three since you don't have flared ports...maybe tune a little lower, if you can.

thevic24
06-05-2011, 05:12 PM
Vent mach is just that, the speed of the air in the port. Mach= 580 miles/hour.

.1 or .05 or .01 = whatever of 580 miles/hour.

---------- Post added at 02:41 PM ---------- Previous post was at 02:40 PM ----------

And I question the accuracy of multiple ports in winisd.
Sorry for the "jack"
but when you refer to "Mach" are you referring to the speed of sound or the air flow through the port?

RAM_Designs
06-05-2011, 05:13 PM
So a lower port velocity will get louder than a higher port velocity? Is this why you see such huge ports with spl boxes?

The reason for the huge port is because the port acts as a radiating surface, displacing more and more air as you approach the tuning frequency. Just play around with some tones with your own box and feel how much air is being pushing in and out of the port depending upon the frequency being played.

Buck
06-05-2011, 05:40 PM
Sorry for the "jack"
but when you refer to "Mach" are you referring to the speed of sound or the air flow through the port?

It's one in the same.

It's the speed at which the air is traveling through the port.

kushy_dreams
06-05-2011, 06:01 PM
I'd do three since you don't have flared ports...maybe tune a little lower, if you can.

MTX recommends 38. I played around with it in winisd and anything below 38 gives it a real goofy shaped response curve. Plus 38 still gives an f3 of 30.

Buck
06-05-2011, 06:05 PM
Winisd response curve is useless in a car audio environment.

My BL's look like the worst sub ever in winisd.

kushy_dreams
06-05-2011, 06:14 PM
Winisd response curve is useless in a car audio environment.

My BL's look like the worst sub ever in winisd.

I was kinda wondering this when I plotted some sa8's a little while back. It had all sorts of peaks and dips.

So if you think the vent match with more than 1 port is off and the response curve plot is off, then whats a good free/cheap program to use?

Buck
06-05-2011, 06:15 PM
I would tune to 34,35 and see how you like it. 38 hz is just too high.

kushy_dreams
06-05-2011, 06:22 PM
Well if I tune below 38 I can only use 2 ports cuz the depth is only 17inches.

Buck
06-05-2011, 06:23 PM
The depth of what is only 17"

Do a slot port. Problem solved.

kushy_dreams
06-05-2011, 06:50 PM
The depth of what is only 17"

Do a slot port. Problem solved.

yea well the woods already been laid out and cut though :blackeye:

and I kinda dont like slot ports and dont know how to do 45s so I like to stick to round/aeroports.

Maybe I could side fire 3 round ones

Buck
06-05-2011, 06:58 PM
Get a 90 degree elbow from HD or Lowes for 4" pipe.

kushy_dreams
06-05-2011, 07:04 PM
If I do that then how would I calculate port length? Just measure down the middle like with a slot?

Buck
06-05-2011, 07:06 PM
If I do that then how would I calculate port length? Just measure down the middle like with a slot?

Yes.

kushy_dreams
06-05-2011, 07:13 PM
Ok, I think I know what I'm gonna do. Thanks for all your help, it is tremendously appreciated :cool:

Buck
06-05-2011, 07:23 PM
No problem man.