MTX 7500 series port area

[THATpurpleKUSH 5,000+ posts]

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.

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[THATpurpleKUSH 5,000+ posts]

Really no one can offer any help?

 

[RAM_Designs 5,000+ posts]

What exactly do you mean by "port tubes"?

 

[THATpurpleKUSH 5,000+ posts]

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 5,000+ posts]

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.

 

[THATpurpleKUSH 5,000+ posts]

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 5,000+ posts]

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.

 

[THATpurpleKUSH 5,000+ posts]

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 5,000+ posts]

I'd do three since you don't have flared ports...maybe tune a little lower, if you can.

 

[thevic24 5,000+ posts]

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 5,000+ posts]

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 5,000+ posts]

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.

 

[THATpurpleKUSH 5,000+ posts]

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 5,000+ posts]

Winisd response curve is useless in a car audio environment.

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

 

[THATpurpleKUSH 5,000+ posts]

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?