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2 ports vs 1 for two tens.

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Synastr

Synastr

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So currently I have a box built under my 01silverado with two ten inch re subs. The subs are temporary till I get American bass xrs. My box is 2.8 roughly before ports and subs. I'm looking at 1.2 after the subs. Right now the box has two 4x10" ports. I'll say it's extremely loud and punchy but it dies t get low at all. So, I plugged off a port and it digs deep. I'm looking to tune at 29-31hz. My main question is should I lengthen the two ports or use one? I'm thinking if I use one, I'll step up to a 6". I have roughly 20" on either side for length unless I stay 4" then I can go all the way through the box. Which I think was 56" Experienced tuners help me on thus one. The current subs are re audio Sr pros. Running @1ohm to a ampere 1000.1

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Not completely sure but the 6" areo will be more port area than two 4". But this would mean a longer run of areo to achieve the desired tuning. Now if it was me and i couldn't fit the 6" because of length constraints. i would try tuning around 33Hz. This will still hit nice and low! I tune most of my box's at 33 to start out. This has always been my happy medium digs low still hits up high. If nothing else do the 2x4". I used 2 4" pvc pipes to tune my obsidian 12's enclosure. It worked well but huffed and puffed while murdering the lows. So i moved up to 6" aeros at 32 Hz and wow. The 4"s should be sufficient while the 6 might help with port noise.

 
well what you should do is plug three ports, so you have just one being active. then what you wanna do is study the air velocity. play a song with a lower frequency and turn it up and see how much air velocity there is. yes there are formulas to calculate the port area required, but that is just a "general rule of thumb". in reality what matters is the air velocity. if the port air speed is too low the box will sound hollow and not get low, and if the air speed is too fast then air turbulence and box impedance rise can be problematic.

 
Help me clarify something if you will. You say you have 2.8ftⁿ of gross volume but it's only 1.2ftⁿ net. That's a 1.6 cube difference.

The subs should displace ~.12 cubes each and 2-4" x 10" ports displace ~.15 cubes. So how do you go from 2.8 cubes to 1.2 cubes by adding .38 cubes of mass?

If your box is indeed 2.8 cubes gross then your net volume would be 2.42ftⁿ.

Did I miss something or is there a typo?

 
Ah. That makes more sense. :)

The difference between two 4" & one 6" port is basically the difference between 6 and half a dozen, unless you go from PVC to an aero, so it seems like sticking with the ports you have would be best. For 30Hz you'll need the ports to be 28.5" long.

And just as an FYI, two 4" ports is 25in² & 1 6" is 28in².

 
While the numbers are generally not accurate in WinISD, you can use it to see the correlation of port diameter to velocity and length. When the mach is too high in WinISD, the number will be red. When you have the mach (velocity) in an acceptable range, the number will be green. Torres Box Calculator will give you more accurate port numbers, but doesn't show the velocity.

 
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Synastr

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