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help with porting an enclosure


vroom

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hi guys, im just in the process of building some boxes for my old school Rockford PWR-415 subs to run in my house. The manual recommends 5" port 7" long for a 4 cubic foot box. i have exactly 4 feet internal volume after sub displacement (forgot to factor in the port) but i cant find any 5" diameter PVC, biggest i can find is 4". Any advice as whether 4" would work? and how do you work out the length if diameter is changed?

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How much power are you going to be running?  How big of a port you will need is very dependant on input power. 

Here is something else to think about, that 5" port is going to tune you to about 35 Hz.  Depending on what you intend to use those subs for you may want to tune a bit lower for in home use.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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9 hours ago, vroom said:

All being well they should be getting around 1000-1200watts. They will be ran with a pair of linn isobariks with active crossover set 90hz

OK, I crunched some numbers.  I assume you have a pair of these so each sub will be getting 500-600 watts?

On that amount of power you will want to use a 6" port, a 4" port will be significantly undersized and you will almost certainly get a lot of port noise.  Port noise is really noticable in home audio applications so it something you will want to avoid.  A 6" port will need to be 11" long to tune it to 35 Hz.  

If it were me, I'd tune a bit lower since you don't get all the cabin gain you would normally get if this sub was used in a car,  30 Hz would probably be a good spot, the 6" port will need to be 16.5" long.  

I would be very careful with the power on these subs.  These older drivers don't have much Xmax (only 6.2 mm).  Modeling software shows you exceeding that significantly (almost double) on 600 watts.  It would be easy to damage these subs.  Be sure to set your subsonic filter 1/2 octave below tuning.  

 

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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2 hours ago, vroom said:

Cheers for that. Just to clarify, each sub is in its own seperate 4ft box.....so i need a 6" port for each box?

Yup, a 6" port for each. 

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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  • 2 months later...
6 hours ago, vroom said:

So finally got round to porting these boxes, i have 2 6" pipes at 16" long but will need to fit an elbow on each one as the boxes arent deep enough. My question now is how do i allow for the curved elbow in the total length? 

Measure down the centerline of the elbow when looking at it from above.  You may want to lay a string along the top so you can follow the curve and then measure the string.  Don't worry if you can't do it super accurately, if you are off by a 1/2" inch is not really going to matter much.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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