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Port area question for two DD 508's (Port Noise)


Mike Gann

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Hello there,

I was hoping I could find a straight answer on my own about this one but I've been searching around the internet for hours. Hopefully it's an easy one for someone to answer here. I'm designing a box for someone's truck, he has two 8" DD508 woofers and I was planning to use flared aero ports for them. I was wondering if two 4" flared ports would work for this. WinISD says the port velocity would be about 32/ms. Is this too high? I can't fit a 6" port unfortunately or I'd just go with the safe route.

Also I was thinking how handy it would be to have a box tuning calculator that took the NET volume and showed me the port length that I need to tune it down to a certain frequency that I give. Then tells what the actual box volume would be after this port is put into it. Can just tell it the maximum volume that I have to work with. Anyway what would you guys recommend I do for this, just keep trying new lengths and changing the volume after port displacement until the numbers work out?

Trying to fit this box under his bench seats in a truck. Surprisingly I have enough volume to work with under there keeping within 1-1.25 cuft per woofer but the low profile wedge shaped box is preventing me from using 6" ports unless I maybe forget about keeping it symmetrical.

The box I'm replacing, that he's unhappy with, he paid some guy to make. The guy has the two 10" woofers facing flat onto the ground of his truck. No wonder he's unhappy with the sound.

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32 m/sec is the absolute upper limit for port velocity IMO. I prefer to keep things closer to 22-24 m/sec, but sometimes compromises have to be made due to design constraints. If all you can fit is a pair of 4" ports the box should work OK and I wouldn't lose any sleep over it, its just won't be ideal.

As far as a box calculator goes, what you are describing is pretty much exactly what Torres does, if I understand you correctly.

"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."

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