Air velocity?

[J216 10+ year member]

When designing a ported enclosure, is there an acceptable range for the air velocity?

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[RAM_Designs 5,000+ posts]

I assume you mean for the port? If you download winISD it'll give you the port velocity for any given enclosure/port size...it's also pretty helpful for designing boxes as well.

 

[muskyhunter567 10+ year member]

i think if you just keep you port width and depth under 9 to 1 you should be ok

 

[RAM_Designs 5,000+ posts]

i think if you just keep you port width and depth under 9 to 1 you should be ok

Having too small of a port causes port noise too...

 

[muskyhunter567 10+ year member]

yea, i guess just stick to the 14-16" of port are per cubic ft. and keep it under 9-1 ive never had problems following those two rules

 

[SSS 18734 5,000+ posts]

I don't know the specific answer to your question, but as a workaround, there are calculators you can use to determine the minimum port area you should have in order to avoid port noise. Search minimum port area calculator or something like that. The 15 sq.in. per cubic foot isn't really accurate. Necessary port area is driver dependent.

All you need are your subwoofer's Vd (Sd x xmax), airspace, and desired tuning.

 

[J216 10+ year member]

Sorry. I didn't realize that was so vague until I read it again.

I think I'm looking for a threshold.

Here's an example of one that I was playing around with for a home theater sub.

I built the box at 2.5 net cubic feet, tuned to 24.5hz. the port is only 2.625"D x 7.75"L. As I expected I ended up with a bunch of port noise. The velocity was around 165 ft/s. according to WinISD.

I guess my question should have been how low does the velocity need to be? And is there such a thing as too low?

 

[RAM_Designs 5,000+ posts]

Sorry. I didn't realize that was so vague until I read it again.
I think I'm looking for a threshold.

Here's an example of one that I was playing around with for a home theater sub.

I built the box at 2.5 net cubic feet, tuned to 24.5hz. the port is only 2.625"D x 7.75"L. As I expected I ended up with a bunch of port noise. The velocity was around 165 ft/s. according to WinISD.

I guess my question should have been how low does the velocity need to be? And is there such a thing as too low?

If you're using winISD, when you're inputting your port dimensions, it should give you the "vent mach". It says anything below .15 is usable, but I don't end up any higher than .05 with the boxes I design.

 

[J216 10+ year member]

Thanks for the help. I think I kind of get it now. Mach .15 is roughly 165 ft/s. So, slower than that should be good. I suppose, probably a lot less, if the port is facing you. As with my home theater sub

But, I gotta bug you about this one more time. Where do you find the "vent mach" in WinISD. I can't seem to find it. I looked on the vent page and all I can find is the Port area and the 1st port resonance. I looked in the options for the rear port air velocity and I could change the units. But, no mach. Maybe I'm using a different version.