Manufacturer recommended boxes port velocity higher than expected

[DIZ Audio]

I've been playing with WinISD to try and design a sub box for the JL 10TW3-D4.  After modeling it, the port velocity was 30+ m/s.  The research I've done says it should be 17-20 m/s to prevent chuffing.  I tried other driver's recommended ported box designs and it was pretty much the same.  What's the deal? 

 

FYI, the drivers modeled were JL 8W3v3 (50+ m/s),  JL 10TW3 (30+ m/s) and a Dayton Audio DSA135-8 (40+ m/s) at their full RMS power ratings. 

[aculous]

have you looked at Trit's calculator on this forum for port size recommendations? It would be helpful I would bet. And Torres Calc/spreadsheet. I would guess a bigger port is going to lower your velocity but up your tuning freq. which would mean you would most likely have to elongate the port to drop the freq. Thats a super tiny port. Also adding ports will up freq. from what I have modeled. 

 

But I am armchair quarterbacking this with a beer in hand. i.e. don't take my word for it ask someone with better knowledge, Trit/Joe X/Anyone but me. 

 

So for example for a JL10W3(v2 in this case) Bassbox pro recommends a 1.5 cu ft box with a Fb of 34hz and a F3 of 26hz. This is with one 4"x 10.43" round, non-flared or precision port.  

 

Also look at the QTS of those drivers. the TW3 is not meant to be put in a vented box. The W3 is 50/50 closed or vented. Most drivers are meant for specific applications and shoehorning a driver into a ported setup may not be the best idea based on the EBP value and the QTS. 

 

Calculating EBP (says mh-aduio.nl) = Fs/Qes

 

EBP of 50 or less = sealed

EBP 100 or more = ported or passive radiator

Qts of .3-.5 = single tuned bandpass (bandwidth with vary)