Port Velocity Discussion

[CompressionFed]

For those of you who build a lot of boxes, what considerations do you make regarding port velocity?  I have heard that your goal should be to keep your port velocity's value less than 5% of the speed of sound (1130ft/sec) to keep noise down.  That sounds low to me.

Is this a situation where more is not better?

Please discuss.

[Forevrbumpn]

Me personally. When I use BB6.0, I mainly keep an eye on the impedance graph, phase respnse, gains-dips. I seen what you and the other guys were talking about in the other forum-Helix, or somethin. And they did say high velocity is good for spl, but me, I usually keep it low, to keep down wind noise, and still get high spl boxes. But I have also done high velocity long port, firing into a large mouth that equaled about 3 times the regular port area, and I was amazed with the spl out put, and how clean it sounded, since it was in a vette, and the box is right behind the guys head, that was important to me, and him.  But think of this too, to achieve max vent velocity, you have to make a smaller port area, smaller  port areas, usually lack spl, but are better on sq, and low end gains. Long large ports will get the highest spl, based on if that is what the woofer likes, for example a high Qts woofer, (0.5-0.

I see that you found BBPro6.0 in another thread, down load it, and try it out. Try these variables to, and then play with port length,

my personal guidlines for ported are:

SPL  50% of woofers cone area, length based on air space, and Fs

SQ  25% of woofers cone area

even another formula, which is simple, and straight forward and non biased of SPL/SQ, find the woofers  QTS, and cone area  Multiply Cone area, by Qts

say a 12" with a 90sq in cone area, with a QTS of .30 is a 27"sq port area

That seems to be the most optimum, easiest way to find port area, and to find velocity, like I said, mess with box air space, and port length

thats my 2cents