Port questions

[Bbisig]

Im building a new box and need to know a few answers

1. How does the lenth of the port work is the measurement from the outside face including the board thickness or is it how deep the port must sit behind the inside face of the box?

2 will a slot port of 2"Wx8"Hx9"D be comparable to a round port 4"x7.25"?....i used this calculator to get that http://www.carstereo.com/help2/Articles.cfm?id=31

3. Whats the difference between a square and slot port

 

[jol50]

Port can be round, square, or slot and will work the same within reasonable and proper sizes. The length would be end to end of the port tube of continuous same size, you can only count part of a taper if you taper the ends...depending on how you taper the port. I don't think you want any step or interruption in or at end of port, or change in size. That can make noise and/or change tuning. You need a tube the same size/shape one end to the other, the tapers help flow the air in/out of the tube so it can be smaller and not make noise going around the corner at the ends. That number looks good, if you use a net calculator I'd just check it on another one elsewhere. I like winISD its simple and works for me.

 

[Bbisig]

i just looked online the square inches of a 4 inch round port is 12.56" and a port 1.5"x8" is 12 square inches could i use that with the round port lenth?.....the specs are for the box the port be a 4" round port 7.25" long

 

[jol50]

The larger the tube area, the longer it needs to be to tune to same frequency. It is like a ratio of area (size) to length of the tube that determines the frequency it works at...that you want for your box. That should be very close, dropping that half inch of area at same length would tune it slightly lower. You should put it in a box program and look at it though.