[SteveRB]

Hello,

Is there a way of calculating an appropriate diameter for reflex ports -- or perhaps a decent rule of thumb based on woofer diameter?

thanks

[mcgsxr]

From what I have seen playing around with freeware to optimize port size for a given enclosure and tuning, it comes down to speed of air through a port.  Too small and the port chuffs or makes other odd noises.  Too large and the port length becomes unmanageable.

winisd is what I use to model enclosures.  When you pick a port diameter, it calcs both port length, and a mach reading (speed).  It color codes mach readings to help interpret the results.

What size box, and what tuning do you seek?

[SteveRB]

I have been using WinISD to calculate different tunings of a 15" woofer in a 6 cuft box.

I am trying to understand the tuning of my Altec 846B enclosures (2 ports at: 4"x6").  I want to understand the difference between this system and the 846A which uses the same components in a semi aperiodic configuration.

[mcgsxr]

4 inch ports 6 inches long is either tuned high or in a HUGE box.  I would call 6 cubic feet huge, I have never built anything larger than 3 cubic feet.

Aperiodic tuning is essentially a lossy sealed enclosure.  Science types will no doubt rankle at my simplification, but in the end that is what it is.

So to oversimplify - the semi sealed box potentially provides deeper bass with a smoother roll off, but likely at the expense of efficiency in the mid bass.  IE the sealed box can play lower than the sealed box, but will not be as loud at certain frequencies.

If the winisd port calc is green (less than 0.16 by memory for mach) then you should not face issues with port noise.

[SteveRB]

That is my basic understanding as well.

Back to my question though, is there a basic rule of thumb for port diameter?

[SteveRB]

My plan is to build a new front baffle that can be easily converted from 846A aperiodic to 846B ported...

[JLM]

No rule of thumb as it varies with the driver.  But the theory works best if the length of tube is longer than it's diameter so that you're moving a cylinder of air versus a diaphragm of air.