Posted by GM [ 4.138.65.125 ] on July 21, 2005 at 17:03:27:

In Reply to: 704-8A tuning posted by spkrman57 on July 21, 2005 at 13:29:51:

Greets!

You're welcome! Uh, no, not per se anyway. I mean you use whatever size vent that's required to keep vent speed low at whatever Fb you've chosen, and if it's big and/or long, then I recommend damping down its harmonics as required to smooth its response out.

WRT designs that use 3/4" long vents (baffle thickness only), it's my understanding that high cross sectional area (CSA):length vent ratios don't have enough acoustic inertance to work as well as when the ratio is reversed, so can be overdriven easier, allowing the driver to overexcurse since it needs a longer time period to 'pump up' (for lack of a better phrase). IOW the ducted port's much more rigid air mass 'piston' damps the driver better and is acoustically more efficient than the large, flimsy membrane of the shallow vent.

That said, I've compared them and found they both perform well and have designed/built many well received speakers using big CSA:length ratio vents rather than making/recommending multiple smaller, longer ones since learning of this, so I'm not going to lose any sleep over it.

As always though YMMV.

GM

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