Port Tuning

[FellCrustacean8]

I heard that you can increase the box size and reduce the port size to keep the same tuning frequency. But is there any difference in performance between changing these parameters and how will it change compared to the basic formula. And if this is true, what are some formulas for box to port tuning frequencies. Does the formula remain the same and size just increases? the Vb increases to the desired volume and keep the Fb the same? I got the basic formulas from diysubwoofers.org

 

[kiwijunglist]

Port size is a bit vague. Do you mean port radius/length/volume.

I think you should have a go at installing winisd vary the parameters and look at the results. It's easy to use.

Sent from my SM-G900I using Tapatalk

 

[FellCrustacean8]

oh sorry port length

 

[tb46]

Hi FellCrustacean8,

Here is a web site you might fing interesting: Collo's DIY Subwoofer Enclosures

It's all trade-offs, but, one thing you want to watch for is the port particle velocity, keep it below ~15m/sec @ your actual listening level (or, @ Xmax).

I like to use Hornresp as it lets me simulate more complex port shapes than other programs, e.g.: WinISD or BoxPlot.

Regards,

 

[richie00boy]

You got it the wrong way round. If you increase box size you need to decrease port size to maintain the same tuning frequency.

As others have suggested have a play with winisd.

 

[weltersys]

You got it the wrong way round. If you increase box size you need to decrease port size to maintain the same tuning frequency.

As others have suggested have a play with winisd.

Or play around with the old nomograph below. As you can see, as box size increases, so does port size for the same fB. The dilemma with large displacement drivers in small boxes is large port diameters are required to keep vent velocity reasonably low, which requires a longer vent, so the vent area becomes much larger relative to the larger box.

 

[hollowboy]

You can make a rough test box with an external port, like a snorkel, to easily cut and try different lengths.

Large cross section port gives less noise (turbulence) at high excursion. Bigger boxes can be better such as by being less sensitive to speaker variation (heating during use etc), but are harder to adequately brace / move / fit in the same room.

Sidewinder Subwoofer

 

[weltersys]

You can make a rough test box with an external port, like a snorkel, to easily cut and try different lengths.

The idea of testing the port tuning is good, but the port must be inside for testing (unless you plan to leave the port external), as the area displaced by the port, and end correction will change if the external port is moved inside, which will change Fb.