Help with port length please

[Bobhof]

Hi All, I am a newbie building a sub and speaker pair. I described my system in this post (ignore the cabinet design images, they were modified after getting some advice on this forum): Help with ar.com kit from madisound

Everything is going well. My cabinets are built and the varnish is drying. I just wanted a bit of help with deciding the final port lengths. I have calculated the internal dimensions of my boxes and subtracted the volumes of the braces etc. The details are as follows:

SPEAKERS:
Vas: 27.7
Qts: 0.44
Fs: 36.8
Volume of box: 12 liters
Port diameter: 5 cm

SUB:
Vas: 46.8
Qts: 0.38
Fs: 30
Volume of box: 27 liters
Port diameter: 4.5 cm

Note that the ports are different diameters. The system will be used in a relatively small room.

Thanks for any help,
Rob

[Curmudgeon]

This is not the answer you're looking for, but....

After the drivers are broken in, experiment with different port lengths. This is something you should do in any event. Drivers have been known to differ from their published specs, and details such as box stuffing, (both amount and material) box flexure, room placement, and personal taste all influence the ideal port length.

It's pretty easy to do, and the port can protrude a bit from the box to make changing simpler. Ideally, the two speakers should be somewhere pretty close to the final location, and you should make the changes to both L and R speakers.

[richie00boy]

I would say that the satellite speaker should be sealed as the box is really too small to go vented successfully (due to the high Qts), with a sub or in a small room IMO.

The sub should be tuned in the region of 27-33 Hz so make the vent as long as you practically can because with that diameter you are going to need a hell of a long vent to get down to those frequencies in that relatively small box. I would even say it's practically impossible unless you downsize the vent diameter considerably. Which I guess you can quite easily - am I right in guessing it's an 10 inch unit?

[Bobhof]

Thanks for the advice.