design basics

[amos]

I'm considering building a pair of large and low tunes sub in the future, and have a few, ...well... alot of questions.

Ports: Does the port have to be entiely contained within the enclosure? I would assume not.

Is the air column of the port considered part of the effective enclosure volume? Or is it subtracted.

If the air column is added, then the volume of an external portion of a port would need to be added, Right?

I get really confused when I read about high pass filters. If I set my speakers to small in bass managment of my receiver, Isn't high pass taken care of by the receiver?

Thanks in advance for anyone's help. I've been lurking in the forum for a while and have been inspired. All Heritage HT in the works!

[michael hurd]

The port can be either internal or external. ( like a chimney ) You must consider the port as a solid projection into the box, when calculating volume.

There is a good free program on the internet called "boxnotes". You enter in external dimensions and it calculates the volume for you, taking into accont the volume of the port displacement, the driver and bracing. ( for the style of window brace that they calculate ) That program also calcuates the internal resonances and highlights them. Moving the subwoofer driver up or down can have an effect just as changing dimensions and keeping the net volume the same. Most of these resonances are above the intended passband of the sub, but can be triggered by the driver none the less.

[Jay481985]

actually the receiver does low pass..... it passes the low signals to the subwoofer. The high pass basically cuts whatever off so it does not over excursion.