Is ok to use a metal tube as a sub box port?

It depends on the metal. Aluminum will ring strongly, may actually make more noise than the woofer and at a high midrange frequency for most typical lengths.

Iron not so much. Steel a bit more. Don't really know about copper. But the best would be lead.

Of course there is plastic pipe and that could be best if it is rated for pressure. That would have a thicker wall than something lighter duty.
 
Last edited: