Optimal Port Placement.

[Juggy]

Hello,

I understand there was a recent post here regarding front or rear port.

I wanted to elaborate on that question, as i am wondering myself, what the 'rules' are in terms of port placement. I have never completely understood front vs. rear port placement.

I'm designing a set currently, and was wondering where to place the port. I know that downward firing ports produce good dispersion and rear ports do eliminate further mid-range leak. But want to know how i should determine where the port is placed.

Thanks for any help.

[SaSi]

The only information I've read on the matter is that:
A front vent is prone to produce audible "breathing", especially if the vent has inadequate diameter.
A back vent is eliminating this but is more difficult in placement as the enclosure should not be close to the back walls.
A downward firing vent combined with purpose built stands is good as the stands ensure there is nothing obstructing the vent.

There is also the possibility of an upward firing vent, although I've never read about that placement. I do have a vintage B&W subwoofer with a vent firing upwards when the unit is in the upright position.

[schmutziger]

There are atleast 3-4 loudspeakers that uses upwardfiring ports that i'm aware of.

Carlsson OA58
Carlsson OA58.2
Larsen 4
Larsen 6
http://www.carlssonplanet.com/oa58.php
http://www.carlssonplanet.com/oa58ii.php?lang=sv&
http://www.larsenhifi.com/larsen4.htm
http://www.larsenhifi.com/larsen6.htm

[badman]

Upfiring is bad in that it allows objects and dust to drop into the enclosure.

[seagrasser]

Would anyone consider putting the port on the side of the enclosure if there is adequate clearance.

Just a thought.

[Vigo]

I build some speakers that had a vent upwards, the speaker was not that good. Dont know if it was beacuse just of the vent but it was not realy ideal for many reasons. But i wanted to try it sow i did.

[schmutziger]

Originally posted by badman
Upfiring is bad in that it allows objects and dust to drop into the enclosure.

Is there a real disadvantage to have the port upward?

[Juggy]

I'm guessing that with an upward firing port there is not boundry re-inforcement. With a downward firing port there is a boundry quite close by. Same with putting the port lower on the front or back of a speaker.

[schmutziger]

Originally posted by Juggy
I'm guessing that with an upward firing port there is not boundry re-inforcement. With a downward firing port there is a boundry quite close by. Same with putting the port lower on the front or back of a speaker.

Let me qoute from the first link i posted about OA58
"...The OA-58 like all other OA speakers shall be placed against a wall. The room is a part of the design of the speaker where the bass-boost supplied by the wall is included in the design in order to have a correct sound-reproduction. "

I read somewhere that a dowwnfiring port could make the port to appear longer due to reflected air.
But it was considered a small problem.

Guess its all about implementation.