Front or rear port placement?

[JLC7]

Are there any pros or cons to placing a port on the front as opposed to the rear or vice versa? More flexibility in placement? Aesthetics?

I'm trying to figure out whether it'd be a good (or bad) idea to place the port in the front, making the speaker taller and taking advantage of the increase in volume to tune lower. Seems like there's nothing wrong with that, let me know if it's not.

Thanks.

edit: While we're at it, do you add an inch in length to the calculated port length when using flared ports? So if you need a 3" port, your port will end up being 4" long including the flared portion? Is this correct?

[peter_m]

Port measurements: http://www.psp-inc.com/psp-inc.com/p...calculator.cgi

Peter

[Geek]

Hi,

After trying both, I definately will keep them off the rear from now on. Positioning is too critical... a few inches can make the difference between mud and sweet.

Cheers!

[audiokinesis]

I use rear porting and variable-length ports (Precision Ports' modular system).

The "mud" referred to by Geek is caused by excess boundary reinforcement of the port's output. The answer, in my opinion, is to tune the port lower so that the port's output peaks at a lower frequency, were the additional boundary reinforcement is welcome. When done right the result, instead of mud, is deeper bass extension than you'd have had otherwise.

I readily admit borrowing the technique of taking advantage of boundary reinforcement of the port's output from Audio Note UK.

In addition to optimizing for boundary reinforcement, changes to port length can also optimize for amplifier output impedance.

Note however that the longer the port, the more likely you are to get midrange coloration from pipe resonance within the port itself (imagine talking through a cardboard tube). The possible presence of such coloration is another argument for placing the port on the back rather than the front of an enclosure.

All that being said, I think that most professional designers opt for placing the port on the front of a speaker. If I wasn't using an adjustable-length port system, I probably would too.

Duke

[bastek]

I have dual ports in mine. One front one back. Depending on room and application, stuff one up really tight and you're set.
Any drawbacks?

[audiokinesis]

Sounds like a good idea to me, Bastek!

Multiple ports, where you can plug one or more, is another way of changing the port tuning. In theory you would lose bass linearity at a lower maximum SPL with one or more of the ports plugged because you'll run into turbulence sooner, but if you're not pushing the speakers that hard (or if you had more than enough port area to begin with) then it won't be an issue.

Duke

[Brett]

I much prefer the ports in the rear or on the bottom with the speaker raised; works best on carpeted floors. Neither should make much difference to the LF response, but any unintended higher freq info that comes out of the port will not mess with the direct sound.

I tune ports once the box is completed and ant calculations are only intended to get me close.

[ZilchLab]

Rear ports confer the advantage of being able to use heavy fill with less concern regarding blocking the duct inlet(s)....

[LineSource]

I follow the B&W science and put the port on the bottom of the cabinet, using legs and a base plate to create a horizontal "V" shape bottom opening - closed in the back - that pushes the bass sound forward.

This port design
1) gives max floor gain
2) gives most uniform gain in different placements & floor material
3) avoids any direct path to your ear from rear-cone waves
4) typically allows the longest port tube inside the box
5) the rear cavity in base can hold Xover compoments
6) hides ugly big port holes with massive radius flare

[harwoodspark]

I prefer front ported speakers. Speakers with rear ports usually prefer being pulled out into the room. Not really feasable in my living room.

Si.