Port placement

[Radik]

Always wondered if the placement of a port can be a great impact on a sub's performance / output. Ok, below are 3 enclosures,(now i am not the best artist around)so excuse the crappy drawings. Anyway, would jus like to know which would give the best SQ, best SPL, would go the lowest, etc. Tell me what u think. Oh yea, all the enclosures are same size, ports the same length, same sub. Everything same except port placement.

http://www.we-todd-did-racing.com/we...ZmQzMXk1NDE%3D
(Click the link then open). Thanx

[Radik]

The link isn't working so i'll have to post the pics a different way.

[chengs]

I am having some questions about the port tuning. I am in the process of making a new cabinet for a pair of old Celestion. I would like to put the port in front and just wondering where can I get answers for my questions below:
1. If everything else stays the same, can I place the port location wherever I want? Such as moving from back to front baffle or moving a few inches away from the original position? I know a front port will be easier for speaker placement, but do I have to change the port length and dia?
2. The total length of the original port is 4 inches and with a 2" inside dia. I am trying to increase the thickness of all walls from 1/2" to 1 1/2" but will have the same internal volume, do I have to also increase the length of the port by 1 inch, so it will have the same inside length(3 1/2") as the original to stay in same tune? Is it only the inside length(the part of port measured inside the wall) and dia of the port that matters or something else? Or, is it the total length and dia that matter? If this is the case, I guess we can not have a port length smaller than the thickness of the wall. I remember seeing somewhere there was this ported sub with a pipe sticking out of the box a foot or so.....wondering if there is any part of the port sticking out into the box?
Thanks in advance for answers and point of direction for info that I can look up.

[Ron E]

Port location is not very sensitive at all, it can go anywhere inside or outside the enclosure as long as it isn't a long way away from the woofer. A long way means (conservatively) more than 1/10-1/20 of the wavelength - which would be ~2.5-5 feet for a 20Hz tuning or half that for a 40Hz tuning.

It can be better to put it on the back because it diffuses any extraneous noise from the port.

[Radik]

which would be ~2.5-5 feet for a 20Hz tuning or half that for a 40Hz tuning

Correct me if i'm wrong, but does this mean that the further the port is from the speaker, the lower it is tuned?

[Salas]

Hello,

The only real consideration about reflex port placement in a speaker is the severity of the tube inner standing wave modes that do change in harmonic content and level in accordance with its position in box relative to the woofer too.
If you have enough clearence from back wall (50cm at least for a sub) put it in the back not to have added tube aural dirt on axis.
It takes good software modelling else.

[Ron E]

Correct me if i'm wrong, but does this mean that the further the port is from the speaker, the lower it is tuned?

No, it means the lower a port is tuned, the longer the wavelength, and the farther it can be from the woofer and still maintain the proper phase relationships.

The actual tuning of the port does not change with distance.

[fortyquid]

It's not a rule, but it is generally a good idea to place the port as low (close to the floor) as possible, as the will increase the bass efficiency considerably by boosting the port gain, due to a "louder" reflected floor source. There was a discussion about flared ports that you could dig up that addressed this issue a while back. Also, check out PolkAudio.com's little tutorial about their "Power Port", designed with the same concept in mind.

http://www.polkaudio.com/home/techno...=3&speaker=164