Rear Mounted Port Tube Location

[Uncle Paul]

Any reason not to position rear mounted port tubes directly behind the woofer?
What is the best practice for rear placement?

Thanks,
Paul

[johnaec]

I have a number of JBL cabinets that have rear ports and the main problem I've found is that distance of the cabinet from the wall can have a dramatic effect on LF response when the cabinet gets close to the wall - it really seems to change the LF resonance out of the port, depending on distance, though I couldn't tell you the exact quantitave difference...

As far as location of the rear ports in the cabinets, I don't know what differences there might be.

John

[Zilch]

Supposedly, the port should not be directly behind the woofer, though JBL does it in some designs....

[Mr. Widget]

I've found is that distance of the cabinet from the wall can have a dramatic effect on LF response when the cabinet gets close to the wall - it really seems to change the LF resonance out of the port, depending on distance...

I've noticed this too. In general I prefer speakers away from walls anyway though.

though I couldn't tell you the exact quantitave difference...

Me either...

Supposedly, the port should not be directly behind the woofer....

I've read that too, then again I have also read that the port(s) can be anywhere on the cabinet.


Widget

[Robh3606]

You don't want it behind the driver so there is no direct radiation off the back of the cone that could bleed out of the port. If you look at JBL's with the port that lines up with the driver you see the magnet only not the cone.


Rob

[Mr. Widget]

Sitting around on a Friday evening talking about the best location for a reflex port... geez!

I am outa here!



Widget

[Robh3606]

No I am watching SG-1 this is a commercial break!

Rob

[GordonW]

Bah, TV sux, build speakers instead!

Regards,
Gordon.

[DavidF]

Bah, TV sux, build speakers instead!

Regards,
Gordon.

Only between innings.

Have to get around to listening to them some time, right?

Put them anywhere they will fit and still have several inches elbow room to spare around the interior port end. If you have the choice, place them near the woofer.

David

[duaneage]

Try to keep the opening at least 3 inches from a cabinet wall and 1 inch on the side. If the port is too close to a cab wall it may not operated with enough linearity. This can cause power compression at high volume levels.

[stevem]

Try to keep the opening at least 3 inches from a cabinet wall and 1 inch on the side. If the port is too close to a cab wall it may not operated with enough linearity. This can cause power compression at high volume levels.

Does this hold true with slot ports? I used slots on either side of my woofers, and one wall of the port is formed by the sidewall of the cabinet. I have tuned them to my target frequency with no problem. The box software I used was pretty accurate in predicting the port length. I just had to do a little trimming. Any idea of what level any power compression might be audible?

[Guido]

The 250ti has it exactly centered behind the woofer!

It shouldn't make any difference.