Port Dimension question

[SOOTSHE]

Hi,

I'm building a pair of Altec 620 cabinets for a pair of GPA 604-8H coaxials.
I'm making the front baffle from 2 thicknesses of 3/4 inch MDF, so 1&1/2 inch thick.

I'll be using the same slot port as the standard 620 cabinet, but I'm wondering if I need to alter the dimension to account for the extra baffle thickness?

Cheers.

[604man]

Hi,

I'm building a pair of Altec 620 cabinets for a pair of GPA 604-8H coaxials.
I'm making the front baffle from 2 thicknesses of 3/4 inch MDF, so 1&1/2 inch thick.

I'll be using the same slot port as the standard 620 cabinet, but I'm wondering if I need to alter the dimension to account for the extra baffle thickness?

Cheers.

I would use 6in PVC pipe rather than the slot, and with a
coupling on the end you can make it variable, do not glue.

If the extra thickness bothers you, mount the x-over external in it's own cabinet..........GC

[SOOTSHE]

I would use 6in PVC pipe rather than the slot, and with a
coupling on the end you can make it variable, do not glue.

If the extra thickness bothers you, mount the x-over external in it's own cabinet..........GC

The extra thickness won't be an issue as far as cabinet volume is concerned, as I'll be keeping the internal volume the same as standard & so the cabinet will be slightly larger than standard.
What I'm wondering is....what size does the slot need to be if the front baffle is 1&1/2 inches thick? The standard slot is 11" x 2&1/2".

If I go with the 6" PVC pipe, what would the length be for standard tuning to match the 11" x 2&1/2" slot?

[SOOTSHE]

Found these calculators on line & they seem to be accurate.

I worked backwards from what I want to achieve....so, I determined that the 620 cabinet box tuning is 40Hz by entering the slot dimensions & changing the tuning frequency until I got a slot length of 3/4".

Then I changed the slot dimensions until I got a slot length of 1&1/2".

From my calculations, with a front baffle 1&1/2" thick, I should need a slot of 11" x 3" to maintain the original 40Hz tuning.

The second attachment shows the results when using a round port.
For this you need 2 x 7.9cm ports 1.4" long......or 1 x 6.5" port 1.4" long.

I prefer to use the rectangular port option to maintain the original look of the cabinets.

Cheers.

[604man]

http://greatplainsaudio.com/wp-conte...604_8H_III.pdf

Resonant freq is listed as 33.70 hz

The classical method of tuning is to tune the cabinet
to the resonant frequency of the driver.

You may get "chuffing" from the rectangle vent.

The PVC duct is easily tuned with the coupling.

I would use Baltic birch, apple birch plywood. 13 plys
for 3/4 inch plywood.

[SOOTSHE]

http://greatplainsaudio.com/wp-conte...604_8H_III.pdf

Resonant freq is listed as 33.70 hz

The classical method of tuning is to tune the cabinet
to the resonant frequency of the driver.

You may get "chuffing" from the rectangle vent.

The PVC duct is easily tuned with the coupling.

I would use Baltic birch, apple birch plywood. 13 plys
for 3/4 inch plywood.

Thanks for your input.

[aditya]

Found these calculators on line & they seem to be accurate.

I worked backwards from what I want to achieve....so, I determined that the 620 cabinet box tuning is 40Hz by entering the slot dimensions & changing the tuning frequency until I got a slot length of 3/4".

Then I changed the slot dimensions until I got a slot length of 1&1/2".

From my calculations, with a front baffle 1&1/2" thick, I should need a slot of 11" x 3" to maintain the original 40Hz tuning.

The second attachment shows the results when using a round port.
For this you need 2 x 7.9cm ports 1.4" long......or 1 x 6.5" port 1.4" long.

I prefer to use the rectangular port option to maintain the original look of the cabinets.

Cheers.

Yes, for a vent depth doubling, it requires the vent opening area to be increased by 25% approx in order to keep the tuning same.
The shape and location changes it a little on both the sides, meaning +/-.

Yes, a rectangular port is quite reminiscing compared to a circular one.