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Port Area

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Andrew Watts:
I am modifying some sub boxes to house 1x18 inch driver.
The driver is a B&C 18PXB46. The cabinet is only 140 litres, but models an acceptable response tuned to 40hz. The cabs have a single 6 inch port. At 40hz, it only needs to around 4 inches long. Do you think the port would be large enough to gangle the air movement without artifacts?

David Morison:

--- Quote from: Andrew Watts on October 28, 2022, 09:08:01 PM ---I am modifying some sub boxes to house 1x18 inch driver.
The driver is a B&C 18PXB46. The cabinet is only 140 litres, but models an acceptable response tuned to 40hz. The cabs have a single 6 inch port. At 40hz, it only needs to around 4 inches long. Do you think the port would be large enough to gangle the air movement without artifacts?

--- End quote ---

Probably not, no.

First though, can I check if you meant 18PZB46 please? (Easy typo to make after all, & I've never heard of a PXB, unless it's an OEM for some other company that you're re-using?)

Assuming PZB, then in 140l tuned to 40Hz you're going to have vent airspeed about 37ms-1 when driven to XVar, so I'd expect it would be worth adding a second vent, even though that does mean more surgery to the cab and a slight reduction in net cabinet volume.

HTH,
David.

Andrew Watts:

--- Quote from: David Morison on October 29, 2022, 09:54:19 AM ---Probably not, no.

First though, can I check if you meant 18PZB46 please? (Easy typo to make after all, & I've never heard of a PXB, unless it's an OEM for some other company that you're re-using?)

Assuming PZB, then in 140l tuned to 40Hz you're going to have vent airspeed about 37ms-1 when driven to XVar, so I'd expect it would be worth adding a second vent, even though that does mean more surgery to the cab and a slight reduction in net cabinet volume.

HTH,
David.

--- End quote ---

Sorry David. Yes a typo. It’s very tight in the cab face, so I’m not sure how I’ll go. I just tried the driver with the single port. Seems to sound good, but I haven’t driven it to Xmax

Ivan Beaver:

--- Quote from: Andrew Watts on October 29, 2022, 06:20:24 PM ---Sorry David. Yes a typo. It’s very tight in the cab face, so I’m not sure how I’ll go. I just tried the driver with the single port. Seems to sound good, but I haven’t driven it to Xmax

--- End quote ---
Where the port area starts to matter is at higher levels of excursion.  At lower levels a smaller diameter port can work fine.

A smaller port cannot pass the larger amount of air without "chuffing" or whistling and other sounds.

It is best not to force the air through the port, and rather "let it flow".

Andrew Watts:

--- Quote from: Ivan Beaver on November 01, 2022, 08:15:58 AM ---Where the port area starts to matter is at higher levels of excursion.  At lower levels a smaller diameter port can work fine.

A smaller port cannot pass the larger amount of air without "chuffing" or whistling and other sounds.

It is best not to force the air through the port, and rather "let it flow".

--- End quote ---

Thank.

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