Figure port length of a 90° elbow?

[chuey_316]

I need to use 90° elbows on my ports to get the length needed for my abc boxes tuning. Does anyone how much port length the 90° elbow adds, and/or how to figure it? They are 4" ports btw. Thx in advance.

[philrab]

Port length is measured down the center. Measure the inner radius of the elbow, and outer radius, and the average of the two should give you the center.

[ChevyBoy95]

Well, the port length is measured down the center of the port..... like this....

Black line is actual port length, so 23.25" + 11.75" = 35" of port length

Red line is length of the inner port wall (most way noobies think it is measured.) This would result in 20.75" + 9.25" = 30" which would give incorrect tuning from what your were desiring.

[ChevyBoy95]

So, for a tube or circular elbow, you imagine a line floating through the DIRECT center of it.

For you to know the exact length it creates, you need to do some math on your own.

If the 90 degree tube is as small as it could possibly be, the port length of it would be 3.14" (diameter * pi / 4),

but in reality PVC 90 degree tubes are a bit bigger (with a small bend at the short side). But a good estimate would be like 4" or so.

[chuey_316]

Had thought about putting a cap on each of the straight pieces, and filling them with something like sand. Then adding the elbow and measuring the empty space after the sand fills the elbow. Would that be an accurate way of measuring the added length?

[islandpride684]

Why? Just use the above method using a measuring tape or a long ass ruler or an L....

[chuey_316]

I'll use the method above. Just curious about the sand method is all. With most boxes the port being a little off is no big deal, but it can dramaticaly alter the performance of an abc box, so anything that gets a closer estimate the better. I do appreciate the info.