Port calculation STUFFED vented box - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 4 Old 05-21-2020, 01:56 PM - Thread Starter
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Port calculation STUFFED vented box

Hi

I hope I didnt mess up...

I just built a ported box of 310L netto volume and stuffed it with insulation. I didnt stuff the port to prevent stuff coming out.

I read stuffing makes the box 20% bigger. This would mean my port is too short???

Its a slot port...

Will adding stuffing to the vent increase its virtual volume as well and solve the issue?

If not, the box is built but I could if needed add a tube port by just cutting a hole and putting in a pipe. But how to calculate a mix of round and slot ports?

Damn...

I added some pics. The sub is for my attic, so looks not important. Driver is not in yet
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post #2 of 4 Old 05-21-2020, 02:12 PM
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Originally Posted by belgiansound View Post
Hi

I hope I didnt mess up...

I just built a ported box of 310L netto volume and stuffed it with insulation. I didnt stuff the port to prevent stuff coming out.

I read stuffing makes the box 20% bigger. This would mean my port is too short???

Its a slot port...

Will adding stuffing to the vent increase its virtual volume as well and solve the issue?

If not, the box is built but I could if needed add a tube port by just cutting a hole and putting in a pipe. But how to calculate a mix of round and slot ports?

Damn...

I added some pics. The sub is for my attic, so looks not important. Driver is not in yet
Usually you dont add too muh stuffing to a ported box the way you do with sealed. Its only to solve some internal reflections and standing waves.

It will not model like the box is bigger if you add stuffing, you will lose up to a couple of db at the port tuning by adding too much.

Why dont you try it and see how you like it, experiment with it.

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Last edited by Javs; 05-21-2020 at 02:36 PM.
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post #3 of 4 Old 05-23-2020, 11:15 PM
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Quote:
Originally Posted by belgiansound View Post
Will adding stuffing to the vent increase its virtual volume as well and solve the issue?
It might "solve" it by drastically cutting down the output, so NO. And the air in the box is like a spring, the air plug in the port like a mass, they are two different things, somewhat like a car on its suspension springs.
- Stuffing the ported box is fine, I like it. DO clear out several port "diameters" inside the box to let the port breathe.
- Nah don't change to circular ports.
- Yes your tuning may come out a bit high, try it and see, port simulations aren't always too exact. You can always graft on an extension, a bit of a pain but not the end of the world. OR, glue in a flat piece to reduce the port height, yes you might lose a bit of flow.
- Per Harman/JBL research, radius those port edges as big as possible (1" roundover bit looks like), and add a flat flange inside (doesn't need to be too strong) so the inside of the port has a "wall" for more symmetric/linear airflow. Maybe extending 4-6" on each side of the port.
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post #4 of 4 Old 05-24-2020, 10:57 AM
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Quote:
Originally Posted by belgiansound View Post
I read stuffing makes the box 20% bigger. This would mean my port is too short???
Quote:
Originally Posted by head_unit View Post
Yes your tuning may come out a bit high, try it and see, port simulations aren't always too exact.

If the box is effectively bigger, Fb would be lower, so the port would be too long, not too short.

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