[Danny Richie]

You can put a divider down the port without effecting too much.

Doubling up the panel thickness will help a lot too.

[mlundy57]

You can put a divider down the port without effecting too much.

Doubling up the panel thickness will help a lot too.

Thanks. I had thought about a divider down the center of the port but was worried about two issues. First was the fact that it would displace some of the port volume and second has to do with wave action when it flows around an obstacle.

The second concern is based on my knowledge of water flow rather than sound waves. When a flowing current of water meets an obstacle such as a bridge piling in the center of the river it splits and passes over the leading edge smoothly. However, when it passes over the back end of the obstruction it does not recombine smoothly. The current is turbulent, swirls, and even flows backwards in a small area (eddy current).

What do you think about designing the divider so it is rounded at the leading edge and tapers to the trailing end, sort of an elongated teardrop shape?  Should the divider be a short piece (3"-4") in the center of the panel or should it extend all the way to the mouth of the port?

Should I make the port length longer to compensate for the divider's displacement or will it be negligible?

[Danny Richie]

Thanks. I had thought about a divider down the center of the port but was worried about two issues. First was the fact that it would displace some of the port volume and second has to do with wave action when it flows around an obstacle.

The second concern is based on my knowledge of water flow rather than sound waves. When a flowing current of water meets an obstacle such as a bridge piling in the center of the river it splits and passes over the leading edge smoothly. However, when it passes over the back end of the obstruction it does not recombine smoothly. The current is turbulent, swirls, and even flows backwards in a small area (eddy current).

What do you think about designing the divider so it is rounded at the leading edge and tapers to the trailing end, sort of an elongated teardrop shape?  Should the divider be a short piece (3"-4") in the center of the panel or should it extend all the way to the mouth of the port?

Should I make the port length longer to compensate for the divider's displacement or will it be negligible?

A 20Hz wavelength is 56 feet long. 40Hz is 28 feet long. The divider will have no effect on the sound waves.

If you want to equate it to water then imagine 15 foot waves passing by and you are sticking a pencil in front of it.

Round the corners and edges though because of air flow around it. You don't want to create a little wind noise around it. You need smooth air flow.

And if the port diameter decreases slightly then it is the same as if you made it a little longer. So to tune it the exact same the port would need to be shorter. Just flare both ends with a radius and it will just about equal out.

[mlundy57]

Will do. Thanks Danny

Mike

[nickd]

A short panel between the top plate and the next plate down (in line with air flow) will do it. Same on the bottom. The flat brace at the woofers will have to have multiple holes on each side of the "truss brace" instead of the one large hole. That will allow a surface for glue down. Tying the two panels together with an in line "truss brace" will add quite a bit of strength and should not impede airflow. the brace does nor need to run full length front to back. just long enough to support those big panels so they don't resonate.

[bdp24]

A short panel between the top plate and the next plate down (in line with air flow) will do it. Same on the bottom. The flat brace at the woofers will have to have multiple holes on each side of the "truss brace" instead of the one large hole. That will allow a surface for glue down. Tying the two panels together with an in line "truss brace" will add quite a bit of strength and should not impede airflow. the brace does nor need to run full length front to back. just long enough to support those big panels so they don't resonate.

3/4" dowel would work fine here, wouldn't it?

[bdp24]

A 20Hz wavelength is 56 feet long. 40Hz is 28 feet long. The divider will have no effect on the sound waves.

If you want to equate it to water then imagine 15 foot waves passing by and you are sticking a pencil in front of it.

Round the corners and edges though because of air flow around it. You don't want to create a little wind noise around it. You need smooth air flow.

And if the port diameter decreases slightly then it is the same as if you made it a little longer. So to tune it the exact same the port would need to be shorter. Just flare both ends with a radius and it will just about equal out.

That reminds me, Danny, and this seems like a good time to ask you: With 20Hz being 56 feet long, how does a shorter room support frequencies that low? I've wondered about that since thinking of it in terms of low frequencies in cars.

[Danny Richie]

That reminds me, Danny, and this seems like a good time to ask you: With 20Hz being 56 feet long, how does a shorter room support frequencies that low? I've wondered about that since thinking of it in terms of low frequencies in cars.

For one, they can reflect around. Secondly just like in car audio it is all about pressure.