Small VS. Big Aero Ports

[ShagggDiesel 25]

I haven't had much experience with the science behind port tuning/building, but I've been doing a little research and some calculations and have a question concerning port "size".

Let's say I have a 1 cu.ft box, and I want to put a aero port in it with a tuning of about 33hz. I used a calculator and I came up with a 2" diameter port with a length of 6.3 inches.. or a 3" port with a length of 15+ inches.. My question is, what's the difference in having the 2" short port as opposed to the 3" long port and achieving the same tuning? To me it would just seem logical to go with the small and short port to save space and material, and just be an overall convenience.. but this is one of those situations where I feel it's too good to be true. What are the pro's (if any) and cons to using the smaller port as opposed to the larger?

Note: This is not a situation I'm in, I'm just using a simple 1cu.ft enclosure as an example.

Thanks ahead.. I'm probably going to bed soon so if I don't reply tonight i'll check back on this thread tomorrow morning.

-Shag

[Julian 641]

More port area, What woofer are you using?

[Duran 387]

Depending on the woofer, more or less port area is required to be effective.

[ShagggDiesel 25]

Like I said, this isn't to help me out with a situation I'm in, it's just to build my knowledge with the subject a little bit for future references. But let's say in one box I have a $30 12" Dual subwoofer from Wal-Mart, and in another box (exact same dimensions) I have something like a Fi SSD, What would the difference be?

[magicguyken 0]

The Fi driver is going to move ALOT more air than the Dual driver. I would use the larger port for the Fi driver. Various "elbows" and connectors are available, to help fit the longer port inside the box. Aero ports do a great job at reducing port noise, but I think that the smaller port would suffer from unwanted turbulence. The smaller port would probably be OK for the Dual woofer.

Edited September 11, 2010 by magicguyken

[Julian 641]

different woofers require more or less port area, if i remember correct port area and xmax corolate with eachother.

[KU40 173]

Not sure why nobody has said it, but one of the main reasons to have larger port area is port noise. If you use too small of a port, the air will have to move faster through the port since the area is smaller, and it can cause a chuffing sound and even hinder performance of the sub. It would be similar to sucking through a coffee straw vs. a regular straw. If you have x amount of air to move through a port, it will have to move faster through a smaller port to get it all through in the same amount of time (one stroke of the subwoofer's cone). If the port is too small, all of the x amount of air may not make it through the port in time before the cone has changed direction, and now that amount of air that didn't make it through is pushing the opposite direction on the sub's cone, which is trying to pressurize the box in the opposite direction.

Larger diameter subs and those with higher xmax need larger port area because they displace more air with each stroke So while your walmart sub may only have 8 mm xmax so it may be ok with a 3" diameter port, an SSD has three times that amount and would likely need at least one 4" port or larger.

[Tirefryr 1,742]

Not sure why nobody has said it, but one of the main reasons to have larger port area is port noise. If you use too small of a port, the air will have to move faster through the port since the area is smaller, and it can cause a chuffing sound and even hinder performance of the sub. It would be similar to sucking through a coffee straw vs. a regular straw. If you have x amount of air to move through a port, it will have to move faster through a smaller port to get it all through in the same amount of time (one stroke of the subwoofer's cone). If the port is too small, all of the x amount of air may not make it through the port in time before the cone has changed direction, and now that amount of air that didn't make it through is pushing the opposite direction on the sub's cone, which is trying to pressurize the box in the opposite direction.

Larger diameter subs and those with higher xmax need larger port area because they displace more air with each stroke So while your walmart sub may only have 8 mm xmax so it may be ok with a 3" diameter port, an SSD has three times that amount and would likely need at least one 4" port or larger.

While this is mostly true, just because the driver is capable of more throw than the other, doesn't mean it is going to use it.

[ShagggDiesel 25]

Thanks for the info guys. Just wanted to clear some things up and further my knowledge, and as always, the SSA forum family helped a ton.

[SpeakerBoy 64]

What about the same driver in two different boxes? The first box with reccomended port area and the other with a larger diameter (but longer) port. What differences would there be in performance?

[Duran 387]

What about the same driver in two different boxes? The first box with reccomended port area and the other with a larger diameter (but longer) port. What differences would there be in performance?

The one with sufficient port area will probably perform better

[SpeakerBoy 64]

more specifics please ^