15" sub with port compression vs 12" without compression

[Therock482]

I have been spending the last hour reading Triticum's Port Calculator and realize that my box is causing port compression and limiting the output of my Fi Q 15. Currently I have 2.8 cubes with (2) 4" aeroports. 

I have a 2000 watts of power and can do a maximum box dimension of 49.5"L x 19.5"H x 10"D with (3) 4" aeroports, this equals 2.8 cubes and 37 sq. in. of port. According to Tritcum's calculator I need a minimum of 41 sq. in. of aeroports.

My questions is this: Will my 15" Fi Q with port compression still have better output than say a 12" Fi Q without port compression that has more ideal port area?

Thanks

 

[Triticum Agricolam]

What vehicle is this going in?

So here is the thing with port compression, with your current setup it is probably costing you around 6 dB of output (I'm estimating).   However this loss is only going to be right around the tuning frequency.   Increasing your ports up to three 4" ports will certainly help, probably will gain you around 2 dB (again, estimating).  I think that adding that additional would be worth doing, especially if you are getting noticeable port noise now. 

As far as switching to a 12" goes, you may get a little better output between 28-40 hz, above that point port compression isn't going to be an issue anyway so the 15" is going to beat the 12" pretty handily.

What your best course of action is depends on what you goals are the system.  If its just for music, I'd probably add the third port and see how it sounds.  If you don't get noticeable port noise, I'd not worry about it and just roll with it.  If you compete with it and/or 30-40 Hz output is really important to you, then maybe dropping down to the 12" in a more port optimized box might be better.  

[Parker Grundy]

U could get a PSI high excursion passive radiator 18, or 2 15s. My box is 1.85ish net. It sounds great.  

Ssa icon 12,  psi high excursion passive radiator 15, ssa 2200rms monoblock, ssa 4 channel,  us acoustics 4 channel, 2 crescendo supers, 2 ssa tweets, 4 ssa midbasses, and  2 focal 7x10 3 way 100rms speakers..

[Therock482]

This is a "Mid Gate" Box for a chevy avalanche, I took the factory mid gate out and used it as a template to make my box. This box is just for music, not competition

 

A passive radiator is an interesting idea, does anyone know if that would yield a better outcome that (3) 4" aeroports?

 

Thanks for the help 

[Triticum Agricolam]

1 hour ago, Therock482 said:

This is a "Mid Gate" Box for a chevy avalanche, I took the factory mid gate out and used it as a template to make my box. This box is just for music, not competition

 

A passive radiator is an interesting idea, does anyone know if that would yield a better outcome that (3) 4" aeroports?

 

Thanks for the help 

Using passive radiator/s (PRs) would work better than three 4" aeroports, IMHO.  They would also free up some space to increase your box volume a bit, like up to 3.5 cu or so.  The primary disadvantage of PRs is their additional cost.  Generally you need twice as much PR cone area as you have sub cone area, so you would be looking at two 15" PRs (one 18" PR wouldn't be enough).  

Here is what I'd suggest:

https://psicaraudio.com/product/15-passive-radiator/

[Joe X]

If you can do 12D you can go with this (figure is just an assembly guide):

 

 

 

It could actually be done even smaller but the sub will work better and be louder in the 3.5-4 net range than in some 2.8 net or so.

 

 

[Therock482]

Thanks for the replies guys!

Joe X, I don't think I can stretch it to 12" deep, I have a wakeboard boat and put wake surf boards in the back of the bed and to maintain room for the boards. I appreciate the design.

Triticum, would the PSI 18" High excursion radiator work? I think I have barley enough width for (3) 15's if that is what it takes. 

[Triticum Agricolam]

2 hours ago, Therock482 said:

Thanks for the replies guys!

Joe X, I don't think I can stretch it to 12" deep, I have a wakeboard boat and put wake surf boards in the back of the bed and to maintain room for the boards. I appreciate the design.

Triticum, would the PSI 18" High excursion radiator work? I think I have barley enough width for (3) 15's if that is what it takes. 

In my opinion the 18" high excursion PR isn't going to be enough, unfortunately.  

[Therock482]

10 hours ago, Triticum Agricolam said:

In my opinion the 18" high excursion PR isn't going to be enough, unfortunately.  

I really appreciate your input, I have 2 more questions for you:

1) By my calculations the (2) 15" PRs only have 9% more displacement as compared to the (1) 18" high excursion PR, is my math right? The cost is about the same either way, I was leaning towards the 18" PR because it would take up a little less space inside the box.

2) It is possible to estimate how much db gain the PR scernario would give more over the box with (3) 4" aeroports?

 

Thanks again!

Jake

[Triticum Agricolam]

3 hours ago, Therock482 said:

I really appreciate your input, I have 2 more questions for you:

1) By my calculations the (2) 15" PRs only have 9% more displacement as compared to the (1) 18" high excursion PR, is my math right? The cost is about the same either way, I was leaning towards the 18" PR because it would take up a little less space inside the box.

2) It is possible to estimate how much db gain the PR scernario would give more over the box with (3) 4" aeroports?

 

Thanks again!

Jake

1. Your math is correct, but the single 18" PR has quite a bit more excursion compared to the two 15" PRs.  You can probably get away with the single 18" PR if you set your subsonic filter to no lower than 26 Hz.  

2. Here is a graph of the approximated difference in output between the PR box (orange line, 3.5 cu ft net tuned to 32 hz), vs your three 4" aero port box (green line, 2.8 cu ft net tuned to 32 Hz)