How do you know when your box is too big?

[Reilly]

Op,

Too big, the sub unloads and pops easy. Becomes very one dimensional, usually just plays lows(depending on tuning).

You are right about peaking low even with a high tuning, but about the unloading issue, you are almost correct, you can always fight against this by using a loading wall, i saw a vid of Ric´s truck demoing terry brocks, he has a big ass box for a 10" just like he said, he´s using sub and port side, i´m pretty sure he´s doing it because the side of the car helps to control the cone acting like a loading wall since he´s using a big ass efficient box, but i might be wrong, would like to get his input on this

I was answering the question of "how do you know when your box is too big", not how to fight it.

[Torres]

i've seen talk about using a subs specs to figure the port area of a specific sub, which won't change regardless of box size, since the port is made for the sub itself (meaning a sub will have the same port area whether it's in a 3 cubic foot box or a 6 cubic foot box). but i haven't seen any talk on how to do this. i know little pieces, but i'm curious

[BJD3]

i've seen talk about using a subs specs to figure the port area of a specific sub, which won't change regardless of box size, since the port is made for the sub itself (meaning a sub will have the same port area whether it's in a 3 cubic foot box or a 6 cubic foot box). but i haven't seen any talk on how to do this. i know little pieces, but i'm curious

^^

One time bump.

[RAM_Designs]

i've seen talk about using a subs specs to figure the port area of a specific sub, which won't change regardless of box size, since the port is made for the sub itself (meaning a sub will have the same port area whether it's in a 3 cubic foot box or a 6 cubic foot box). but i haven't seen any talk on how to do this. i know little pieces, but i'm curious

I believe we briefly talked about this before. I use a method where i find the displacement of the sub in cm^3, then multiply by .016, and that gives you a somewhat optimal amount of port area to use in in^2. For example, let's use the Fi SSD line of subs. All of them have 20mm of xmax one way, so 4cm of xmax p2p.

10" model

sd: 310cm^2

multiply by 4cm to get the volume of air displaced: 1240cm^3

multiple by .016 to get "optimal" amount of port area: 20in^2

12" model

sd: 480cm^2

multiply by 4cm to get the volume of air displaced: 1920cm^3

multiple by .016 to get "optimal" amount of port area: 31in^2

15" model

sd: 810cm^2

multiply by 4cm to get the volume of air displaced: 3240cm^3

multiple by .016 to get "optimal" amount of port area: 52in^2

18" model

sd: 1210cm^2

multiply by 4cm to get the volume of air displaced: 4840cm^3

multiple by .016 to get "optimal" amount of port area: 77in^2

Now I realize that optimal might not be the best word to use, but you really can't go wrong by using these figures if installing these subs using the manufacturer's recommended box size and power. Adjustments can obviously be made if you're going to be routinely running the sub past xmax and might need more port area because of that.

[mr.p]

You can calculate all you want...

End of the day there are so many variables, you might have a perfect design on paper, but lacking experience to actually make it perform can be a deal breaker.

I trust some peoples "opinions" on what they have seen work in their application and sometimes it works in your own sometimes its 3db down. You will not know until you build and test and test and test.

[RAM_Designs]

You can calculate all you want...

End of the day there are so many variables, you might have a perfect design on paper, but lacking experience to actually make it perform can be a deal breaker.

I trust some peoples "opinions" on what they have seen work in their application and sometimes it works in your own sometimes its 3db down. You will not know until you build and test and test and test.

I was simply referring to a recommended port area to avoid port noise and still provide good reinforcement around tuning. Honestly, port area is not the most important determinant in the overall picture. So long as you're not introducing port noise, going from 50in^2 to 60in^2 isn't going to make much of a difference. You're always going to have to sacrifice something if trying to gain something else. If you're just trying to be loud and don't care about your sub unloading quickly under tuning, then go for a huge port. But just remember that you are making sacrifices in other fields when throwing a huge port in a box. Audio is always give and take...can't have your cake and eat it too. Box volume/tuning/placement is far more important in a daily driver setup that wants to sound good and isn't worried about the TL.

I agree that building and testing is the best way to do it if you're looking for spl and worried about what you're hitting on the TL(obviously). I'm not referring to that though.

[Nightshade]

I've come to find that even with a smaller enclosure you can increase efficiency output equal to or greater than that of a larger size enclosure by increasing the amount of port area. The amount of port area and sqin of port per cuft of box has a lot to do with both output and efficiency.

In most of my applications I tend to run a smaller then suggested box size due to agressively overpowering the sub. In order to make up for this decrease in box size which does greatly effect efficiency I tend to increase the amount of port I have per cuft of box after displacement. I'll give a couple of examples where I've adjusted size of box and port area and had greater results with increased efficiency in the smaller enclosure.

I tried a single Nightshade 15 with 2 saz2000d's strapped at .5 ohms in a 4.5 cube enclosure with 3 4" aeros. This is exactly 37.68sqin of port total and 8.37sqin of port per cuft. The tuning of the box was set to 46hz and peaked in car at 51hz. Total spl for this box was a 150.4 at 51hz on the dash sealed legal for NSPL(which is the same as Db Drag). Also the amps were clamped to get the total power being made for power class reasons in NSPL. With the amp's seeing .25 each since they were strapped at .5, they ended up rising to 2.04 ohms total or 1.02 per amp. The amperage was 43 amps and voltage ac was 88 volts. This comes out to be a total of 3784 watts.

Next I adjusted the enclosure size and dropped it down to 3 cubes after displacement. Then to compensate for the loss of internal volume I went with a single 8" flared port which is 50.24sqin of port being exactly 12.56sqin more of port or equivalent to adding another 4" aero to the first box. The port to box ratio for the new enclosure was 16.74sqin of port per cuft, which is double the amount of port area per cuft then the first box. The tuning was kept the same so that the vehicle's resonant freq could be used as a base point for the highest spl in vehicle. So being tuned to 46hz actually made this box peak at 52hz in car, being 1hz higher then the larger box that was tuned to the same freq. This is probably due to the added port area as well since this box will naturally want to play higher since there is more port area involved. The spl that was achieved out of this smaller box with more port area was 152.6db on the dash legal. That is a 2.2db increase over the first larger box that was built and tested. Here's the surprising numbers that help explain the large gain a little.

The amperage of this box was measured at 47 amps with each amp seeing .25 ohms nominal still. Then voltage that was measured was 90 volts ac. That when calculated made the reactive impedence 1.91 ohms, being .13 ohms lower impedence rise then the first box. Also a great increase in the amperage and not a large increase in the voltage shows a much more efficient box then the first. Total power when calculated is 4230 watts, which is an increase of almost 600 actual watts.

Now in all reality everyone is aware that it should take more than 600 watts to give a 2.2db increase in spl, but in this case the woofer behaving in a more efficient way performing to it's potential allowed for the excess spl that the power doesn't account for. This means that the sub wasn't making the best use of it's power in the first enclosure because it didn't allow it to create the necessary back pressure like the smaller box did to transfer the spl out of the box to the front of the vehicle as effective. The smaller box was actually more efficient in using it's power, by creating much more back pressure and loading more correctly then the larger box allowed it to do.

Okay so one example is enough, but I just wanted to show that a smaller box is not always going to be less efficient then a larger box. Certain factors come into play such as port area, frequency, and most of all what the sub actually likes to begin with. End of rant

[Tarball]

Just buy a woofer tester. Lol

Didnt i tell you to do that last week??? Haha

Wow, I totaly thought this was B.S. like...go grab me a cable stretcher or...pass the bumper fluid...along those lines.

Good Stuff,

Now maybe I can get some basic info on my RE-MT.

/cheers