Few questions.

[netzero 10+ year member]

These might be dumb but i've had a brain fart, so bare with me lol. First, when building a box with a round port, do you make the length and tune it to after all displacements? But not including port displacement correct?

And my other question was, I've seen a few people say to fill hatch rear doors and quarter panels with foam spray... Why and how big of a difference will i see? Thanks

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[netzero 10+ year member]

Anyone?

One other question, would three 4" aero ports be enough for two RE SE12s? That or one 8" not flared. Thanks

 

[Rashaddd 5,000+ posts]

Net volume is after subtracting the port displacement as well as the subs displacement, this is what you base your tuning calculations on.

Filling hollow and rattly areas with expanding foam will overall quiet down your ride and often helps to stop the annoying rattles and can even help stop resonances.

Three 4" aero's is plenty for two 12's

 

[netzero 10+ year member]

Thanks man, I'm really trying to save space and money, do you think two 4" aeros would be ok for daily fiberglass box? Or should i go with 8" custom?

So If i have a box 40 wide, 17 high, and 17 deep which is 5.35 cubes, to tune it with say the 8" I would take the .3 for the subs and .1ish for bracing and take that away and i'm left with 4.95 ft^3.

Then if i use the psp port calc, would i put in the port diameter and tuning and get a length and just put the port in? for 33 hz and one 8" port I get 20" flared. So, i would just stick that in and it would be set? And if i find port displacement and take that away from the 4.95 thats how much the subs will see? Thanks

 

[Rashaddd 5,000+ posts]

Thanks man, I'm really trying to save space and money, do you think two 4" aeros would be ok for daily fiberglass box? Or should i go with 8" custom?
So If i have a box 40 wide, 17 high, and 17 deep which is 5.35 cubes, to tune it with say the 8" I would take the .3 for the subs and .1ish for bracing and take that away and i'm left with 4.95 ft^3.

Then if i use the psp port calc, would i put in the port diameter and tuning and get a length and just put the port in? for 33 hz and one 8" port I get 20" flared. So, i would just stick that in and it would be set? And if i find port displacement and take that away from the 4.95 thats how much the subs will see? Thanks

two 4" flared aeros should be fine in terms of port noise

The ports also take up space, so get your first measurement, then calculate how much volume the ports are at that length, then subtract that from the 4.95, then recalculate port length withyour new volume, then recalculate port volume from your new length, etc, until you are close enough for your liking. One thing that makes it easier and faster is to estimate compensation for the difference in your first calculation, and as you get used to it you'll end up being very accurate on your first try many times.

 

[netzero 10+ year member]

hmm I don't know if i understand what your saying, but i'll try. So I have 4.95 after sub and bracing displacements, and i put 4.95 in the port calc and get 20". Then I do (16*3.14*20)/1728 and get .58 ft^3 for 8" port displacement.

So then I would subtract .58 from 4.95 to get 4.37 and put that in the calc? That pushes the length to 23 1/2". So I use 23 1/2"? Thanks

 

[Rashaddd 5,000+ posts]

hmm I don't know if i understand what your saying, but i'll try. So I have 4.95 after sub and bracing displacements, and i put 4.95 in the port calc and get 20". Then I do (16*3.14*20)/1728 and get .58 ft^3 for 8" port displacement.
So then I would subtract .58 from 4.95 to get 4.37 and put that in the calc? That pushes the length to 23 1/2". So I use 23 1/2"? Thanks

I think you pretty much get it, but now remember you just added 3.5 inches to the length, which means you lost another .1 cubes out of the net airspace, which means tuning will be slightly higher again and you'll need to add slightly more length. As you continue this process you get closer and closer. I'd put in 4.27 to the calc now and see what length that gives you and use that, as it will definitely be close enough that it won't make enough of a difference in the volume of the box to justify adjusting it yet again

 

[netzero 10+ year member]

Thanks so much Rashaddd, I think I'm getting it now. Ya I think at those #'s I would do a 24 1/4" long 8" port. But still not sure if I wanna do that or two 4" aeros.

Regarding the 8", I would be using sono tube of course, but I would have to put a 90* bend in it.. The only 90*s I can find in that size are AC duct bends, but they're made out of sheet metal... So you think If I formed it all together and bondo'ed out the bumps and glassed the outside of the bend would there be a problem with and reverberations from it being thin? Here are a few pics of what I would be dealing with.

Thanks again

 

[IDSkoT 5,000+ posts]

You have to bondo it up nice. Those aluminum sheets are weak as hell. You have to make sure it's solid.

But I'd kick the 8" idea out of the window, and get 4". You can just get PVC, and PVC elbows and the like, and would be much easier and a lot cleaner looking.

 

[netzero 10+ year member]

You have to bondo it up nice. Those aluminum sheets are weak as hell. You have to make sure it's solid.
But I'd kick the 8" idea out of the window, and get 4". You can just get PVC, and PVC elbows and the like, and would be much easier and a lot cleaner looking.

Thats what I was thinking, it was the only 8" 90* i could find though... I have plenty of 4" pvc laying around the house so i would just want the flared ends. On thriller audio they sell everything flared, which one would i need to use with standard 4" pvc?

http://www.thrilleraudio.com/detail.aspx?ID=426

or

http://www.thrilleraudio.com/detail.aspx?ID=425

The first says inside flare and the second 4" outside flare? Thanks

 

[Rashaddd 5,000+ posts]

Thats what I was thinking, it was the only 8" 90* i could find though... I have plenty of 4" pvc laying around the house so i would just want the flared ends. On thriller audio they sell everything flared, which one would i need to use with standard 4" pvc?
http://www.thrilleraudio.com/detail.aspx?ID=426

or

http://www.thrilleraudio.com/detail.aspx?ID=425

The first says inside flare and the second 4" outside flare? Thanks

You also will need much less port length if you use two 4" as that's about 1/2 the port area of a single 8, you may not even need to bend it

 

[netzero 10+ year member]

Ya I'm thinking a max of 12 in. or so if i did 2... Any allusion to the port flare thing? Does inside and out side just mean inside the box and outside the box, or does the mean the outside flare being 4" means the actual hole is smaller? Thanks

 

[MisterE 10+ year member]

Just be careful with expanding spray foam, sometimes with certain kinds ive heard you put in too much and it buckles the metal

 

[netzero 10+ year member]

Just be careful with expanding spray foam, sometimes with certain kinds ive heard you put in too much and it buckles the metal

Thanks man I'll keep that in mind... that would ****. lol

I think I'm pretty much set, but does anyone know about this \/\/ inside/outside flare thing? Which, or would both, would work with standard lowes 4" PVC? Thanks

Thats what I was thinking, it was the only 8" 90* i could find though... I have plenty of 4" pvc laying around the house so i would just want the flared ends. On thriller audio they sell everything flared, which one would i need to use with standard 4" pvc?
http://www.thrilleraudio.com/detail.aspx?ID=426

or

http://www.thrilleraudio.com/detail.aspx?ID=425

The first says inside flare and the second 4" outside flare? Thanks