4 cubic feet, tuned to 22 Hz, port area >= 64in^2

[chillin 10+ year member]

Home Depot

 

[emilimo701 10+ year member]

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[RangerDangerV2 5,000+ posts]

tuning that low with that much port can cause damge to subwoofers.... you dont need to tune that low to play that low.

 

[Kangaroux 5,000+ posts]

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Do you know the cabin gain?

 

[RangerDangerV2 5,000+ posts]

Do you know the cabin gain?

theres a way to simulate it in winisd...

 

[emilimo701 10+ year member]

Tuned at 22 Hz it should be around flat with

Tuned at 32 Hz I will gain about +4db centered at 38 Hz, albeit with a little bit of a peak, which may not be that bad and maybe desirable in some cases.

Maybe I will use an expandable aeroport to see what I like the best. I can't really find any 8"+ diameter aeroports on the web. I Might have to use 2 or 3 aeroports on smaller diameter?

What's the minimum port diameter I should use? According to this calculator it's about 64in^2, of course I probably won't be utilizing the full 30mm of excursion. I don't want to beat up on it.

 

[Kangaroux 5,000+ posts]

theres a way to simulate it in winisd...

I know, I was the one that showed you guys that lol. But to simulate it you still need to know what it is.

 

[emilimo701 10+ year member]

tuning that low with that much port can cause damge to subwoofers.... you dont need to tune that low to play that low.

damage how so?

I do intend to set subsonic filter properly. I remember in WinISD Pro there was a feature to determine maximum excursion plot vs frequency for a given subsonic filter. Unfortunately the Pro version doesn't like my new computer.

 

[emilimo701 10+ year member]

Do you know the cabin gain?

Not yet. I do intend on measuring it. I have a thread going at the other car audio forum (I'm not sure if it's against forum rules to talk or give links to the others?). Basically the thread is about spectrum analysis which I have to start soon, as long as my Firebox analog-digital converter will run on Windows 7.

I have a Legacy wagon, which is a fairly common vehicle, maybe it has already been done by other people.

 

[emilimo701 10+ year member]

Two of these would do, but the company doesn't seem to make angled extensions for them, so they'd have to protrude out of the box significantly at 6 feet, but it might help for prototyping

 

[Kangaroux 5,000+ posts]

Not yet. I do intend on measuring it. I have a thread going at the other car audio forum (I'm not sure if it's against forum rules to talk or give links to the others?). Basically the thread is about spectrum analysis which I have to start soon, as long as my Firebox analog-digital converter will run on Windows 7.
I have a Legacy wagon, which is a fairly common vehicle, maybe it has already been done by other people.

Easiest way to figure out a rough idea of cabin gain is to measure from corner to corner of your vehicle and figure out the quarter wave of that.

 

[emilimo701 10+ year member]

Easiest way to figure out a rough idea of cabin gain is to measure from corner to corner of your vehicle and figure out the quarter wave of that.

OK.

So what would the formula be from there?

 

[emilimo701 10+ year member]

Original design. Calculated some of the dimensions wrong.

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[hispls 5,000+ posts]

I'm tuning at 22 Hz based on the specs of the sub, and what I want to get out of the system. I can hear the 20 Hz tone in "Put On" by young jeezy and kanye, so i'm kind of using that as my reference. Right now with the Axis in a sealed box, i'm not getting the output I want. It's about 16db down at 20Hz, and that simply is not cutting it. I want that 20Hz tone to slam with the same authority as the others. If I find out that such a lot tuning isn't necessary, I'll rebuild a new box tuned higher. But right now my goal for the enclosure is firm: 4-4.2 cubic feet tuned to 22Hz. I don't so much want high SPL in the 40-50 Hz range; rather, a flat response with a graceful rolloff. Maybe I won't end up liking it, but I want to at least give it a try, for curiosity's sake if not anything else.
I've done the simulations in WinISD, and have used another online resource that has corroborated the measurements of WinISD.

Right, I have seen recommendations that a rectangular port should not have a ratio higher than 1:8 and have even seen 1:5 as the max. The design I have right now is one rectangular port: 16" x 4". The annoying thing is that it wraps almost all the way around the box, unless I want to incorporate 180 degree turns into the port design.

The benefit to using dual slotted ports (besides the aesthetics) would be that I would be able to locate the wire terminals conveniently in the back of the box without have to route them through the port space. Also, this would mean that the subwoofer would be able to be front-facing and centered.

I was thinking of decreasing the height of the box and going with a 15.5" x 2.25" port on each side. Eh?

You're just plain not going to get a really fierce 20hz tone without a huge box or more cone area. I promise tuned @ 27 you'll be able to play it fine (Mine didn't totally unload until around 18hz).

I haven't had great results with multiple ports though and both would still be very long and now half as narrow

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I knew this woofer wanted to tune that low to model linear. Really I think you'd like the way the peaky looking one sounds though. With vehicle accoustics it should actually give you a good boost in output over a decent bandwidth.

tuning that low with that much port can cause damge to subwoofers...

Wrong. Tuned that low he won't hurt that sub with less than 1500W. Also the point of tuning that low is because that models linear.

Tuned at 22 Hz it should be around flat with
Tuned at 32 Hz I will gain about +4db centered at 38 Hz, albeit with a little bit of a peak, which may not be that bad and maybe desirable in some cases.

Maybe I will use an expandable aeroport to see what I like the best. I can't really find any 8"+ diameter aeroports on the web. I Might have to use 2 or 3 aeroports on smaller diameter?

What's the minimum port diameter I should use? According to this calculator it's about 64in^2, of course I probably won't be utilizing the full 30mm of excursion. I don't want to beat up on it.

Of course physics is really against you trying to play that low regardless of where you tune a conventional woofer just isn't efficient at reproducing ultra low frequency.

damage how so?
I do intend to set subsonic filter properly. I remember in WinISD Pro there was a feature to determine maximum excursion plot vs frequency for a given subsonic filter. Unfortunately the Pro version doesn't like my new computer.

Even tuned in the high 20's you would have a hard time hurting that woofer with less than 1500W of power. I never ran subsonic filter when tuned that low.

OK.
So what would the formula be from there?

length from furthest point in trunk to furthest point on the dash corner to corner in feet. Divide that into 1150 fps, then divide that by 2. Gives your peak freq anyway.

Original design. Calculated some of the dimensions wrong.
View attachment 26533610

Looks decent. What's wrong with that one?

 

[Kangaroux 5,000+ posts]

length from furthest point in trunk to furthest point on the dash corner to corner in feet. Divide that into 1150 fps, then divide that by 2. Gives your peak freq anyway.

Don't you divide it by 4? I thought cabin peak was quarter wave not half wave