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Lonewolf32
12-07-2006, 12:19 AM
I found all the formulas here by searching, but I have a question about this formula

Vb=20*Qts^3.3*Vas

When I use this formula I get a Vb smaller that the Manufacturers recommended.

Is that Normal or am I doing something wrong?

Here is an example using an SI Mag D2

Vb= 20*.05275*1.401992

Vb= 1.478979854cuft

SI recommends 2cuft

Are they using other better means to get this?

j3bus2k3
12-07-2006, 12:24 AM
The Vb from that formula isnt going to be the optimal volume for that driver. For example, alpine recommends somwhere in the 1.75^3 per 12" type-r ported but its widely known that they do best in 2-2.5ft^3 per driver...

Lonewolf32
12-07-2006, 12:50 AM
So it is more of a starting point.

That said how do you find the optimal Vb?

Trial and error?

j3bus2k3
12-07-2006, 01:17 AM
Playing with graphs, and combinations of net volume with tuning while experimenting in car...

Lonewolf32
12-07-2006, 11:40 PM
Lv = Av*1.84*10^8/[vb*1728*(Fb/0.159)^2] - 0.823*sqrt(Av)

This formula should work for all subs right?

I am trying to understand this better so I am plugging differant senarios into the formula. going by Manufacturers recommended and seeing if I get the same length that they do. In the forum a guy was wanting one for a Kicker 18 solox, so I went to the kicker website, and got their recommended, 10cuft, 150sqin and 35hz. I get Lv = 3286.19586" they say it should be 21".

Am I doing something wrong or does this formula only work for small enclosures?

helotaxi
12-08-2006, 02:11 PM
The Vb given by a formula is determined by the alignment that the formula is for ie Butterworth, Chebysev, etc. and will generally give you a relatively flat response. What most people consider the "best" box volume on this forum is the one that gets the loudest with acceptable non-linearity. Many manufaturers know that that is what their customers are looking for as well, and spec their enclosures accordingly. The man. also has to account for the wingnuts out there that will try to run way more than rated power to the sub or just otherwise generally abuse it, and spec an enclosure that won't have nasty cone control characteristics that would lead to warranty claims.

BTW, you messed up something in your calc on the last equation. I got 22.8" which is the same thing that WinISD gave me which is the same as the Kicker number with a different end correction. You misplaced a decimal somewhere. Your number before end correction is off by two decimal places.

Lonewolf32
12-08-2006, 03:08 PM
I made an excel spreadsheet with the formula in it. I had to many zeros for the
10^8. I changed it now and got 22.8 thanks. Just goes to show that even double checking things does not mean there right lol.