Ok, I am building a box for a R2D2-10 Fosgate Sub (Prime 10" R2 2-Ohm DVC Subwoofer | Rockford Fosgate (R))
Click on Box Advisor and you will see that,
Fosgate recommends a box with a (Gross) Vb of 0.59 cu ft.
They say this will give a Qtc of 0.75.
When I enter the woofers Qts (0.47), Vas (1.377), Fs (34.6) and a Vb of 0.59 into a Qtc calculator,
I get a Qtc of 0.85, not 0.75.
Instead, when I use a Vb of 0.9 cu ft I get a Qtc of ~0.75.
What am I doing wrong?
Click on Box Advisor and you will see that,
Fosgate recommends a box with a (Gross) Vb of 0.59 cu ft.
They say this will give a Qtc of 0.75.
When I enter the woofers Qts (0.47), Vas (1.377), Fs (34.6) and a Vb of 0.59 into a Qtc calculator,
I get a Qtc of 0.85, not 0.75.
Instead, when I use a Vb of 0.9 cu ft I get a Qtc of ~0.75.
What am I doing wrong?
Nothing wrong with your math that I can see. No idea where RF is getting those numbers.
Did a double check on the box volume from the dimensions given (see attached): 0.627 - 0.04 = 0.587ft3, close enough to .59ft3
WinISD confirms that driver in .587ft3 has a qtc of .847, and takes 0.89ft3 to get a qtc of .75, just like you found.
Now, you must confess if you bought that driver for the model number! 😉
Did a double check on the box volume from the dimensions given (see attached): 0.627 - 0.04 = 0.587ft3, close enough to .59ft3
WinISD confirms that driver in .587ft3 has a qtc of .847, and takes 0.89ft3 to get a qtc of .75, just like you found.
Now, you must confess if you bought that driver for the model number! 😉
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Don't get too concerned about the exact curve. Unless you're in an anechoic chamber or have the woofer suspended off of the ground in an open field, the response will be nothing like what the software says it will be.
It's good to know how the various enclosures work and how the size affects the response but speakers and their installation in the vehicle are not an exact science.
It's good to know how the various enclosures work and how the size affects the response but speakers and their installation in the vehicle are not an exact science.