Billboard
You don’t necessarily build to the resonant frequency of the driver. That specification is the resonant frequency of the cone in free air... it’s a function of the moving mass of the speaker, mass of the air it’s displacing and the stiffness of the speakers suspension. This along with other specifications determine how the speaker will act when placed in a box.
To use a box calculator you need the following driver data:
Vas
Qts
Fs
Plugging these is will give you an “optimum” box volume which in my case was far to physically large to actually build. (They’re effin big as is). The Box volume (Vb) will give you an idea what the driver wants by its specs, you can alter this within reason, then you move on to port calculations which are based on the chosen Vb. Within reason you can tune different Vb’s to the same frequency although the response graph may be different. An online box calculator/simulator will show you the effects of these changes.
Here’s a good site for some reading. This fella gave me some excellent advice by email too.
(Thanks)
http://audiojudgement.com/
Roccus, no, I didn’t put any damping material in my boxes. That is used in ported boxes to dampen peaks in response caused by standing waves inside the cabinet. This is why you never build a speaker box as a cube, always three different dimensions. There are “golden ratios” which can help eliminate standing waves but it’s not really a concern on a sub only running up to a couple hundred Hz. (Still don’t build a cube!) There’s not much opportunity for octaves and harmonics. This is more of a problem on oddly shaped speaker boxes and drivers which run a wider range. Think tower speakers (tall and skinny) with a two way set up where the woofer runs up to say, 5kHz.
In a sealed box, box volume sets the resonant frequency, filling the box with stuffing lowers this frequency. Ported boxes are lined only, not stuffed and is only beneficial if needed to eliminate standing wave peaks.
What are you going to use for a crossover on your subs? An active filter or a passive low pass?
