In or Out Firing Formula

I remember a while ago that someone posted a formula that told you if it was appropriate to mount your sub firing in (magnet ouside of the box firing into the enclosure). The formula ued the specs of the sub. if it was between a certain two numbers it was alright to fire in.

Anyone know this?

This would also probably be a good sticky when someone posts it.

THX!!

Found this ... Dyohn posted it...

Subwoofer Qualification Formula For Downfiring Configurations

I am often asked if a particular driver is suitable for using in a down-firing configuration. Below is a formula that takes into consideration the effects gravity will have on the "sag" of the cone structure of any woofer. You will need the Fs, Vas, Sd (surface area of the cone), and the Xmax to determine the relative long term usefulness of up or down-firing any woofer.

You can calculate the sag of a driver from:

Percentage of Sag = 24,849 / ( Xmax * Fs²)

where

- 24,849 is a constant value based on the relationship of acceleration due to gravity and Pi.
- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm).
- Fs is the free-air resonant frequency of the woofer (Hz).

The following is the same formula, including the relationship of acceleration and Pi in this case:

Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)²)

where

- 981,000 is acceleration due to gravity (mm/S²) * 100 (for the percentage).
- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm). - Fs is the free-air resonant frequency of the woofer (Hz)
- Pi is the ratio of a circle's circumference and diameter, usually rounded to 3.14.

As a general rule of thumb, any time the sag exceeds 5% of the driver's Xmax, it's not recommended for a down-firing subwoofer application.

-- from Parts Express resource index

One point: that formula has nothing to do with inverted mounting per se, which is what I think you're asking about ("firing in or out.")  Percentage of sag is important in any down-firing configuration: downfiring being any time the woofer cone faces down, no matter the type of mounting used.

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ohhhhh

i see now. I always thought that down firing was anytime it was firing into the box.

That makes me descision a lot easier!