G

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G

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Yeah, 4" should be fine with a 15".

G

thanks, time to get the brad nailer.

When you say the surface area of the opening, are you refering to the cylindrical section between the endcap and baseplate? For a 15" driver this distance between the endcap and baseplate would be approximately 3.75". Yet people seem to be more commonly using 5" in this situation.

Anyone else have a more scientific solution to this question?

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gap = nominal diameter / 4 for most drivers or

gap = nominal diameter / 3 for high excursion drivers

Air movement generated by the driver shouldn't encounter any reduction in the CSA through which it has to flow

The smallest area is represented by the green cylinder, and has a total area of:

gap * circumference = gap * pi * (nominal diameter)

This must equal the Sd of the driver, or in our example, pi * (nominal dia / 2)^2

gap * pi * (nominal diameter) = pi * (nominal dia / 2)^2

gap * (nominal diameter) = (nominal diameter^2) / 4

gap = (nominal diameter) / 4

You could go more accurate by calculating actual diameter from Sd, and factoring in the height of the surround vs driver rebate depth, but this method is going to be fairly close.

If you have a driver with a large Xmax, you would build a bit of leeway in by dividing by 3 instead of 4

This would give you.....

A 10inch driver wants between 2.5 and 3.3 inches gap depending on excursion

A 12inch driver wants between 3.0 and 4.0 inches gap

A 15inch driver wants between 3.8 and 5 inches gap

A 18inch driver wants between 4.5 and 6.0 inches gap

I ask this, because IIRC correctly, SVS used their (some, maybe not all) baseplates for assisting in loading the driver.

My box design already has a low Q, around .5 or so, so it'll be kinda dry to begin with, but what other effects would that have, I read SVS used a shorter height to increase response to a givin area of response...

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