Here is a typical rolloff for a ported 12" driver:


The -3db point is 24Hz. If I go down 7Hz from there (the equivelant of 21Hz in my room) the sub is down another 11db. Typically room gain is 4-6db per octave meaning that at 12Hz you would see 4-6db of gain.

In contrast, 11db gain by 21Hz is a huge amount of gain. I think this is more than can be accounted for by room gain.

Fred

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