Crossovers depend on cutoff slopes as well. Typical slopes are 6db, 12db, 18db, and 24db. So if your amp has a lowpass filter for your sub with a 12db/octave cutoff slope and it's set to 100Hz then your sub will actually play 200Hz frequencies but they will be lowered by 12db in volume. This can be used to your advantage to blend your sub and midbass speakers.

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My Car Domain page
2006 Nissan Frontier Nismo 4x4
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2008 Results:

Oct 19, 2008 - 2nd Place - SQi Rookie, Team Shadow (IASCA Canadian Western Finals)

Sep 21, 2008 - 2nd Place - SQi Rookie, 604 Autosound (IASCA Event)

Aug 10, 2008 - 3rd Place - SQ Rookie, Andre's Audiotronic Kamloops

July 20, 2008 - 1st Place - SQ Rookie/3rd Place - Best SQ, Andre's Audiotronic Penticton

Jun 15, 2008 - 2nd Place - SQi Rookie, Sounds Good Auto (IASCA Event)

May 18, 2008 - 1st Place - SQ Open Class, Absolute Car Audio