Home Speaker Asylum

General speaker questions for audio and home theater.

RE: confusing phase and acoustic source position graphs

A sealed box has 180 degrees phase shift when going from well above to well below the low corner frequency while a vented alignment has 360 degrees of phase shift. This follows the same "minimum phase" relationship that normal crossovers have which is 90 degrees of shift per order (6dB/oct slope). The sealed alignment nominally rolls off at -12DB/oct while a vented alignment is nominally -24dB per octave.

This means that the low frequency portion of the sound is behind in time and is the same as one finds with the named crossover slopes.

When examined in "time" the amount of delay depends on the frequency, the lower the frequency, the longer period any amount of phase represents.
Hope that helps
Tom

Fwiw, you might want to look up Dick Heyser one of the under appreciated audio giants, he is the one who figured out how to measure this stuff and is part of his papers on "loudspeaker arrival times"



Edits: 07/20/16

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