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http://www.neumann-kh-line.com/klein-hummel/globals.nsf/resources/resolution_kh310_v12.6sr.pdf/$File/resolution_kh310_v12.6sr.pdf
"One advantage of adopting a sealed cabinet design is evident in the acoustic source position (Figure 5). Here, the low frequencies appear to emanate from a position only 2m behind the speaker; this is half of the distance commonly found with ported designs. There is some evidence of a small delay (equivalent to about 30cm in position) in the mid frequency range due to the three-way crossover."
So lower frequency comes out later.
Now see the phase graph of the same speaker here.
https://www.youtube.com/watch?v=mnnzHVK2vfY
On the phase graph, as the frequency goes from low to high, the phase decreases (+ phase at low, - phase at high). This makes people think that high frequency comes out of the speaker later. This is opposite of the statement about the acoustic source position in the above pdf file.
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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
TomFwiw, 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
My question is why positive phase shift in bass, thought bass is more delayed in time.
Sealed box: positive 180 degrees; vented box: positive 360 degrees. So it sound as if the bottom end frequency comes out earlier from vented box speaker than from sealed box speaker. However, the article says the acoustic center for bottom end frequency is more behind the speaker in the case of vented box.
If you have a positive phase change, you are adding phase (delay) to the reference but if you have a negative phase change, you are subtracting it which makes the delay time shorter.
From both a normal crossover (the familiar named ones like Butterworth, Bessel, L&R etc) AND the lf response corner of a woofer or any speaker , the low end is behind the upper end in time.
How much time depends on the frequency and slope your dealing with and time is probably not the best window to this as what's normal at say 100Hz, is twice as long at 50Hz for the same slope.
Search out the work of Dick Heyser who pioneered this area of investigation. Try "determination of loudspeaker arrival times" as a good start.
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