"orders." This terminology was first used in the sixties by two Australian scientists Neville Thiele and Richard Small (this is where Thiele Small parameters originated from.) They referred to sealed enclosures as "second order", vented enclosures as "forth order" and also developed other designs named third-, fifth-, and sixth-order.
1st order - free air/baffle mounted
2nd order - sealed enclosure/air suspension
3rd order - ported enclosure/bass reflex
4th order - bandpass enclosure (single port)
5th order - bandpass enclosure (single port) with a lowpass xover wired to the speaker
6th order - dual port bandpass/dual reflex (both front and rear chambers are ported or one chamber is ported to the other chamber which is ported outside the box also called series tuned.)
7th order - single or dual port bandpass with lowpass xover wired in.
sealed boxes (2nd Order) - Small, good low frequency extension and control, good transient response, simple to build ... see more ...
http://mobile.jlaudio.com/support_pages.php?page_id=149
ported boxes (3rd Order) - Efficient, low distortion around port tuning ... see more ...
http://mobile.jlaudio.com/support_pages.php?page_id=150
bandpass (4th Order) - Can pass lots of output through a small opening. see more ...
http://mobile.jlaudio.com/support_pages.php?page_id=151
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