ct0517,
i was in a bit of a hurry this morning when I posted my comments on the B&W BAF (had to get to the gym for some stress relief! ;-) ). Anyway, a couple of more comments on the B&W BAF
* Ken Rockwell's dissertation says that w/ the B&W BAF the overall response is 6th order (I'm hoping in the bass region because he did not clarify)....
The Bessel alignment also has the advantage that adding a very simple second-order electrical filter (this equalizer) allows one to create a completely different kind of alignment, a sixth-order Butterworth alignment, whose frequency response is also flat, and extends and extra half-octave deeper in the bass.
i looked at the freq plot that B&W Europe sent you & it does not look 6th order by any stretch of the imagination. If it's 6th order then i'm expecting to see a 36dB/octave roll-off in the deep bass region. I don't see such a steep roll-of. Take a look yourself - the roll off is in the 10dB region at best.
Another observation - there is a dotted line that says "with filter" & a 2nd dotted line that says "without filter". what is the solid line in the bass region that seems to stop around 50Hz? The dotted line "without filter" is not on top of the solid line which i believe is the speaker freq response. How did B&W Europe get that "without filter" dotted line that is completely mismatched to the speaker's frequency response solid line? It's not making any sense to me.....
* Ken Rockwell's dissertation says & you have cut & pasted the same text verbatim on your system page ....
Without this equalizer, the naked B&W Matrix speakers are a vented fourth-order design, specifically in a Bessel alignment. "Fourth-order" is an engineering term that refers to all vented and passive-radiator speakers; sealed boxes are "second order."
this is not a true statement. When I owned a pair of Green Mountain Audio C1.5i floor-stander 3-way speakers the bass box was sealed & was 1st order both electrically & acoustically. There's nothing that says that a sealed box must be 2nd order. You can make it any order you like if the speaker designer knows what he/she is doing.
The B&W BAF is really a very simple concept & elementary filter design - put a 6dB peak at the speaker's bass resonant freq such that the bass driver's droop in freq response is compensated by a boost by the 6dB peak such that the combination's freq response is flat. They chose a 2nd order Bessel - good choice since Bessel filters have maximally flat group delay & you need this to ensure good quality bass, no boomy bass.
But the fundamental question still arises - why was a BAF required? The answer to that is - the bass drivers used in the Matrix series speakers were simply not up to the task of reproducing deep bass (20-40Hz). For a speaker manuf that makes all of its own drivers or has them contract manuf by giving the 3rd party tightly controlled driver specs, this is an inherent flaw in the design & the BAF is a band-aid for the speaker. The correct thing to have done back then was to invent a bass driver that was linear into the sub-sonic region so that it natively could reproduce deep bass. Instead B&W used whatever bass driver they had in stock & made users buy the BAF.
Ken Rockwell's dissertation clearly says that in later years B&W dropped the BAF & the new N, S, D series speakers all have bloated/boomy bass. B&W has still not been able to design the correct bass driver for their speakers!!! wow! what in the world does that say for this manuf??
