Loudspeaker Designs and Articles for the DIY Enthusiast
Jim Holtz's:

Big sound from a monitor sized
speaker design using high
value drivers.
Crossover Design:

Curt: The Finalists is a relatively simple crossover for a 3 way, as the driver allowed for shallower slopes and more overlap and perhaps better driver
integration. The RS225 low pass resembles an acoustic 2nd order Linkwitz-Riley transfer function with the fc at about 250 Hz. The RS28F emulates a 2nd
order L-R with its fc of 2 kHz. Due to the differences in acoustic centers of the drivers and their individual characteristics, the NE149’s transfer function does
not follow a textbook transfer function but roughly emulates a 2nd order L-R high pass @ 320 Hz, while the high pass starts off with a very relaxed roll off,
but changes to 3rd order acoustic above 5 kHz. Because of the 2nd order transfer functions, the midrange is connected with reversed polarity, while the
woofer and tweeter are connected with normal polarity. The phase tracking is very good on the design axis with wide, deep nulls for both crossover points
when the midrange polarity is reversed.  Note the switch for the near wall / far wall selection. This implementation was again much simpler than some of our
other designs. For far wall only applications R0011 and S0001 can simply be eliminated and replaced with a jumper. R2051 serves a dual purpose in that it
ameliorates the midrange impedance peak at 50 Hz, providing a smooth transfer function and eliminats a dip in the summed response with the woofer in that
region. As it is a relatively low value and is directly across the NE149, it may also aid in electrical damping of the mid potentially reducing distortion, although
this aspect was not tested nor proven.   
Links to:

Main / Design Goals

Driver Selection

Cabinet Construction

Crossover Design


Listening Impressions
Finalists Classic Transmission Line Modeled Response
Note the f3/f6 of the transmission line models to be 43Hz/31Hz respectively, with an effective roll off similar to the 12 dB/octave of a sealed design. The
lower impedance peak typical of a normal vented design is no longer present. Terminus velocity near the woofers excursion limitation is low enough for
terminus noise to be considered inconsequential. The woofer excursion does not exceed Xmax+15% until just above 20 Hz at this level.
 Response plot with the midrange normal polarity reversed: