RBH WM-24, WM-30, FM-45 Build Quality
The FM-45s feature a D’apollito M-T-M arrangement, with the drivers mounted near the top of the tower, the 1” silk dome tweeter ~ 38” above ground level. The two 8” woofers are arranged in a side-firing configuration, ported out the back of the cabinet. 2 pair of 5-way binding posts, configurable for biamping via a pair of included removable jumpers. The cabinets are built of MDF and metal stock, lined\stuffed where appropriate and wired with 18AWG cable throughout.
The woofer pair is wired in series and connects directly to the bottom two binding posts. There are no passive components in the signal path between the woofers and the binding posts; RBH chose instead to rely on the inherent lowpass amplitude response of the series-wired drivers to determine the lowpass characteristics of the LF system’s response. A purist approach if there ever was one!
The highpass amplitude response characteristic of the LF system’s response is controlled not only by the duct fastened into the back of the cabinet but also by two ports found in the bulkhead that partitions the LF cabinet from the tower. One such port can be seen on the right interior side of the cabinet showing in the photo above right.
Mid-way or so up the tower an internal bulkhead separates the 4” midrange drivers & tweeter from the woofer. Both woofers and midranges feature aluminum cones and half-roll surrounds. The mids are wired in parallel and the tweeter features a series blocking cap in the circuit that serves to protect it from electrical damage. The crossover itself is located between the two mids and directly behind the tweeter, as seen in the photo, below right.
The WM-24s and WM-30 are similarly constructed, sharing many design features with the larger FM-45. Like their larger sibling’s M-T-M tweeter/midrange configuration, the WM-24s & WM-30s have their driver complement arrayed in an M-T-M, or more accurately, W-W-T-W-W. Though the FM-45s are vented and the WM-24s & WM-30s are not, the latter make use of a pair of passive radiators that function in much the same way as does a port. Similar hardware, similar specs - such as sensitivity, frequency response & so forth - and you’ve got what amounts to, sonically speaking, a well matched set. More on this later.
You might have put in the wrong SPL vs FREQ graphics. The ones there show roll offs at 70 hz & 10K hz. On the other hand, I can't recall another review that used the phrase "remains largely within +/- 3dB of that figure from about". It's usually "IS within +/- 3dB".
Check the graphs again. Despite the dip at 10kHz, its still within +-3dB as Mark states. Its 3dB point is also around 45Hz on the low end as he states.
as for his choice of wording, hey he is Canadian, and they do things a little differently