I've been curious for a while about the woofers on my RM40's. The upper woofer plays upper and mid bass but no low bass. The lower woofer plays low bass but no upper bass. I know the low woofer is a "megawoofer" with a double magnet designed to play lower, but my question is why does it not play any upper bass? It seems to me that if both the top and bottom woofers played up in to the upper bass, a lot of peoples observations about "thin-nes" in the upper bass would go away. Just curious about the reasoning behind the design decision.
1) The two woofers are wired in parallel to the upper BPs.
2) There is a 2.8 mH iron core inducter wired in series on the positive side.
This is a very simple 1st order XO. Depending upon the actual impedence of the two drivers, it will XO ~200Hz. There is also a resistor wired directly between the positive and negative upper BPs. This can have several effects, but it is probably meant to smooth and adjust the actual impedence of the drivers, which varies depending upon frequency and amplitude of the input signal.
The ~200Hz 1st order XO lets a LOT of higher frequencies through. My ears tell me it lets more and higher frequencies than a 4th order 700Hz XO ! Someone could probably find graphs to confirm or dismiss this.
The bottom line is that both woofers receive exactly the same signal. This signal contains a LOT of higher frequency energy as well as all of the low frequency energy below ~200Hz. Any sound difference between the two drivers is completely due to the physical design differences in the drivers.
