RDC-7.1 Bass Management
To test my assumption, I used the Audio Precision SYS 2722 Audio Analyzer to run some measurements via the analog two-channel inputs of the RDC-7.1 configured in two-channel and multi-channel surround modes. What the SYS 2722 told me was that the LFE crossover setting only affects LFE info as stated in the menu. This is a good start, implying if you set all other channels to a lower frequency, critical LFE info will NOT get truncated. Many processors unfortunately do truncate LFE bass under this circumstance, the RDC-7.1 is not one of them.
This is a plot of the subwoofer LPF and Main Channels HPF when set to the THX recommended 80Hz crossover setting. Notice the HPF is down -3dB at 80Hz with a 12dB/Octave slope while the subwoofer is -6dB down at 80Hz with a slope of 24dB/Octave as per THX.
The reason for asymmetric filter responses between the HPF and LPF is to account for the natural roll off of the satellite speakers which is typically 12dB/octave. This allows the best blend between the subwoofer and satellite system.
In the Blue Traces, we set all channels but the mains to 150Hz (extreme case), while the mains were set to 80Hz. Notice how the subwoofer crossover -6dB cutoff has extended from 80Hz to 100Hz. This is good news.
Granted, ideally it should have extended to the frequency of the satellite speaker with the highest crossover setting (in this case 150Hz), but I suspect Integra Research limited the cutoff of the LPF of the sub to 100Hz or so to avoid excessive bass energy from a single source which is localizable at frequencies above 80Hz and to avoid having too much overlap of the speakers with HPF's set to a lower value. The Red Traces represent all channels set to 80Hz. Notice the better summation at the crossover points.
Let's take a closer look at the subwoofer output while varying the multiple crossover settings between the main speakers having high and low crossover settings, while the other speakers have low and high crossover settings, respectively. The RDC-7.1 is configured in PLIIx Music Mode.
The Red trace represents all channels set to 80Hz. The sub out, as expected, exhibits -6db at 80Hz.
The Green Trace represents the subwoofer output while the main channels are set to 120Hz while all others are set to 40Hz. Notice the uneven response of the subwoofer output that appears to be rolling off at 40Hz, then rises until it rolls off again at 120Hz.
The Blue Trace represents the Main channels set to 40Hz while all other channels are set to 120Hz. Notice how the subwoofer output -6dB point is around 40Hz. Essentially any speaker groups set above this point will not properly recombine bass back into the subwoofer. In other words, that information will be lost or extremely attenuated. Initially I was disappointed until I thought about the logistics. The RDC-7.1 was receiving a two-channel source. Thus it was defaulting the LPF of the subwoofer to whatever setting the main channels were configured too.
The true test was to verify if the RDC-7.1 was smart enough to incorporate independent LPF's for each channel group when playing a discrete source such as DD or DTS. Since my SYS 2722 doesn't have a built in Dolby Digital decoder, I couldn't input a digital 5.1 source to the RDC-7.1. Thus I had to rely on my trusty Avia test disc and Sencore FFT analyzer. Using the bass sweeps in Avia I verified that each speaker group's crossover setting was independent of the main channels so the RDC7.1 does in fact have independent LPFs for each speaker group! As an example, if the center and surround channels are set to 100Hz and the main channels are set to 40Hz, the bass from the center and surround channels will get correctly recombined into the sub for all discrete sources.
Overall this multi-crossover system appears to be one of the most flexible offerings to date, and can be very effective if used within confined limits. We would suggest to always select satellite speaker systems with a -3dB point of 80Hz or lower, especially when using a product of this caliber in a full-blown high performance home theater system. We also suggest maintaining a difference of no greater than 20Hz between crossover settings of all speaker groups and using caution when setting the main channels' crossover setting too low (especially when listening to two-channel sources in surround sound) to avoid loss of bass information from the other channels. Always start at the 80Hz reference point and only deviate when absolutely necessary for your particular situation. In my system, I set all channels, including the LFE, to 80Hz (THX setting) except for the main channels which I set to 100Hz because I achieved better acoustical bass integration with my subwoofers and main satellite speakers.
The RDC-7.1 provides three (3) subwoofer outputs and two (2) sets of 7.1 speaker outputs. Unfortunately, these outputs are not independently configurable and rely on the settings you pick for the primary speaker system. This is a disappointment since it would have been very useful to have independent level control, and distance compensation, especially if configuring a separate surround sound zone, or running a complex multi-subwoofer system.
One final but important note in closing our discussion of the RDC-7.1's bass management system:
The RDC-7.1 has a feature in the subwoofer mode to toggle between "LFE Only" and "D.Bass". In most cases use the latter since "LFE Only" will NOT allow any bass information from the satellite speakers to be recombined to the subwoofer channel. "D.Bass" will output front channel info (even in two channel mode) as well as all speakers that have bass management applied to them. Use this setting!