Originally Posted by DigiPete
If you set the sub to 'no', and surrounds/center to small, you are taking the frequencies being sent to those speakers that are below crossover freq, and sending them... nowhere (no sub).
Source direct sets all speakers to large, so you do get some bass to the surround and center speakers. You can get the same effect by setting all speakers to large in the setup menu.
Thanks for the reply Digi,
My test results showed that this is not the case. If I set the sub to "NO", the bass from the small speakers would get routed to the large speakers.
Only if I set sub to "yes" and didn't actually have one plugged in, then the bass would get routed from small speakers to the unconnected sub channel....nowhere.
Test1: I set front=large, center+surrounds=small, sub=no, xover=100Hz
1a: low frequency sweep to R front, would output full range of sweep (as low as the speaker could handle anyway) out the front speaker @ ~ 72dB
1b: low frequency sweep to R surround, would output sweep to from surround @ ~ 72dB until about 120Hz then would drop to ~ 68dB until around 100Hz when some signal would be output from the fronts as well. Around 80Hz, enough signal is coming out of the combined R surround and both fronts to add back up to ~ 72dB overall.
As the sweep drops lower, the output from the fronts continually intensifies while the output from the R surround continually drops. The overall signal output varies significantly with several +/- 3dB peaks and dips as the sweep moves down to ~ 40Hz and lower where I ultimately begin to lose output as I hit the limits of my speaker's low freq. response.
Test2: same as test 1 except sub is set to "yes"
2a: low freq sweep to R front, resulted same as in 1a, the large front passed full range @ ~72dB
2b: low freq sweep to R surround, would output from R surround @ ~ 72dB until about 120Hz where it steadily dropped to about 68dB by 100Hz and continued to fade as the bass was redirected to a non-existent sub, no R surround signal was redirected out the large fronts.
Test3: 3910 set to source direct mode
3a: low freq sweep to R front output @ ~ 84dB across full range of sweep from 200Hz until about 40Hz, lower frequency outputs varied from about 78dB to 74dB until response faded away completely.
3b: low freq sweep to R surround output @ ~ 84dB across full range of sweep from 200Hz until about 50Hz, lower frequency outputs varied from about 78dB to 74dB until response faded away completely.
hypothesis1: with bass management on and no sub, the low freq is redirected from the small speakers to the large speakers but overall output is down about -12dB relative to source direct mode. There is also a large dip of more than -4dB as the signal passes over the crossover point and bass is redirected from the smalls to the large (This is opposite of what you would expect in my setup where you would expect a slight overall increase in output as signal is redirected from a single RB-35 bookshelf to the 2 larger and more sensitive RF-35 floorstanders).
Additionally, the overall output across the sweep is very non-linear with several additional +/-3dB peaks and dips.
hypothesis2: with sub set to "yes", large speakers are passed full range signal with no redirection, small speakers get bass redirected to the sub channel which in my case had nothing connected to it.
hypothesis3: the source direct mode outputs about +12dB higher than "managed" mode. There is no bass management in source direct mode. But, in my setup, the result appears to be a much more linear response with much better fidelity than with using the bass management.
for further investigation:
Why is there a drop in overall output as the bass management redirects signal from 1 bookshelf R surround to 2 floorstanders when, if anything, it would seem the opposite should occur? I would expect the overall system response to be fairly linear until I hit the crossover point and then should get an increase in bass response as signal is redirected from a single bookshelf to two floorstanders.
By adjusting the crossover frequency setting, I should have been able to find a setting where the increase of bass response was not too disproportionately high to the amount of signal being redirected from the small speaker.
This just wasn't the case, more signal was lost from the small speaker than was redirected to the large speakers at any crossover frequency setting from about 1/2 octave above the crossover point until about 1/2 octave below the crossover point.....WHY!? WHY!? WHY!?
Is the additional observation of +/-3dB dips in the bass managed output really a characteristic of the 3910 bass management, or is it just accentuating variances in the freq response of my speakers or listening room that I'm failing to observe in my source direct test measurements? (since it's outputting +12dB higher and I'm not doing a careful freq response plot, just listening and watching a SPL meter in real time)
To answer this, I'll need to do a more careful freq response plot of my system in source direct mode and compare it to a plot in managed mode.
A few other things I learned/observed during my testing:
The crossover filter employed by the 3910 doesn't appear to be a very high Q filter, maybe about 2nd order, as there was still quite a bit out output at 50Hz from the small speaker with the xover set at 100Hz. A careful plot will tell more about this.
In source direct mode, the channel level controls still work and will affect output levels from the multichannel outs even in source direct mode. It was not clear from the manual whether this was the case. (All my channel levels were left at 0dB in all my testing)