klettermann
Senior Member
I’ve been doing a slightly unconventional room treatment experiment that I thought might be of interest. The starting point is an already optimized 2.2 system: Magnepan mains plus a time-aligned/EQ’d mono dual-sub array. Overall response is good, it sounds great in fact, but there have always been a few annoying irregularities through the transition/lower-midrange region that simply don't respond to conventional PEQ. No surprises there, I guess that's pretty normal and something most of us suffer from to varying degrees.
So, rather than asking the existing sources to do something they apparently can’t do, what happens if I introduce another independently located acoustic source with a different room response that can be used to compensate?
The experiment
I added a modest “helper” speaker (Magnepan SMGa) on its own DSP channel. It was placed horziontally centered against the front wall behind a large TV and angled up at about 45deg. Why like this? Cause that's the speaker I had and that was about the only place it could go. The aim was as a very limited correction source whose only job is to contribute where 2.2 system still has deficiencies. The existing 2.2 system remains the baseline. The idea is simply existing acoustic response + separately controllable spatial source to improve the region that more EQ can't improve. The "helper" had independent control of:
Effect of Helper Timing
The helper is about 40 inches behind the mains so time misalignment would be expected. Rather than calculate I ran a series of delays in case of possible latency issues with the DSP stuff. See below.
There obviously isn’t one delay that phase-aligns two physically separate sources across several octaves. That isn’t what I’m trying to achieve. The task is to find the delay giving the most useful compromise across the particular deficiencies I want the helper to address. The broad optimum ended up around 3.25 ms in this setup.
Gain - Less is More
Below shows progressively reduced helper gain. The inital setting was obviously way too high. Less is more. 1/3 smoothing gives a better sense of the effect than 1/6.
Provisional Result after EQing
Below is the end result after a little helper EQing (almost). Black is the optimized 2.2 system alone. Red includes time alighned and level matched helper. Finally, blue is same as red but mildly EQing the helper. The wild transition swings are greatly improved.
So, the idea seems to have worked. Transition nulls that are uncorrectable by EQ don't mean the acoustic response itself is immutable. Adding another spatial degree of freedom can change the problem. This obviously has conceptual relatives in multisub optimization, Sound Field Management, Dirac ART/support speakers, etc. I’m certainly not claiming to have invented multiple-source acoustic control. What struck me as less commonly explored is extending the concept in a 2.2 system upward into the awkward ~100–400 Hz transition/lower-midrange region with a dedicated low-level helper channel.
There are also obvious qualifications. I still need to:
So, rather than asking the existing sources to do something they apparently can’t do, what happens if I introduce another independently located acoustic source with a different room response that can be used to compensate?
The experiment
I added a modest “helper” speaker (Magnepan SMGa) on its own DSP channel. It was placed horziontally centered against the front wall behind a large TV and angled up at about 45deg. Why like this? Cause that's the speaker I had and that was about the only place it could go. The aim was as a very limited correction source whose only job is to contribute where 2.2 system still has deficiencies. The existing 2.2 system remains the baseline. The idea is simply existing acoustic response + separately controllable spatial source to improve the region that more EQ can't improve. The "helper" had independent control of:
- placement
- bandwidth
- gain
- polarity
- delay
- PEQ
Effect of Helper Timing
The helper is about 40 inches behind the mains so time misalignment would be expected. Rather than calculate I ran a series of delays in case of possible latency issues with the DSP stuff. See below.
There obviously isn’t one delay that phase-aligns two physically separate sources across several octaves. That isn’t what I’m trying to achieve. The task is to find the delay giving the most useful compromise across the particular deficiencies I want the helper to address. The broad optimum ended up around 3.25 ms in this setup.
Gain - Less is More
Below shows progressively reduced helper gain. The inital setting was obviously way too high. Less is more. 1/3 smoothing gives a better sense of the effect than 1/6.
Provisional Result after EQing
Below is the end result after a little helper EQing (almost). Black is the optimized 2.2 system alone. Red includes time alighned and level matched helper. Finally, blue is same as red but mildly EQing the helper. The wild transition swings are greatly improved.
So, the idea seems to have worked. Transition nulls that are uncorrectable by EQ don't mean the acoustic response itself is immutable. Adding another spatial degree of freedom can change the problem. This obviously has conceptual relatives in multisub optimization, Sound Field Management, Dirac ART/support speakers, etc. I’m certainly not claiming to have invented multiple-source acoustic control. What struck me as less commonly explored is extending the concept in a 2.2 system upward into the awkward ~100–400 Hz transition/lower-midrange region with a dedicated low-level helper channel.
There are also obvious qualifications. I still need to:
- test several nearby microphone positions to see how much of the improvement survives spatially;
- do substantially more listening with helper on/off;
- examine the time-domain tradeoffs more carefully.
- figure out other tradeoffs, such as stereo separation
