In recent weeks when trying to switch off thinking about work, I have turned my thoughts to Room Response Equalisation. There is much discussion about this in some parts from Linn and from REW users etc, but I was intrigued why sometimes the results can be really poor and artificial sounding when trying to compensate for room reflections…
I am also curious about speaker room coupling and why some speakers sound very bright in a room and others not…
So I started reading research papers. I found a particularly interesting scientific paper review of current thinking and trends on RRE: Room Response Equalization - A Review; Cecchi, Carini, Spors.
In short the paper goes into the RRE with a view of improving sound reproduction performance, and discusses the errors and pitfalls in some equalisation processes and speaker design. Also why sound performance changes with room temperature and humidity
I applied some of their observations and thinking to a response filter I created for my living room; essentially I took an average room measurement around the listening area; I then edited the correction (inverse response) to smooth out the adjustments, I shortened and simplified the filter by reducing the number of poles… and most importantly I did not compensate for the natural room / speaker coupling response which falls away in the high end and low end, around 100 Hz and gently from 10 kHz. (This is configurable in REW to experiment with)
The result was subtle on simple well recorded music… like a jazz quartet etc, or well recorded rock or pop, but play back an old recording or compressed rock recording and the effect was astounding … voices sounded certainly far more real and far more intelligible, strings sounded real, drums had tune … and no matter how compressed or old the music usually bounded along. We all enjoyed some old Ska recordings like we hadn’t before. Yes that initimate exaggerated Hi-Fi type affect is reduced on some recordings, but I conclude that is an artificial response anyway, and simply gets in the way of more complex recordings… where instead the realism and naturalness instead starts to dominate.
In a way I felt the response was similar to my vinyl replay… and looking at the response curve in places it resembled an RIAA curve for vinyl… so there might be something in that.
So the key was about effectively creating a smoothed inverse response, where the smoothing is proportional to the frequency, that, importantly, does not compensate for the natural room speaker coupling response which otherwise would be adding artefacts and making the sound unnatural or perhaps what some call ‘digital’
I do think some speakers are tuned to compensate for this fall off, which is why in some rooms they can sound too bright.
Anyway I thought I’d share… it’s certainly was a revelation to me, and a most beneficial and enjoyable one. I will post my filter response later. Might be food for thought with anyone wanting to try whose music replay is in a living space, not a recording studio.
