Right. However, AE latent in a production, or AE manifest in reproduction, are not easily quantifiable. Even a systematic vocabulary is missing, after 40 years of academia mostly only considering reproduction timbre.
As much as I appreciate Floyd and Harman’s excellent research on loudspeaker directivity and timbre, it is about time to also consider the hard problem of reproduction: Spatial qualities of the listening room+system, from an AE perspective. AE is even the primary perceptual and emotion-inducing potential 3D sound has to offer over stereo, regardless if AE is naturally recorded or constructed.
Hi Thomas,
Everything is important, but each in its own time . . . When I began my research 59 years ago (!), sound quality was a huge problem, and stereo was a novelty. I know you appreciate what I and my research teams have contributed to alleviating the sound quality issue. It is a good start to pleasure when voices and musical instruments sound as they should. Mediocre loudspeakers still exist, but there is no excuse for them any longer. The industry has measurable performance targets that correlate highly with subjective ratings acquired under controlled, blind, conditions and Amir on this website delivers them.
But neutral loudspeakers do not ensure neutral reproduction because of small listening rooms. The early reflections modify directional/spatial perceptions and stereo itself its a fundamental limitation, corrupting both sound and spatial qualities. Low frequency room resonances contribute audible excesses (booms) and gaps (missing or attenuated notes), and these effects are different in different seats. Equalization can improve sound quality for a single listener, if that is the objective. However, movies, video concerts and the like are often social events, to be shared, so seat-to-seat variations become a consideration. It turns out that multiple subwoofers, employed in specific active and passive arrangements can alleviate the seat-to-seat variation problem and global equalization can then address the sound quality issue for multiple listeners. It can work very well from the sound quality perspective.
All of that was achieved with no real consideration of low-frequency spatial perceptions, probably because, over the years, the bulk of what was regarded as important in listener envelopment (LEV) was focused on what was happening in the octave bands from 250 Hz to 2 kHz, and they are still, it seems, an important basis for evaluating concert halls. This, of course, is overly simplistic, as what is measured is typically reverberation time (RT), a time-domain phenomenon. The desirable spatial effects are assumed to follow because of quasi-random arrivals of reflections from many incident angles, and research even identifies "preferred" angles - mainly those associated with side wall reflections. So far so good, because envelopment has been considered to be a prime factor in evaluating concert halls. But to me the generally applied science could be improved.
Bass frequencies have always been a concern, but my observation indicates, in the 125 years of concert hall acoustics, that it is only recently that the attention has included considerations of more than RT and amplitude. From our understanding of the binaural hearing mechanism (my PhD thesis), there has to be more, and David Griesinger was my introduction to anyone paying more than passing attention to directional/spatial/enveloping perceptions at very low frequencies. In large venues it makes absolute sense, and it is one of my continuing pleasures over decades of season tickets to classical concerts. It is real.
However, in small listening rooms there are challenges. The collection of resonances themselves perceptually characterize the size of a room. Very large rooms tend not to exhibit many problematic, distinctively audible, low-frequency resonances - the Schroeder frequency of a concert hall is likely to be around 100 Hz, maybe lower - not my area of expertise. But small rooms have distinct "personalities" - think of singing in the shower. Eliminating clearly audible small-room resonances seems like a fundamental step in the direction of reproducing the sound of large-rooms.
The next challenge is to deliver the necessary poorly correlated low frequencies to the ears of listeners - without losing the desirable attenuation of resonances, and, optionally, reduced seat-to seat variations. Immediately we confront decisions and priorities. Ideally we can identify a method within which multiple objectives can be simultaneously satisfied.
Years ago David Griensinger mounted a test of what might be possible in a "stereo bass" configuration in a relatively dead listening room at Harman. A group of highly experienced and opinionated listeners experienced a protracted experiment of variables, including digitally concocted signals and many musical selections. We heard some spatial effects, but all were in the subtle end of the scale and there was no benefit from bass management crossover frequencies below about 80 Hz. David appeared to be more sensitive than some of the others, and this might suggest a learning curve. He has written that the effect is audible in concert halls down to 60 Hz. You, Thomas, have said 50 Hz, I believe. So it is agreed that there is a low frequency limit, as is likely associated with the spacing of the ears. Obviously, a real test should begin outdoors - most anechoic chambers would not qualify. Once a baseline for audibility is established, add reverberation and vary the crossover frequency to see at what points the desired auditory envelopment is degraded.
That or any other research is no longer my concern; I am retired. But suffice it to say that our understanding of binaural hearing indicates that these effects should be audible, and they are in large halls. Translating the phenomena enjoyed in real halls to multichannel delivery systems in small rooms is the challenge - without degrading sound quality for one or more listeners. As the recording is a key variable, I wish future researchers good luck.
In the meantime, I have a real-life situation to deal with - I have relocated from a comfortably large listening room in California to a significantly smaller (13' x 16'. 4m x 4.9m) room in Ottawa, Canada. It has been convenient that the room is rectangular, making modal control simple, but equipment and furniture are restrictions. It turns out that two small 80 Hz low-passed, bass managed, subs can be located 25% of the distance from the side walls and the rear wall. In the furniture arrangement they are not obvious, and they attenuate the first three width modes, across which the listeners are arranged, and couple poorly into all but the first order length mode. One can walk from side to side across the listening area and little changes, but there remains a first-order mode excess in the rear seats. I am now running the front broadband, floor stander, loudspeakers full range to destructively interfere with the length mode. The front loudspeakers deliver what "stereo" bass there is, but not from the best locations in the room. Playing Davids DropBox files of correlated and decorrelated 100 Hz low-passed noise indicated that I now seem to have retained the desired resonance control while delivering some of auditory envelopment. It is definitely somewhat "out-there", not mono. Interesting, and I may not be done yet. But, when it is good, mono low bass is highly enjoyable with the majority of program material. Cheers.