Hello Duke, By definition, reflections have lower levels than the direct sound. How then is a reflection capable of masking the direct sound? The mere existence of perception thresholds would be evidence to the contrary?
Thank you for your in-depth reply, Klaus.
Perception thresholds do not preclude partial masking, or more precisely, partial backwards masking.
I hear a loss of clarity when the early reflections are included in those Griesinger clips, and consider that to be evidence of masking under those circumstances. Of course what I claim to hear is merely "anecdotal", so I cannot expect my claim of hearing anything on those clips to constitute evidence for anyone other than myself.
It is not clear (to me) what exactly the recording was: was it a Lokki recording with electronic orchestra? Did Griesinger make the recording himself, and where?
I don't know the details of how Griesinger made the recording but I think it was in Boston Symphony, from the seat he had a ticket for, and I speculate that he used a binaural microphone setup with tiny microphones in his own ears.
I really don’t think that one can take this particular recording of a recording of concert hall sound as evidence for early reflections having detrimental effects of reproduce sound in a domestic setting.
The
basic principles in play are these, as described by Griesinger:
"Envelopment is perceived when the ear and brain can detect TWO separate streams: A
foreground stream of direct sound, and a
background stream of reverberation. Both streams must be present if sound is perceived as enveloping."
"The earlier a reflection arrives the more it contributes to masking the direct sound.”
Griesinger's clips are an
illustration of these principles in action in a concert hall.
Because of the shorter timeframes, my guess is that a corresponding set of recordings in a home listening room would not show as dramatic a difference.
...there is no evidence, as far as I’m aware, for detrimental effects of these [early] reflections.
Have you ever owned fullrange dipole speakers, like Maggies? If so, did you notice an improvement in clarity from pulling the speakers farther out from the wall? If you did, I suggest that was evidence of the detrimental effects of early reflections, and of the benefits of later-onset reflections.
In one of his listening rooms Toole used a diagonal speaker placement, which geometrically minimizes early sidewall reflections. What he has to say about that configuration certainly implies a lack of early sidewall reflections is desirable:
“This was deliberate. I think many people are unaware of the advantages of a diagonal arrangement. There are essentially no sidewall reflections.”
Again quoting Toole, from the third edition of "Sound Reproduction", page 194:
"Go into almost any recording control room and there is a high probability that early lateral reflections have been eliminated or attenuated by appropriately angled reflecting surfaces or massive absorbers, or both.... Using only professional sound engineers as listeners, [researchers] found that narrow-dispersion loudspeakers were required for good reproduction of voices in radio dramas; dance and popular music were also desirably "aggressive" with "highly directed" loudspeakers. The majority of these same listeners, however, preferred wide-dispersion loudspeakers for the reproduction of symphonic music at home."
In other words, what Toole is saying is that recording engineers, who rely on clarity to do their jobs well, prefer to minimize early reflections when listening on the job. But for recreational listening at home, the majority prefer wide-dispersion speakers. Why might this be?
Here is what I think is going on: The early reflections at home degrade clarity just like they do at work, but a wider pattern results in more late-arriving reflections, and the net benefit of those additional late-arriving reflections outweighs any detriment from the early ones.
If this is indeed the case, then the "best of both worlds" might be the suppression of early reflections, followed by lot of late reflections. This is exactly what Griesinger's clips demonstrate, and imo this is consistent with the widely-reported experiences of dipole owners.
Reduced early reflections followed by increased late-onset reflections (with a corresponding increase in late reflections) is a goal of my loudspeaker designs, with the intensity of those late-onset reflections being user-adjustable.
Absorbers will absorb reflections regardless of delay, so why specifically aim at 10 ms? They [absorbers] do this [absorb regardless of delay] also on floor and ceiling so I don’t quite understand his approach of breaking up those reflections.
My understanding is that 10 ms is just a point on a multi-dimensional continuum wherein level and frequency and direction and properties of the reflecting surface and the presence of other reflections all play roles. In my opinion a 10 ms target seems to be both practical and beneficial. 12 ms is a little bit less practical and a little bit more beneficial. And so forth.
Seigfried Linkwitz came up with 6 ms as his recommended minimum:
"Reflections generated by the two loudspeakers should be delayed copies of the direct sound to the listener. The delay should be greater than 6 ms. The high frequency content of the reflections should not be intentionally attenuated."
One problem with aggressive use of absorption to kill the early reflections is, that energy is then no longer around to become beneficial late reflections. Another problem is, absorption selectively attenuates short wavelengths more than longer ones, altering the spectral balance of the reflections accordingly.
With all respect, as long as no appropriate controls have been included in listening tests, I would consider personal listening experience as anecdotal at best.
Of course my personal listening experience is anecdotal! Please note that I made a point of NOT claiming my own experiences constituted evidence! The only person my experiences can constitute evidence for is myself; for you and anyone else, any conclusions which I draw from my own experiences are
opinions. My apologies for not making that clear.
This [the delay time of the early reflections determines the impression of the size of the room] relates to the size of the room in which the recording has been made, not the room in which the recording is listened to.
I think it also applies to the playback room. I think I hear a correlation between soundstage depth and distance between speakers and wall, whether the speakers be monopoles or dipoles.