Psychoacoustic effects of front and back reflections?

[Cosmik]

Whatever. Is there a particular subject this thread was about?

Surely we're pretty much on-topic?!!

 

[Blumlein 88]

Whatever. Is there a particular subject this thread was about?

Effects of front and back reflections with a mention of omni vs dipole speakers in the OP. So we should be near about on topic even if we haven't been too informative yet.

 

[Fitzcaraldo215]

I am not seeing the connection to topic, myself. Does the subject of the primacy of time domain accuracy above all else not belong in a separate thread?

As for JW, sorry, but it it is not for others to first scientifically disprove his stated hypothesis and assertion offered without supporting data. Science and scientific reasoning does not work that way. It is up to him and to you, his disciple and endorser, to provide the data backing up that assertion in the first place. My mind is open on the subject. Where is the data supporting it?

 

[Cosmik]

I am not seeing the connection to topic, myself. Does the subject of the primacy of time domain accuracy above all else not belong in a separate thread?

If you want to discuss front and rear reflections, it must surely matter what is being reflected.

As for JW, sorry, but it it is not for others to first scientifically disprove his stated hypothesis and assertion offered without supporting data. Science and scientific reasoning does not work that way. It is up to him and to you, his disciple and endorser, to provide the data backing up that assertion in the first place. My mind is open on the subject. Where is the data supporting it?

Can you name a single area of audio that has been settled by 'science'? As far as I am aware, science cannot even persuade anyone whether high resolution sounds any different from CD 44.1/16 or if digital is better than analogue. Or that lower distortion is always better than higher. Or that multi-channel is unambiguously better than stereo. Or that stereo is better than mono. Or that Class D is better than AB is better than A. Or valves better than solid state. Or feedback is better than no feedback. Or that open baffle is better than box is better than panel. Etc. Etc.

In all these areas, you simply have to 'pick your poison' and this is usually on the basis of rational or irrational reasoning and some fleeting impressions that leave their mark in your mind. I am open to anyone like JW who does the reasoning bit without necessarily supplying 'data' that is always qualified with caveats and conditions and is never unambiguous.

 

[Fitzcaraldo215]

Using reasoning, I can see that there might be a point to timing as it pertains to direct sound especially from multiple speaker drivers. It is controversial, though. Not all believe in its critical importance, though some do. Therefore, it is worthy of discussion in its own thread. I would be interested in that discussion myself.

Here, I thought we were talking about front-back room reflections whose timing spectrum is more diffuse together with other room reflections, regardless of whether the speaker direct sound has perfect timing or not. That is my only point, and I thought JW's points and yours were more about the speaker direct sound rather than the reflections.

I don't think pure logic and reasoning, subject as they are to bias and other faults of omission or commission, are necessarily better than empirical science in cutting through the complexity and getting us closer to the truth. I prefer the science, not mere logical assertions based on uncontrolled anecdotes without in depth objective information. I grant you that science does not have all the answers, so beyond that we must choose what we wish to believe.

 

[oivavoi]

Still waiting on anybody to chime in with actual studies on the effect of reflections from the front and the back... I discovered one on reflections from the back, though. Seems to be important for envelopment. http://www.iida-lab.it-chiba.ac.jp/.../09.The.role.of.reflections.from~.AA-2001.pdf

 

[Fitzcaraldo215]

That article is somewhat technical for me, but I think I understand some of its points. The main emphasis I see is between early and later reflections. I still think that late reflections are preferable for envelopment and other reasons, but unfortunately typical listening rooms tend to have more early reflections than late ones. So, the listening room's mostly early reflections as from the front or back (or side or ceiling) walls are not going to do a good job of putting back envelopment into the sound so as to recreate the concert hall experience, if that is the goal. Early reflections are more likely to have negative effects our ear-brain cannot separate from direct sound.

Multichannel does envelopment and other good things much better via speakers behind the listener's ears using delayed reflections actually captured in the hall. My system is 7.1 capable, but I have not found a significant killer advantage of that over 5.1, using music recorded in those two formats or killing the back channels of 7.1 recordings. My surrounds are at 110 degrees to front dead center, and my back channels are at 150 degrees. I mainly listen to SACDs natively in 5.0/.1 with the back channels off.

I developed some rules of thumb, perhaps erroneous ones, over the years by listening to experts and trying things myself. Of course, one should not sit in close proximity to the back wall where early reflections become even more dominant. I also got the idea somewhere of trying to achieve at least a 10 msec delay of reflection paths. That translates to about 10 ft., I think. So, I have positioned my Martin Logan dipole electrostats at least 5-6 ft. (10-12 ft. two way to my ears) from the front wall for years, and I found I preferred that. I also allow furniture, bookcases, wall hangings to do a bit of random diffusion of the back wave from my dipoles. Side and up/down reflections from dipoles are also generally way down in level due to their dispersion pattern.

 

[Bjorn]

Here's a study related to reflections from the rear wall in a LEDE room:
http://www.aes.org/e-lib/browse.cfm?elib=5242

 

[RayDunzl]

This talks about different studio acoustic design types:

https://www.soundonsound.com/techniques/sos-guide-control-room-design

In the section on Ambechoic Designs, it mentions BlackBird Studio C for which they provide an impulse response measurement.

https://www.blackbirdstudio.com/studio-c

"Blackbird Studio C is based on these principles and is shown in Figure 13. The experience of this room is that one is unaware of sound reflection from the walls: it sounds almost anechoic, yet it has reverberation."

If I overlay my room measurement (ML panels) and their measurement of Blackbird Studio C, I seem to have an even higher ratio of direct to reflected/reverberant/diffused/whatever sound.

Mine is green, theirs gray, vertical is 75dB in both cases, time duration the same.

The only reflection level where I'm higher is at 27ms, which is the speaker to wall above the absorption behind the mic off the wall behind the speakers and back down the room to the mic. It matches at about 7ms, which is the reflection speaker (dipole) to wall behind to mic.

I have some 2' x 4' x 7" rockwool slabs in the corners somewhat behind the speakers, and two slabs standing behind the couch. Sidewalls are CD racks.

Hmmm.

 

[Blumlein 88]

This talks about different studio acoustic design types:

https://www.soundonsound.com/techniques/sos-guide-control-room-design

In the section on Ambechoic Designs, it mentions BlackBird Studio C for which they provide an impulse response measurement.

https://www.blackbirdstudio.com/studio-c

"Blackbird Studio C is based on these principles and is shown in Figure 13. The experience of this room is that one is unaware of sound reflection from the walls: it sounds almost anechoic, yet it has reverberation."

If I overlay my room measurement (ML panels) and their measurement of Blackbird Studio C, I seem to have an even higher ratio of direct to reflected/reverberant/diffused/whatever sound.

View attachment 10114

Mine is green, theirs gray, vertical is 75dB in both cases, time duration the same.

The only reflection level where I'm higher is at 27ms, which is the speaker to wall above the absorption behind the mic off the wall behind the speakers and back down the room to the mic. It matches at about 7ms, which is the reflection speaker (dipole) to wall behind to mic.

I have some 2' x 4' x 7" rockwool slabs in the corners somewhat behind the speakers, and two slabs stanind behind the couch. Sidewalls are CD racks.

Hmmm.

This is why I never embarked on making my own quadratic diffusers. I feared this would be the end result. By the time I sawed the 1x2s for this diffuser pattern I would have been deaf due to the noise of the saw. Maybe I should do it for my video rig and paint them flat black. Stop specular sidewall reflections of sound and light. Then I would run the risk of guest viewers in the darkened conditions stumbling and impaling themselves on the room treatment.

 

[oivavoi]

Here's a study related to reflections from the rear wall in a LEDE room:
http://www.aes.org/e-lib/browse.cfm?elib=5242

Thanks Bjorn! Very interesting!

 

[Bjorn]

The ambechoic principle in Blackbird studio was an experiment and it's also important to remember it was primarily for surround. However, today they have covered several of the diffusors with thick plankets, thus it seemed the principle somewhat failed. While it's much more lively than an anechoic chamber, it's still considered quite dead and far from the liveliness/energy you have in a LEDE/RFZ room.

 

[Cosmik]

...they have covered several of the diffusors with thick plankets, thus it seemed the principle somewhat failed.

But no reason to believe that the blanket version isn't also a failure. Or equally a success. My general impression from a 'meta analysis' of this, is that once a person starts down the route of room treatment (and DSP 'correction'), they can never let it lie, and forever blame their dissatisfaction (real or imagined) on the sound of the room. And all the while, maybe they are 'hearing through the room' anyway, and a very broad range of rooms are equally acceptable. Any real problems are with the speakers, but they can't do much about that. But anyone can saw up bits of wood and fit rockwool panels etc. All to no avail...

 

[oivavoi]

"Blackbird Studio C is based on these principles and is shown in Figure 13. The experience of this room is that one is unaware of sound reflection from the walls: it sounds almost anechoic, yet it has reverberation."
.

Regardless of the sound, I'm pretty sure listening in such a room would give me the sensation of having been abducted by aliens and placed in an intergalactic torture chamber.

 

[svart-hvitt]

But no reason to believe that the blanket version isn't also a failure. Or equally a success. My general impression from a 'meta analysis' of this, is that once a person starts down the route of room treatment (and DSP 'correction'), they can never let it lie, and forever blame their dissatisfaction (real or imagined) on the sound of the room. And all the while, maybe they are 'hearing through the room' anyway, and a very broad range of rooms are equally acceptable. Any real problems are with the speakers, but they can't do much about that. But anyone can saw up bits of wood and fit rockwool panels etc. All to no avail...

«...once a person starts down the route of roomtreatment (and DSP'correction')...»

That’s where a a big part of today’s audio research is aimed.

In other words, you’re on a crusade against most audio faculties out there. Your crusade may have merit, but it seems like your arguments are more based on logic and first-principles without any empirical support.

 

[Fitzcaraldo215]

... My general impression from a 'meta analysis' of this, is that once a person starts down the route of room treatment (and DSP 'correction'), they can never let it lie, and forever blame their dissatisfaction (real or imagined) on the sound of the room. And all the while, maybe they are 'hearing through the room' anyway, and a very broad range of rooms are equally acceptable....

Dissatisfaction? Kal, me and many of my closest friends have been using DSP EQ room correction for over a decade. We have never been happier. Some of us have not changed anything of substance in a decade. Methinks thou dost selectively choose assumptions, anecdotes and mere audiophile testimony rather than empirical data or even conducted thine own subjective listening comparisons. So, thou werest able to fit thine own unproven hypothesis - wishful thinking. We who use it, even to this day, can turn it on and off in rapid succession, and we reach the same conclusion: gotta have it. But, as with all things in audio, YMMV.

I do not disagree that getting into treatments is riddled with potential problems, much time, effort and expense, short lived confirmation bias, etc. Maybe fully optimized treatments are capable ultimately of being even better than DSP EQ, though treatments by their nature are incompatible with meaningful before/after listening comparisons. But, that long road with unsightly treatments is not guaranteed to succeed, even in professional hands. Stories and anecdotes abound of less than successful treatments. It is a far riskier approach.

Sure, many rooms are "acceptable" uncorrected, but maybe not so much after hearing what competently mic-calibrated DSP can do in the same room in A/B. And, sure, some will be dissatisfied with it for a host of reasons, valid or not. For example, it is quite easy to overlook something important, leading to a suboptimal calibration. But, I do not think the "metadata" objectively supports an overwhelming disappointment with it. It is no panacea, curing all audio ills. It is not perfect. But, a strong niche in the marketplace is accepting it in great numbers, and I believe most buyers keep it, then keep it on, not off.

Also, audiophile DNA for many carries the curse of perpetual dissatisfaction, though equipment makers love that. I believe it stems from many imperfections in the overall, insufficiently transparent audio recording and reproduction paradigm, including specific equipment choices in the system, which render the sonic result, at best, still somewhat short of the (unrealistically?) expected realism compared to live. We can only expect very small, very gradual steps to improve that. Although, I may be lucky, but I have heard huge progress over the past decade, myself.

But, one revolutionary step is to now consider the room as an integral part of the playback system. It clearly has measurable and audible effects on the sound as heard by the listener, so why is it not formally considered part of the playback system? While paid lip service in previous generations of audiophiles, the room and its influence are better understood today thanks to science, measurements and the availability, mainly over the past 15 years, of high tech DSP tools, which many proactive audiophiles, not enslaved by tradition, could easily audition in their own systems. I think it is growing and here to stay.

 

[RayDunzl]

However, today they have covered several of the diffusors with thick blankets

Wife hires a new interior decorator.

Honey, I have a surprise! Close your eyes!