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Perceptual Effects of Room Reflections

Marmus

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Here's a crude drawing of my room and what I believe are the direct speaker reflections. I believe this works mainly due to speaker design but do not know for sure. And I think it may work in a larger room provided speakers have reflector panels in place at an optimal distance. This however would require experimentation which I am not able to do.

View attachment 127542
Very interesting, and brave. How does it sound? And have you ever just once done a spectrum analysis in there?
 
D

Deleted member 28849

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Very interesting, and brave. How does it sound? And have you ever just once done a spectrum analysis in there?

I've been sitting on this discovery for 7 years and I'm not going to live forever. This maybe an alternative method of listening to stereo rather than the typical stereo setup. Have not done a spectrum analysis.
Your typical stereo setup has IMO a narrow stereo image it can range from practically non-existence to perhaps 8' depending on the room and the image seems to be behind the speaker plane. Also proponents of typical stereo setup emphasis elimination of first reflection points.

With some experimentation I think my setup could be adapted to bigger rooms using reflective panels replacing backwall which maybe much further back than optimal distance from speaker, to create a good reflected image. Allows for wider sweet spot listening, further back into a room.

Pros:
15' wide phantom stereo image/soundstage (could be expanded given more room space).
Image seems to project off of front wall, giving an accurate forward presentation.
can't locate speaker position.
enveloping nearfield wall of sound.
phantom image can be easily moved left or right to center image just by adjusting speaker toe-in.
don't have to worry about reflection cause you using the reflection to create stereo image.
works in long narrow room.
full range speakers
obstacles or junk in room does not interfere with the reflected image.

Cons:
may require specific speaker design and brand name for optimal imaging as well as being an accurate speaker.
some people may not like a forward presentation or accurate sound.
requires a long wall or wide wall in a room.

That's all I can think of for now.
 

josh358

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Thanks! Credit to my partner James Romeyn for using the vertical plane like that. Based on various things I've read I would have said that keeping the reflections in the horizontal plane was the higher priority, but Jim didn't know any better so he just tried it, and the additional time delay made a big improvement. I went from designing bipolar speakers to designing polydirectionals which deliberately use the ceiling.

We can get within a foot or so of the front wall and still hit our ten milliseconds backwave delay target in most rooms, without electronic delay. The spatial impression (including the sense of depth) changes significantly from one recording to the next so I think it is dominated by the recording rather than the playback room. I think this is because the "playback room" cues are rendered inconsistent by early reflections off some of the walls and the ceiling arriving considerably later than they "should", thereby weakening the "small room signature" package of cues, which in turn offers the recording's package of "venue cues" (whether real or engineered or both) a window of opportunity, assuming they are effectively presented. The later-arriving room reflections have the job of effectively presenting the venue cues which are on the recording (in particular the reverberation tails), so imo we don't want an overdamped room.

The claimed theoretical benefit of this approach is good imaging because the early reflections have been minimized, AND good spaciousness because we have a lot of relatively late-arrival reflections. Like a well-set-up pair of dipoles, our approach arguably offers both qualities at the same time, though with less real estate required because the backwave energy uses the room's vertical dimension.
It's a good idea!
 

375HP2482

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I'm not using electronic delay in order to keep the system from requiring that much complexity, but separate inputs for the rear-firing drivers are provided so DSP delay could be added if desired, and I have at least one customer who has done so. The rear-firing drivers are aimed up-and-back such that, combined with the recommend toe-in of the main speakers, there is typically a multiple-bounce path-length-induced delay of at least ten milliseconds without taking up as much real estate as properly positioned dipoles. You can see a stand with a built-in rear-firing coaxial here, scroll down a bit.

Dr. Amar Bose is smiling down on you.
 

Duke

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Dr. Amar Bose is smiling down on you.

Ha! Rolling his eyes more likely.

We conducted controlled blind in-house testing wherein we allowed listeners to dial in (from the listening chair) their preferred amount of relatively late-onset reverberant energy to add to our controlled-pattern main speakers, and arrived at very different conclusions from what Amar Bose was doing. We found a MUCH HIGHER direct-to-reverberant ratio to be preferred.

By way of illustration, if you imagine starting out with the 120-degree-horizontal radiation pattern of the JBL M2, what we found was that sending about 70 degrees towards the listening area and about 50 degrees elsewhere would be about the right balance. So in effect we have roughly the same direct-to-reverberant sound ratio as the M2, but the temporal "center of gravity" of our reverberant sound is pushed back in time in a normal room, and is closer to what might be found in a room with a deliberate early-reflection-free zone.

Anyway, stop me if you've heard this one:

Paul Klipsch was strolling down the sidewalk when who does he see coming towards him but Peter Walker, Henry Kloss, and Amar Bose. So Paul cups his hands around his mouth, horn-like of course, and calls out, "Hello gentlemen! How are you doing?" Well, Peter Walker is ecstatic; Henry Kloss is infinitely baffled; and Amar Bose turns around to face the opposite direction and says, "Fine, Paul! And how are you?"
 
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375HP2482

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That's a good one, haven't heard it.

In that vein, Bob Carver would have replied, "I'm not sure. How would you like me to feel?"
 

tomeh

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Thanks for inviting me to your new forum Amir. For my first post, allow me to refute the notion that early reflections are ever beneficial in a home-sized room:

Early Reflections

:D

--Ethan
Hi Ethan.

In your link above you state "I'm a big fan of Floyd Toole, so disagreeing with his preference for early reflections doesn't mean I don't respect his other work."

I've checked Mr. Tooles book "Sound Reproduction" and I can't see anywhere that "his preference" is cited?

I do see a methodical approach to looking at one variable at a time, using the blind tests, citing blind test participants preferences, citing broadband detection of first relections versus 500 hz low pass (simulation of common wall mounted treatments) and a standard of seeking repeatable results.

Is there a technical paper or some other place where he stated that, so I could read it in total?

Thanks

Tom eh
 

Andrew s

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Thanks for inviting me to your new forum Amir. For my first post, allow me to refute the notion that early reflections are ever beneficial in a home-sized room:

Early Reflections

:D

--Ethan
I have to say when setting up my 3m wide atic listening room by far the biggest effect was taking out the first side reflections. I had no idea what to expect but it was as is my ears had been prised apart due the the sound stage widening. You could hear the recorded acoustic rather than the room. Base trapping etc had an effect but nothing so dramatic.

Subjective I know and I have not removed it for A/B testing

Regards Andrew
 

tomeh

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Hello Scott. It is so good to hear from you again! I really missed your departure from the last place we hung out together. :) And thanks for the kind words regarding ASR Forum. That is what we strive for and good to see that it shows.


Yes, Kevin is a very good friend and he and I have talked a number of times about this. My sense is that like other professionals you mention, through so much exposure trying to hear speaker sound itself, may have evolved his hearing to be much more sensitive than the rest of when it comes to reflections.

BTW, there was follow up research on Dr. Toole's hunch regarding mixing and mastering engineers in a rather recent AES paper The Practical Effects of Lateral Energy in Critical Listening Environments, this very thing was tested in controlled environment to determine preference for diffusion, absorption or doing nothing (reflections). Here is the test subjects the outcome:

View attachment 10084

View attachment 10082

As you see, it turns out the majority of these professionals actually side reflections than not.

View attachment 10083


:)

As you say, the panel speakers have a sound that when combined with right music, is a very unique experience.

Hope we see you more here.

Thanks for the AES link. An interesting experiment for certain.

I see the Abstract states "Results correlate the presence of strong lateral energy with an initial reduction of subjects ability to complete the task within normal tolerances, but adaptation soon occurs, restoring the subjects to practically normal pace and accuracy."

A can't see anyone disagreeing that our brain automatically rebalances the listening environment and this appears to say that this happens relatively quickly?

Another interesting point for me is "The room, designed for critical mixing, mastering and ear training applications, exhibits an RT60 of approximately 200ms across all frequency bands."

I'd love to see the RT60 vs freq plot. If it was "across all frequencies", the most common low freq rise must have been treated and/or designed out of the room. Wouldn't this make it an execptional room to start with, with the most complicated room sound and energy area dampened very well?

Cheers,

Tom eh
 

tomeh

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My subjective experience is as follows: avoiding side reflections indeed allows hearing more through to the source. But it sounds "fake" to my ears, it doesn't sound like real music happening (because real instruments always excite reflections). Having broad directivity and more reflections diffuses some of the uniqueness about the source, as one hears one's own room as much as the recording venue. It does sound much more real to me though, much closer to how I perceive real acoustic music to be.

My personal experience is that I often prefer the low-reflection type of listening for modern electronic studio music (in a broad sense), since this kind of music is inherently artificial and doesn't resemble real acoustic events. It's like my brain allows me to get fooled by the reflection-free stereo image. Recordings that try to either capture or recreate real acoustic events, on the other hand, feel much more real or convincing to me when listened to on a system with broad directivity and a generous amount of reflections. I have a fair bit of experience with acoustic music, and I suspect that my brain protests when presented with an acoustic image which purports to be real but doesn't excite reflections.

Others will have other experiences and preferences, I guess.

Hi,

I understand what you are saying here and have had similar experiences.

The things that affect all of us when listening to "other" peoples recordings are;

1. We don't know how much of the room reflections were captured in the microphone where it was recorded?
2. We don't know what artificial effects were applied in the form of simulated early, mid or late reflections?
3. We don't know if all the instruments, voices etc. were recorded in the same room and therefore iclude item 1?
4. We don't know the speaker and room character that influenced the mixer and mastering engineer?

It is a lot of Mr. Tooles "circle of confusion."

Each one of these steps has the potential to add reflective information but no one has a real way of removing them.

For a consumer of recorded music I'd guess that the average person makes many, many trials to find an enjoyable balance on the average of the recordings that they play for enjoyment?

On the recording side that I control, I have chosen to leave very little of the room reflections and much more of the direct sound source for in studio recordings. Then place everyone "in the best room for the music."

This changes completely for live recordings of acoustic works in a nice environment. There I choose to balance the room reflections with direct sound source coming into the microphones to capture the total audio experience. And therefore rairly add any artificial effects.

In each case my mastering system is heavily balanced toward direct information so I am confident that what I have created in the studio or captured in the concert hall is what I'm hearing the majority of, not my playback system and room.

Therefore I suspect a lot of people would reject my mastering system and room combination since it might not suit the average of the recordings that they own??

However, as stated above no consumer has a real way of taking out one the recordings reflective information, so they can only add more from their speaker and room combination.

Enjoy the chase and the music.

Cheers,

Tom eh
 

375HP2482

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Thanks for the AES link. An interesting experiment for certain.

I see the Abstract states "Results correlate the presence of strong lateral energy with an initial reduction of subjects ability to complete the task within normal tolerances, but adaptation soon occurs, restoring the subjects to practically normal pace and accuracy."
One can read similar reports about the successful adaptations amputees make over time.
 

Mauro

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That is my impression too. On orchestral music reflections can be heavenly. But on some rock/pop music it can get excessive if the room is too live. So a balance is needed.

@oivavoi @amirm I dare say that the right balance would be modern studio recordings with headphones and acoustic events with speakers!

It’s interesting how (a good chunk of) headphones are characterized by limited number of reflections compared to room listening through speakers.

Nice article anyway Amir. Just reading some of your old ones!
 

josh358

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@oivavoi @amirm I dare say that the right balance would be modern studio recordings with headphones and acoustic events with speakers!

It’s interesting how (a good chunk of) headphones are characterized by limited number of reflections compared to room listening through speakers.

Nice article anyway Amir. Just reading some of your old ones!
Really, neither is right. The headphones put the music inside your heard (assuming it isn't a binaural recording), room reflections impose a "one size fits all" acoustic on everything and limit the width of stereo image because of interaural crosstalk. Really, to do better, you need something more sophisticated than plain old stereo. Crosstalk cancellation with head tracking and HRTF compensation may be the ultimate (wave field synthesis, too, but that's less practical). After that, object-oriented systems with multiple speakers, or multiple speakers with convolving reverb, and after that conventional stereo. Head tracking and HRTF compensation could be even better than the same with loudspeakers and crosstalk cancellation.
 

Mauro

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Really, neither is right. The headphones put the music inside your heard (assuming it isn't a binaural recording), room reflections impose a "one size fits all" acoustic on everything and limit the width of stereo image because of interaural crosstalk. Really, to do better, you need something more sophisticated than plain old stereo. Crosstalk cancellation with head tracking and HRTF compensation may be the ultimate (wave field synthesis, too, but that's less practical). After that, object-oriented systems with multiple speakers, or multiple speakers with convolving reverb, and after that conventional stereo. Head tracking and HRTF compensation could be even better than the same with loudspeakers and crosstalk cancellation.
Dunno. I’ve tried the Audeze mobius which features head tracking and hrtf compensation but I would say we are still far from having a workable consumer product.

I guess we will see in the very next years if it’s going to be the next letdown or marvel!
 

Spkrdctr

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Dunno. I’ve tried the Audeze mobius which features head tracking and hrtf compensation but I would say we are still far from having a workable consumer product.

I guess we will see in the very next years if it’s going to be the next letdown or marvel!

Funny you should bring that up. I have it upon good authority that Amir has a pair of Mobius headphones and will be testing them in about a month or so. Will be interesting to see how they do in a few different sound field modes vs 3D mode.
 

josh358

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Dunno. I’ve tried the Audeze mobius which features head tracking and hrtf compensation but I would say we are still far from having a workable consumer product.

I guess we will see in the very next years if it’s going to be the next letdown or marvel!
The Mobius is primarily aimed at gamers, isn't it? I suspect an audiophile-oriented device would sound better. I think there's only so much you can do with conventional two channel, but at the very least you should be able to get the sound out of your head, and it should have the wide soundstage of crosstalk cancellation and a solidity that the phantom image never has on speakers. You could also potentially add 3D convolving reverb to reproduce the sound of a space, but you'd have to manually select the reverb to match the venue. And you could do a lot with object-oriented audio, place the sound wherever you wanted in a 3D sphere.
 

Mauro

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The Mobius is primarily aimed at gamers, isn't it? I suspect an audiophile-oriented device would sound better. I think there's only so much you can do with conventional two channel, but at the very least you should be able to get the sound out of your head, and it should have the wide soundstage of crosstalk cancellation and a solidity that the phantom image never has on speakers. You could also potentially add 3D convolving reverb to reproduce the sound of a space, but you'd have to manually select the reverb to match the venue. And you could do a lot with object-oriented audio, place the sound wherever you wanted in a 3D sphere.
Actually the Mobius is quite a good headphone, better than most, at least sonically. I was partly perplexed by the artificial head tracking feature that poses a lot of questions.
Unless you want to use AI to extract 3d position of objects from a stereo song (there are ways), your headphones should really become much more similar to a gaming console where 3d content is not previously rendered but rendered on the fly based on your head position, distance from the artificial speakers with many caveats: a standard sound 3d codec for headphones, a powerful processing unit, an efficient processor that doesn’t drain the battery,..
And another big problem has to do with content not being produced for that specific goal, but Apple is opening this new market so I guess we consumers and music industry should have soon a chance to experiment with pros and cons of *artificial* 3d audio!
 

josh358

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Actually the Mobius is quite a good headphone, better than most, at least sonically. I was partly perplexed by the artificial head tracking feature that poses a lot of questions.
Unless you want to use AI to extract 3d position of objects from a stereo song (there are ways), your headphones should really become much more similar to a gaming console where 3d content is not previously rendered but rendered on the fly based on your head position, distance from the artificial speakers with many caveats: a standard sound 3d codec for headphones, a powerful processing unit, an efficient processor that doesn’t drain the battery,..
And another big problem has to do with content not being produced for that specific goal, but Apple is opening this new market so I guess we consumers and music industry should have soon a chance to experiment with pros and cons of *artificial* 3d audio!
3D audio produced by AI would, I imagine, be OK for games -- not so much for acoustical music. And that, I suspect, is why this doesn't work veryh well for music, since the headphones are game-oriented.

Acoustical music would be well served by convolving reverb. (That's true with loudspeakers as well.)

While material mastered for 3D would be ideal, it seems to me that you could get good results with conventional two channel stereo merely by moving the virtual speakers forward (HRTF changing dynamically as the head moves, as well as emulated reflections from the side and rear that are known to be important to front/back localization). Perhaps interaural crosstalk and HRTF could be guessed as well, as in surround upscalers.
 

Mauro

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Just wanted to add that the main issue is that head tracking doesn’t track you while walking or even moving on the chair but it just tracks your head inclination. It’s a very weird effect !

That’s why IMO you need to render sound on the fly. To avoid this unpleasant effect
 
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