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The precedence effekt - very important för the sound enthusiast

Thomas_A

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#21
Here the folks who usually use the phrase "so obvious no need to measure it" also add that "their wife can hear it while she's still in the kitchen". :D

This is a scientifically oriented forum which means for every claim you make you better provide measurement or a link to some research paper making the same claim.
I am a scientist so I know about those discussions since usenet. I have provided measureements that show differences that are well above JNDs.
 

Krunok

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#22
I am a scientist so I know about those discussions since usenet. I have provided measureements that show differences that are well above JNDs.
You have made those measurements only when I asked you. Those measurements didn't show any significant impact on FR but rather on Topt, so they don't really prove your "back wall" theory. I anyhow don't see a logic why reflections from back wall would be any different than from the wall behind your LP or any other room surface. As I said, it is timing of the arrival that differentiate early reflections from late ones.
 

Thomas_A

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#23
You have made those measurements only when I asked you. Those measurements didn't show any significant impact on FR but rather on Topt, so they don't really prove your "back wall" theory. I anyhow don't see a logic why reflections from back wall would be any different than from the wall behind your LP or any other room surface. As I said, it is timing of the arrival that differentiate early reflections from late ones.
Well measurements are just a way to easier communicate results, don't you think? It showed significant differences in FR that is well above JNDs, not only in the bass region but also tweeter section, with 1-2 dB difference in the 2-4.5 kHz region where JND is around 0.25 dB for pink noise. If you read Toole and others you can also see that lateral side reflections are important for minimising the stereo system flaws, since that is how our ears are located (lateral). Damping those reflections will be bad for SQ. There are no gains of having reflection from the speaker side, they are just destructive.
 

Thomas_A

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#24
And to state the obvious, reflections are good if the lateral dispersion mimics the direct response curve. The reflection from the speaker wall is very different from direct response and will not be judged as a harmless reflection.
 
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Krunok

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#25
And to state the obvious, reflections are good if the lateral dispersion mimics the direct response curve. The reflection from the speaker wall is very different from direct response and will not be judged as a harmless reflection.
Toole mentions ALL early reflections, not only one from the back wall. Is it so difficult for you to understand that, for example, early reflections from wall behind LP (and all other room sides) are equally bad?

Btw, have you ever heard of dipole speakers? They actually try to exploit reflections from the wall beside them?
 

Krunok

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#26
Well measurements are just a way to easier communicate results, don't you think?
Sure they are. But you tried to communicate the results by your listening imrpessions, which is of no interest (and value) to anybody here.


It showed significant differences in FR that is well above JNDs, not only in the bass region but also tweeter section, with 1-2 dB difference in the 2-4.5 kHz region where JND is around 0.25 dB for pink noise. If you read Toole and others you can also see that lateral side reflections are important for minimising the stereo system flaws, since that is how our ears are located (lateral). Damping those reflections will be bad for SQ. There are no gains of having reflection from the speaker side, they are just destructive.
From your measurements all I could see was overdamped room with FR that varies more than 15dB. That hardly identifies you as an expert. Not to mention that you started to make measurements only when I asked you to do so.
 

Thomas_A

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#27
Sure they are. But you tried to communicate the results by your listening imrpessions, which is of no interest (and value) to anybody here.




From your measurements all I could see was overdamped room with FR that varies more than 15dB. That hardly identifies you as an expert. Not to mention that you started to make measurements only when I asked you to do so.
I am well aware that my system is imperfect, especially since I have removed the parametric EQ < 100 Hz and that the current panels are effective only to around 200 Hz and I've done nothing to hide that. I don't see myself as an expert but I've been following discussion reading the littterature and experimenting, built DIY loudspeakers for more than 20 years. If you want to hear an expert just ask Toole's view about the importance of lateral reflections in stereo listening. I don't think you get another answer than dispersion from the speaker should mimic the direct response and that it is of no benefit to damp lateral reflections. That is what I've found also during experimenting, and of course a single point measurement will vary quite much due to reflections/comb filtering in the listening part of the room! Reflections from behind the speakers does not mimic the direct response due to beaming (unless you have a omnidirectional speaker, a special case) and give no benefit to the sound.

100 dB.png
 

Krunok

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#28
I am well aware that my system is imperfect, especially since I have removed the parametric EQ < 100 Hz and that the current panels are effective only to around 200 Hz and I've done nothing to hide that. I don't see myself as an expert but I've been following discussion reading the littterature and experimenting, built DIY loudspeakers for more than 20 years. If you want to hear an expert just ask Toole's view about the importance of lateral reflections in stereo listening. I don't think you get another answer than dispersion from the speaker should mimic the direct response and that it is of no benefit to damp lateral reflections. That is what I've found also during experimenting, and of course a single point measurement will vary quite much due to reflections/comb filtering in the listening part of the room! Reflections from behind the speakers does not mimic the direct response due to beaming (unless you have a omnidirectional speaker, a special case) and give no benefit to the sound.

View attachment 33316
Where we disagree is on the fact you are giving exclusive importance only to back wall early reflections like they are the only ones that matter. That is simply not true. Do you have any, and I repeat any research that support that claim?


1/48 smoothing is very unpractical for doing EQ. It also doesn't reflect what and how we hear. I suggest you use var or 1/12 smoothing.
Anyway, in this region only EQ can help. Folks who tried to tame the room with resonant panels ended up over damping it.
100 dB.png


Can you pls show ungated impulse and step response?
 

Thomas_A

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#29
Where we disagree is on the fact you are giving exclusive importance only to back wall early reflections like they are the only ones that matter. That is simply not true. Do you have any, and I repeat any research that support that claim?
I cite Floyd Toole from this forum below. The timbral signature of the reflection from the back wall WILL be very different from the direct sound, as will any speaker that is not omnidirectional. Other reflections, especially the lateral are of benefit again especially in stereo listening (as long as the speaker have reasonably constant directivity). The "over damp" camp tends to damp the side walls for the first reflection etc, which WIILL give a different timbral signature compared with the direct sound = bad. As I've and Floyd also mentioned several times in this forum, stereo is flawed and should have included a center channel from start, e.g. what Bell laboratories did once upon a time. But Blumleins methods became standard, probably due to the limitations of the reproducing medium.

"Loudspeaker directivity is also a factor, but the effects of reflections turn out to be much less of a problem than might have been believed - instinct is not always right. This is especially true if the loudspeakers have relatively constant directivity with frequency, a parameter that is very rarely measured. When the timbral signature of the reflection is different from that of the direct sound, the reflection becomes more apparent. Significant lateral reflections have been shown to have insignificant effect on placement or precision of stereo images, again counterintuitive. The explanation: it is the direct sound that is responsible for sound localization. However reflected sounds can modify the sense of space which may or may not be desired. They also fill in the massive 2 kHz dip in the phantom center image spectrum (caused by acoustical crosstalk), so some reflected sound actually improves the sound quality of the featured artist in stereo reproduction. That is another reason to have a center channel."
 

Krunok

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#30
I cite Floyd Toole from this forum below. The timbral signature of the reflection from the back wall WILL be very different from the direct sound, as will any speaker that is not omnidirectional. Other reflections, especially the lateral are of benefit again especially in stereo listening (as long as the speaker have reasonably constant directivity). The "over damp" camp tends to damp the side walls for the first reflection etc, which WIILL give a different timbral signature compared with the direct sound = bad. As I've and Floyd also mentioned several times in this forum, stereo is flawed and should have included a center channel from start, e.g. what Bell laboratories did once upon a time. But Blumleins methods became standard, probably due to the limitations of the reproducing medium.

"Loudspeaker directivity is also a factor, but the effects of reflections turn out to be much less of a problem than might have been believed - instinct is not always right. This is especially true if the loudspeakers have relatively constant directivity with frequency, a parameter that is very rarely measured. When the timbral signature of the reflection is different from that of the direct sound, the reflection becomes more apparent. Significant lateral reflections have been shown to have insignificant effect on placement or precision of stereo images, again counterintuitive. The explanation: it is the direct sound that is responsible for sound localization. However reflected sounds can modify the sense of space which may or may not be desired. They also fill in the massive 2 kHz dip in the phantom center image spectrum (caused by acoustical crosstalk), so some reflected sound actually improves the sound quality of the featured artist in stereo reproduction. That is another reason to have a center channel."
:facepalm: You have totally missinterpreted the paragraph you quoted.

First of all he doesn't mention back wall reflections at all.

Secondly, that 2kHz part is about importance of using physical center channel instead of phantom in a multichannel setup.

Third, you missed the most important part and that is that directivity is much more important factor than refections.
("Loudspeaker directivity is also a factor, but the effects of reflections turn out to be much less of a problem than might have been believed - instinct is not always right. This is especially true if the loudspeakers have relatively constant directivity with frequency, a parameter that is very rarely measured.")
 

Thomas_A

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#31
:facepalm: You have totally missinterpreted the paragraph you quoted.

First of all he doesn't mention back wall reflections at all.

Secondly, that 2kHz part is about importance of using physical center channel instead of phantom in a multichannel setup.

Third, you missed the most important part and that is that directivity is much more important factor than refections.
("Loudspeaker directivity is also a factor, but the effects of reflections turn out to be much less of a problem than might have been believed - instinct is not always right. This is especially true if the loudspeakers have relatively constant directivity with frequency, a parameter that is very rarely measured.")
Why do he need to mention back wall specifically? It applies to all boundaries. When the timbral signature of any sound that comes after the first mimics the first direct sound, it will be judged as a reflection. If it is significantly different from the first, this sound will be more apparent.

I did not miss that directivity is important, where did you get that? Reflections from side walls are not a problem as long as you have constant directivity and this will also help to reduce stereo system flaws. Leave them as is.
 

Krunok

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#32
Why do he need to mention back wall specifically? It applies to all boundaries.
Allelujah! Isn't that what I was saying in my last 5 post?


When the timbral signature of any sound that comes after the first mimics the first direct sound, it will be judged as a reflection. If it is significantly different from the first, this sound will be more apparent.
Not true. Early reflections affect the sound as brain cannot distinguish them. Late reflections are recognised as reflections. Once again - it's about timing (early vs late arrival of reflections).

You aslo seem to completely fail to undestand that wall behind the speakers is getting only LF (below app 150Hz) as all higher frequencies are radiated in front of the speaker, not behind it. And those panels you've put on the wall behind your speakers would do pretty much nothing to those LF waves.
What those panels are helping with are to absorb the reflected waves bouncing from other walls (especially the one opposite to the speakers) and that is helping with late reflections, as can be seen by Topt and waterfall measruements. Unfortunately, those late refelcetions are not really affecting the SQ that much - anything below 500ms is pretty much ok for home listening (IIRC app 200-250ms is a astandard for recording studios, but that is not really what you should be aiiming for pleasant home listening).

I lost patience repeating the same things over and over, so signing off. :facepalm:
 
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Thomas_A

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#33
Allelujah! Isn't that what I was saying in my last 5 post?
.
You apparently miss the whole point! If you have a true omnidirectional speaker such that you have constant directivity 360°, you will have the same signature of reflections from all walls compared to the direct sound. A traditional with constant directivity up to 90° or so will show the same signature from side walls and hopefully also rather similar from roof and floor (but the lateral reflections are most important due to our lateral ear positions). The last time I repeat this: the reflected sound from wall behind the speaker does NOT have the same timbral signature as the direct sound.
 

ajawamnet

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#34
I wrote an article in dB magazine about using Haas effects - https://www.americanradiohistory.com/Archive-DB-Magazine/80s/DB-1988-09-10.pdf

It's a really basic article on something I've done in mixing for quite sometime. I do a lot of niche metal bands now - but in the past built and ran quite a few larger studios - one here on my website (with a weird problem) :
http://www.ajawamnet.com/ajawamnet/studiohum.html

I rarely use panpots - this is from a Steve Hoffman post I did earlier this year:
https://forums.stevehoffman.tv/thre...-be-in-the-middle.867295/page-3#post-21831280

Typically, bass is pretty much omnidirectional below about 80-100 - the entire structure begins moving.

During studio construction one of the things we do with infinite baffle/soffit mounting designs is to isolate the cabinets from the structure to minimize early energy transfer - this keeps the structure from transmitting bass faster than air to the mix location. Sound travels faster thru solids - recall the ol' indian ear-on-the-rail thing?

Why does sound travel faster in solids than in liquids, and faster in liquids than in gases (air)?

One thing you want to avoid is the bass from speaker coupling to the building structure and arriving at you ear sooner than the sound from the speakers. This can cause a comb filtering where you lose certain frequencies due to cancellation.

Google recording studio monitor isolation and note the tons of isolation devices sold for this reason...

Here's a doghouse design for UREL 813's I did a while ago:


As to mixing - I rarely use pan pots for directional info in my mixes. I use various time-based methods to try and simulate the precedence effect as well as directional cues and stimulate impulse responses / head related transfer functions (HRTF).
Head-related transfer function - Wikipedia
"A pair of HRTFs for two ears can be used to synthesize a binaural sound that seems to come from a particular point in space."

One thing it does is to really open up the mono field, since instruments are now localized and can be sized depending on the early reflections I set up in something like a convolution reverb.

A great write up here on the Convolvotron:
HRTF-Based Systems – The CIPIC Interface Laboratory Home Page

Part of a great resource for modern sound localization efforts for HMI audio:
The CIPIC Interface Laboratory Home Page – Electrical and Computer Engineering

As to low frequency information:
From Sound localization - Wikipedia :
Evaluation for low frequencies
For frequencies below 800 Hz, the dimensions of the head (ear distance 21.5 cm, corresponding to an interaural time delay of 625 µs) are smaller than the half wavelength of the sound waves. So the auditory system can determine phase delays between both ears without confusion. Interaural level differences are very low in this frequency range, especially below about 200 Hz, so a precise evaluation of the input direction is nearly impossible on the basis of level differences alone. As the frequency drops below 80 Hz it becomes difficult or impossible to use either time difference or level difference to determine a sound's lateral source, because the phase difference between the ears becomes too small for a directional evaluation.[11]

Interesting info here from Dr. Bruce Land on sound localization - end of #25 and into #26 - note this is from a college level course on using FPGA's

#25 -- Mandelbrot and sound localization

The meat of it is in lecture 26:

Note the comment concerning using a bus on a DAW to mimic HRTF. Also note his reference to the CIPIC database .

This prevents the "ear pull" associated with unbalanced RMS levels across the ears. As Dr. Land mentions, your ear localizes based on time as well as amplitude. The interaural time difference ITD (Interaural time difference - Wikipedia ) is as critical as Interaural Level Differences (ILD). As he states, humans learn early on to derive directional cues from impulse responses at the two ears.

One thing that has to be said is the significant differences in head related transfer function between various people - but note the chart where he mentions the one person with a -48dB notch at 6kHz - the curves up to around 5kHz are fairly close and in the A weighted range...

Another great lecture on sound localization from MIT:
20. Sound localization 1: Psychophysics and neural circuits


I used various time-based techniques on this:
Remix of WLL

Watch/listen to the Comparison video...

Another technique is to use double tracking and artificial double tracking (ADT) which will spread the instrument/spectra across the panorama - Automatic double tracking - Wikipedia
- tho this can lead to mono compatibility issues... some effects that do this use a bunch of bandpass filters whereas you can set the delays for each band. Note what George Martin and Geoff Emerick mention using older analog style, tape-based ADT during the Anthology sessions. Again, these techniques reduce the unbalanced feeling across the head but still open up the stereo field to allow all the instruments to sit in the stereo image.

Double tracking - both natural and ADT - is prevalent in a lot of the metal mixes - for instance:
Remix of the Curse of the Twisted Tower
Note that the opening of the first clips was locked into what it is since it didn't exist on the multitracks and was flown in on the original release. But on the other samples compare the mixes and notice they don't sound as disjointed across the panorama as does the older, pan-only mixes. One of the band members commented on how he was able to hear his solos better.
 

Krunok

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#35
One thing you want to avoid is the bass from speaker coupling to the building structure and arriving at you ear sooner than the sound from the speakers. This can cause a comb filtering where you lose certain frequencies due to cancellation.
Building structure will absorb high energy LF even if you hang loudspeakers in the air with the magnetic field or air suspension. This absorbance has nothing to do with loudspeaker-floor coupling as energy is simply not going that way but through the air and through the room sides. How much of the LF is passing through the room sides is proportional with the weight of the side (only lowest freqs can pass through very heavy sides).
 

Thomas_A

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#36
You aslo seem to completely fail to undestand that wall behind the speakers is getting only LF (below app 150Hz) as all higher frequencies are radiated in front of the speaker, not behind it.
The typical baffle diffraction and step dictates what the wall gets, and depending on speaker type you can have signifikant radiation below 500 Hz. To counteract that you can use panels like this and I used similar DIY in the past good to 100 Hz. Below that I used separate subs with EQ for the main mode at 47 Hz.

http://downloads.bbc.co.uk/rd/pubs/reports/1992-11.pdf
 

Thomas_A

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#37
Here comes another measurements using extra panels behind the speaker. As seen the SIBR dip around 100-120 Hz is better using panels behind the speakers. And of course the 47 Hz room mode needs taming, either with EQ or using a tuned bass-trap. The dip around 600 Hz is due to wall behind the listener.

Panel again.png
 

Thomas_A

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#39
Are there any others that want to chime in on this phenomenon on the forum? I still claim that a reflection from the direction of the primary source (such as the speaker wall) has no meaning in precedence since the angle of the first and second arriving sound is the same. The key in the precedence effect is that it effectively helps us to localise the direction of the primary sound source in an otherwise reflective environment. The reflections by themselves cause audible effects, such as increased loudness, spaciouness and colouration (within the precedence window) and is to be expected by our auditory system. A reflection from the same direction as the primary sound can only be destructive of the original sound wave and makes us aware of a wall that should not be there for the optimal illusion of the recorded event in front of us. A closely placed wall does not "exist" behind the musicians during the recording process and thus, its effects should be minimised also during playback. (Now all of this could be solved with multichannel if we want to be transferred to the event, and instead have a rather damped room so that the reflections are effectively masked by the sound from the surround channels. But that is another solution to the problem and relies on other venue listening models as compared to the lounge model.)
 

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#40
All I can add is from my own experience. My room is 14' x 13' x 8' high.

Earlier I had my gear placed conventionally on the front wall between the speakers. I thought I may be getting reflections off the gear so I placed a 2" thick absorbent panel (GIK 242 panel) in front of it. As a result I got a tighter sound which I assume was caused by the removal of front reflections. I can only think those reflections came via the rounded baffle of the speaker and then reflected off the gear and front wall (back wall reflections were already absorbed).

This tells me that before introducing the panel, the front reflections were interfering with what I heard. This presumably means that:

1. There was no precedence effect as if there was it would only increase the volume but have no directional cues and so wouldn't lead to a 'looser' sound.
2. There was perhaps comb filtering.

I then moved the gear to the side wall and put panels on the front wall.

With no side wall panels, so allowing reflections off the side wall and gear, the sound was also a bit muddied and possibly with a bit of spaciousness. I then put GIK 242 panels on the outside of each speaker that stopped first and second side wall reflections and that of the gear. The result was a sharper sound, stronger phantom image, and a sound only between or at the speakers but certainly not beyond them. This leads me to think that:

1. There again was no precedence effect as there were directional cues.
2. There may have been comb filtering.
3. Somehow despite reports, the phantom image was stronger not weaker, certainly sharper, without side wall reflections.

I have no measurements to back these thoughts up.

One thing I've never understood is that if the precedence effect has no directional cues how is it that a sense of spaciousness occurs? Spaciousness is surely a directional cue?
 
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