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The myth of "harmful" early reflections - Klaus Rampelmann

tuga

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I've just found this interesting piece revising existing literature on the treatment of early reflection areas titled "The myth of "harmful" early reflections" (attached).

I haven't read it yet because it's in German (which I can't read) and I've been "cleaning up" the Google translation (attached), but the author it seems firmly stationed on the Toole side of the argument.

The myth of "harmful" early reflections
Klaus Rampelmann

If you read online discussion forums, audio magazines and manufacturers' websites,
the constant message that early reflections of the first order are fundamental
are bad and must be eliminated or reduced in level, either by strategic
Positioning of speakers and listening position (Theiss 1996b), through acoustic treatment
(Völker 1998, Völker 1999), or by using loudspeakers with high directivity or
by Dipolen (Linkwitz 2007). Often there are listening conditions in studio control rooms
(Keyword: reflection-free zone) or standards or recommendations such as SSF-01 2002
referred to where reflections should be 10 dB quieter than that within the first 15 ms
Direct sound.
 

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  • Klaus_Rampelmann_Fruehe_Reflexionen_2015.pdf
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Duke

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Mind you the author is not an acoustics guy himself, but a diligent literature researcher with sometimes a bit of bias in the literature he chooses.

I had an extensive conversation with Klaus on the topic of early reflections on another forum. He has an enormous amount of information on the topic and is capable of disagreeing without being disagreeable, which was most welcome, because we disagreed a lot. He taught me a few things which I was not aware of, but neither of us changed the other's mind about whether early reflections are generally a net benefit or a net detriment.
 

617

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Can you summarize his argument for why early reflections are beneficial?

It is a bit of a dogma that they are harmful; to me, 'early' is defined as 'early enough to be harmful', and of course if you think room invariance is a goal for small room speaker design (as in the tradition of Geddes, Linkwitz, Toole and so on) then narrow directivity seems like a no brainer.

As an anecdote I recently swapped a 3 way speaker (17cm, 2" dome mid, 26mm tweeter) for a large waveguide speaker (12" waveguide, 12" woofer) and the subjective difference is significant. I find the latter is actually more spacious sounding but this may simply be that the ambiance in the recording is less muddled with my room's sound. It's almost like the recording ambiance is more intelligible, along with everything else.

I don't know what to attribute it to - the new speakers have effectively zero distortion (huge PA drivers at apartment levels) so that may be a factor, but the level of musical articulation is totally different. I do think the directivity plays a big role.

Part of me wants to get a pair of BMRs to compare.
 
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Duke

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Can you summarize his argument for why early reflections are beneficial?

Klaus disagreed with my statement that early reflections are detrimental, arguing that there is no hard scientific evidence of that. He also objected to me applying Griesinger's findings about the psychoacoustics of concert halls to the psychoacoustics of small rooms.

Klaus cited research (which I did not read) indicating that early reflections play a role in distance perception, but not in room size perception. He said that room size is conveyed by the reverberation time, again citing research which I did not read. I should probably take the time to do so.

As an anecdote I recently swapped a 3 way speaker (17cm, 2" dome mid, 26mm tweeter) for a large waveguide speaker (12" waveguide, 12" woofer) and the subjective difference is significant. I find the latter is actually more spacious sounding but this may simply be that the ambiance in the recording is less muddled with my room's sound. It's almost like the recording ambiance is more intelligible, along with everything else.

... I do think the directivity plays a big role.

I think that the reduced early reflections + spectrally-correct later reflections give the ambience on the recording the best possible chance of being effectively presented (and being perceptually dominant), within the limitations of two-channel stereo.

When the sense of space changes significantly from one recording to the next, that cannot be a playback-room-interaction artifact adding spaciousness because the playback room would be imposing the same spatial signature on every recording. So it must be that the venue spatial cues on the recording are perceptually dominant over the playback room's spatial cues.
 
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617

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Klaus disagreed with my statement that early reflections are detrimental, arguing that there is no hard scientific evidence of that. He also objected to me applying Griesinger's findings about the psychoacoustics of concert halls to the psychoacoustics of small rooms.

Klaus cited research (which I did not read) indicating that early reflections play a role in distance perception, but not in room size perception. He said that room size is conveyed by the reverberation time, again citing research which I did not read. I should probably take the time to do so.



I think that the reduced early reflections + spectrally-correct later reflections give the ambience on the recording the best possible chance of being effectively presented (and being perceptually dominant), within the limitations of two-channel stereo.

When the sense of space changes significantly from one recording to the next, that cannot be a playback-room-interaction artifact adding spaciousness because the playback room would be imposing the same spatial signature on every recording. So it must be that the venue spatial cues on the recording are perceptually dominant over the playback room's spatial cues.
That seems to be the case. Listening to synthetic music like, pop or kraftwerk or whatever is very 'dry' with high clarity but orchestral music, or distant mic'd piano sounds spacious.

This was the case with my other wide dispersion speakers as well, just less so. Reducing near wall reflection clearly helps the perception of the recorded space rather than the room effect, as would be the case with headphones.

I always describe narrow directivity speakers as being headphone like.
 

Neuro

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Have read the English translation and supplemented with a quick reading of the German.
Very ambitious summary of some research with an impressive reference list.
It would have been more interesting if the author highlighted all the arguments that early reflexes are harmful and argued why these are not scientifically correct.
The analyzes of some well-known studies are not compatible with my view.
"The myth of "harmful" early reflections" attacks the psychological perception of reflexes without any psychological analysis. We have known for many years that many neuropsychological and neurophysiological processes are active in the experience of reflexes in space. Description of physical stimuli is not enough to understand how we hear in the neurophysiological and psychological dimension. We don't hear like a microphone.
Lacks a more rigorous analysis with clear citations of referenced research reports and a clarity of the author's opinions.

I have not been convinced that early reflexes are not harmful.
 

fpitas

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That seems to be the case. Listening to synthetic music like, pop or kraftwerk or whatever is very 'dry' with high clarity but orchestral music, or distant mic'd piano sounds spacious.

This was the case with my other wide dispersion speakers as well, just less so. Reducing near wall reflection clearly helps the perception of the recorded space rather than the room effect, as would be the case with headphones.

I always describe narrow directivity speakers as being headphone like.
Yes, as a fellow horn listener, that's my impression too. I figure the increased ration of direct vs reflected sound accounts for it.
 

617

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Yes, as a fellow horn listener, that's my impression too. I figure the increased ration of direct vs reflected sound accounts for it.
I wonder how much of the 'big woofer' dynamics are actually due to the uncluttered and focused reproduction of percussion.

It's hard to decouple a large woofers directional characteristics from its size, but we do have high xmax midwooders and I much prefer the sound of a big come moving a little than a small one moving a lot. I always chalked it up to distortion or thermal compression but restricted directivity may play a big role in that effect.
 

617

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Have read the English translation and supplemented with a quick reading of the German.
Very ambitious summary of some research with an impressive reference list.
It would have been more interesting if the author highlighted all the arguments that early reflexes are harmful and argued why these are not scientifically correct.
The analyzes of some well-known studies are not compatible with my view.
"The myth of "harmful" early reflections" attacks the psychological perception of reflexes without any psychological analysis. We have known for many years that many neuropsychological and neurophysiological processes are active in the experience of reflexes in space. Description of physical stimuli is not enough to understand how we hear in the neurophysiological and psychological dimension. We don't hear like a microphone.
Lacks a more rigorous analysis with clear citations of referenced research reports and a clarity of the author's opinions.

I have not been convinced that early reflexes are not harmful.
I respect the effort a lot but a lot of this goes over my head. I'm somewhat familiar with Griesingers assertions about near reflections impacting speech intelligibility, and I believe this area of research has a lot less ambiguity since intelligibility is an important metric in learning spaces and emergency PA applications.

My memory is tat DG then extends this logic to musical articulation but I don't find this totally convincing. Not all music has power from articulation as anyone who has seen a punk show in a concrete basement can attest, or echoey choral music in a stone church.

I fear that a lot of this discussion can get caught up in definitional arguments which audiophile discussions are prone to. There is no authority on what sounds good, and even the idea of artistic intent is hard to define. Floyd sidesteps this by creating a sort of utilitarian metric called 'preference' but I think most audiophiles would agree that the crowd's preference differs from their own.

Coming back to reflections this may be an issue of personal preference. Linkwitz favored, or perhaps idealized, an auditory scene in a normally furnished room. Geddes and others make the argument for no absorbative room treatments as they serve to suck HF energy out of the music. Both favor restricted dispersion; Siegfried by dipoles and Geddes by horns.

Personally I think some sidewall absorbtion and maybe some diffusion is a good idea, but making a room that eats treble is not, and that the conventional wide dispersion box speaker only works in a big room, but since that's the only economical type of speaker, it's the only reference point most have.
 

fpitas

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I wonder how much of the 'big woofer' dynamics are actually due to the uncluttered and focused reproduction of percussion.

It's hard to decouple a large woofers directional characteristics from its size, but we do have high xmax midwooders and I much prefer the sound of a big come moving a little than a small one moving a lot. I always chalked it up to distortion or thermal compression but restricted directivity may play a big role in that effect.
I use 6.5" SEAS W18 mids in an MTM quad, two above and two below the horn to match the horn directivity, as well as a 15" woofer below. Unconventional, but it does give a headphone sort of presentation, and the percussion is visceral. I think you're right about directivity, although some people love it, and some hate it, just like MTM.
 

fpitas

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I respect the effort a lot but a lot of this goes over my head. I'm somewhat familiar with Griesingers assertions about near reflections impacting speech intelligibility, and I believe this area of research has a lot less ambiguity since intelligibility is an important metric in learning spaces and emergency PA applications.

My memory is tat DG then extends this logic to musical articulation but I don't find this totally convincing. Not all music has power from articulation as anyone who has seen a punk show in a concrete basement can attest, or echoey choral music in a stone church.

I fear that a lot of this discussion can get caught up in definitional arguments which audiophile discussions are prone to. There is no authority on what sounds good, and even the idea of artistic intent is hard to define. Floyd sidesteps this by creating a sort of utilitarian metric called 'preference' but I think most audiophiles would agree that the crowd's preference differs from their own.

Coming back to reflections this may be an issue of personal preference. Linkwitz favored, or perhaps idealized, an auditory scene in a normally furnished room. Geddes and others make the argument for no absorbative room treatments as they serve to suck HF energy out of the music. Both favor restricted dispersion; Siegfried by dipoles and Geddes by horns.

Personally I think some sidewall absorbtion and maybe some diffusion is a good idea, but making a room that eats treble is not, and that the conventional wide dispersion box speaker only works in a big room, but since that's the only economical type of speaker, it's the only reference point most have.
I think it is preference. A few years back, a reflective room was all the rage. Supposedly any damping made a room dead, or some such nonsense. JBL even fell for it for a while in their Salon2 room at Times Square. The gf and I noticed a bunch of fluttery reflections that just sounded weird. The salesman looked sort of uncomfortable, and next time we visited the walls had massive diffusers/absorbers. Much better!
 

theyellowspecial

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Don't need science for this one. Place your speakers near the sidewalls and experiment with a wide range of toe-in/out.
 

goat76

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Harmful or not, that depends on what the goal is. :)

If the goal isn't high-fidelity reproduction of the recording, early reflection can probably provide something that a particular listener like, subjectively speaking. If so, it's not harmful.

But if the goal is high-fidelity reproduction, strong early reflections from the listening environment can only mask the recorded signal until the point where it takes over completely. In this case, it will be harmful.
 
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