• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Perceptual Effects of Room Reflections

Mike-48

Active Member
Joined
Feb 2, 2020
Messages
103
Likes
140
Location
Portland, Oregon
Most of my listening is classical, and most of that orchestral, and I'm always trying to listen through the system to some subjective notion of real instruments in a real hall. And I find that most systems tend to create, as an exaggeration, a loud, confusing, miniaturized orchestra in my room. Whereas sitting relatively close to directive speakers tends to create more of a sense of listening through a window into the hall - at least with decent recordings, which are much more prevalent in classical than in the dire wasteland of modern pop engineering.
Scott -- nice to see you here. My experience has paralleled yours considerably. I still am using the Janszen hybrid electrostatic speakers I've had for 7 years now. They damp their back wave internally and are quite directional; the room is well damped, though by no means anechoic. Listening mostly to classical and other acoustic music, I find the presentation more like listening to an ensemble on a stage than I did with more wide-dispersion speakers. The sound is not as superficially impressive and airy as with more reflections, but each recording sounds unique, the ensemble remains firmly situated, timbres are realistic, and I enjoy the results a lot.
 

Bjorn

Senior Member
Manufacturer
Joined
Feb 22, 2017
Messages
476
Likes
562
Location
Norway
No at all. Even the abstract tells you otherwise:

View attachment 112348

And in the paper itself:
View attachment 112349

The "preference" was which setup they liked best for doing this work.
The study is clearly on preferences only. That's nothing to debate if one has read the paper. There's no research here on the actual effect in regards to accuracy. And none of the treatment were of great quality. The absorptive area is for example covering too much vertical area and not a surgical treatment of specular reflections. And who knows, perhaps the speakers suck. I guess it doesn't matter in regards to a universal truth that they only listened to one type of music genre and artist?
In a departure from previous testing, this testing was limited a single musical genre. All of the musical material was taken from a single commercial release of soprano voice and orchestra.
What about those who experience this completely different? Should we overlook every experience and studies because one or a few tells us differently?
The fact is that early arriving lateral reflections have far more detrimental effect on accuracy vs most types of distortion we see from modern electronics.

People should experiment for themselves rather than finding an answer in every paper which has a huge amount of variables. It's easy to hear to greater pin pointing, more details and improved clarity as long as the treatment is good, speakers and electronics hold good quality with attenuating early arriving specular side wall reflections. It's also one of the reasons why many hear far more details from head phones. Their room and reflections messes things too much up.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
32,923
Likes
110,676
Location
Seattle Area
Thread Starter #323
The study is clearly on preferences only. That's nothing to debate if one has read the paper.
I have read the paper, multiple times. It is clear you have not. I quote exactly the appropriate sections, you have not.

What about those who experience this completely different?
What about them? Have they published a peer reviewed controlled test like I quoted? If not, biases and myths abound in room acoustics, among pros and consumers. So we don't even know if your preferences are what you think they are let alone you representing others.

Go ahead and replicate the test scenario in the paper and have someone else grade you and post the results here. Until then, there is no there there. We have heard what you say from countless people. That is not science. It is not research. It is just words. And often concepts promoted by people in the business of selling acoustic products.

It's also one of the reasons why many hear far more details from head phones. Their room and reflections messes things too much up.
There are plenty of reflections inside headphone cups or we would not have the deep cancellations that we see in every measurement. I suggest not going there when you haven't even made the case for speakers.
 

krabapple

Addicted to Fun and Learning
Joined
Apr 15, 2016
Messages
773
Likes
803
The study is clearly on preferences only. That's nothing to debate if one has read the paper. There's no research here on the actual effect in regards to accuracy. And none of the treatment were of great quality. The absorptive area is for example covering too much vertical area and not a surgical treatment of specular reflections. And who knows, perhaps the speakers suck. I guess it doesn't matter in regards to a universal truth that they only listened to one type of music genre and artist?

How do you wish to test *accuracy*? Measurements at the MLP compared to the source?

Research already exists that tells us listeners tend to prefer neutral ('accurate') loudspeakers. At the MLP research tells us they tend to prefer an acoustic that offers gradually tipped down treble, tipped up bass. Then on top of that, there's the preferences data about reflections. On top of that we have data on professional vs. 'recreational' listening. How would you design an 'accuracy' preference test distinct from all that?

Or have you done this work already? Please point us to it.
 

Bjorn

Senior Member
Manufacturer
Joined
Feb 22, 2017
Messages
476
Likes
562
Location
Norway
How do you wish to test *accuracy*? Measurements at the MLP compared to the source?

Research already exists that tells us listeners tend to prefer neutral ('accurate') loudspeakers. At the MLP research tells us they tend to prefer an acoustic that offers gradually tipped down treble, tipped up bass. Then on top of that, there's the preferences data about reflections. On top of that we have data on professional vs. 'recreational' listening. How would you design an 'accuracy' preference test distinct from all that?

Or have you done this work already? Please point us to it.
You test the audibility and threshold of comb filtering and reflections and how they are perceived. Some researchers does this with head phones. Others with speakers in room with either speech, music material or pink noise. We have numerous studies of this over years. Audibility, threshold and how they perceived will depend on many factors. For example what level, the time delay vs the direct signal, direction of the reflections and possible masking effects of other high gain reflections. If you a lot of early specular reflections, the threshold of invdidual ones goes way down. Eveything is somewhat a blur and you can't detect individuals anymore.

Studies give it different description. Olive and Toole called the result of lateral reflections "image spreadening" or "image shift". If the reflections arrive sufficiently late, they also add to spaciousness. Another study descriped it as following:
"According to most listeners, the source width increased and the source focus decreased in the presence of early reflections. Some listeners (20%) experienced changes in the environment width, timbral differences, and changes in loudness."

Bottom line is the "imaging" suffers but a sense of space can increase. And worse imaging is the same as degradation of clarity, intelligibility, localization and tonality depending on several factors. And this is accuracy as you are not able to hear the recorded signal as well anymore. You basically can't have both great imaging/accuracy and spaciousness in regards to lateral contributions or not. You have to pick. The only way to get some of both is by introducing diffusion. But certainly not Skylines placed on side walls which don't diffuse much and waste energy in wrong directions.

While it's true that headphones have their own issues, generally the imaging is of good quality and much better than what's experienced in untreated rooms. I'm sure many can attest to that.

When it comes to preferences, many variables will come into play. But generally very early reflections are not preferred but late lateral ones can be under certain conditions with certain music genres. Often classical is the genre that benefits from later laterel reflections. None of these studies have done much research in different types of treatment of the room though, and they generally use quite poor acoustic treatment. But much research went into accurate critical listening rooms decades ago.

It's also worth noticing that in a home, people seldom have perfectly reflective walls. There will often be furnitures, windows, drapes, pictures, etc. which give a much complex impedance and thus altering the reflections differently from room to room.

That's why and combined with listening to various music material over time may a give a different experience as a short blind test with one music genre, I recommend people to experience for themselves. While I'm strong believer in blind tests when it comes to distuinguishing differences, I don't necessarily believe they give us answer to our preferences over time in our environments that highly differ. A comment from a study in regards to another possible issue in homes:
If, however, the reflection arrangement had been unsymmetrical, then an image shift would probably have been perceived toward the strongest reflection plane or hemisphere
FIY: I develop speakers with constant directivity. In regards to commercial interests it would far better for me to advocate that customers only need such speakers and no treatment. But I know this is simpy not the case. Your mileage will vary.

Below is a threshold for different instruments from a research. As you can see, there's no argument here that it's audible or not. The question is whether what you prefer in your own listening room.
It is clear from the results that a very high proportion of subjects detected the difference in the sound field of the room with reflections on and off. It was interesting to note that the highest percentage of correct results was for sounds with a pronounced transient nature and with a mainly mid- and high-frequency spectrum; in this case for cornet and trumpet
stimulus reflections.jpg


I encourage people to rear up on different researchers. Some are available as papers that can be bought and others can be "hidden" in books and in certain organizations. But do you own testing as well if you can. It doesn't have to be a blind test when we already know it's audible. There are so many factors that come into play with "preferences", that being conclusive in regards to what's scientific in the matter is a moot IMO.
 

thewas

Major Contributor
Forum Donor
Joined
Jan 15, 2020
Messages
2,490
Likes
5,400
Bottom line is the "imaging" suffers but a sense of space can increase. And worse imaging is the same as degradation of clarity, intelligibility, localization and tonality depending on several factors.
While I agree with you on most you wrote above and finally that the preference depends on many variables and therefore everyone should do his own comparisons I would just like to add that according to Tooles book reflections do not worsen but supposedly improve intelligibility, but on the other hand I wonder if this is just a result of the higher sound power when the direct sound level has been kept constant.
Just to show the others side here is also a literature overview of the side that claims that side reflections are advantageous (to which I personally, like you, don't fully agree):
https://www.aktives-hoeren.de/downloads/Klaus_Rampelmann_Fruehe_Reflexionen_2015.pdf
It is unfortunately in German language so best to translate it in https://www.deepl.com/translate
 

Bjorn

Senior Member
Manufacturer
Joined
Feb 22, 2017
Messages
476
Likes
562
Location
Norway
While I agree with you on most you wrote above and finally that the preference depends on many variables and therefore everyone should do his own comparisons I would just like to add that according to Tooles book reflections do not worsen but supposedly improve intelligibility, but on the other hand I wonder if this is just a result of the higher sound power when the direct sound level has been kept constant.
Just to show the others side here is also a literature overview of the side that claims that side reflections are advantageous (to which I personally, like you, don't fully agree):
https://www.aktives-hoeren.de/downloads/Klaus_Rampelmann_Fruehe_Reflexionen_2015.pdf
It is unfortunately in German language so best to translate it in https://www.deepl.com/translate
With lateral reflections you get a strengthening of the signal as you mention. That's why it's not beneficial to absorb too much in a room that's used for speech (i.e. class room) and why a product like BADs are often preferred for that purpose.

When testing this with music, ideally one should perhaps compensate the level which is lost with absorption. Whether that's done or not, it very important than the absorption is broadband and not too band limited. In one of Olive/Toole research they mainly used drapes for absorption. That a poor way of treating specular reflections as it will highly equalize the content. That's generally a problem with many of these studies. They simply don't treat properly and end up with altering the spectral content greatly. In those cases, it's not a surprise that reflections can be preferred.

Thanks for the paper.
 

eliash

Senior Member
Joined
May 29, 2019
Messages
324
Likes
148
Location
Bavaria, near lake Ammersee
How do you wish to test *accuracy*? Measurements at the MLP compared to the source?

Research already exists that tells us listeners tend to prefer neutral ('accurate') loudspeakers. At the MLP research tells us they tend to prefer an acoustic that offers gradually tipped down treble, tipped up bass. Then on top of that, there's the preferences data about reflections. On top of that we have data on professional vs. 'recreational' listening. How would you design an 'accuracy' preference test distinct from all that?

Or have you done this work already? Please point us to it.
Not trying to measure accuracy by number, a simple test is to compare headphones and speakers and judge about the differences.
I can tell you from my own practical experience that I liked (good dynamic) headphones better, before limited room treatment was installed (absorbers and diffusers in an aspired DE/LE configured room, speaker in the rather dead end). Especially perceived mid and high frequeny distortions and voice/instrument images from far outside speaker locations were annoyingly present.
After careful and only minimal treatment (60x60cm elements) with absorbers in the "visible by mirror" wall and (tilted) ceiling locations plus some diffusors in the LE I prefer the speakers on a sustainable basis. After that treatment I upgraded to Stax L700 and still I prefer the sound from speakers in most cases. My previous habit to put on HPs to analyse musical details for better recognition has effectively changed.
RT and bass room resonances are not significantly changed by these measures, latter still defined by speaker and listening positioning...
 

Bjorn

Senior Member
Manufacturer
Joined
Feb 22, 2017
Messages
476
Likes
562
Location
Norway
A good way of checking the effect of side wall reflections is listening to B&O Beolab 90 or Beolab 50 and change the beamwidth between wide (180°) and narrow (120°). While 120° doesn't avoid audible side wall reflections, it does minimize it compare to 180° directivity. The speakers measure very well off-axis in both settings.

nedlasting.jpg
90).jpg


I've listened to both several times and it least for me the differenc is very noticeable between the two settings. I tend to prefer the narrow mode with reflective side walls as I like good imaging and hear details in the recorded signal.
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
393
Likes
316
I have read the paper, multiple times. It is clear you have not. I quote exactly the appropriate sections, you have not.


What about them? Have they published a peer reviewed controlled test like I quoted? If not, biases and myths abound in room acoustics, among pros and consumers. So we don't even know if your preferences are what you think they are let alone you representing others.

Go ahead and replicate the test scenario in the paper and have someone else grade you and post the results here. Until then, there is no there there. We have heard what you say from countless people. That is not science. It is not research. It is just words. And often concepts promoted by people in the business of selling acoustic products.


There are plenty of reflections inside headphone cups or we would not have the deep cancellations that we see in every measurement. I suggest not going there when you haven't even made the case for speakers.
Forgive me if this was covered already -- I've just stumbled on this thread and haven't yet read all the way through it -- but did they compare to a geometric RFZ room and was the recording made with a stereo pair or close miked? In my experience, a geometric room is superior to absorption, diffusion, and side walls. Otherwise, in a basement studio or
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.
Sorry for coming in late -- I'm catching up on the thread, so I hope I'm not going over old ground -- but did they compare an RFZ arrangement? That would pretty much be the state of the art for control room design. It uses reflection, but with walls angled in such a way that the early reflections arrive at the mix position no less than 20 ms after the direct sound. I'd expect it to sound better than most untreated reflective spaces, as well as those that meet the ITU specs with absorption or diffusion.
 

Bjorn

Senior Member
Manufacturer
Joined
Feb 22, 2017
Messages
476
Likes
562
Location
Norway
@josh358
No. There's not study there on the RFZ design. Neither on LEDE or other design principles. Toole never investigated it either. I doubt they even know what it is.
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
393
Likes
316
If I were to write an article on room design, I too would NOT mention RFZ, NE rooms, etc. As far as I am concerned, they are all non-scientific methods invented years ago for studio use. There is no reason to mention them any more than your doctor telling you that there are older options beside antibiotic when you have a bacteria infection.
Whoa, I'd have to disagree with that! There's nothing "non-scientific" about those design principles: they do precisely what they're intended to.

A control room in which the early reflections arrived sooner than the early reflections reach the microphone means that the recording engineer will mix to the control room, rather than the studio or venue. A good concert hall will typically have an ITD of 20-25 ms and if the early arrivals in the mix room arrive before that, you won't get a sense of the size of the venue.

LEDE, RFZ, NE are different, but they're based on sound (and very straightforward) psychoacoustic principles. (They aren't particularly old, either; LEDE and RFZ were developed in the 80s, NE in 2008).

What would you replace them with? A POB (Plain Old Box) room? If that worked, we would have stuck with it -- after all, control rooms start their lives that way. But it doesn't work well at all. Hell, it doesn't work at all. Mixes made in such a room don't translate.

Just about every approach to room design has been tried since Edison invented the phonograph, and so far, these are the approaches that work best. Perhaps something better will come along someday, but writing this off as pseudoscientific nonsense will raise the eyebrows of some very capable acousticians, as well as the pros who use the rooms.

The home listening space is, I think, a different matter, because you're going for a pleasing effect rather than a mix that has to translate into other spaces. From what I've seen in this thread so far, the experience of others is similar to my own: broadly speaking, you can achieve spooky realism between the speakers -- a window into the performance space -- the limit being a consequence of interaural crosstalk; or you can use reflections to get something mushy, warm, and wide, but not particularly real.

Personally, I don't find it an easy choice since it's shuffling deck chairs on the Titanic -- two channel stereo just has limits -- in the absence of crosstalk cancellation, HRTF correction, and head tracking, at any rate. But personally, I find myself coming back to an RFZ approach, something that I don't think I could do well with monopole speakers, not without trashing the RT60, anyway -- but that can be achieved pretty easily with dipoles. The realism when I do that is just stunning, even if it is bounded by the speakers on either side.
 
Last edited:

josh358

Senior Member
Joined
Jun 13, 2017
Messages
393
Likes
316
It's been explained a number of times now that accurate assessment in stereo becomes more difficult, hence the variation. Please take this on board.

Regardless, the order of preference remains the same.

Toole has been explicit about this. Stereo tests never changed the order of preference over mono. So you can say you don't beleive it as much as you like but until you show some quality objective evidence that contradicts the conclusion, I will stick with Tooles decades of professional research.

@tecnogadget summed it up very concisely.
It may not have changed the order of preference, but it seems to me that it closed the gap considerably. And that's without knowing how the speakers were set up -- dipoles are notoriously finicky about placement.

What matters, ultimately, is what the listener hears, and unless he's stuck in a time warp, what the listener will hear is stereo.

A wide dispersion speaker might well sound better in mono than a narrow dispersion one, because room reflections are more important when listening in mono.

I can think of speakers -- Amir reviewed one recently -- that sound bad in mono because they're in symmetrical pairs. Alternately, I can think of some dreadful speakers from ages past in which the drivers were laterally offset the same way *in both speakers* -- those speakers will sound OK in mono, but not in stereo.

In any case, the message I get from the ranking is that speakers should be evaluated in stereo rather than mono.
 
Joined
Feb 18, 2021
Messages
38
Likes
27
Josh358 on home R.F.Z and mixing rooms is dead on my experience. The spooky real between speakers vs analytically mixing. Angled walls and a lot of absorption is great for analytics. A room with well done reflections (given ALL the effects) but maintaining S.P.L (given diffusion, modes etc) gives a very real 3D performance. Equipment probably less important than careful setup for the home listening.

Where do we find more information on tests with that kind of space vs sterile in-between speaker (like headphones) sound on this site?

I have been pointed toward great work here and this topic is important to me to find that same level of scrutiny. Maybe this is the end of that thread?

Thanks
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
393
Likes
316
Josh358 on home R.F.Z and mixing rooms is dead on my experience. The spooky real between speakers vs analytically mixing. Angled walls and a lot of absorption is great for analytics. A room with well done reflections (given ALL the effects) but maintaining S.P.L (given diffusion, modes etc) gives a very real 3D performance. Equipment probably less important than careful setup for the home listening.

Where do we find more information on tests with that kind of space vs sterile in-between speaker (like headphones) sound on this site?

I have been pointed toward great work here and this topic is important to me to find that same level of scrutiny. Maybe this is the end of that thread?

Thanks
I know of a little bit of research in that area -- IIRC, Floyd tool did some research (or someone did, it's been a long time) that found that recording engineers preferred a dead acoustic for mixing, and a live acoustic at home, for the reasons you mention -- the dead room was more analytical, the live one more congenial for listening. More recently, they did an experiment in which they experimented with sidewall diffusion at the first reflection point and found that both recording engineers preferred hearing the first reflection. However, some objections were raised here to their methodology, e.g., they used the wrong kind of diffuser, so I guess that's still up in the air.

Personally (and I of course am the ultimate arbiter here, LOL) I prefer reflections in a home listening environment. Two channel stereo needs help from the room. I've rarely mixed recordings myself, so I'm not qualified to say what I prefer, just that you can hear more issues in an analytical environment. And I've never heard convincing imaging from far field monitors in a studio environment, true. With the dipole speakers that I favor, the best results are achieved by pulling the speakers out as far from the front wall as you practically can to delay the initial reflection, and using diffusion to attenuate it. This keeps some reverb up front, which a LEDE room doesn't, and it's just plain realistic, with a good recording stunningly so -- though Amir pointed out in the LRS thread that the effect is artificial and said he doesn't like it. But monopole speakers also have an artificial effect, image widening from sidewall reflections.

In practice, I'm never sure in home listening what I like best. As I said, with dipoles, I prefer diffusion behind the speakers (and diffusion behind), but I think that the pinpoint imaging of a drier room sounds cool, even if it isn't as realistic. I have found that delaying and diffusing the initial reflection so that it moves into the reverberation range is important. But I don't think there's a one-size-fits-all solution, since what works for a folk singer doesn't work as well for an orchestra and vice-versa. You really need more than two channels to do it right, unless you're going for an in-the-room effect.
 

Trdat

Senior Member
Forum Donor
Joined
Sep 6, 2019
Messages
422
Likes
126
Location
Armenia "Sydney Born"
Has anyone popped up this link before?

file:///C:/Users/PC/Downloads/The%20myth%20of%20harmful%20early%20reflections%20.pdf

It's a great summary on the benefits of early reflections and what consitutes as early. Many of the experiments were complicated but the summary is enough to keep you informed. Mind you a horrible translation.

I would say it supports in many ways and coinscides with many of Grisenger's points on reflections.

It seems that when we say early reflections are bad we are only talking about "early early" reflections(I have read this somewhere else I think on Floyd Toole's power point papers available somewhere) at about 5ms and according to Mathew Poes this is room dependant and still not totally agreed upon. Also the paper says that up to 20ms(from the 5ms) or even up to 30ms lateral reflections are beneficial which I think is also in Toole book and from his research.

It also mentions a concept that I didn't totally understand. Does it say that if sounds arrives at different times to each ear it helps with spaciousness or general improvement in sound? I ask this cause this was also brought up in Audioholics with Anthony Grimmani suggesting a treatment option with left and right reflecton correlating less with each other but Mathew Poes not being in agreeance to this.

Thought this was interesting.
 
Last edited:

josh358

Senior Member
Joined
Jun 13, 2017
Messages
393
Likes
316
Has anyone popped up this link before?

file:///C:/Users/PC/Downloads/The%20myth%20of%20harmful%20early%20reflections%20.pdf

It's a great summary on the benefits of early reflections and what consitutes as early. Many of the experiments were complicated but the summary is enough to keep you informed. Mind you a horrible translation.

I would say it supports in many ways and coinscides with many of Grisenger's points on reflections.

It seems that when we say early reflections are bad we are only talking about "early early" reflections(I have read this somewhere else I think on Floyd Toole's power point papers available somewhere) at about 5ms and according to Mathew Poes this is room dependant and still not totally agreed upon. Also the paper says that up to 20ms(from the 5ms) or even up to 30ms lateral reflections are beneficial which I think is also in Toole book and from his research.

It also mentions a concept that I didn't totally understand. Does it say that if sounds arrives at different times to each ear it helps with spaciousness or general improvement in sound? I ask this cause this was also brought up in Audioholics with Anthony Grimmani suggesting a treatment option with left and right reflecton correlating less with each other but Mathew Poes not being in agreeance to this.

Thought this was interesting.
Yes, that's called interaural cross correlation (IACC) and a low IACC is one of the attributes of the best concert halls. They also have an initial time delay gap (time to first reflections) of 20-25 ms, which is why it's generally considered good to delay early reflections in the room by 20 ms or more -- that prevents them from masking the ITD gap in the recording. Paradoxically, this can help not just with a sense of a large acoustical space but with up close instruments as well.

I couldn't get your link to work, but it sounds interesting. Here's a great chart from Floyd Toole's book:
Toole -- Subjective Effect of Room Reflections.jpg

One of the interesting things about it is that if you reduce early reflections below -20 dB, both tone coloration and image shift go away, which is why it's a standard. The problem is that when you do that, you lose spatial impression. One thing this chart doesn't represent, though -- spatial impressions are not the same, since we use them to judge the size of a room. That's where the 20 ms ITDG criterion comes in -- but that's hard or impossible to achieve in a home listening room, since it requires about a 20 foot path length difference (speakers have to be roughly 10 feet from the front wall, somewhat less from the sides).
 

dasdoing

Major Contributor
Joined
May 20, 2020
Messages
1,115
Likes
587
Location
Salvador-Bahia-Brasil
"good for analytical hearing, not good for listening" is paradox imo.
why would you create an acoustical room if there is one in the recording?
I would agree if the recordings were totaly dry.

no matter how you construct your reflections, it will always be coloration. obviously there is no law saying "you shall listen to the cleanest reproduction possible", but in a strict way it is not HiFi
 
Last edited:

Trdat

Senior Member
Forum Donor
Joined
Sep 6, 2019
Messages
422
Likes
126
Location
Armenia "Sydney Born"
Yes, that's called interaural cross correlation (IACC) and a low IACC is one of the attributes of the best concert halls.
Great to know so then Anthony Grimanni's comment has merit in small rooms as his work is usually for small acoustic spaces. Good to know. So the goal here is to just have a slightly different time delays from left to right? Did I understand that correctly...?

They also have an initial time delay gap (time to first reflections) of 20-25 ms, which is why it's generally considered good to delay early reflections in the room by 20 ms or more
This paper mentioned more like 5ms but it was specifically for small rooms and for lateral reflections. If I understood correctly the studies were confusing.

That prevents them from masking the ITD gap in the recording. Paradoxically, this can help not just with a sense of a large acoustical space but with up close instruments as well.
Yes but I am guessing at the cost of spatial representation?

I couldn't get your link to work, but it sounds interesting. Here's a great chart from Floyd Toole's book:
Fixed the link.

One of the interesting things about it is that if you reduce early reflections below -20 dB, both tone coloration and image shift go away, which is why it's a standard. The problem is that when you do that, you lose spatial impression. One thing this chart doesn't represent, though -- spatial impressions are not the same, since we use them to judge the size of a room. That's where the 20 ms ITDG criterion comes in -- but that's hard or impossible to achieve in a home listening room, since it requires about a 20 foot path length difference (speakers have to be roughly 10 feet from the front wall, somewhat less from the sides)
.

The paper supports the idea of lateral reflections but obviusly it mentions that it will be a certain DB down anyway in a small room and nothing to worry about but reccomends that early reflections be also a certain DB down probably more in tune to what you mention leaving the lateral reflections relatively strong. Mathew Poes recomendations which are based on Floyd Toole's research anyway recommends ceiling absorbers but leaves the idea of lateral reflections open for interpretation(don't quote me on his take).

Yes 10 feet to the sides is difficult but it seems that even if you can direct the speakers in a way to get the lateral reflections delayed by 5ms then your doing okay in a small room.

I wish there was chart that can give us an approximation of the general time delay of a reflection according to the distance of the speaker to the side wall that way we have a way to start designing(redesigning in my case) our rooms.
 

Trdat

Senior Member
Forum Donor
Joined
Sep 6, 2019
Messages
422
Likes
126
Location
Armenia "Sydney Born"
While I agree with you on most you wrote above and finally that the preference depends on many variables and therefore everyone should do his own comparisons I would just like to add that according to Tooles book reflections do not worsen but supposedly improve intelligibility, but on the other hand I wonder if this is just a result of the higher sound power when the direct sound level has been kept constant.
Just to show the others side here is also a literature overview of the side that claims that side reflections are advantageous (to which I personally, like you, don't fully agree):
https://www.aktives-hoeren.de/downloads/Klaus_Rampelmann_Fruehe_Reflexionen_2015.pdf
It is unfortunately in German language so best to translate it in https://www.deepl.com/translate

I just popped up a link with a horrible translation of a paper on Reflection Myths and its quite similar to yours perhaps its the same paper?

file:///C:/Users/PC/Downloads/The%20myth%20of%20harmful%20early%20reflections%20.pdf
 
Top Bottom