Early Reflections 101

Nyal Mellor

Industry Expert
Jul 14, 2010
591
2
0
SF Bay Area, CA, USA
#1
"One of the most common “generic” acoustic treatment recommendations is to treat the reflection points. Unfortunately properly managing early reflected sounds is actually very complex psychoacoustically. Blindly treating reflection points with the wrong kind of products can make your sound worse. For a high performance high-end audio listening room, home recording studio or home theater there are many factors that need to be considered. These include the level, delay, spectral content and direction of reflections. Only then can a truly high performance acoustic treatment plan be designed and implemented."

Enjoy! http://www.acousticfrontiers.com/early-reflections-101/
 
Apr 3, 2010
15,820
1
0
Seattle, WA
#3
I don't know what to think of Earl just blessing David Griesinger's work as opposed to Dr. Toole. There is no data, research or theory there.

As to David, he himself held a different view consistent with body of research that says side reflections create attributes that we like as listeners. This is from his AES paper: Theory and Design of a Digital Audio Signal Processor for Home Use



Note the source of research is not even Dr. Toole but this intro to above: "The work of Marshall, Barron,Ando, Blauert, and others has shown that listeners prefer halls with significant sideways reflected energy...."

Yes, in his latest papers David seems to have a different opinion but from what I recall, those were in the context of large performance spaces. And only anecdotally in work he has done and not any kind of controlled testing.

The solution to this riddle is simple: unless you know you don't like side reflections, there is a good chance that you do! :)
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
2
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Dallas, Texas
#4
Amir,

Here is the research.
http://www.davidgriesinger.com/spac4.pdf

Earl is right. David pretty well takes Toole apart with regard to Toole's theory that untreated lateral reflections create spaciousness. David seems much more qualified on this topic since he's devoted his research in this area. I think Earl is 100% correct.

I don't know what to think of Earl just blessing David Griesinger's work as opposed to Dr. Toole. There is no data, research or theory there.

As to David, he himself held a different view consistent with body of research that says side reflections create attributes that we like as listeners. This is from his AES paper: Theory and Design of a Digital Audio Signal Processor for Home Use



Note the source of research is not even Dr. Toole but this intro to above: "The work of Marshall, Barron,Ando, Blauert, and others has shown that listeners prefer halls with significant sideways reflected energy...."

Yes, in his latest papers David seems to have a different opinion but from what I recall, those were in the context of large performance spaces. And only anecdotally in work he has done and not any kind of controlled testing.

The solution to this riddle is simple: unless you know you don't like side reflections, there is a good chance that you do! :)
 
Apr 3, 2010
15,820
1
0
Seattle, WA
#5
Amir,

Here is the research.
http://www.davidgriesinger.com/spac4.pdf

Earl is right. David pretty well takes Toole apart with regard to Toole's theory that untreated lateral reflections create spaciousness. David seems much more qualified on this topic since he's devoted his research in this area. I think Earl is 100% correct.
Again, I am not seeing any research from Earl so not sure why his opinion matters substantively.

I will read the paper later but I hope you appreciate the difference between spaciousness and ASW. In my quick scan, I see nothing inconsistent in David's paper and Dr. Toole's. This is an example from Dr. Toole's book:

"Figure 7.1 shows the approximate frequency ranges over which perceptions
of envelopment, image shift, and broadening may occur. In addition to these
frequency divisions, there is also time. Image shift [ASW] and broadening effects are
influenced by reflections that arrive within approximately the first 80 ms, as
are some “early spatial impressions” restricted to the frontal hemisphere,
whereas true envelopment tends to be created by later arrivals—those 80 ms
and beyond. Obviously, the longer delays are far beyond those that can be generated
by strong individual reflections within small listening rooms.
Envelopment
therefore requires multiple loudspeakers delivering recorded sounds
containing the appropriately delayed sounds from the appropriate directions"


Again, I have only scanned David's paper quickly and maybe there is work there that disagrees and appreciate direct quote of it and Dr. Toole's position. Based on what I have quoted and highlighted in bold, I hope you see the agreement between them.

For now, side reflections help pull the loudspeakers toward the reflection and hence, create a wider image that listening tests show to have preference. They don't create 3-D images behind you and such which is "envelopment."
 
Nov 3, 2014
394
0
0
#6
Again, I am not seeing any research from Earl so not sure why his opinion matters substantively.

I will read the paper later but I hope you appreciate the difference between spaciousness and ASW. In my quick scan, I see nothing inconsistent in David's paper and Dr. Toole's. This is an example from Dr. Toole's book:

"Figure 7.1 shows the approximate frequency ranges over which perceptions
of envelopment, image shift, and broadening may occur. In addition to these
frequency divisions, there is also time. Image shift [ASW] and broadening effects are
influenced by reflections that arrive within approximately the first 80 ms, as
are some “early spatial impressions” restricted to the frontal hemisphere,
whereas true envelopment tends to be created by later arrivals—those 80 ms
and beyond. Obviously, the longer delays are far beyond those that can be generated
by strong individual reflections within small listening rooms.
Envelopment
therefore requires multiple loudspeakers delivering recorded sounds
containing the appropriately delayed sounds from the appropriate directions"


Again, I have only scanned David's paper quickly and maybe there is work there that disagrees and appreciate direct quote of it and Dr. Toole's position. Based on what I have quoted and highlighted in bold, I hope you see the agreement between them.

For now, side reflections help pull the loudspeakers toward the reflection and hence, create a wider image that listening tests show to have preference. They don't create 3-D images behind you and such which is "envelopment."
My own subjective opinions mean little, except to me, of course. But, I am in complete agreement with Amir and the sources he cites. My own discovery about 8 years ago of discretely recorded multichannel sound of classical concerts recorded in the hall was the biggest sonic "epiphany" of my life. It changed my entire outlook on home audio in an immediate and exciting way more than any other experience.

We can talk of adding an additional geometric dimension, going from a 1D two channel speaker array to a 2D 5 or 7 channel array. Each has their own augmentation by listening room lateral and vertical reflections and by phantom imaging extending the image somewhat in terms of width and depth, within the constraints of the number of channels and speaker layout. We can also speak in terms of the additional information captured by more channels from the complex direct and reflected sound field in the hall being reproduced in the home with greater faithfulness to the sound field in the hall. But, the real subjective, listening payoff is that sense of envelopment one gets from quality Mch reproduction on a good system.

To me, this relative lack of envelopment in stereo, now more fully addressed by Mch playback, has been the big breakthrough for me. Envelopment is one of the key characteristics of hearing live music in a good hall. When reproduced, it provides a much more enjoyable, much greater sense of realism compared to the live event. So, there is no going back to plain stereo for me. Whenever I hear stereo now, I am only too keenly aware of what is missing.

Fortunately, there are thousands of very good Mch classical recordings available on SACD, BD-V and -A. My current library is built around those. Fans of other genres are not so lucky, unfortunately.

Today's Mch is 2D, but I am keeping my eye on Auro 3D to see if it ever comes to fruition as a viable source to further extend the idea into the missing height dimension. I attended a demo in New York last week. But, available recordings are quite rare. Time will tell.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
2
0
Dallas, Texas
#7
My reading of the study cited above is reflected room energy determines apparent image spaciousness. That's a good starting point with universal agreement. The difference between Toole and Giessinger is that Giessinger says that reflected energy less than 50ms does not directly increase spaciousness. Whereas Toole's research demonstrates that listeners prefer untreated first reflections. The first reflections will almost always be less than 50ms behind the impulse.

Giessinger works for Lexicon and he is responsible also for large venue room acoustics. He studies reverb and decay. That's his thing. He uses headphone tests to study various reflected sound phenomenon. Toole didn't study this in the same way and I don't think Toole has the body of research Giessinger has in this area. So I would defer to Giessinger on this topic.

It may be that Toole's experiment was valid under his test conditions. But I think Giessinger seems to nail the decay times down. Basically, Giessinger says that spaciousness is controlled by the later arrival; eg.160ms.

Maybe both Toole and Giessinger agree in the end. We all know that when one treats the first reflections with fiberglass all room reflections are substantially reduced, including later arrivals. Maybe more research is needed. But there's no question this is a much more complex topic than some folks want to believe. I really think it will vary greatly and treating first reflection points can be done in a way which has no negative effect on spaciousness.
 

dallasjustice

Member Sponsor
Apr 12, 2011
2,067
2
0
Dallas, Texas
#8
Amir,
To your point about earl: I think he cites Giessinger because he thinks this research validates his slightly different approach to speaker design. Maybe it does or maybe it doesn't. It's not that important to me. Of course, he's a waveguide proponent and wants to create a RFZ for the listener.
 

DaveC

Industry Expert
Nov 16, 2014
2,519
373
83
#9
IME, Toole is right that people prefer their 1st reflections but there are qualifiers...

- As Nyal points out in his article if you simply try to absorb 1st reflections there is a good chance the result will be frequency dependent, as if the speaker had uneven off axis FR, which we know is not ideal. So if you test whether people like 1st reflections using the same wide-dispersion speakers and absorbing 1st reflections or not then this is not a valid test imo. You need a very similar speaker that has different dispersion characteristics. I have actually done this kind of testing with other people, I have a waveguide I can easily remove from my test speakers. This is a whole different thing vs trying to absorb 1st reflections from a wide dispersion speaker.

- People are used to 1st reflections and don't know any better. When you first listen to a system without them it seems odd at first, it takes some time for your brain to adjust. IME people think my speakers with the waveguides sound weird for a few minutes, but after their brain adjusts and they hear the improvements there is no going back. Everybody thinks the speakers are far better with the waveguides, but not necessarily at first listen. So I think Geddes is right-on, if people had the same amount of experience with and without 1st reflections I think the vast majority of people would prefer the system without.


One of the issues not mentioned so far is the recording generally has spatial information in it already and the room can mask these spatial cues. Once your brain gets used to listening without 1st reflections most people find the experience to be a revelation and they realize that the artificial spaciousness caused by 1st reflections gets in the way of the recording. Think about this... your room is always the same size and just like any other non-linearity the effects are added to every single piece of music your system reproduces so you get the same sense of spaciousness in every recording. If you get rid of first reflections your brain now fixates on the spatial information that is already in the recording, and the soundstage is no longer determined by your room boundaries. In a good system not only do the speakers disappear, so does the room boundaries. Without the room in the way the soundstage can expand past the boundaries of the room, the speakers can now project images in front and behind the speakers. Sound goes from 2D to 3D in a way few people have experienced before. You get a sense of the venue the recording was made in, or in the case of a studio production you get to hear the reverb added by the sound engineers instead of the same room reflections muddying everything up.

But to achieve this kind of sound you need a very resolving system and every little thing matters. Many systems are not capable of resolving fine detail in the recording, so without the room's added reflections the music can sound flat. This is one area cables make a big difference, a typical copper interconnect does a good job of smoothing out the spatial information and reverb in recordings. Most "HiFi" systems are not resolving enough to create this kind of a 3D soundstage, and if they are room acoustics often gets in the way. IME, once people have heard a controlled directivity speaker in an extremely resolving system playing in a decent room it is an epiphany...
 
May 30, 2010
15,313
596
113
Portugal
#10
IME, Toole is right that people prefer their 1st reflections but there are qualifiers...

- As Nyal points out in his article if you simply try to absorb 1st reflections there is a good chance the result will be frequency dependent, as if the speaker had uneven off axis FR, which we know is not ideal. So if you test whether people like 1st reflections using the same wide-dispersion speakers and absorbing 1st reflections or not then this is not a valid test imo. You need a very similar speaker that has different dispersion characteristics. I have actually done this kind of testing with other people, I have a waveguide I can easily remove from my test speakers. This is a whole different thing vs trying to absorb 1st reflections from a wide dispersion speaker.

- People are used to 1st reflections and don't know any better. When you first listen to a system without them it seems odd at first, it takes some time for your brain to adjust. IME people think my speakers with the waveguides sound weird for a few minutes, but after their brain adjusts and they hear the improvements there is no going back. Everybody thinks the speakers are far better with the waveguides, but not necessarily at first listen. So I think Geddes is right-on, if people had the same amount of experience with and without 1st reflections I think the vast majority of people would prefer the system without.


(...)
Very interesting points. When I started doing experiments with lateral absorption I got what is considered an excellent absorber - eight RPG abffusors. They sound completely different and much preferable IMHO than some panels of 3" rigid fiber glass I also tried. I stayed some time with them, removed them, replaced them with RPG flutter free diffusors several times along years and I now prefer the sound without the absorbers.

F. Toole refers to the problem of partial and incomplete absorption of first reflections and the use of poor improper materials in his book "Sound Reproduction". BTW, since it seems to me people are using envelopment with different meanings is this thread, I quote his definition of listener envelopment.

Listener envelopment (LEV) is a sense of being in a large space, of
being surrounded by a diffuse array of sounds not associated with any
localizable sound images. This is regarded as perhaps the more
important component of spaciousness, differentiating good concert
halls from poor ones. Envelopment was absent from monophonic
reproduction and only modestly represented in stereo reproduction, so
music lovers have experienced decades of spatial deprivation. Through
multichannel audio systems, moviegoers have occasionally been
exposed to better things for many years, and now, finally, the
capability can be extended to the music repertoire
 

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Nov 3, 2014
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#11
Very interesting points. When I started doing experiments with lateral absorption I got what is considered an excellent absorber - eight RPG abffusors. They sound completely different and much preferable IMHO than some panels of 3" rigid fiber glass I also tried. I stayed some time with them, removed them, replaced them with RPG flutter free diffusors several times along years and I now prefer the sound without the absorbers.

F. Toole refers to the problem of partial and incomplete absorption of first reflections and the use of poor improper materials in his book "Sound Reproduction". BTW, since it seems to me people are using envelopment with different meanings is this thread, I quote his definition of listener envelopment.

Listener envelopment (LEV) is a sense of being in a large space, of
being surrounded by a diffuse array of sounds not associated with any
localizable sound images. This is regarded as perhaps the more
important component of spaciousness, differentiating good concert
halls from poor ones. Envelopment was absent from monophonic
reproduction and only modestly represented in stereo reproduction, so
music lovers have experienced decades of spatial deprivation. Through
multichannel audio systems, moviegoers have occasionally been
exposed to better things for many years, and now, finally, the
capability can be extended to the music repertoire
I find Toole's definition quite perfect, really. And, it completely squares with my Mch music listening experience. One of my points was not to underestimate the number of high quality Mch releases available, though, selfishly, I would like to see many more. Classical music is overwhelmingly favored in those releases, as I would have expected. And, classical music is indeed the very best test of live vs. recorded sound, because of the relatively wide availability of live classical concerts in good halls. But, my collection, now at about 3,000 disks still has much room for growth even among currently available releases.
 

DaveC

Industry Expert
Nov 16, 2014
2,519
373
83
#12
I also think the effect of absorbing 1st reflection points with wide-dispersion speakers depends a lot on the overall high frequency energy in the room, since many people prefer a slightly rolled off top end they may prefer absorption more with a speaker that is flat and the highs don't roll off as much moving off-axis. A good example is Focal, which some find unbearable, and are often setup at shows in bright, untamed rooms. I got the chance to hear the big Focals at Boulder Amplifier's room which is VERY dead, and it was the best I've heard them sound, the soundstage was closer to what I'm used to with my waveguides/horns... very enveloping, fine detail was preserved and you could hear the recording space without the room interfering. I heard they tried Wilsons in the same room and they sounded dead in comparison...

So a lot of these findings about preference are true but not set in stone, people can change their preferences depending on the speaker and given the chance to really listen to a good controlled dispersion system they may find they prefer it after they get used to it. A large all-horn system would be ideal for my own preferences... just not practical for many reasons.
 
Nov 3, 2014
394
0
0
#13
My reading of the study cited above is reflected room energy determines apparent image spaciousness. That's a good starting point with universal agreement. The difference between Toole and Giessinger is that Giessinger says that reflected energy less than 50ms does not directly increase spaciousness. Whereas Toole's research demonstrates that listeners prefer untreated first reflections. The first reflections will almost always be less than 50ms behind the impulse.

...
Lest I sound like a broken record on Mch sound, I think the answer is clear. In spite of quibbles about Toole vs. Giessinger, the path to improving the qualities of spaciousness and envelopment is already there in discrete Mch recording and playback. With proper setup of your home system, the recording engineers basically do this for you via discrete Mch recordings.

The notion that possibly the room dimensions could be increased to provide a necessary amount of delay to provide some fixed "spaciousness" on stereo recordings from 2 speakers is, of course, absurd. The way to do it is to control the room acoustics as usual via treatments and/or EQ, then introduce the appropriate level of delayed sound via discretely recorded surround channels. Those channels via discrete recording are the actual sounds of the delayed, hall reflected sound which are now presented to your ears at playback with the proper delay. This idea simulates what you hear in the real hall quite well, and it has the advantage of being adaptable to recordings in halls of all sizes, shapes and characteristics.

Not to get bogged down or too far off topic, but the center channel adds considerably, well beyond phantom center 4.0 or 2.0 in my experience, to the perception of detail, dimensionality and depth of the important area in the center of the soundstage, where our ears are quite sensitive. The best Mch music recordings contain unique information from that perspective via mikes located there. It is not just a redundant L+R summation.

But, wait, all this and more has been understood and consumer packaged for many years into 5/7.1 channel HT systems, many of which can do a really good job of Mch music playback. Even some $500 AVR's have all the necessary engineering built in, including low end room EQ. Ok, there are many sonic compromises in a $500 AVR, so I am not recommending that, especially not in this forum. But, separate preamp/processors, some like Trinnov well into the $30k range, are basically just an all out refinement of the same engineering notions of how to do Mch sound in 5/7.1 and optionally beyond that into Auro 3D, etc.

Is artificially derived Mch from stereo sources any good from a 5/7.1 system? It is not too bad, and some of my classical listening friends like it a lot. However, I prefer listening to archival performances in straight stereo, as they were recorded, myself.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
2
0
SF Bay Area, CA, USA
#14
My reading of the study cited above is reflected room energy determines apparent image spaciousness. That's a good starting point with universal agreement. The difference between Toole and Giessinger is that Giessinger says that reflected energy less than 50ms does not directly increase spaciousness. Whereas Toole's research demonstrates that listeners prefer untreated first reflections. The first reflections will almost always be less than 50ms behind the impulse.

Giessinger works for Lexicon and he is responsible also for large venue room acoustics. He studies reverb and decay. That's his thing. He uses headphone tests to study various reflected sound phenomenon. Toole didn't study this in the same way and I don't think Toole has the body of research Giessinger has in this area. So I would defer to Giessinger on this topic.

It may be that Toole's experiment was valid under his test conditions. But I think Giessinger seems to nail the decay times down. Basically, Giessinger says that spaciousness is controlled by the later arrival; eg.160ms.

Maybe both Toole and Giessinger agree in the end. We all know that when one treats the first reflections with fiberglass all room reflections are substantially reduced, including later arrivals. Maybe more research is needed. But there's no question this is a much more complex topic than some folks want to believe. I really think it will vary greatly and treating first reflection points can be done in a way which has no negative effect on spaciousness.
Like Amir I read through that paper and couldn't find anything that directly challenged anything Toole had written. Toole's conclusions are based on the results of studies of listener preferences for lateral reflections. I am not super familiar with Griesinger's work but that paper is talking about different definitions for spaciousness and the levels/delays required to achieve it. I'm curious to know exactly what part of Greisinger's work Earl is referring to.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
2
0
SF Bay Area, CA, USA
#15
IME, Toole is right that people prefer their 1st reflections but there are qualifiers...

- As Nyal points out in his article if you simply try to absorb 1st reflections there is a good chance the result will be frequency dependent, as if the speaker had uneven off axis FR, which we know is not ideal. So if you test whether people like 1st reflections using the same wide-dispersion speakers and absorbing 1st reflections or not then this is not a valid test imo. You need a very similar speaker that has different dispersion characteristics. I have actually done this kind of testing with other people, I have a waveguide I can easily remove from my test speakers. This is a whole different thing vs trying to absorb 1st reflections from a wide dispersion speaker.

- People are used to 1st reflections and don't know any better. When you first listen to a system without them it seems odd at first, it takes some time for your brain to adjust. IME people think my speakers with the waveguides sound weird for a few minutes, but after their brain adjusts and they hear the improvements there is no going back. Everybody thinks the speakers are far better with the waveguides, but not necessarily at first listen. So I think Geddes is right-on, if people had the same amount of experience with and without 1st reflections I think the vast majority of people would prefer the system without.


One of the issues not mentioned so far is the recording generally has spatial information in it already and the room can mask these spatial cues. Once your brain gets used to listening without 1st reflections most people find the experience to be a revelation and they realize that the artificial spaciousness caused by 1st reflections gets in the way of the recording. Think about this... your room is always the same size and just like any other non-linearity the effects are added to every single piece of music your system reproduces so you get the same sense of spaciousness in every recording. If you get rid of first reflections your brain now fixates on the spatial information that is already in the recording, and the soundstage is no longer determined by your room boundaries. In a good system not only do the speakers disappear, so does the room boundaries. Without the room in the way the soundstage can expand past the boundaries of the room, the speakers can now project images in front and behind the speakers. Sound goes from 2D to 3D in a way few people have experienced before. You get a sense of the venue the recording was made in, or in the case of a studio production you get to hear the reverb added by the sound engineers instead of the same room reflections muddying everything up.

But to achieve this kind of sound you need a very resolving system and every little thing matters. Many systems are not capable of resolving fine detail in the recording, so without the room's added reflections the music can sound flat. This is one area cables make a big difference, a typical copper interconnect does a good job of smoothing out the spatial information and reverb in recordings. Most "HiFi" systems are not resolving enough to create this kind of a 3D soundstage, and if they are room acoustics often gets in the way. IME, once people have heard a controlled directivity speaker in an extremely resolving system playing in a decent room it is an epiphany...
Good comments!

With respect to waveguided speakers, you still have a lateral side wall reflection, it's just that it has a lot less high frequency energy than a wide dispersion cone dome.

Most waveguided speakers only have directivity control on the tweeter.

Many people call waveguided speakers "constant directivity" but really they are not, they are just constant directivity for a range of frequencies, bound at the lower end by the crossover to the woofer or midrange, and on the other end by the size of the tweeter. http://www.acousticfrontiers.com/201435speaker-off-axis-controlled-directivity-speakers/

For music localization is mostly achieved by focusing on harmonics with frequencies > 1000Hz. Hence you can understand why a speaker with a waveguided speakers the level of the sidewall reflection is reduced but only across a certain band of frequencies. There is much potential with waveguided speaker for the direct and lateral side wall reflection to be very different spectrally, causing timbral shift.

Toe in I have not heard people discuss much before, but I did a little thought experiment with it...most of the time by toeing you are making the direct and first lateral reflections MORE spectrally dissimilar: http://www.acousticfrontiers.com/speaker-off-axis-understanding-the-effect-of-speaker-toe-in/.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
2
0
SF Bay Area, CA, USA
#16
Good topic,

What is an ideal or theoretical perfect two channel stereo playback as far as speakers and not headphones?

two point sources in a non reflective environment or is it something different? If we don't know or agree the ideal how can we even proceed?

101 indeed!
It would be probably be a speaker that was constant directivity from 300Hz (doesn't matter so much below as we're into the room mode dominated region) to 20kHz. Either a dipole a la Linkwitz or maybe a CBT: http://www.acousticfrontiers.com/speaker-axis-constant-bandwidth-transducers/
 

DaveC

Industry Expert
Nov 16, 2014
2,519
373
83
#17
Good comments!

With respect to waveguided speakers, you still have a lateral side wall reflection, it's just that it has a lot less high frequency energy than a wide dispersion cone dome.

Most waveguided speakers only have directivity control on the tweeter.

Many people call waveguided speakers "constant directivity" but really they are not, they are just constant directivity for a range of frequencies, bound at the lower end by the crossover to the woofer or midrange, and on the other end by the size of the tweeter. http://www.acousticfrontiers.com/201435speaker-off-axis-controlled-directivity-speakers/

For music localization is mostly achieved by focusing on harmonics with frequencies > 1000Hz. Hence you can understand why a speaker with a waveguided speakers the level of the sidewall reflection is reduced but only across a certain band of frequencies. There is much potential with waveguided speaker for the direct and lateral side wall reflection to be very different spectrally, causing timbral shift.

Toe in I have not heard people discuss much before, but I did a little thought experiment with it...most of the time by toeing you are making the direct and first lateral reflections MORE spectrally dissimilar: http://www.acousticfrontiers.com/speaker-off-axis-understanding-the-effect-of-speaker-toe-in/.

That's true, sort of... in the case of Geddes' speakers the woofer's dispersion narrows to match the waveguide at the crossover point so the directivity is narrowing well before the crossover point (usually around 900 Hz), in my speakers I use a large waveguide/horn to achieve directivity control down to ~350 Hz for one configuration and ~225 Hz in another. This is low enough to avoid the timbral shift issues you mentioned, and in a properly designed speaker the difference in on vs off axis FR changes smoothly, which is more important than the FR staying flat.

WRT to toe-in, if the speaker maintains directivity low enough in frequency then toe-in simply gets rid of 1st reflections, this is how my speakers are intended to be used and also how Geddes and most others that build controlled dispersion speakers recommend their speakers be set up as well.

IME, once people experience the advantages of eliminating/greatly reducing 1st reflections that is their new preference. The oldest acoustic device the world has known is still the best... while it is true dipoles, especially panels like Sanders, can achieve a very tight dispersion pattern there is too much rear-radiating energy to deal with and it often ruins the sound, so the room requirements are more involved vs a horn/WG speaker. Also, the off axis cancellation is never going to be perfect. I don't think dipoles are anywhere close to ideal, but that's just my own preferences.
 

Nyal Mellor

Industry Expert
Jul 14, 2010
591
2
0
SF Bay Area, CA, USA
#18
That's true, sort of... in the case of Geddes' speakers the woofer's dispersion narrows to match the waveguide at the crossover point so the directivity is narrowing well before the crossover point (usually around 900 Hz), in my speakers I use a large waveguide/horn to achieve directivity control down to ~350 Hz for one configuration and ~225 Hz in another. This is low enough to avoid the timbral shift issues you mentioned, and in a properly designed speaker the difference in on vs off axis FR changes smoothly, which is more important than the FR staying flat.

WRT to toe-in, if the speaker maintains directivity low enough in frequency then toe-in simply gets rid of 1st reflections, this is how my speakers are intended to be used and also how Geddes and most others that build controlled dispersion speakers recommend their speakers be set up as well.

IME, once people experience the advantages of eliminating/greatly reducing 1st reflections that is their new preference. The oldest acoustic device the world has known is still the best... while it is true dipoles, especially panels like Sanders, can achieve a very tight dispersion pattern there is too much rear-radiating energy to deal with and it often ruins the sound, so the room requirements are more involved vs a horn/WG speaker. Also, the off axis cancellation is never going to be perfect. I don't think dipoles are anywhere close to ideal, but that's just my own preferences.
Good points.

Do you have any pictures of your waveguide speakers?
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
6,550
976
113
Beverly Hills, CA
#20
When I started doing experiments with lateral absorption I got what is considered an excellent absorber - eight RPG abffusors. They sound completely different and much preferable IMHO than some panels of 3" rigid fiber glass I also tried. I stayed some time with them, removed them, replaced them with RPG flutter free diffusors several times along years and I now prefer the sound without the absorbers.[/I]
I am curious, microstrip -- what caused you first to prefer absorption and then later diffusion? Did component changes drive the room treatment changes? Or did a personal preference trigger the change in room treatment?
 

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