Why evaluating the sound of a single speaker is essential

[Floyd Toole]

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A forum member has just alerted me to this discussion, and my name is being circulated, so I have decided to add some clarification. The topic of sound quality is of fundamental importance, and stereo soundstage and imaging are undeniably key factors in our entertainment. However, the factors affecting all of these perceptual dimensions interact with each other, sometimes in destructive ways. Adding enormous complications is the fact that much of what matters to all factors, especially soundstage and imaging is determined by recordings. Stereo is a directionally and spatially deprived format, and since its inception listeners have sought to "fill in the blanks" with imaginative loudspeaker designs, electronic processing, and audio jewelry of various kinds. There is no "hardware" solution, no "perfect" loudspeaker or wire or amplifier that will suddenly bring "reality" to the listening room. But, audio forum activity indicates no end of trying. In this context, the notion of evaluating loudspeakers in mono sounds ludicrous - or is it?

The manuscript of the 4th edition of my book is now with the publisher, anticipating publication around September. In it this subject is, I would like to think, exhaustively examined and explained, using scientific evidence. Long story short, human listeners are increasingly less sensitive to sound quality degradations in loudspeakers as the channel count is increased from one to two and two to five. The overall result of adding channels is more spatial and directional information, which can be highly entertaining, but the end result is that the binaural hearing system has difficulty separating the spatial cues in the recordings, from the spatial cues in the listening room. Increasing channel count increases the persuasion of the recorded space. As a result listeners are unable to discern timbral errors caused by resonances in loudspeakers with the same sensitivity as in mono/single-loudspeaker comparisons.

The reality is that most stereo and multichannel recordings include isolated, hard-panned, sound images providing instances when the true character of the loudspeakers can be heard. In simple stereo recordings instruments often appear in left and right loudspeakers - mono. All phantom images are double mono. This explains why loudspeakers that win monophonic comparison tests always win stereo and multichannel tests, The reverse is not always true. So, to determine how good your loudspeakers are, do comparison listening tests in mono. Then, if they are good, impress your friends in stereo and multichannel - but choose the recordings carefully: they are a major determinant of what is heard.

Here is something I wrote a couple of years ago - it is long but still not the complete story, as it is currently understood.

 

[BadAudioAdvice]

Then, if they are good, impress your friends in stereo and multichannel - but choose the recordings carefully: they are a major determinant of what is heard.

Thank you for sharing your knowledge and research.

Are there any recent recordings that you recommend (and enjoy) for mono evaluation, and stereo demonstration?

 

[Floyd Toole]

Thank you for sharing your knowledge and research.

Are there any recent recordings that you recommend (and enjoy) for mono evaluation, and stereo demonstration?

As explained in AES papers and my books, the most revealing music in multiple-loudspeaker comparison tests tends to have complex instrumentation - a dense spectrum - wide bandwidth - especially bass extension - and reverberation. The musical genre is unimportant.

For listening pleasure or demonstration the choice is yours.

 

[BadAudioAdvice]

Anyone else in the thread, I'm open to any suggestions - I have a Genelec 8030C next to a Magnepan MG1.7 that I've been trying to compare, but I'm not sure if the music I'm using meets the criteria of complex instrumentation - a dense spectrum - wide bandwidth - especially bass extension - and reverberation.

 

[Newman]

As explained in AES papers and my books, the most revealing music in multiple-loudspeaker comparison tests tends to have complex instrumentation - a dense spectrum - wide bandwidth - especially bass extension - and reverberation. The musical genre is unimportant.

For listening pleasure or demonstration the choice is yours.

I once took a CD of orchestral works to a large hifi show, and asked for a track to be played on a pair of $100,000 speakers in one of the rooms. They refused. They said to come back tomorrow 30 minutes before the official opening time and they will play it for me. Which we did.

Ever since then I have raised a mildly sceptical eyebrow and made a quiet note to myself when demonstrators play simple arrangements and imply that the excellence of the recording will be the test of the speaker.

Now I am wondering what reception I would get at a hifi show if I asked them to turn off one speaker so we can better assess them!

 

[Floyd Toole]

Anyone else in the thread, I'm open to any suggestions - I have a Genelec 8030C next to a Magnepan MG1.7 that I've been trying to compare, but I'm not sure if the music I'm using meets the criteria of complex instrumentation - a dense spectrum - wide bandwidth - especially bass extension - and reverberation.

Here is the result of evaluations by Sean Olive in 1994,(Olive, S.E. (1994). “A Method for Training Listeners and Selecting Program Material for Listening Tests”, Audio Eng. Soc. 97th Convention, preprint 3893.) and as reported in Figure 3.15 in the 3rd edition of my book. This shows the success rate of listeners reporting hearing resonant flaws in loudspeakers. You will see poor correlation with entertainment value.

 

[Jaxjax]

Anyone else in the thread, I'm open to any suggestions - I have a Genelec 8030C next to a Magnepan MG1.7 that I've been trying to compare, but I'm not sure if the music I'm using meets the criteria of complex instrumentation - a dense spectrum - wide bandwidth - especially bass extension - and reverberation.

I just discovered Techno a few months ago......I'm 58. I can't get enough of it. Why....? Because some of it has crazy complex tones & all levels of bass & real 100 ish slam . Reason I bring this up is it might not be the music your comfortable with that is a test of what ya got going on.

 

[Newman]

Here is the result of evaluations by Sean Olive in 1994,(Olive, S.E. (1994). “A Method for Training Listeners and Selecting Program Material for Listening Tests”, Audio Eng. Soc. 97th Convention, preprint 3893.) and as reported in Figure 3.15 in the 3rd edition of my book. This shows the success rate of listeners reporting hearing resonant flaws in loudspeakers. You will see poor correlation with entertainment value.

Yes, and a few people here have scoffed at yours and Sean's use of "Fast Car" in tests, without realising that it is actually a science-based choice!

 

[Blumlein 88]

Yes, and a few people here have scoffed at yours and Sean's use of "Fast Car" in tests, without realising that it is actually a science-based choice!

Why listen to Fast Car when you can use pink noise instead? Just kidding, I actually have the Tracy Chapman album that is on.

I may be mis-remembering, but I think that same music was one of the best for testing MP3 codecs.

PS-others have pointed out this was in error. It was a Suzanne Vega track used in MP3 testing.

 

[Blumlein 88]

That's a vast oversimplification of what Floyd Toole reports in his book.

To take just one example, subjective ratings of dipole speakers (BB) change much more significantly from mono to stereo than subjective ratings of forward-firing speakers (AA and E):

View attachment 437512

I have heard a 5 channel rig with Soundlab ESLs on all 5 channels in a space large enough for that to make sense. It was nice, but then again, I owned a pair of Soundlabs already.

 

[thewas]

I may be mis-remembering, but I think that same music was one of the best for testing MP3 codecs.

In the early stages Fraunhofer institute who developed it mainly used Tom's Diner from Suzanne Vega due to the importance of non artefacts where they are most obvious for us, namely human voice.

 

[Hayabusa]

A forum member has just alerted me to this discussion, and my name is being circulated, so I have decided to add some clarification. The topic of sound quality is of fundamental importance, and stereo soundstage and imaging are undeniably key factors in our entertainment. However, the factors affecting all of these perceptual dimensions interact with each other, sometimes in destructive ways. Adding enormous complications is the fact that much of what matters to all factors, especially soundstage and imaging is determined by recordings. Stereo is a directionally and spatially deprived format, and since its inception listeners have sought to "fill in the blanks" with imaginative loudspeaker designs, electronic processing, and audio jewelry of various kinds. There is no "hardware" solution, no "perfect" loudspeaker or wire or amplifier that will suddenly bring "reality" to the listening room. But, audio forum activity indicates no end of trying. In this context, the notion of evaluating loudspeakers in mono sounds ludicrous - or is it?

The manuscript of the 4th edition of my book is now with the publisher, anticipating publication around September. In it this subject is, I would like to think, exhaustively examined and explained, using scientific evidence. Long story short, human listeners are increasingly less sensitive to sound quality degradations in loudspeakers as the channel count is increased from one to two and two to five. The overall result of adding channels is more spatial and directional information, which can be highly entertaining, but the end result is that the binaural hearing system has difficulty separating the spatial cues in the recordings, from the spatial cues in the listening room. Increasing channel count increases the persuasion of the recorded space. As a result listeners are unable to discern timbral errors caused by resonances in loudspeakers with the same sensitivity as in mono/single-loudspeaker comparisons.

The reality is that most stereo and multichannel recordings include isolated, hard-panned, sound images providing instances when the true character of the loudspeakers can be heard. In simple stereo recordings instruments often appear in left and right loudspeakers - mono. All phantom images are double mono. This explains why loudspeakers that win monophonic comparison tests always win stereo and multichannel tests, The reverse is not always true. So, to determine how good your loudspeakers are, do comparison listening tests in mono. Then, if they are good, impress your friends in stereo and multichannel - but choose the recordings carefully: they are a major determinant of what is heard.

Here is something I wrote a couple of years ago - it is long but still not the complete story, as it is currently understood.

Thanks for your answer!
No need to convince me that listening in mono has a preference in the evaluation of speakers.
Only point I want to make is that also doing a stereo test would help in evaluation stereo imaging, as although we can to some extend predict stereo imaging from the full spinorama measurements its still difficult to predict in some (most?) cases (room/speaker interaction, directivity/planar/dipole etc).

 

[DavidMcRoy]

In the early stages Fraunhofer institute who developed it mainly used Tom's Diner from Suzanne Vega due to the importance of non artefacts where they are most obvious for us, namely human voice.

I personally use familiar spoken word audio for testing, such as BBC, NPR and cable TV news channels. I worked in broadcast TV audio production for a few decades and I'm comfortable with that "genre." The beauty of spoken word is that the contrast between the sounds of a single human voice and the frequent silences between them leave no place for sonic artifacts to hide. There's no instrumentation to mask noise, distortion, and acoustic energy storage in speakers and listening rooms.

 

[amirm]

I may be mis-remembering, but I think that same music was one of the best for testing MP3 codecs.

That was Suzan Vega's Tom's Diner track. It is a pure vocal that is very difficult to compress without causing roughness to her voice (due to pre-echo).

 

[Newman]

...Only point I want to make is that also doing a stereo test would help in evaluation stereo imaging, as although we can to some extend predict stereo imaging from the full spinorama measurements its still difficult to predict in some (most?) cases (room/speaker interaction, directivity/planar/dipole etc).

But would it? Dr Toole's posts, above, seem to suggest that:-

1. If we prefer Speaker A over B in a single-speaker test then we will prefer it in a two-speaker test.
2. Spatial preference (which I presume is where your term 'stereo imaging' falls) doesn't flip from A to B when we add a second speaker.

He has also suggested elsewhere that doing it with sighted listening is almost self-defeating, if the goal is to know what the sound waves themselves sound like. And suggested that he would rather evaluate a speaker from its Spinorama than by sighted listening.

A final point: the evidence seems to suggest that 'stereo imaging' is strongly dominated by the room, the listening setup, and the recording itself. So what possible interest is it to a thousand readers in a thousand homes, if a reviewer comments on the stereo imaging of a speaker when he had it in his home, his setup, and using a specific recording or two? The dominant potential is for the reader to be thoroughly misled as to what stereo imaging he might experience if he bought it, especially in a comparative sense vs competing speakers. But who knows: maybe that is the shared desire of reviewers and readers alike, and to have that desire thwarted is terribly dissatisfying...

cheers

 

[Hayabusa]

But would it? Dr Toole's posts, above, seem to suggest that:-

1. If we prefer Speaker A over B in a single-speaker test then we will prefer it in a two-speaker test.
2. Spatial preference (which I presume is where your term 'stereo imaging' falls) doesn't flip from A to B when we add a second speaker.

He has also suggested elsewhere that doing it with sighted listening is almost self-defeating, if the goal is to know what the sound waves themselves sound like. And suggested that he would rather evaluate a speaker from its Spinorama than by sighted listening.

A final point: the evidence seems to suggest that 'stereo imaging' is strongly dominated by the room, the listening setup, and the recording itself. So what possible interest is it to a thousand readers in a thousand homes, if a reviewer comments on the stereo imaging of a speaker when he had it in his home, his setup, and using a specific recording or two? The dominant potential is for the reader to be thoroughly misled as to what stereo imaging he might experience if he bought it, especially in a comparative sense vs competing speakers. But who knows: maybe that is the shared desire of reviewers and readers alike, and to have that desire thwarted is terribly dissatisfying...

cheers

lets agree to disagree..

 

[Newman]

I didn't give an opinion...

 

[MarkS]

In the figure I posted earlier from Toole's book, the average "spatial quality" rating of speaker E is lower than that of speaker AA in mono, but higher in stereo.

Though the stereo ratings would be equal within error bars, which are not shown in the figure but can be inferred from the spread of individual points.

 

[Blumlein 88]

I didn't give an opinion...

You have facts to inform an opinion.

 

[Hayabusa]

I didn't give an opinion...

ok, then lets disagree to disagree haha