Don't forget that mono does not suffer the deleterious effects of comb filtering apparent in conventional two-channel stereo - unless you listen to it through two speakers, which seems rather defeating. Nor does it suffer the LF loss in the lateral S channel information. Try the same recordings again but in stereo with the shuffling and see what you think. IMHO the mono and compensated stereo sound more like the same recording than the two stereo variants.
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And you know what? I have been listening to stereo with one ear for critical listening. I mean my face is 75-90 degrees off from the speakers.
This is silly, unless you say what you mean and are a bit more forthcoming it just looks like FUD
Mmmm....move closer. In my room I get best sound nearfield and almost between them, but I have no room treatment (shock/horror) yet...........
It's whatever your preference is the point... The industry research shows peoples preference is for smooth on and off axis frequency response.
In the industry guideline I referenced earlier, a spec range for directivity index is given. The JBL's I listen begin to have constant directivity starting around 400 Hz. I have reviewed the Kii THREE and Dutch and Dutch 8c which have constant directvity starting around 100 Hz using cardioid tricks.
The graphic above shows the measured directivity over frequency for a double 15” and 90 x 50 CD horn, which are the JBL 4722’s (what I listen to). The 15” woofer and 120 x 100 CD are the JBL M2’s and the Domestic cone/dome system is the Revel Salon 2. The KEF LS50 is a cone and dome system and likely similar to the Salon 2 from a directivity perspective.
For harsh music, which unfortunately has a lot to do with the loudness war with extra midrange distortion due to too much dynamic range compression, a narrower directivity speaker may sound less harsh than a wider one. This is because the wider directivity speaker is adding more room sound at those same midrange frequencies and just accentuate the harshness (assuming both speakers have similar frequency responses). You can hear the comparison on the binaural recordings I referenced earlier between the JBL 4722 (very narrow directvity) and the KEF LS50 with much wider directivity.
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Vivid discussion here yesterday, thank you all!
Originally Posted by Kal Rubinson :
...I think the attention to pop/rock is due to his current fascination with DSP tools to improve the experience with stereo recordings. He is O'Toole.
I find this almost funny! First make sharp and detailed stereo, then add more "life" to it with multichannel dsp tricks. But no offence, in love and hifi, all tricks are allowed! I found my love with dipole stereo speakers...
Originally Posted by Kal Rubinson :
...I think the attention to pop/rock is due to his current fascination with DSP tools to improve the experience with stereo recordings. He is O'Toole.
I find this almost funny! First make sharp and detailed stereo, then add more "life" to it with multichannel dsp tricks. But no offence, in love and hifi, all tricks are allowed! I found my love with dipole stereo speakers...
Mitch !
One question to you, as you have experience in this category:
Assume you have 2 different pair of speakers - both flat no axis under anechoic condition.
Both have a more or less medium wide dispersion and ok directivity.
Both are in your medium treated room, flattened to your personal liking target curve via Acourate's psychoacoustic filter.
( if that sounds a bit like your Dutch vs. JBL situation its no surprise ... 🙂 )
BUT, assume one has a tiny lobing issue off axis (despite flat on-ax-anechoic) resulting in a gentle 5dB dip and one peak in the midrange - on your listening position.
I think we all agree this can happen as the listening position includes (if not gated away) the sum of room energy and speaker.
Now as you flattened both pairs to the same response (ON THE SOFA!) and conclusively eliminated the coloration of that one lobing....
... how would you describe the audible difference ??
cheers
Josh
One question to you, as you have experience in this category:
Assume you have 2 different pair of speakers - both flat no axis under anechoic condition.
Both have a more or less medium wide dispersion and ok directivity.
Both are in your medium treated room, flattened to your personal liking target curve via Acourate's psychoacoustic filter.
( if that sounds a bit like your Dutch vs. JBL situation its no surprise ... 🙂 )
BUT, assume one has a tiny lobing issue off axis (despite flat on-ax-anechoic) resulting in a gentle 5dB dip and one peak in the midrange - on your listening position.
I think we all agree this can happen as the listening position includes (if not gated away) the sum of room energy and speaker.
Now as you flattened both pairs to the same response (ON THE SOFA!) and conclusively eliminated the coloration of that one lobing....
... how would you describe the audible difference ??
cheers
Josh
This is from one of Earl's papers on the subject of directivity
"Many say that an omni-directional loudspeaker response is the ideal, but I do not accept this for a small room. That's because the Very Early Reflections (VER) increase dramatically with this type of source because of its very wide polar pattern. Because of the omni-directional response, this type of source cannot be situated such that it does not excite every possible VER, and there simply is no way to fully absorb these VER without creating a room that is so dead as to be acoustically lifeless. As the directivity gets narrower and narrower however, it should be intuitively obvious that I can orient the speaker in such a way as to avoid the nearer boundaries and thus minimize the VER to a much greater degree. In fact, it can be shown that the higher the directivity, the greater the average Reflection Free Time (RFT) immediately following the direct sound. Ideally this would be about 20 ms, but that is never going to happen in a small room. Even 10 ms requires some significant room modifications to achieve in typical sized listening rooms. However, it is quite true that the more that can be done to extend this RFT the better the image will be, with diminishing returns beyond about 10 ms.
It is also true that VERs and a short RFT do add to the perception of spaciousness, which is considered to be, by many, a good thing, but just as certainly it is know that they detract from the ability to image the content of the source because of the confounding influence of the VER. Toole is a strong proponent of a large amount of VER because of its increase in the spaciousness effect. He appears to discount the negative aspects of this on imaging however. (Dr. Toole, does not make
many statements about “image”, perhaps being concerned over its loose definition.) It seems to me that if I can create “spaciousness” without increasing the VER, then I can achieve the best of both worlds. This can in fact be done by making the room fairly reverberant, particularly behind the listener, which will improve the feeling of spaciousness through the multitude of lateral and rear reflections that will occur. However, the use of this technique with wide directivity speakers is not
going to yield a very good image due to the VERs from the nearer walls, and the speakers should have a fairly constant frequency response in all directions, i.e. the power response, otherwise the sound quality will be colored. If the speakers do
have a narrow directivity then the frontal VERs have been lowered, hence improving the image, and yet I can still retain the
feeling of spaciousness because the room itself is fairly reverberant. In fact, if most of the reflections are coming from the
sides and rear, as opposed to the front, then the quality of the spaciousness is know to improve. Hence a narrow directivity
lowers the VERs and extends the RFT yielding good imaging, while the rooms high reverberation yields good spaciousness. It is most curious that this is quite often the opposite of what is done in many rooms."
http://www.gedlee.com/Papers/directivity.pdf
I'm still trying to grasp some things. So you want to avoid early reflections and have a good RFT. This preserves imaging and just sounds right.
Basically you want breathing room around the speaker. This makes sense because if anything other than the baffle is affecting the sound it will change its frequency response.
Another thing that makes sense is you want to the reflections to match the speakers direct sound. This is the whole power response thing that everyone agrees with.
What doesn't seem to come up is how much reflected vs direct sound is desirable. You could follow these rules and still get more direct sound or less direct sound.
It seems to me that the more indirect sound you get the more modulated and softer it will be since the transients are weaker. Physically the sound is weaker and spread out over time. This also explains why a more direct speaker is better in a large reverberant room because it cuts through the ambience.
A lot of people recommend tube amps with very direct speakers like horns, maybe they create a more ambient affect in some way?
One more thing, if you're going to use the technique of aiming a directional speaker off axis in a small room to avoid early reflections, then wouldn't it be good to build a speaker that is aimed at something like a corner since this is a spot that will create more reflections?
Also @mitchba, thanks for the reply.
"Many say that an omni-directional loudspeaker response is the ideal, but I do not accept this for a small room. That's because the Very Early Reflections (VER) increase dramatically with this type of source because of its very wide polar pattern. Because of the omni-directional response, this type of source cannot be situated such that it does not excite every possible VER, and there simply is no way to fully absorb these VER without creating a room that is so dead as to be acoustically lifeless. As the directivity gets narrower and narrower however, it should be intuitively obvious that I can orient the speaker in such a way as to avoid the nearer boundaries and thus minimize the VER to a much greater degree. In fact, it can be shown that the higher the directivity, the greater the average Reflection Free Time (RFT) immediately following the direct sound. Ideally this would be about 20 ms, but that is never going to happen in a small room. Even 10 ms requires some significant room modifications to achieve in typical sized listening rooms. However, it is quite true that the more that can be done to extend this RFT the better the image will be, with diminishing returns beyond about 10 ms.
It is also true that VERs and a short RFT do add to the perception of spaciousness, which is considered to be, by many, a good thing, but just as certainly it is know that they detract from the ability to image the content of the source because of the confounding influence of the VER. Toole is a strong proponent of a large amount of VER because of its increase in the spaciousness effect. He appears to discount the negative aspects of this on imaging however. (Dr. Toole, does not make
many statements about “image”, perhaps being concerned over its loose definition.) It seems to me that if I can create “spaciousness” without increasing the VER, then I can achieve the best of both worlds. This can in fact be done by making the room fairly reverberant, particularly behind the listener, which will improve the feeling of spaciousness through the multitude of lateral and rear reflections that will occur. However, the use of this technique with wide directivity speakers is not
going to yield a very good image due to the VERs from the nearer walls, and the speakers should have a fairly constant frequency response in all directions, i.e. the power response, otherwise the sound quality will be colored. If the speakers do
have a narrow directivity then the frontal VERs have been lowered, hence improving the image, and yet I can still retain the
feeling of spaciousness because the room itself is fairly reverberant. In fact, if most of the reflections are coming from the
sides and rear, as opposed to the front, then the quality of the spaciousness is know to improve. Hence a narrow directivity
lowers the VERs and extends the RFT yielding good imaging, while the rooms high reverberation yields good spaciousness. It is most curious that this is quite often the opposite of what is done in many rooms."
http://www.gedlee.com/Papers/directivity.pdf
I'm still trying to grasp some things. So you want to avoid early reflections and have a good RFT. This preserves imaging and just sounds right.
Basically you want breathing room around the speaker. This makes sense because if anything other than the baffle is affecting the sound it will change its frequency response.
Another thing that makes sense is you want to the reflections to match the speakers direct sound. This is the whole power response thing that everyone agrees with.
What doesn't seem to come up is how much reflected vs direct sound is desirable. You could follow these rules and still get more direct sound or less direct sound.
It seems to me that the more indirect sound you get the more modulated and softer it will be since the transients are weaker. Physically the sound is weaker and spread out over time. This also explains why a more direct speaker is better in a large reverberant room because it cuts through the ambience.
A lot of people recommend tube amps with very direct speakers like horns, maybe they create a more ambient affect in some way?
One more thing, if you're going to use the technique of aiming a directional speaker off axis in a small room to avoid early reflections, then wouldn't it be good to build a speaker that is aimed at something like a corner since this is a spot that will create more reflections?
Also @mitchba, thanks for the reply.
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Hi soundbloke,
1.
Do you have an opinion why so many people desire putting the speakers closer together than the classic 60° triangle? Does that minimize the comb filters?
I did that once with electrostatics, very narrow together, close to a bare backwall (strong reflection), the M-channel got almost as authentic as the sides.
2.
Boosting back the S channel. Isnt that artificial manipulation of source material? Does it still sound natural? Do you mean linear by loudness to increase space (how many dB for instance, 1-2?) ??
Or you mean the earlier mentioned low octaves of S only (you said 6dB/Oct but that seems brutal lot, from wich point on actually??)
3.
M vs S modal excitation: I agree. Even when I voice my target curve, I notice it makes huge difference in measuring S and M. Most people do S only. But as many recordings contain emphasised M lows, tonal experience can still be everything but flat. For a flat M & S I also target a not flat but congruent phase between left and right speaker. That helps towards having S and M congruently flat.
cheers
Josh
I think you are going to have to bite the bullet and buy Mr Toole's book, you know the one I mean 🙂 This is discussed in depth, surprise surprise, and contrary to what seems to be often implied, they are not all his impressions, but those of large groups of people.
A necessarily rushed reply, sorry...
1. With the speakers close together, the comb filtering can be compensated to some degree. If they are close enough - or at least the high frequency drivers are, then the second null in the comb (the first in-band one) can be sufficiently high to avoid a problem: It is the ability to compensate the S channel that is enabled by narrow-angle stereo. With electrostatics, they are most likely too large to achieve this; And close to the back wall would introduce an additional comb filter too. But a three loudspeaker arrangement can deliver the most authentic "M" channel rendition 🙂
2. No. With "coincident" microphones, the S channel is subject to the dipole roll-off due to the first null at 0Hz that leaves the 6dB/octave slope as we head towards the first peak. Shufflers were originally intended (I believe) to compensate as best as possible for the difference between this dipole and that which would be evident from two ears spaced around a head. Boosting S further can offset that which the loudspeakers attenuate. (The 6dB/octave roll-off cannot be extended to 0Hz, however, for obvious reasons. Thankfully, the near field of a velocity source - such as that of two spaced loudspeakers reproducing the S channel - has a natural 6dB/octave rise at LF which, if compensated, also serves as a welcome curtailing of LF S boost).
For any extra S boost, the shuffler should reduce M so that the energy content remains unchanged. This way the source is not "artificially manipulated", but a higher fidelity reproduction is rendered. This is different from the added "spaciousness" from boosting the S channel in an uncompensated manner, usually below a 400-700Hz transition; This does artificially manipulate the source material by adding lateral energy in an attempt to make stereo reproduction more enveloping by decreasing the correlation of signals between the ears.
Most relevant to the discussion here, however, is what happens with non-coincident microphone recordings. Here the microphone spacing is used precisely to introduce uncorrelated parts of the L and R signals, and thereby impart a sense of space replicating that we perceive in a diffuse sound field. It requires "smearing" the recorded source that compensates slightly for the comb action - that is, it is a distortion deliberately introduced as it sounds "better" to some people in their listening environment.
Where analysis goes by the wayside is when we consider material that has been assembled in a studio - some of which has yet to make any air move. Here, stereo can be panned but is not likely to generate any lifelike sound field - largely because there was never one to start with. In such cases, artificial reverb is often added to the mix too. I also put the term spaciousness above in quotes for good reason: It is a term that describes the effect of late, lateral energy in a live acoustic environment. It is not strictly the same as that used for S channel LF boost in a reproduced sound field.
But one issue from acoustics that does have direct relevance with listening over loudspeakers concerns early reflections - normally much earlier than in a typical recording space. A factor often overlooked is that these reflections enable us to perceive the position of an acoustic source in its environment - that is its distance from us and relative to other sources. With a loudspeaker, there is then the potential for a second, earlier set of reflections that compromise any perception of depth in a recording - and highlight the presence of a loudspeaker. And in an artificial stereo sound field with no acoustic reference, a perception of depth can be apparent or not, depending on the loudspeakers and the room. There is lots yet to be debated and lots of reasons for different personal preferences! 🙂
This would be true for the most part, until more recently. Early on I only did and quoted scientifically valid studies, but the funding for those became harder to come by. To me, things like nonlinear distortion perception and room response have all been resolved with good science. But, the directivity issue still remains and there is little to no good data, so one is forced to more heuristic approaches.
My book is legitimately free. May be over a lot of heads however. Toole's is more for the home practitioner and mine for the working professional.
One last set of comments.
I do find Soundbloke's comments to be hard to follow as I am sure that he is not using many terms correctly. I.E., I meant to question him in detail about his use of the word diffusion, etc.
What I think gets lost in many many of these discussions is the temporal aspect of room reverberation and reflections. Temporal behavior is at least as important as the energy response. And lets not forget that our temporal perception is frequency dependent, making the discussion even more complex.
What can be proved is that higher DI speakers will have less early temporal reverberation than low DI speakers. This increases the direct to reverberant ratio as well as limiting the VER, especially in a small room. These attributes are known to improve imaging but tend to degrade spaciousness. Spaciousness can be enhanced/recovered with a highly reverberant room as long as one is using a high DI speaker. Low DI speakers in a highly reverberant room will have almost no imaging at all. I think that this is much of Mr. Ohmholt's point, although he can be truly annoying while expressing it.
Mitch - what is your take on the comb filtering inherent in stereo? It is my opinion that this is handled by the sound engineer to the extent that is necessary because they also mix in stereo. Where do you fall on this topic? It's never been a big one for me.
I do find Soundbloke's comments to be hard to follow as I am sure that he is not using many terms correctly. I.E., I meant to question him in detail about his use of the word diffusion, etc.
What I think gets lost in many many of these discussions is the temporal aspect of room reverberation and reflections. Temporal behavior is at least as important as the energy response. And lets not forget that our temporal perception is frequency dependent, making the discussion even more complex.
What can be proved is that higher DI speakers will have less early temporal reverberation than low DI speakers. This increases the direct to reverberant ratio as well as limiting the VER, especially in a small room. These attributes are known to improve imaging but tend to degrade spaciousness. Spaciousness can be enhanced/recovered with a highly reverberant room as long as one is using a high DI speaker. Low DI speakers in a highly reverberant room will have almost no imaging at all. I think that this is much of Mr. Ohmholt's point, although he can be truly annoying while expressing it.
Mitch - what is your take on the comb filtering inherent in stereo? It is my opinion that this is handled by the sound engineer to the extent that is necessary because they also mix in stereo. Where do you fall on this topic? It's never been a big one for me.
About direct/reverb ratio and delay, doesn't also spectrum of reflected sound have an effect?
A speaker with high DI in treble and specially undulating DI, makes reflected/reveberating sound to have a dull tone. Reflections are not 100% either, absorption/reflectiveness varies per frequency from different surfaces.
With REW we can get RT, EDT and C50 in octave or 1/3oct bands. Other way to look at this is Decay window where user can set time, IR windowing and intervals. Spectrum of decay can also be plotted.
The problem is how to analyze and interprete these measurements. They show the total sum of all reflections and modes at mic's spot in a room. My own measurements don't show a radical difference between a dipole and a regular speaker.
A speaker with high DI in treble and specially undulating DI, makes reflected/reveberating sound to have a dull tone. Reflections are not 100% either, absorption/reflectiveness varies per frequency from different surfaces.
With REW we can get RT, EDT and C50 in octave or 1/3oct bands. Other way to look at this is Decay window where user can set time, IR windowing and intervals. Spectrum of decay can also be plotted.
The problem is how to analyze and interprete these measurements. They show the total sum of all reflections and modes at mic's spot in a room. My own measurements don't show a radical difference between a dipole and a regular speaker.
That almost seems obvious at this point. VERs also kill frequency response right? Also if you use a higher DI speaker and point it away it should be constant directivity or otherwise it will sound strange?
Lets say you can't achieve perfect constant directivity since I can't find any tweeters that do. Then do you equalize flat on axis and hope it sounds right?
btw, after reading through about 50 pages of the "what causes listener fatigue" thread here, I can say I am the one who's completely rational in wanting to "enjoy" the music and forget about what's producing it. A lot of people completely burn themselves out.
I like answers and appreciate the good ones and this is an interesting hobby, but theres a bit too much lecturing and theory instead of answers, often from people who haven't worked these things out for themselves.
@scott, feel free to share?
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