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Home » Audio » Measurement » On axis measurements in nearfield listening (I don't experience this as an issue... maybe you do??)
| On axis measurements in nearfield listening [message #60876] |
Tue, 15 September 2009 18:22  |
Marlboro
Messages: 403
Registered: May 2009
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Illuminati (1st Degree) |
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On the PE Tech forum, I asked a question as to whether when one is listening in the nearfield, and when the speakers are facing a central listening couch, whether there is any issue with speakers being off axis at all? Its a big measurement question that is always brought up.
Many people seemed confused that I would bring up a question about something that I didn't actually experience, I guess because asking questions just to find something out is not done. I'm not sure. Other people told me all about how I could fix the problem, even though I had already indicated that I could hear no issues with off axis response. Other people assured me that my line array was clearly wrongly placed against the wall, and other things.
I was told by someone I respect immensely that my system clearly had bad smearing of the sound stage(meaning I couldn't tell what instrument was placed where), and that combfilter distortion was rampant cutting out my highs. He's never heard the system, and I know both of these things are so wrong that I'm on the other side of the universe with them.
Nobody confirmed my listening tests that in the nearfield with the speakers angled directly toward the listening, that there is essentially no hearing observable effect of off axis response issues.
I'm really not sure what any of this means. But I have suspected for years, and Jim Griffin has taken many professional engineers to task many times to try to explain that the whole listening experience in a full line array is fundamentally different from point source speakers, and that line arrays aren't just big point source speakers.
Marlboro
p.s.: when I get 43 more posts, I graduate from Grandmaster to Illuminati 1st degree. Wayne is Illuminati 33rd degree, but he has 12000+ posts, and I'm sure I'll never get that many posts for the rest of my life. Does this qualify me to be in the Movie?
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| Re: On axis measurements in nearfield listening [message #60879 is a reply to message #60877] |
Tue, 15 September 2009 20:52  |
Marlboro
Messages: 403
Registered: May 2009
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Illuminati (1st Degree) |
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Wayne,
Asking questions about line arrays on PE invariably sends the various university trained electrical and audio engineers into some kind of joyful excursion of audio engineer language, which almost always excludes those of us who are not engineers. I think they do it on purpose so they don't have to answer questions in a way that a normal person can understand. Usually they get kind of angry when I ask for an explanation in laymen terms, like who do I think I am asking a question that I can't understand their answers for. 
I'm sure what you said makes good sense to an audio or electrical engineer. Unfortunately, you lost me near the beginning.
Could you respond to my question about my listening to my line array in the nearfield with the speakers slightly angled so that they are essentially facing the listening couch, and whether in that circumstance, off axis performance is actually hearable. As someone suggested who has always been a voice of reason on PE stated, I should have smearing of sound stage and loss of highs, but I most clearly DO NOT. Later in their discussion they started a technical argument as to what smearing actually means, and then lost me completely.
Are you suggesting that I have a uniform reverberant field? I was under the impression that that was a characteristic of listening in the nearfield. Also that the brain ignores any reflection that comes in under 38 milisecs, and listening in the nearfield pretty much eliminates any sound reflections that would be interpreted as anything other than the primary information.
As to the polars, doesn't a line array listened to in the nearfield produce a fundamentally different pattern that has less to do with polars?
Thanks so Much.
Marlboro
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| Re: On axis measurements in nearfield listening [message #60881 is a reply to message #60879] |
Tue, 15 September 2009 22:34 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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What I'm saying is that a loudspeaker produces sound eminating all directions from it, not just straight forward. This goes without saying, I suppose, and you're aware of it or you wouldn't have brought it up here. What I'm also saying is that I believe (as do many others in the field) that the off-axis response is as important as the on-axis response, especially when used indoors. The reason is pretty simple - the sound going straight in front of the speaker is only a tiny fraction of the total sound radiated by the speaker (in all directions). You don't just hear the sound coming straight at you, but also you're enveloped by the sound reflected back at you from the walls. This is called the reverberent field, and it makes up a great deal of what each listener hears.
Off-axis sound also plays a part in the width of the sweet spot. If you have a speaker that only sounds good on-axis, then it has to be pointed directly at the listener. That doesn't leave much room for guests. If you want good seat-to-seat coverage, you have to use a speaker that generates a sound field that is spectrally balanced over a wide range of listening positions. What that means is it should sound pretty much the same 20° or 30° on each side as it does straight on. This allows a much wider range of listening positions.
I don't know what kind of spectral balance your speakers have off-axis, but I do know that arrays generally provide a pretty wide coverage area. If the speakers are spectrally balanced over a wide enough arc, I've found you can improve the speaker's imaging with toe-in. The idea is to cross the speakers in front of the listening area so that the stereo image is self-balancing. This requires reasonably uniform off-axis coverage to work. Here's a post about the technique:
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| Re: On axis measurements in nearfield listening [message #60919 is a reply to message #60876] |
Fri, 18 September 2009 15:36 |
AudioFred
Messages: 377
Registered: May 2009
Location: Houston
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Illuminati (1st Degree) |
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| Marlboro wrote on Tue, 15 September 2009 18:22 |
I was told by someone I respect immensely that my system clearly had bad smearing of the sound stage meaning I couldn't tell what instrument was placed where...
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I've often been told something will sound terrible, yet when I do it anyway I find, as your have, that there's little of no difference. A good example is whether to position a tweeter at the center of the baffle or slightly offset to reduce diffraction. Maybe some people can hear a huge difference, but I can't.
In the case of your speakers, I notice they are positioned almost against the side walls of the room and pointed straight ahead. Their closeness to the side walls means the timing of the reflected sound will not be much different from the direct sound, but with highly reflective walls your ears will perceive the sound of each speaker is eminating from two positions, the speaker's position and the position where the refleced sound off the wall seems to be coming from. This may cause some smearing, but not so much as your first date's lipstick after you kissed her good nite on her dad's front porch.
I've found that corner-placed speakers often soundstage best when they are angled at 45 degrees, with the axis crossing in front of the listener's head. This extreme toe-in seems way too much, and I actually have to use a carpenter's angle thingee to force myself to position them this way, but it does work, at least with speakers whose tweeter is positioned directly above the mid or the woofer. I don't know if a line array with tweeters alongside the mids will do the same thing, but it shouldn't be too hard to try it.
Some people are fascinated with a precise soundstage, where each instrument's position can be exactly located. To me this sounds nothing like live music, and what I look for instead is a more convincing soundstage, where breadth and depth sound real to me based on the live music I hear at least three times a week.
If it's not too hard to move your speakers, try the 45 degree thing and let us know what differences you hear.
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| Re: On axis measurements in nearfield listening [message #60952 is a reply to message #60877] |
Mon, 21 September 2009 11:28 |
selahaudio
Messages: 56
Registered: September 2009
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Baron |
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| Wayne Parham wrote on Tue, 15 September 2009 19:20 |
I have found that most folks on the PE forum rarely (or never) do measurements. They trust their models instead. I'm not against models by any means, using them extensively. In fact, I think most people have better results with models than they would with measurements because making good measurements is not trivial and requires good equipment. But still, a good measurement trumps a good model any day. And off-axis stuff is harder to accurately model because there are complexities that aren't included in the simplifying assumptions.
To me, off-axis performance is as important as on-axis response. The total power is radiated in all directions, not just on-axis. In a room, much of this energy is reflected back, so it really is what sets the tonality of the sound field. A uniform reverberent field is just as important as a uniform on-axis response curve. Most experts agree with that, and I think a few minutes with a speaker that generates good polars will convince most any audiophile.
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I think not enough people building line arrays depend on measurements like they should. Measurements are extremely important with arrays if you want the best sound.
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| Re: On axis measurements in nearfield listening [message #60955 is a reply to message #60952] |
Mon, 21 September 2009 12:22 |
Marlboro
Messages: 403
Registered: May 2009
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Illuminati (1st Degree) |
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ONCE again, you are making a blanket statement that implies that if a DIYer does not have access to an extensive and possibly expensive measuring system, s/he he should not even attempt a line array. You leave nothing open to the DIYer who wants to design something they'd love, and just enjoys doing it.
I would disagree with that statement, from personal experience.
Its what I heard from many people in the manufacturing area: you can't do that because you don't have enough money or you don't have enough skills, or you don't have the right measuring equipment.
The implication again is: Only we have all those things, so don't even try.
I disagree fundamentally.
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| Re: On axis measurements in nearfield listening [message #60967 is a reply to message #60955] |
Mon, 21 September 2009 18:33 |
darkmoebius2
Messages: 37
Registered: August 2009
Location: Los Angeles, CA
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Baron |
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| Marlboro wrote on Mon, 21 September 2009 12:22 | ONCE again, you are making a blanket statement that implies that if a DIYer does not have access to an extensive and possibly expensive measuring system, s/he he should not even attempt a line array.
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That's not what he said or implied. He simply said that "Measurements are extremely important with arrays if you want the best sound.". I can't see anything factually incorrect or elitist/condescending about that statement, especially since he added "The margin for error is greater with the complexity of an array if you don't have the right tools"
I suppose Selah's opinion could be invalidated if someone who had designed/built arrays both using testing equipment, and without, came forward to say that they found absolutely no performance difference between the two in the end.
But, as of yet, that hasn't happened, so his is the most qualified opinion we have with regard to that issue.
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