Results 1 to 12 of 12
  1. #1
    Audio casualty StevenSurprenant's Avatar
    Join Date
    Apr 2002
    Location
    Illinois
    Posts
    592

    Surround spacial imagery

    In stereo reproduction, the sweet spot is equidistant from the two loudspeakers and set back to form an angle of 60 degrees. From this sweet spot, the listener can perceive spatial imagery at the speakers locations and also phantom images in between.

    In multi-speaker reproduction, the sweet spot is roughly equidistant from all speakers. Phantom images are well defined between the front two speakers and the rear, but extremely fragile on the sides. What this means is that, (for this example we'll use a 4 speaker setup spread equidistant around the listener), if an image is panned between the speakers so that, conceptually it would go around the room, the phantom image would be easily located when it is between the front two speakers or the rear two speakers, but when this image is traversing between front and back or back to front, the image does not move smoothly between the speaker locations. In addition to this, the perceived image, to the side, has a preferential for the front speaker. As the image is panned from, let's say front to back, the image will “stick” to the front speaker during most of the time that the image is being panned and as the panning continues, we experience a loss of localization . What this means is that even though we perceive the sound coming from the front, our perception of where this image is in space will be less defined. At one point during this panning, a side image may form, but where it will form to the side is hard to determine. From there, a small incremental move in panning will cause the image to be perceived as coming from the back, but localization in space will still be indeterminate until the image is panned completely to the back speaker.

    If the listener sits outside the sweet spot, the “precedence effect” will have an impact on the listeners spacial imagery. Normally we perceive the “precedence effect” as image shift in a 2 speaker (stereo) system. We've all heard it, but there is a little more to it. If the signal from one speaker is delayed between 0ms to 1ms, the image will shift closer to the nearest speaker (the speaker with the least delay). The closer the delay gets to 1ms, the closer the image gets to the closest speaker (or the speaker with no delay – same thing for our purposes). At 1ms, the image is perceived to be coming directly from the closest speaker. This assumes that the amplitude of both speakers remain identical to each other. This time delay can be created electronically or by simply moving one speaker further away. From 1ms to about 5ms delay, the image will appear to be coming from the closest speaker and the furthest speaker, for all practical purposes, will be undetectable. We can also say the same thing this way... The image will appear to be coming from the speaker whose signal arrives at our ears first. Once the delay exceeds 5ms, then what is called the “echo threshold” is reached and we begin to hear the further speaker again, but as an echo. The “echo threshold” can also be considered as the point where the “precedence effect” is being released. The fly in the ointment for these delay times I have given is that, sonic material with a more continuous content will change this threshold point.

    To put this in a more realistic context, imagine that we have a typical 2 channel setup and that the speakers and the listener are all equidistant from each other and that the amplitude from each speaker is equal and remains so during the entire scenario- (Don't touch that dial!). Also, we send a signal to the stereo pair so that a phantom image is produced directly between each speaker. The listener remains sitting and listens while another person begins to move the right speaker further away. As the speaker moves further away, the listener will begin to hear the phantom image move closer to the left speaker. When the right speaker is about 1 foot further than the left, the image will appear to be coming directly from the left speaker. Now as the right speaker is moved further away, the listener hears no change, the image remains in the left speaker and for all practical purposes, the right speaker is undetectable. This continues until the right speaker is moved approximately 5 or 6 feet away at which point the “echo threshold” is reached and the listener begins to hear the right speaker as an echo. Keep in mind that this “echo threshold” varies with the content being fed into the speakers. The most interesting thing about the “precedence effect” is the range between 1 foot and 6 foot. The problem with using feet instead of delay time is that the larger the triangle we used when we set up our system, the further we have to move our speakers to achieve the delays required to hear this effect.

    When speakers are further from a listener such as in a movie theater, the sweet spot is larger than compared to a typical home theater set up. What this implies is that the “precedence effect” is less prominent in a larger room, but what's important here is that room size (or speaker distance from listener) can greatly affect spatial imagery. A way to use this information is when you are setting up your system at home. The further away from the speakers you sit while maintaining an equilateral triangle, the larger sweet spot you have and the less image drift occurs when the listeners move laterally. You can also widen the sweet spot by simply moving the speakers further apart outside the equilateral triangle, but there are other issues created by doing this which is outside the scope of the subject matter that I am presenting at the moment.

    At this point, I should also mention that this effect is the reason why surround systems uses a mono channel for dialog. A center speaker prevents image drift and so the dialog remains in the center of the screen regardless of where we sit. In other words, the “precedence effect” is eliminated from the center channel. The “precedence effect” still occurs in a surround system, but it is minimized in the front channels.



    This is pretty much Audio 101 and there are many more aspects to consider if one's goal was to explain audio more in depth, but for my purpose, this is enough for now.

    I hope some of you found this interesting.

    Source information: Dr. Gary Kendall - School of Music and Sonic Arts, Queen's Univeristy Belfast
    Last edited by StevenSurprenant; 10-23-2011 at 03:44 AM.

  2. #2
    Super Moderator Site Moderator JohnMichael's Avatar
    Join Date
    Apr 2005
    Location
    Central Ohio
    Posts
    6,239
    Steven I am curious as to your post. Is this your research, experience or opinion?
    JohnMichael
    Vinyl Rega Planar 2, Incognito rewire, Deepgroove subplatter, ceramic bearing, Michell Technoweight, Rega 24V motor, TTPSU, Funk Firm Achroplat platter, Michael Lim top and bottom braces, 2 Rega feet and one RDC cone, Ortofon OM20, Moon 110LP/PSU
    Digital
    Sony SCD-XA5400ES SACD/cd, Marantz SA 8001
    Int. Amp Krell S-300i
    Speakers
    Mobile Fidelity OML1's/Bell'O 224 stands
    Cables
    AQ Rocket 44's, Diamondback XLR's & IC's

  3. #3
    Audio casualty StevenSurprenant's Avatar
    Join Date
    Apr 2002
    Location
    Illinois
    Posts
    592
    Quote Originally Posted by JohnMichael View Post
    Steven I am curious as to your post. Is this your research, experience or opinion?
    Anyway, it's not opinion and it's not research that I've done. It's based on research that others (professionals) have done. Also, this is not cut and paste. If any interest is shown, I'll publish my sources.
    Last edited by StevenSurprenant; 10-22-2011 at 09:07 AM.

  4. #4
    Super Moderator Site Moderator JohnMichael's Avatar
    Join Date
    Apr 2005
    Location
    Central Ohio
    Posts
    6,239
    If you are using information from published sources you might want to include those sources or links to your sources.
    JohnMichael
    Vinyl Rega Planar 2, Incognito rewire, Deepgroove subplatter, ceramic bearing, Michell Technoweight, Rega 24V motor, TTPSU, Funk Firm Achroplat platter, Michael Lim top and bottom braces, 2 Rega feet and one RDC cone, Ortofon OM20, Moon 110LP/PSU
    Digital
    Sony SCD-XA5400ES SACD/cd, Marantz SA 8001
    Int. Amp Krell S-300i
    Speakers
    Mobile Fidelity OML1's/Bell'O 224 stands
    Cables
    AQ Rocket 44's, Diamondback XLR's & IC's

  5. #5
    Super Moderator Site Moderator JohnMichael's Avatar
    Join Date
    Apr 2005
    Location
    Central Ohio
    Posts
    6,239
    I was just asking about your post. We have many new members looking for education and I wondered as they might how accurate is this information. I thought if you worked in the field or was using known sources it might give more credibility to your posts. Several members have shared their professional involvement in audio and I think that helps the newbie feel they are receiving good knowledge.
    JohnMichael
    Vinyl Rega Planar 2, Incognito rewire, Deepgroove subplatter, ceramic bearing, Michell Technoweight, Rega 24V motor, TTPSU, Funk Firm Achroplat platter, Michael Lim top and bottom braces, 2 Rega feet and one RDC cone, Ortofon OM20, Moon 110LP/PSU
    Digital
    Sony SCD-XA5400ES SACD/cd, Marantz SA 8001
    Int. Amp Krell S-300i
    Speakers
    Mobile Fidelity OML1's/Bell'O 224 stands
    Cables
    AQ Rocket 44's, Diamondback XLR's & IC's

  6. #6
    M.P.S.E /AES/SMPTE member Sir Terrence the Terrible's Avatar
    Join Date
    Jul 2002
    Posts
    6,818
    Quote Originally Posted by JohnMichael View Post
    I was just asking about your post. We have many new members looking for education and I wondered as they might how accurate is this information. I thought if you worked in the field or was using known sources it might give more credibility to your posts. Several members have shared their professional involvement in audio and I think that helps the newbie feel they are receiving good knowledge.
    JM,
    His information is correct, but is muddled and lacks context. For instance, when discussing the effects of panning, it helps to include the speaker setup plan you are using.(i.e. 4.0 quad setup, 5.1 or 7.1). Or whether it is the ITU-775B speaker setup, the 90 degree set up, or surround with a single or dual rear wall set up.

    When talking about the Precedence effect, the context would be the importance of equidistant speaker placement.

    This is not really audio 101, but more like audio 103. Audio 101 is basic speaker set up, and calibration. Audio 102 would be intro to basic acoustics. After those two, then you get to this.
    Sir Terrence

    Titan Reference 3D 1080p projector
    200" SI Black Diamond II screen
    Oppo BDP-103D
    Datastat RS20I audio/video processor 12.4 audio setup
    9 Onkyo M-5099 power amp
    9 Onkyo M-510 power amp
    9 Onkyo M-508 power amp
    6 custom CAL amps for subs
    3 custom 3 way horn DSP hybrid monitors
    18 custom 3 way horn DSP hybrid surround/ceiling speakers
    2 custom 15" sealed FFEC servo subs
    4 custom 15" H-PAS FFEC servo subs
    THX Style Baffle wall

  7. #7
    frenchmon frenchmon's Avatar
    Join Date
    Dec 2005
    Location
    St. Charles Mo
    Posts
    3,147
    man...I have to give it to you guys.I have two home theaters and they both are old. The main system, I have a Marantz SR 5500 home theater reciever....Paradigm Monitor towers 7v3 for fronts...Klipsh KM 4's towers for rears, and a Sony center channel. It can use a new home theater reciever and a tune up bad. It does not sound bad....but it really needs a new home theater reciever...something like a reciever with HDMI I suppose. Steve thanks for the advice...and Sir T I guess I will have to go back to the basics of 101. Man, I have been stuck in 2 channel mode for years...
    Music...let it into your soul and be moved....with Canton...Pure Music


    ----------------------------------------------------------------------------------------------
    Vincent SA - T1/Vincent SP-331 MK /MF XRAY v8 /MMF-7.1/2M BLACK/ Creek OBH MK 2/Canton Vento 830.2

  8. #8
    Audio casualty StevenSurprenant's Avatar
    Join Date
    Apr 2002
    Location
    Illinois
    Posts
    592
    Quote Originally Posted by frenchmon View Post
    Man, I have been stuck in 2 channel mode for years...
    Due to trying to keep this post short, I left things out that weren't pertinent to understanding the concept. The concept is 101, understanding the whys just takes a little more reading and is not important unless you want a more complete understanding. Once the concept sinks in, it will seem simple to you, but it's that way for most everything we learn in life.

    BTW, HDMI is the best thing since sliced bread. I still love my 2 channel set up. Perhaps it's because it's easier to afford quality speakers and electronics in a 2 channel system, but as long as I am in the "sweet spot" , hands down, the 2 channel system is better. Also, as long as I am in the "sweet spot" there doesn't seem to be any advantage to having a center channel. However, the surround channels make a big difference when it comes to movies. I reserve the right to change my mind on this because my 2 channel and my surround system use completely different speakers and electronics.

    Many years ago (about 35 years ago), before home surround was even talked about, I gave much thought about a center channel because image drift was a constant irritation to me. I even spoke to people about constructing the circuitry necessary to split the signal into 3 parts, but no one seemed interested and I didn't have the skills. Without going into details... The concept was to remove what was common to both channels and sending it to a center speaker. This would, in a sense, create two stereos out of one, the Left/Center and the Right/Center. Done correctly, it would have sounded identical to a 2 speaker set up, except the drift would be tremendously reduced. At least in concept. I'm not the only one that was thinking along these lines back then.

    You might also find it interesting that some of us were using back surround in the 70's. It was far from perfect, but interesting. We, in simple terms, subtracted the left from the right and sent what was derived to rear speakers. Hardly comparable to the surround that we use today, but still... there it was.

    Anyway, this is archaic. I just thought that you might enjoy knowing that home audio people were talking about surround long before it made its debut.

  9. #9
    M.P.S.E /AES/SMPTE member Sir Terrence the Terrible's Avatar
    Join Date
    Jul 2002
    Posts
    6,818
    Quote Originally Posted by frenchmon View Post
    man...I have to give it to you guys.I have two home theaters and they both are old. The main system, I have a Marantz SR 5500 home theater reciever....Paradigm Monitor towers 7v3 for fronts...Klipsh KM 4's towers for rears, and a Sony center channel. It can use a new home theater reciever and a tune up bad. It does not sound bad....but it really needs a new home theater reciever...something like a reciever with HDMI I suppose. Steve thanks for the advice...and Sir T I guess I will have to go back to the basics of 101. Man, I have been stuck in 2 channel mode for years...
    Two channel is where your heart is, so that is were your focus has been. Mine has always been multichannel because of my film background. HDMI is a Godsend. Before it, the equipment room looked like a well organized spaghetti factory. Now it almost looks sparse in comparison.
    Sir Terrence

    Titan Reference 3D 1080p projector
    200" SI Black Diamond II screen
    Oppo BDP-103D
    Datastat RS20I audio/video processor 12.4 audio setup
    9 Onkyo M-5099 power amp
    9 Onkyo M-510 power amp
    9 Onkyo M-508 power amp
    6 custom CAL amps for subs
    3 custom 3 way horn DSP hybrid monitors
    18 custom 3 way horn DSP hybrid surround/ceiling speakers
    2 custom 15" sealed FFEC servo subs
    4 custom 15" H-PAS FFEC servo subs
    THX Style Baffle wall

  10. #10
    Shostakovich fan Feanor's Avatar
    Join Date
    Jun 2002
    Location
    London, Ontario
    Posts
    7,843
    Quote Originally Posted by StevenSurprenant View Post
    ...

    You might also find it interesting that some of us were using back surround in the 70's. It was far from perfect, but interesting. We, in simple terms, subtracted the left from the right and sent what was derived to rear speakers. Hardly comparable to the surround that we use today, but still... there it was.
    ...
    See hifitommy's post about DynaQuad.

  11. #11
    Audio casualty StevenSurprenant's Avatar
    Join Date
    Apr 2002
    Location
    Illinois
    Posts
    592
    Quote Originally Posted by Feanor View Post
    See hifitommy's post about DynaQuad.
    Learn something every day! For a moment, I completely forgot about DynaQuad.

    Since my memory has been refreshed, I remember them well. They weren't on the market very long. It seems that many people, back then, didn't want that many speakers in their living room. There was also an issue with how the audio was recorded. In many recordings, they made excessive use of separating the instruments discretely in all 4 speakers. Some people didn't like this. Still it was fun and I am sure that many people did like it..

    This excessive use of steering instruments to the back is still an issue with some SACD's, at least from what a friend has told me. I watched a concert at an audio store not that long ago and they were piping some of the bands instruments to the rear which sounded odd. However, my friend told me that when he programs his receiver to only play through the 3 front channels (no rear), he likes it better than 2 channel.

    The method I used was less sophisticated. I ended up with two speakers to the rear, but the same info (mono). This was before Quad receivers made their debut. What was nice about it was that the singer always stayed in the front (middle). This method was especially cool when playing live recordings. The back channels would stay pretty quiet until the audience would start cheering/clapping and then it was like you were part of the audience. Besides, it didn't cost anything to implement. except the extra speakers. I didn't use it long because my front and rear speakers sounded too different, which was distracting. I had Phase Linear Andromeda III's in the front and Bose 301's to the rear.

    Thanks for reminding me.

  12. #12
    Forum Regular hifitommy's Avatar
    Join Date
    Dec 2001
    Location
    sylmar, ca. in beautiful so cal earthquake country
    Posts
    1,389
    bose speakers in the rear, perfect. i have repeatedly made that recommendation for 901s and the 301s (perhaps their best value) would do nicely there utilizing the dispersion vane to aim direct sound just out of the ear's pathway and not distract the listener. of course the level has to be right too.

    when my celestion county (long ago) rear speakers were in close proximity of my listening spot, one of my final adjustments was of the angle of the axis of the rear spkr to take direct sound just out of the perceptible zone.

    once properly adjusted, my speakers rendered all six surfaces of the king's chamber of the giza pyramid in paul horn's "inside the great pyramid". it was eerie. this was all using the dynaquad for ambience recovery.
    ...regards...tr

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Latest AudioReview Articles

Hot Deals

Latest News

AudioReview on Facebook