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Thread: Bass localization: an experiment

  1. #21
    Tester Extraordinaire ErinH's Avatar
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    Quote Originally Posted by cvjoint View Post
    What I think happened is that I was referring to correlation of program material whereas the purpose of your quest is temporal correlation. I was a bit off topic then.

    I forget if it was you that recommended a neat experiment, introduce a correlated buzzing/rattle in the front speakers to pin the stage down in front. My car is sort of a realized experiment of this. With LATs in the back and conventional midbass up front, the rattles up front completely overwhelm the ones in the back (which are also less correlated temporally, not just lower output). The stage is pinned up front better than before but I suspect if I change my midbasses to LATs some of the correlation will disappear and maybe the back will be more localizable again. That would be unfortunate.

    I understand where you guys are coming from, but I'll just say this...
    If I got in your car and heard a rattle that was audible, my attention would never move past that rattle and the entire experience, for me, would be out the window. So, while it's a novel idea to purposely have a rattle up front to over ride the rattles in the rear with the goal of focusing your attention to the front, it would completely backfire for me. I get straight up OCD with rattles or anything else that's glaringly wrong. I've heard cars with a split stage and could never give any criticism past that because I couldn't listen 'through it'. Rattles?... I might as well get back out of the car. I've actually helped people diagnose rattles at shows/meets because I couldn't evaluate the stereo until the problem was fixed. Not sure if that sounds snobbish... I'm just saying... if it's a problem, it's a friggin' problem.
    Your ears: The best tools you have... and they're free, too!

  2. #22
    Senior Member cvjoint's Avatar
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    All cars rattle, but the magnitude varies. With a decent build masking takes over and rattles are not apparent for most program material but that doesn't mean they are not there. Try muting your midrange entirely, not -20db but true mute and play your usual music selection with sub 200hz drivers only, 5khz up tweeter add in is ok too. Without the midrange cars sounds like ass. There are too many movable parts in a car to be a rattle free environment, it doesn't exist.

  3. #23
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    Quote Originally Posted by ErinH View Post
    I understand where you guys are coming from, but I'll just say this...
    If I got in your car and heard a rattle that was audible, my attention would never move past that rattle and the entire experience, for me, would be out the window. So, while it's a novel idea to purposely have a rattle up front to over ride the rattles in the rear with the goal of focusing your attention to the front, it would completely backfire for me. I get straight up OCD with rattles or anything else that's glaringly wrong. I've heard cars with a split stage and could never give any criticism past that because I couldn't listen 'through it'. Rattles?... I might as well get back out of the car. I've actually helped people diagnose rattles at shows/meets because I couldn't evaluate the stereo until the problem was fixed. Not sure if that sounds snobbish... I'm just saying... if it's a problem, it's a friggin' problem.
    Totally on board with what you're saying about rattles. But I think it helps demonstrate some of the points I've made regarding the importance of correlation in different parts of the frequency spectrum. "Rattles" (presumably of high-ish frequency) steer bass localization. That statement by itself is a pretty big deal, IMO. I observed something similar yesterday when I had a bottle of laundry detergent in the passenger seat in a plastic bag. The bass would make the plastic bag create a noise, which was audible (and obnoxious) relative to the rest of the system. It felt like it altered the bass perception rightward -- of course, I was looking for it, so it's hard to judge whether it was real or not.

    My suggestion in the past was to experiment with introducing distortion in a center speaker to harness some of these effects. The distortion would have to be well controlled to prevent it from becoming a nuisance. And that's one of the questions I don't have an answer for: how prominent does this distortion have to be (for example, can it be subthreshold when it comes to distortion-detectability?), and what properties of this distortion would be necessary to evoke the effect?

    Edit: this is also the basis for one of my observations, that shallower crossover slopes in the front speakers help steer bass localization forward.
    Last edited by MarkZ; 05-20-2012 at 11:05 PM.

  4. #24
    Senior Member cvjoint's Avatar
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    I can tell you how I would go about it. Find 50+ subjects. Grab a recording and make it possible to have it be reproduced on a stereo with 4 drivers, 2 full range capable drivers up front and 2 more behind. Two sources are necessary for each pair of drivers. Alter the recording randomly with combinations of 10th order+ HD of various frequency and amplitude and LP filters. Label each unique recording with a number and corresponding noise added. Play the tracks for each individual as many times as you can afford it in as wide of an interval as you can afford by number but not by distortion pattern (this makes the experiment double blind). Question the subject as to the location of the sound source. The answer to this question is your outcome variable. Every combination of tracks is an observation.

    Run a person fixed effects regression model that conditions on listening time frames (captures ear fatigue), gender and other controls that are know to affect hearing ability. The outcome variable is location, will be binary and the regressors of interest will be main effects for noise frequency, amplitude, and LP filter settings. Include interactions of all regressors of interest. This will capture nonlinear effects.

    That's the tip of the iceberg. Ideally you would want to have several random recordings and introduce fixed effects for all of them. I assume rattles can be approximated with high order HD but you would need to find out exactly what rattles are in a quantified manner. If randomization fails the fixed effects methodology should still allow identification. If it works you don't need this elaborate framework as randomization will do away with internal validity concerns and the effect of interest can be tabulated, or identified through simple mean differencing.
    Last edited by cvjoint; 05-20-2012 at 11:39 PM.

  5. #25
    Founding Member Subwoofery's Avatar
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    Anything else from these tests?

    Asking coz I'm bored - not enough advanced subject lately

    Kelvin

  6. #26
    Controller AL9000's Avatar
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    For the first time, I noticed while re-reading about Richard Clarke's Grand national he mentioned that he added mass to the seat backs to minimize vibration, therefore helping eliminate bass localization. I have been curious about the tactile effect on bass localization, especially after this discussion: http://www.mobilesoundscience.com/f4...17/index5.html
    I recently got a bunch of 5/8" rare earth magnets. If I put like poles together, I cannot make them touch no matter how hard I try. I've been wanting to build a magnetically levitated base to sit my speaker box on to isolate any vibrations due to coupling. Reviving this thread has re-peaked my curiosity.


  7. #27
    Founding Member Subwoofery's Avatar
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    Dunno, when my phase (polarity + EQ) & my T/A is correct, I never had a problem with the back of my seat vibrating...
    I get a light thump in the chest even at medium volume and a strong one when listening a bit louder than I'm used to - when the recording calls for it
    ^ the above is with my girlfriend's car (ID horns) - subwoofer under the passenger's front seat (with me in the cabin)

    Kelvin

  8. #28
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    Quote Originally Posted by Subwoofery View Post
    Anything else from these tests?

    Asking coz I'm bored - not enough advanced subject lately

    Kelvin
    Not yet. I'd like to continue, but it's tough finding time these days...

  9. #29
    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by MarkZ View Post
    Not yet. I'd like to continue, but it's tough finding time these days...
    I hear ya

    Kelvin

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