Stereo or mono reflections

April 22, 2022
 by Paul McGowan

My friend, Keith Howard, wrote me a wonderfully insightful note that I will share with you.

“I find it helpful to think of reflections as mono or stereo, in the manner of Manfred Schroeder when he performed his analysis of concert hall acoustics and confirmed the importance of lateral reflections.

Sidewall reflections are ‘stereo’ because they arrive at the ears from wider angles than the loudspeakers, so they increase interaural disparity (hence spaciousness). All other room first-order reflections (floor, ceiling, back wall, front wall) are ‘mono’ because they arrive at the ears at narrower angles than the loudspeakers and so reduce interaural disparity.

I’m not a fan of quelling side-wall reflections as you are, but if you do it then it’s essential not to mess with the spectrum of the reflection. Simple absorbers are bad news because they are more effective at treble frequencies than lower frequencies, so the spectral disparity between direct and reflected sound is increased, as if the reflected sound came from further off-axis. Why do speakers usually sound better pointed straight down the room? Because this results in smaller disparity than if the speakers are toed-in.


PS. Worth reading: – published in 1979 but nobody took any notice!

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15 comments on “Stereo or mono reflections”

  1. Happy Earth Day 2022! – Back to where it all began one year after the 1969 oil spill.

    If you’ve never been it’s a lovely little venue in a natural setting. Reflecting back to the 70s, the lanky singer is soulful and the guitar picker is a Fender master. Live to video in the moment, no patchwork quilt here.

    Ladies also love this music so open a bottle of wine and enjoy a pleasant summer evening.

    1. Ahh 2005…before Putin, China & Trump were major
      world problems…life was so much simpler then 😀
      I’m starting to understand what is meant by “the good ol’ days”.

      1. Outdoor music reproduction is challenging due to the elements (altitude, humidity, thermal, wind etc) boundaries are seldom an issue.

        While observing speakers from Magico, Wilson & YG Acoustics its instructive to note their most expensive component are the enclosures which leads us to one of the reasons why Magneplanars are a righteous value.

        No box!

        1. For sure…but let’s not forget ‘Open Baffle’ designed loudspeakers
          like the Spatial – ‘M4 Sapphire’ & GR-Research –
          ‘NX-Treme’ & ‘NX-Otica’; also “No box!”

          Maggies, unfortunately, are too lean on dynamics
          for Rock ‘n Roll at realistic volume levels.

          1. I’ve always enjoyed listening to music through competent electronics consisting of properly set-up Magneplanars. Their ability to reveal the recording space is unparalleled at their price points.

            Loud volume listening at home is overrated imho and any dynamic limitations Magneplanars may have are not an issue for me and the many thousand happy owners around the planet.

            PS -> Outdoor music reproduction should read ‘Sound Reinforcement’. Oops…

  2. $33 that I’d rather spend on CDs.
    I’m not going back to mono just because of this article.
    “The room sounds as it does”…get over it & enjoy the music ✌

    1. I agree that $33 ( US ) seems steep for an AES paper. If it were $5 or $10 I would probably pay for a copy since it seems very interesting.

  3. Oh no! Again trying to distract the readers from the inherent core problem of stereo: inter-speaker crosstalk resulting in strange comb-filter effects! Eliminate this crosstalk and you get the best holographic sound image ever. In order to even minimize unwanted (!) effects from side wall reflections I have my loudspeakers place along the long wall of my listening room. And most important: diffusers on both floor and ceiling.

  4. Doesn’t it matter if it’s a good recording that captured a real live space. Then you might not want your room reflections. They’d be an artificial addition to the recording spatial affect and then be a distortion of fidelity. I always believed that’s what Bose didn’t understand. Sometimes his speakers reflected the reflections that were already recorded.

    Then again in a complex mixed studio recording, especially those where players are recorded separately and mixed together with whatever the engineer chooses ,it probably doesn’t matter adding room reflections, Just set up a good room the way it sounds best for you.

    Perhaps it’s a nearfield versus far field listening question. My 1st paragraph would probably be most accurate near field. Complex mixes could be up to the listener.

    This isn’tn’t meant as an answer, just thoughts I’ve had over years and it’s meant mainly to think about.

  5. That’s really interesting!

    Although I generally prefer a medium to near field setting (at least in less optimized listening situations), where side reflections play a minor role generally, it’s very interesting to understand…

    – that speakers heading quite straight into the room are better in the mentioned regard
    – in more distant listening situations
    – but only if side reflections are tamed (as otherwise reflections are unequal, too)
    – and only if tamed in the proper manner, considering equal effect for all frequencies
    – which probably hardly anyone did so far

    Always important to understand how right or wrong general recommendations (like much or little toe in or general side wall measures without quite exact design towards the overall frequency spectrum) can be, if not thought out more or less completely.

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