Stereo Sound and Multiple Speakers?

Discussion in 'Digital Audio' started by Bodhi395, Apr 10, 2012.

  1. Bodhi395 macrumors 6502a

    Jul 23, 2008
    I'm trying to understand more about audio, but I'm confused about one point. I've heard almost all music is recorded in stereo sound, which is meant to be listened to on two speakers (or a pair of headphones). So what happens when you play stereo music through more than two speakers, such as in a car (which some have 10 speakers), or if you listen to music on a surround sound home theatre system. Is the stereo signal simply split up evenly into the speakers? So if you have 6 speakers, 3 will have one side and 3 will have the other. Or do stereos and amplifiers do more advanced things in playing stereo music through multiple speakers.

    I do realize movies are different and have sound encoded specifically for surround sound on multiple speakers. I'm only talking about pure music.
  2. SchwartzSound macrumors newbie

    Apr 2, 2012
    A car is typically intended for stereo playback, even with all of those speakers. The multiple speakers are simply meant to serve multiple zones/locations or frequency ranges. This is generally true for most sound systems with multiple speakers and fewer source channels -- if they're not serving other locations or frequencies, the speakers probably shouldn't be playing.

    In the car, for example, there might be a speaker on the left/right front doors, as well as one each on the left/right rear doors. The left speakers would all be playing the same left signal, only each one is located to better serve the riders in the back or front seats. Additionally, some cars may have a smaller speaker higher up on the left and right side of the dashboard -- those are also playing the same left/right signal as the other speakers, but they are targeted at reproducing mid-high frequencies better, to give you more clarity at head/ear level (the door speakers are likely better suited for mid-lower frequencies). A subwoofer speaker would simply play the low frequency content, derived also from the stereo signal.

    For home theatre sound system, it may depend on the mode the receiver is in. Typically, if you're just listening to stereo sound, it should only play back from the left and right speakers of the surround system (possibly also the sub). They may also play from the center speaker as a summed mono (L+R) signal.

    However I've seen receivers with modes that you can set to play back the same stereo sound from all the speakers (rear L/R, etc...). Not the best idea for the intended "sit and listen" playback, as the similar soundwaves from the speakers can interfere with each other. You could however use that mode if you are using the system for a multi-location setup and have the other speakers located in another room, or perhaps if you're having a social gathering and need the sound to fill a room full of people without being too loud.
  3. Bodhi395 thread starter macrumors 6502a

    Jul 23, 2008
    Great info, that's exactly what I was looking for. I was contemplating setting up a really nice sound system in my basement just for music. I initially thought maybe getting a surround system, but seems if it's just music I'll be using it for all I really need is two good speakers.
  4. PAPO macrumors 6502

    Aug 24, 2009
    keep in mind SACD's DVD-A and BD-A all have surround sound, and something like Pink Floyd DSOTM is absolutely incredible in SACD 5.1 so at lest consider a surround AMP to allow additional speakers at a later date
  5. nateo200 macrumors 68030


    Feb 4, 2009
    Northern District NY
    AV Receivers for home theaters have processing technology called "Matrix" decoders. They extract extra channels from stereo encoded tracks or matrix encoded stereo sources. Look up Dolby Pro Logic II, DTS NEO:6, Dolby Digital EX, etc. to get a better idea of the concept. Matrix decoding has been a technology for >30 years now so its nothing new but most people don't have intimate knowledge of the of it.
  6. SchwartzSound macrumors newbie

    Apr 2, 2012
    Both points true, I suppose "pure music" doesn't necessarily mean only stereo, but that seemed to be the direction the original poster was going. If you're going to listen to multichannel music like an audio DVD, which are rather common these days, they do actually have surround mixes that would benefit from a surround playback system.

    As for Dolby matrix decoding, their algorithm uses digital signal processing to derive pseudo-surround channels from a basic stereo signal, but I would perhaps argue that if the authors of the music did not intentionally provide a surround mix, you don't really need to artificially add one. Some people may however prefer the potentially more immersive feel while others may want to stay true to the original stereo mix, it is really a subjective matter of preference.

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