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Prescription Speaker Placement

All,

I'm looking for a way to dial in speaker placement to create as accurate a soundstage in my room as possible. I'm hoping to find a description of a piece of music that would help with this, beyond the often used 'dog in the distance' scenario. My ideal would be that the tune is played by a group of five to ten musicians, and the recording and mastering preserved the location of the instruments in relation to the microphones. Someone would then have described the spatial relationship of the players to the mics from side to side and front to back. During playback, the listener would be able to use the description of the location of the players to help place speakers to recreate the positioning of the instruments.

Has anyone come across such a description, or have any related advice? I'm guessing that, in the absence of such a definitive text, a chamber music or similar classical piece where instruments are typically known to be placed might help, but I don't know that kind of music well enough. Any responses would be appreciated. Thanks.

C
128x128cmjones

Showing 1 response by brownsfan

brownsfan
1,508 posts
 
cmjones, Great question.  I am pretty much in agreement with a lot that has been said so far, but I will encourage you do some work around getting speaker placement and listening position right before you worry about dialing in imaging and soundstage.  This is because what you need to do to get the spacial clues dialed in is relevant only to one particular speaker position within a room.   If you get your imaging dialed in but still have huge problems with low frequency ringing and deep nulls you are not going to be happy.

If you want to get serious about your room, the best thing to do is to download REW room measurement software (free) and learn how to use it.  Specifically with respect to imaging, if you learn to use and interpret the impulse graphs you will have an incredibly powerful tool to use when trying to optimize spacial clues.

If you want a quick and dirty approach without doing actual room measurement, I would suggest the following.

  1. As mentioned by MC, EVERYTHING in your room forward of the listening position should be symmetrical right to left.
  2. In many rooms, the best position for speakers will be 20% of the room length out from the front wall, and 20% of the room width from the left and right sidewalls.  There is a dynaudio you tube video describing this.  I set my room up for optimal frequency response through a very laborious process of measuring and critical listening and ended up with my speakers within inches of the 20% rule.  In the same way, in many rooms you will find the optimal listening position for frequency response is 20% off the back wall.  
  3. Once the speaker and listening position is established, you can begin to get serious about treating your side and back walls to improve imaging.  Human hearing is highly sensitive to spacial clues derived from reflections generated in the horizontal plane.  So ceiling and floor reflections are less important than side wall and back wall treatments.  You can use a mirror to determine first reflection points on side walls by having a second person hold a mirror along the side wall while you sit in the listening position and shine a laser light into the mirror.  When the reflected light hits each of your speaker, you have located the first reflection points on the side walls.  These points are not points, but really are zones, meaning you will need to effectively treat a foot or two foot wide area on your side wall.
  4. The early reflections that confuse spacial clues and mess up imaging are those that arrive at your ear within the first 12 milliseconds or so later than the direct signal coming from the loudspeaker.  Any reflection in that time frame, and especially those that are derived from the side and back walls, should be treated so that the SPL of the reflected sound is 15 -20 dB lower than the sound coming directly from the loudspeaker.  
  5. I prefer not to treat sidewalls between the front wall and the first reflection point.  Sometimes a little treatment is necessary if the room is excessively bright, but no treatment in that front side wall area usually gives the widest soundstage.  You should be able to hear images wider than the width of the room if you get this right.
  6. If your listening position is more than 12 ft  away from your back wall, back wall treatment is less important for imaging.  The same is true of sidewalls, but we rarely have rooms that are 30 ft or more wide.
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