Prescription Speaker Placement

You don’t need certain music, or any music at all really. The formula for imaging is as simple as everything must be perfectly symmetrical and equidistant.

This is how I set up mine, and everyone else’s, up to and including the speakers in the Talon Audio room at CES. Which I did after several others spent a couple hours laboring in vain. My method took 20 minutes and everyone was happy.

I am going to skip over the initial steps involved in getting the right frequency balance and go straight to what you asked about, imaging. So there is more to it. But in terms of imaging, this is it!

First we get the speakers perfectly symmetrical and equidistant. To do this we tape a string to the outside bottom edge of the right speaker, wrap it clockwise around the base and over to the left speaker, wrapping around and taping it to the outside edge.

If the speakers are perfectly straight ahead then the bases will be perfectly flush with the string. If they are toed in a little then the inside corner will form a gap with the string. Measure this distance. Change toe of one or the other until this is exactly the same on both sides.

Now measure to the exact middle of the string. Exactly half way between the speakers. Use a framing square to go 90 degrees from this mid point. Place your listening chair somewhere along this line. Not half an inch one way, not 1/4" the other. Exactly on this line.

Sit and listen. Pretty freaking amazing, eh? Now, for the final touches.

Listen for image focus, and stage width. Speakers pointed straight at you will image like a laser, but the stage may not be very wide. Speakers pointed straight ahead will produce a much wider stage, but without much focus. I find the best balance with almost all speakers has them pointed at each shoulder, or converging a little behind me. But that is my preference. May not be yours.

Don’t waste your time with recordings. They are all over the map, and cannot be used for this. There are a lot of awfully confused people out there happy to confuse you as well, because misery loves company. Use string, tape, square, and be happy.

I do it all by ear but MC has it right. The only thing I can add is that every loudspeaker is different and some need to be pulled far out from the front wall, some more some less. And, some loudspeakers just are not good at imaging. 

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.

Thanks to everyone so far.

MC, thanks for your straightforward approach to getting good imaging. In the reply you mention the steps to get the right frequency balance. I know there are apps which assist this, but I wonder if you have a straightforward approach that gets you most of the way to a good balance.

C

millercarbon,

 I find you speaker setup very interesting. I never thought of the string trick. I always measured from the back wall. I would love to hear the rest of your speaker setup  guide.