The imaging on my monitors is poor (symmetry of room)?

The room into which you place your studio monitors should always be symmetrical to achieve the best imaging. Differences in the direct and reflected sound paths from each monitor will result in different frequency responses at the listening position. This will cause the image to shift slightly to the left or right at different frequencies resulting in poor imaging.

Symmetry applies not only to the room shape (which will affect low frequency imaging) but also to the equipment in the room (which will affect mid-range imaging).

Below is an example where the room was symmetrical but the equipment placed in it was not. The room had almost no absorption so the reflections were very strong.

It can be seen that the left and right monitors 'see' different rooms due to the equipment positioning, therefore the frequency responses at the listening position will be different. This is shown by the red and green lines in the graph below:

The effect of the unsymmetrical equipment positioning can be seen on the blue line: this is the difference between the left and right frequency responses. Any deviation away from the centre line (0 dB on the right axis scale) means that the phantom image will shift left or right depending on which monitor is louder. The dB difference vs. image movement is a linear relationship and 20 dB will swing the image totally left or right. In this case the image is shifted by almost 5 dB to the right (about 75 cm (30") in the room itself) at 1.5 kHz, whereas at 150 Hz the image has moved in the opposite direction by almost the same amount. The imaging in this room could be considered to be poor. Moving the equipment so that everything in the room is symmetrical left to right would remove these problems.

Finally, 1037B/C monitors have a frequency response that extends to 35 Hz. When placed into this room the frequency response only extends down to 52 Hz (about the same as a 1030A!). This is due to the rear wall reflection cancellation, which should have been damped using absorbing materials. Enough damping would reduce the reflection sufficiently and the response would extend smoothly down to 35 Hz. The large bumps between 60 & 100 Hz and around 200 Hz are caused by the constructive interference associated with the reflection. The destructive interference associate with the reflection can be seen below 60 Hz and between 100 & 200 Hz. This is called comb filtering.