38% rule

SlowcarIX

http://www.realtraps.com/art_room-setup.htm

THE 38 PERCENT RULE

The placement method used here is based on the "38 percent rule" which theorizes that the best listening position is 38 percent into the length of the room, when measured from either the front or rear wall. This offers the best compromise of peaks versus nulls for any given room size. For 2-channel listening you'll get the flattest low frequency response by sitting 38 percent of the way back from the front wall. However, this is not practical in many home theaters, especially those with large screens, because that puts you too close to the screen. Fortunately, you can get the same benefit by sitting 38 percent of the room length when measured from the rear wall.

Please understand that 38% is one theoretical best location to begin measurements, but it may not end up the best place to sit due to other factors - wall properties, speaker location, speaker type, furnishings in the room, and a host of other conditions that can affect frequency response. The only way to know which location really is most flat is to measure the low frequency response at high resolution using software such as ETF, FuzzMeasure, or Room EQ Wizard..................