This calculator is based on a rule-of-thumb formula to space ceiling speakers that shoot straight down at the floor in a distributed speaker system. Conical Dispersion, which is given on Lowell’s specification sheets, is the coverage angle of a speaker measured at an equal distance from the speaker where the sound pressure level (SPL) at the 2kHz octave band (important for speech articulation) is no more than 6dB lower than the SPL on-axis (straight out in front of the speaker). Conical Dispersion is shown on the left in the drawing below with the black arrows showing the conical -6dB down points. It’s easy to see on the drawing that for a wide dispersion speaker, the conical -6dB measurement points will be up in the air, far above the average listening height. The Conical Dispersion specification is only useful to compare the dispersion of one speaker to another speaker. At Lowell, we call the angle of dispersion with the -6dB points calculated at the average listening height, the Linear Dispersion as shown on the right in the drawing above. The Linear Dispersion angle is usually narrower than the Conical Dispersion angle, but only by using the Linear Dispersion angle in the formulas to determine speaker spacing, will you get an accurate representation of the SPL at the average listening height (where the listener’s ears are). This calculator uses Linear Dispersion data for all speaker spacing calculations. Although the calculator is Lowell product-specific, it’s also useful for general calculation of standardized ceiling speaker products. No login required.
http://www.lowellmfg.com/resources/distributed-speaker-spacingtool.php
