It gives you a mathematical plot of where the low bass modes will have the strongest deviations (response dips) from the reference level by pinpointing the freqency of each mode at the 1/2, 1/3, and 1/4 points of each dimension of the room.

The 3 numbers note which mode is being discussed by which dimension, he takes it out to 3 modes in each dimension: Room Length (L), Room Width (W), and Room Height (H).

the 1,0,0 frequency is the first mode (which is the strongest mode) by length and gives you a frequency that is affected at the halfway point between front and back. If the length is the longest dimension, then his is going to be the lowest freqency mode, and if you placed your sub and/or yourself on this exact point, you will have the worst deviation along that dimension (at any width and height) from reference at the freqeuncy listed.

0,1,0 repesents lists the calculated frequency of the first mode by the width of the room, and 0,0,1 is the calculated freq of the first mode by the height of the room.

First mode is exactly the halfway point of the listed dimension, Second mode is at the 1/3rd and 2/3rd points of the listed dimension, and third mode falls on the 1/4, 1/2, 3/4 points of the noted dimension.

If you were to sit at the exact center of the room, at the halfway point of both length and width and halfway between the ceiling and floor, then the you will have issues at the 1,0,0; 0,1,0; 1,1,0; 0,1,1; and 1,1,1 frequencies. This is the worst spot in the room as far as smooth response is concerned, but you would be surprised how many theater chairs in "professional" rooms are almost right on this exact spot.

All of these calculations are valid IF the walls, floor and ceiling are completely solid and reflective to these frequencies...

The modes still exist either way, but the variations depend on how greatly the construction affects these freqencies. Using traditional construction with drywall spaced on studs and joists creates hundreds of diapragmatic absorbers for bass frequencies at different points in the room, plus the lowest frequencies pass through these materials and should be correctly measured to the nearest solid surface behind these materials. Each of the "absorbers" mentioned is roughly tuned to the height and width of the unsupported span and the depth of the cavity behind it.

This calculator only goes to about 150hz or so, because it uses the theory that bass frequencies are omnidirectional (travel in all directions at the same intensity), and are reflecting 100% of the energy from each wall/ceiling/floor surface.

For midrange and HF modeling, you have to take dispersion characteristics of the speaker(s), and the reflection vs. absorption characteristics of the room's surfaces into account to accurately model, and even the most scientific modeling software is an educated guess at best.

If you desire, you can take grid paper and layout the room in 3-D, draw in the 1/2, 1/3, and 1/4 dimensions, and then color code the modes by frequency and see if and where they stack up.
In theory the second mode is half as strong as the first and the third mode is half as strong as the second, so attention to first and second modes for the subs and the money seat(s).
The goal is to place the sub(s) and seating locations in the gaps for the smoothest response. This is why the "magic formulas" for room dimensions don't mean sh*t unless there are also sub and and seating location recommendations for that specific room dimension.

This message was edited by 2nd rick on 03/06/05 21:47 ET.