The room modes calculator
This calculator determines the spatial modes or room modes of rectangular rooms. These are frequencies at which an increased reverberation time is determined what usually leads to resonating frequencies in the bass range.
A window shows the arrangement of these important room modes within the range of the frequency. The modes are shown as dashes. Long lines are axial modes (between two walls). The more walls are involved with the mode, the shorter and bluer is the line. The goal is to choose a room dimension that increases the room modes continuously and eliminates (if possible) every gap and cluster.
The “Bonello” window shows this increase of room modes per frequency range in thirds.
The Bolt-Area originates from a period of time when such calculators were not yet possible. In this range (area) an increased amount of rooms is located whose length ratios lead to a more homogeneous distribution of modes.
Furthermore there is a window that accurately indicates the pitch of the selected mode, just like it would be shown by a tuner for instruments.
In the section “Additional data about the room” you can see general information about the room, its volume and the total surface of the walls.
In addition, the calculator lists the modes in a table below. So you can read the determined frequency, the pitch and the indices of the individual room modes again. The latter are describing the situation of the modes in the room.
The location of the modes:
There are three indices in the calculator that are specified per mode.
The first stays for the length, the second for the width and the third for the height of the room. A room mode has on the wall always a pressure maximum.
The indices 1-0-0 represent the first longitudinal mode. That means on the back and front wall are pressure maxima. The mode there is good excitable and audible or measurable. In the middle of the room is a pressure minimum and the room mode there is not audible or excitable.
The 2-0-0 room mode is one octave beyond that. It thus has twice the frequency of the 1-0-0er mode.
0-1-0 stays for the room mode that spans across the width of the room. The maxima are therefore on the side walls. In the center there is a minimum.
0-0-1 finally identifies a room mode between floor and ceiling.
All these modes, which arise only between two walls, as mentioned earlier, are called axial modes. The calculator marks them in red and shows them with the longest line.
1-1-0 for example is a tangential mode. It arises between four walls. In this case in the length and width of the room. Thus between the front and rear walls and the side walls.
The modes arising between all six walls, for example 1-1-1, are called oblique in English (crooked or straight). The calculator shows them with the shortest line. They have on every room limitation a maximum and therefore they are good measurable.
Measuring the room modes:
In principle, if you want to capture all room modes by monitoring, the corners are qualified for that. Put the sound source in one corner and the monitoring microphone in another corner. This reflects then most likely the results of the calculator, namely all modes.
If one wishes to “go into the matter” of a certain room mode, you can see using the index view (as described above) between which walls you can hear (and measure) the curve between pressure maxima and minima.
If you have a fixed listening position, you can of course measure predominantly there. Rarely all modes are a problem at any point.
If you are lucky enough to be able to position your subwoofer flexibly, you can set it up so that it does not excite the possible modes that are problematic at the listening position.