Use the Single Dimension tab to enter either the length of a room dimension (often the longest dimension, to estimate the lowest axial mode) or the corresponding fundamental axial mode frequency. The calculator will compute the other value. Use the Room Modes tab to calculate the primary axial mode frequencies for each room dimension.

Room Resonant Frequency Calculator

Single Dimension
Room Modes

Enter any 1 value to calculate the missing variable

Room Resonant Frequency Formula

A room has many resonant frequencies (modes). The formula below calculates the fundamental axial mode for a single room dimension (a 1D standing wave between two opposing surfaces).

\text{RRF}=\frac{c}{2L}\approx \frac{1130}{2L}

Variables:

  • RRF is the fundamental axial mode frequency along the chosen dimension (Hz)
  • c is the speed of sound in air (the calculator uses c ≈ 1130 ft/s ≈ 344 m/s; actual c varies with temperature and humidity)
  • L is the length of the room dimension (use consistent units with c; if using 1130 ft/s, then L is in feet)

To estimate the fundamental axial mode frequency for a given room dimension, divide the speed of sound by the product of 2 times the dimension length. Using c ≈ 1130 ft/s and L in feet yields the frequency in Hz.

How to Calculate Room Resonant Frequency?

The following steps outline how to calculate the fundamental axial mode frequency for a single room dimension.

  1. First, determine the length of the room dimension (often the longest dimension for the lowest axial mode).
  2. Next, choose the speed of sound (c) to use (a common room-temperature approximation is 1130 ft/s).
  3. Next, gather the formula from above: RRF = c / (2·L) ≈ 1130 / (2·L) (when L is in feet).
  4. Finally, calculate the frequency.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

length of the room dimension (ft) = 15

RRF =  1130 / (2*L) = 1130 / (2*15) = 37.6667 Hz (≈ 37.67 Hz)