RealTraps - Frequency/Distance Calculator

Calculate Quarter-Wavelength Distances



"This program displays all quarter wavelength multiples from 1/4 through 9/4 as either frequencies or distances."



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Frequency/Distance: Click the image above for a full-sized version.

Click HERE to download the Windows version of our Frequency/Distance Calculator (1.3 MB). There's nothing to install - just Unzip the files into any folder, then run the freq-dist.exe program file. If you have a slow dial-up connection you can click HERE to download the older DOS version of the program (only 34 KB).

Reflections off the wall behind you create peaks and deep nulls at predictable distances from that wall. If you know how a "flanger" recording studio effect works, acoustic interference is very similar. In a flanger the original signal is sent through a short delay, then the original and delayed versions are combined which creates peaks and deep nulls. The same thing happens with reflections off a rear wall, though in that case the delay and combining happen acoustically in the air.

This program accepts a fixed distance you enter, and from that calculates a series of quarter wavelength frequencies. Or, optionally, it converts a single frequency to a series of quarter wavelength distances. It is intended to help you analyze a room's low frequency response, to determine if a particular peak or null is modal or non-modal. We wrote it for our own needs, but it's so useful we wanted to share.

For example, let's say you measure a deep null at 100 Hz at a distance of 34 inches in front of the rear wall. This calculator will confirm that 34 inches is indeed 1/4 wavelength at 100 Hz. So in this case the null is not necessarily caused by a room mode, but rather by the listener's distance from the rear wall. (Nulls are common at other odd multiples from the rear wall, such as 3/4 wavelength, 5/4, 7/4, and so forth.)

The program displays all quarter wavelength multiples from 1/4 through 9/4 as either frequencies or distances. It's very clever because you can enter either a distance or a frequency - then it figures out what you entered and displays the opposite series of parameters.

This program is also useful for predicting SBIR frequencies and distances. SBIR stands for Speaker Boundary Interference Response, and it describes the peaks and nulls whose frequencies are related to the distances between the loudspeakers and nearby room boundaries. LBIR is similar to SBIR, where L refers to the Listener. In this case the program will help you identify peak and null frequencies related to the listener's distance from the room boundaries as described above.

Please understand that the true frequency response at any given location in a room is the sum of the direct sound plus many competing reflections from all of the room's boundaries, not just the one surface that is nearest. Top

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