Relative Power Calculator

Determining Transducer Power Requirements

Figure 1. Parameter Input Screen


The Relative Power Calculator program estimates the relative power contained in two filtered pink-noise signals. (Note that Pink Noise is defined as having equal energy in each octave.) It does so by "integrating" to find the area under the two filter-response curves. These areas are then compared. During the integration process a logarithmic frequency increment is used to preserve the "pink noise" character of the "signals" being compared. The program is useful in determining how much power one transducer (e.g. a tweeter) must be able to handle based on the power rating of another transducer (e.g. a woofer), as afunction of the respective frequency bands that each transducer must reproduce and the relative sensitivities of the two units.

Relative Power Calculator is distributed as Freeware. It was written in Visual Basic and runs under the Windows operating system.*

Figure 2: Graph Screen Showing Shape of "IEC Noise" and Ideal Two-Way System

Noise Stimulus:

Three types of noise signals are available: Flat Pink Noise (1 Hz - 100 KHz), Filtered Pink Noise (20 Hz to 20 KHz, 12 dB/Octave) and IEC Shaped Pink Noise, which is filtered to approximate the power spectrum of audio program material. IEC Shaped Pink Noise is often used by manufacturers in the development of power ratings for loudspeakers.


First through sixth order Butterworth filter models are used to simulate anactive or passive crossover system. These filters are also used to define the upper and lower limits of the system stimulus. Flat responses are also available by setting the filter order equal to zero.

Figure 3. Graph of Results from Data Entered in Figure 1


A graph screen allows the user to view the filter responses and relative levels. This is useful as a check of one's input data and provides an intuitive understanding of what's going on.


1. The program cannot take equalization into account. This may strongly affect the relative power handling of the two transducers.

2. Actual drive levels will vary with the impedance of the transducers. This too is not accounted for.

3. All calculations are made for the frequency band of 1 Hz to 100 KHz. Energy contributions outside of this band are not considered. Using "Pink Noise 20-20K" or "IEC Shaped Noise" will further limit the range of the calculation.

*Visual Basic and Windows are registered trademarks of the Microsoft Corporation.

This page Copyright (C) 1998 by Frank Ostrander. All Rights Reserved.