How to Interpret a Loudspeaker’s Frequency Response Range

A loudspeaker’s frequency range is usually specified together with an allowable sound pressure level tolerance, such as 500 Hz to 20 kHz (±3 dB). This means that within the specified frequency range, the frequency response remains within 3 dB above or below the reference sound pressure level. Therefore, the overall response is relatively flat, without significant variations in output level. For example, if a loudspeaker produces a reference sound pressure level of 90 dB with a 1 W input measured at a distance of 1 m, while the sound pressure level at 500 Hz is 87 dB, the difference is 3 dB and still meets the ±3 dB specification. It should be noted that ±3 dB represents the allowable variation above and below the reference level. Therefore, the maximum difference between the highest and lowest points of the response curve may be as much as 6 dB. The smaller the allowable dB tolerance, the stricter the requirement for frequency response flatness. According to relevant IEC standards, the effective frequency range may also be determined using the frequencies at which thesound pressure level falls by 10 dB relative to the reference level. If an out-of-range variation occurs only within a narrow frequency band of less than one-ninth of an octave, it may be treated as a localized peak or dip and excluded from the primary determination of the effective bandwidth.