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Loudspeaker measurements and performance metrics

Introduction

Accurate measurement of speakers is vital for understanding their performance and ensuring optimal sound reproduction. By quantifying parameters like frequency response, sound pressure level, directivity, sensitivity, distortion, impedance, and dynamic range, objective speaker measurements provide valuable insights into their quality. This article explores the setup, techniques, and parameters involved in loudspeaker measurements, helping users make informed decisions when selecting and optimizing speaker systems for various applications.

Measuring setup

Loudspeaker measurements are conducted in controlled environments like an anechoic chamber or semi-anechoic room to minimize room reflections. Additionally, using a Klippel Near-field Scanner (NFS) offers the advantage of measuring loudspeakers not only in an anechoic chamber but also in a regular listening room. During the measurement process, a known and controlled test signal, such as a swept sine wave or pink noise, is used to drive the loudspeaker. This allows for accurate and reliable measurement data. Finally, a high-quality calibrated microphone captures the emitted sound, providing valuable information for further analysis and evaluation.

Measurement software

Specialized software, such as Room EQ Wizard (REW), facilitates test signal generation, microphone response capture, and performance parameter calculation. This software enables detailed analysis of frequency response, distortion, directivity, impedance, and more.

Performance Metrics

Frequency Response

Frequency response is a fundamental and essential measurement metric for evaluating the performance of audio systems, including loudspeakers. It provides valuable insights into how accurately a speaker reproduces sound across the audible frequency range. A flat frequency response indicates that the speaker is reproducing sound without significant emphasis or attenuation at specific frequencies, resulting in a more faithful and balanced sound reproduction. Evaluating the frequency response helps identify any potential irregularities, peaks, or dips in the speaker’s output, allowing for adjustments or optimizations to ensure a more accurate and enjoyable listening experience.

Sound Pressure Level (SPL)

SPL measures the loudness or volume a loudspeaker can produce, quantified in decibels (dB) and representing the output power. Higher SPL values indicate a louder sound output capability. In practice, loudspeaker manufacturers usually report maximum SPL for their speakers. 

Directivity

Directivity describes how sound is dispersed or radiated in different directions by a loudspeaker. It measures the degree of forward bias in the radiated sound, comparing the on-axis curve to the sound-power curve. A speaker with good directivity fills the room with sound more evenly, reducing the subjective impact of the listening spot.

Sensitivity

Sensitivity, a crucial measurement in assessing loudspeaker performance, reveals the efficiency with which electrical power is converted into sound output. Typically expressed in decibels (dB) at a specific distance, it denotes the sound level produced by a given input power. A higher sensitivity rating indicates the loudspeaker’s ability to deliver louder sound with less input power. To measure sensitivity, a microphone is positioned 1 meter away from the loudspeaker, while a 1W sine wave signal at 1 kHz is applied. In the case of piezo speakers, achieving the desired 1W power level involves incorporating a series resistor, facilitating current and phase angle measurements in the RC circuit. This setup enables accurate assessment and adjustment of power consumption. Additionally, it is important to note that the sensitivity of a flat panel piezo speaker is influenced not only by the piezo exciters but also by the size and construction of the panel itself.

Distortion

Distortion refers to unwanted changes or additions to the original audio signal, affecting sound quality and fidelity. Low distortion levels ensure accurate reproduction of audio content.

Dynamic range

The dynamic range of a loudspeaker represents its ability to reproduce a wide range of sound amplitudes without distortion or loss of fidelity. It spans from the lowest level (noise floor) to the highest level (maximum output). Dynamic range is evaluated by testing the loudspeaker’s response to varying amplitudes in test signals.

Impedance

Impedance measures the resistance a loudspeaker offers to electrical current flow, expressed in ohms (Ω). Matching the loudspeaker’s impedance to the amplifier’s output impedance ensures optimal performance. Impedance can be measured using an impedance analyzer. 

Conclusion

Loudspeaker measurements are essential for objective assessment and prediction of subjective preferences. Through careful setup in controlled environments, such as an anechoic chamber, and the use of specialized measurement software, various performance metrics can be accurately evaluated. These metrics include frequency response, sound pressure level, directivity, sensitivity, distortion, impedance, and dynamic range. By understanding and analyzing these measurements, users can make informed decisions when selecting a loudspeaker that meets their specific needs, ensuring optimal audio reproduction and an enhanced listening experience.

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