Voice Coil Lab Notes: Phase, Group Delay, and Impulse Response - A Quick Primer

This short article by Chris Struck (CJS Labs) is mainly focused on the definition and interpretation of phase, helping to make sense of complex data. This reference article is an expanded version of a previous Lab Note published by CJS Labs, and is certainly a great summary of essential knowledge in speaker design. This article was originally published in Voice Coil, December 2020.

Passive crossover filter networks for multi-way loudspeakers generally require a resistive termination for optimum performance. The driver itself generally presents a reactive load. Inductive rise with frequency above resonance of the loudspeaker electrical impedance is semi-inductive due to eddy current losses. The L2/R2 impedance model represents the electrical impedance as seen by the amplifier output. An improved compensation network can be realized by using the analogous circuit “dual” of the L2/R2 model. This represents a dramatic improvement to the basic two-component Zobel network and compensates for the non-ideal semi-inductive behavior of the loudspeaker driver across the entire frequency band.

Christopher J. Struck (CJS Labs) discusses all options available for headphone testing and calibration. The article discusses what should be included in a complete headphone test system, considerations on electrical impedance, considerations on repeatability of the results, free and diffuse field corrected responses, left-right tracking, and the use of two-tone distortion measurements. Reference reading material. This article was originally published in Voice Coil, July 2019.

A sound source, such as a loudspeaker, will experience an increase in directivity with increasing frequency, as the wavelength of sound becomes small compared to the baffle’s size. Since the baffle the driver is mounted on is larger than the driver, this occurs at a lower frequency than for the driver diaphragm itself. This article was published originally in Voice Coil, July 2016

When performing electroacoustical response measurements, an important practical consideration is the reduction of uncorrelated background noise. Synchronous averaging (i.e., “complex averaging,” “time domain averaging,” or “vector averaging”) is a technique originally developed to analyze the vibration signature or rotating machines and gearboxes. It can be used to improve the S/N ratio measurement. This article was published originally in Voice Coil November 2012.