A Bessel filter is a linear filter that is used in electronics and signal processing and has a flat group delay (also referred to as a maximally linear phase response). These filters are commonly used in audio crossover systems and preserve the wave shape of any filtered signals across the group delay in the passband.
Who Invented the Bessel Filter?
The Bessel filter is named after Friedrich Bessel, a German mathematician who lived from 1784 to 1846 and created the mathematical theory that the filters used today are based on. The filters are also referred to as Thomson or Bessel-Thomson filters because of W.E. Thomson’s work. He was the first person to apply the Bessel functions to creating a usable filter.
What is an Audio Crossover?
An audio crossover is an electronic filter that is used in audio applications. Since most speaker drivers cannot cover the entire audio spectrum with the correct distortion control and volume range, they use a combination of speakers and drivers to do so. Audio crossovers can split the audio signal into different frequency bands that can then be routed to the speakers that are optimized to use these bands while playing music. Audio crossovers also permit multi-band processing and amplification when the signal is split into adjusted bands before they are mixed together as is done in Dolby A noise reduction.
What Does an Audio Crossover Filter Do?
Audio crossovers can split incoming audio signals into separate bands that cannot overlap. This improves the audio equipment’s performance. A stereo system uses one of many crossover filters depending on the complexity of the stereo equipment being used. Typically, a two/three way crossover filter is constructed using low-pass, high-pass, and band-pass filters where applicable. The 4-way crossover filter is not common in industry due to its complexity and the cost for minimal performance gain to be realized. Bessel filters are typically used as second order filters in the crossover and are the second most used type after the Butterworth filter.