Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems New firmware release 19th May 2014

There was an intriguing article by the late Peter Mitchell in the December 1995 issue of Stereo Review on the subject of group delay in loudspeakers. Group delay is a measure of how sharply the phase of a signal changes with frequency. Mitchell was an acclaimed audio expert, reviewer, and commentator whose views and writings were very highly regarded. He was a founding member of the nationally-known Boston Audio Society. I remember he caused quite a stir at a Bose press conference several years ago with his pointed, relentless questioning and was summarily banned from all future Bose press events. His passing several years back was quite a loss for the audio enthusiast community.

Bass Reproduction & Group Delay
In this article, Mitchell puts forth the idea that there is a definite correlation between the subjective quality of bass reproduction and superior group delay performance. Speaker systems can be thought of as minimum-phase filter devices, so the magnitude response (amplitude vs. frequency) of a speaker will determine its phase, time (impulse) and group delay characteristics. All things being equal, sealed speakers (2nd -order high pass filters) have superior (lower) group delay characteristics than ported or bandpass systems (4th - or 6th -order high pass filters). As Mitchell�s article states, �Sealed-box�speaker systems consistently have the least group delay (under 10 milliseconds), and they usually deliver the tautest bass transients, the deepest-sounding bass tones, and the most clearly resolved bass textures. Bass reflex and bandpass systems often exhibit substantial group delay [in excess of 50 milliseconds]�and their sound tends to be thicker, fuller, and �slower�.

ENHANCED BASS ALIGNMENT (EBA)
High or low, all sounds travel at the same speed, so all the sounds from a live musical event arrive at your ear at the same time, whatever frequencies they contain. Loudspeakers, however, have a problem when playing low frequency sounds at the same time as mid and high frequencies � the bass arrives late, and the deeper the sound, the later it arrives. This delayed bass causes music to lose its impact and reduces the sense of the recorded space � it is often described as �boomy�.

The goal is to have time-accurate loudspeakers, where all reproduced frequencies start and end at the same time. In a loudspeaker, this timing is affected by the crossover, driver, and enclosure type. To eliminate the delay between low, and mid and high frequencies, Meridian has designed a combination of digital filters and time delays for the mid and high frequencies. This solution enables the mid and high frequencies to �wait� for the low frequencies, delivering perfectly-timed music playback.

Mid and high frequencies are delayed to time-align them, while upper bass is delayed with a special type of patented filter. These features must be implemented entirely in the digital domain, making them impossible to achieve in any passive or analogue-active loudspeaker design.

Enhanced Bass Alignment provides accurate time-alignment of the drivers in the system, delivering exceptional imaging and a clear, transparent, more lifelike sound.