The physical loudspeaker is only half of the loudspeaker system, behind that loudspeaker lies a world of electronics that provides the correct drive signal.
Only 20 years ago there was very little that could be done to assist the drive units in their task, many so-called professional monitoring loudspeakers employed passive crossover units and left amplifier choice up to the customer. It was a total lottery how a loudspeaker would sound in use, and many simple problems were left untreated.
When two transducers are joined at crossover and they exist in different points in space they will interfere with each other as they produce the same sounds at up to 6dB or so to the output of each other. In many cases with passive crossover three and four-way systems this was the entire critical listening bandwidth, the whole system was nothing except temporally dislocated interfering drive units creating a fuzzy mess in the time domain. Furthermore, in some systems out-of-band anomalies with some transducers could be so strong as to return to interfere with other drive units way beyond the expected roll-off frequency. Even in better quality systems where active crossovers of high order (24dB – Oct) were used we could still see high degrees of temporal problems and out-of-band interference where transducers were not correctly and precisely time aligned.
It is no surprise that many multi-band three and four-way passive loudspeakers were said to sound soft, or warm. Any degree of transient accuracy was sadly lacking, transient wave fonts would arrive at the listener dislocated, and often resonating in the passive filters and acoustic systems.
Some 30 years ago, with the introduction of early TEF analysis we could begin to see such issues if we actually looked close enough, although most people did not, but even if we did see the issues there was very little we could do about it with technology of the time.
Active loudspeakers were often constrained to the slopes and frequencies of separately designed active crossover units and the phase differences (if any) between those slopes.
While we knew that dislocating transducers physically in space there was very little we could do within the geometry of the transducers to re-locate them. Even placing transducer’s acoustic source on the same physical planes did not take into account the issues with group delay from the transducer itself, crossover, or cabinet.
It was only about 15 years ago that finally, high quality analysis, and high quality digital signal processing became accessible to the system designer.
Now we are able to study the acoustic slopes of crossover after the drive unit and correctly balance and adapt the drive signal so every single driver can perfectly sum at the listening position.
What is more, we can now choose transducers with superior time response that may not have ideal frequency response and correct those drive units. Previously we were left only to choose drive units with the best frequency response that could not, and cannot, be corrected in the time domain. Thanks to digital signal processing we have a completely different set of design criteria from which we can design far better loudspeakers.
In the past, people tried to correct problems with analogue equalisers, but the crude and limited nature of the equalisers and lack of adequate analysis equipment resulted in horrible degradation of the sound leaving most to conclude that it was better without equalisation. Now thanks to DSP and modern FFT analysis we can create precise and accurate inverse correction of driver responses that when correctly applied not only correct the amplitude response but also correct the phase response.
When properly applied a perfect inverse filter of a minimum phase anomaly will correct both amplitude and phase response. An incorrect filter will not show the same correction in both domains, thus that filter should not be applied.
All Electromotive Laboratories loudspeaker systems use DSP filtering and time response correction responsibly and carefully applied. Each system has had hundreds of hours of tuning and critical listening in many environments to get us to where we are now.
All Electromotive Laboratories loudspeakers use the minimum possible number of crossover points to avoid temporal dislocation of multiple sources. In every case we use super-high-order filters exceeding 48dB octave to reduce the band where possible temporal dislocation of simultaneously generated sound can occur. All Electromotive Laboratories loudspeakers have precise time alignment between bands in the acoustic domain, aligned to within 1/100th of a millisecond resolution.
As critical listening systems we are super critical of the quality of DSP processor, converters and algorithms we use, only the finest sounding components are selected for use within our loudspeaker systems.
It is our opinion that no modern high-quality reference monitoring loudspeaker can perform to its best unless it has adequate signal processing of the drive units. FFT analysis and DSP processing has been the single biggest revolution the loudspeaker industry has experienced since the invention of the moving coil loudspeaker and the transistor amplifier.
A Division of Newell Acoustic Engineering
Funchalinho, Caparica, Portugal