Loudspeakers for AEC: Measurement and Linearization

The performance of an AEC is hard-limited by the loudspeaker’s non-Linear-Time-Invariant-ness (non-LTI-ness), which is researched.

The performance of an AEC is hard limited by loudspeaker’s non-Linear-Time-Invariant-ness (non-LTI-ness). The assumption of “all loudspeakers are sufficiently LTI and essentially the same” had been been useful only for poor, essentially half-duplex AEC.

Its validity is being verified on the sample of various 3"...5.25" loudspeaker drivers (plus about 10 more ommited as copycats):

- ADAM X-ART F5

- ADAM X-ART F5 AMT tweeter

- AIYIMA MJD4

- AIYIMA 3.5" silk film 12 Ohm 50W

- Bowers & Wilkins CWM-650 tweeter

- Focal PS130F

- Gooldwood Sound GW-205-W

- Gooldwood Sound GT-501

- HIVI Research DM-7500

- Infinity 4032

- LABO LB-PS1401D

- PYLE PRO PDBT19

- SB Acoustics SB12CACS25-4

- Sounderlink AMT-920 (aka NEO8)

- Vifa (Tymphany) NE95W-04

- JmLAB Spectral 908.1 as the reference.

LTI distortions vary wildly between loudspeakers. They can not be easily identified during a “regular” teleconferencing. Therefore, for an AEC striving to perform in the maximally transparent full-duplex mode, the aforementioned assumption is wrong and must be explicitly discarded. An adaptive filter can be more or less generic but a good AEC can not be generic. A better-performing AEC must be tied to a specific hardware.

Generally, there is not much point in improving AEC without improving loudspeakers first. However, beside using better and very expensive drivers, we can reduce LTI distortions by current driving and relatively simple cone mods shifting cone resonances to higher frequencies and damping them.