The advantages and current limitations of sub-band approaches to echo cancellation are reviewed. Polyphase allpass IIR half-band decimators and interpolators are presented. Their performance is compared to QMF structures in NLMS sub-band echo cancellation for hands-free telephone signals recorded in a car. The polyphase allpass IIR case is shown to give around 2 dB more ERLE with one fifth of the number of multiplies compared to direct form QMF.