Until recently, the transducers that were available to the hearing aid designer imposed major limitations on the performance which could be offered in headworn hearing aids. Within the last decade, however, these limitations have been largely removed. Today's subminiature microphones and earphones permit a wide variety of hearing aid characteristics, up to and including true high‐fidelity performance: a claim substantiated in recent physical and psychophysical experiments [Killion, J. Acoust. Soc. Am. Suppl. 1 64, S103(A) (1978)]. The usable performance of subminiature transducers may be largely determined by their acoustic couplings—so much so that a meaningful definition of their frequency response requires that the coupling system be specified—and a crucial factor in recent performance improvements has been a systematic examination of the acoustic coupling systems available to headworn hearing aids. While sometimes considered a nuisance or worse, the acoustic couplings can be exploited in hearing aid design to (a) improve directional performance, (b) provide desirable frequency‐response tailoring, and (c) reduce battery drain. Earmold construction in particular becomes increasingly important as the bandwidth of hearing aids is increased. At low (below 1 kHz), medium (1–3 kHz), and high (above 3 kHz) frequencies, the use of earmold venting, damping, and a stepped‐diameter sound channel. respectively, can provide substantial (and predictable) modifications to the real‐ear response of hearing aids; modifications which can often be performed at the dispenser level. Examples of the performance allowed by today's transducers and acoustic couplings will be given.