Audio quality will still be ok at -71 dBm.
In retail environments, there is potential for multipath and an 802.11b client with a non-diversity antenna may not work well unless using the lower data rates only (i.e. 1 & 2 Mbps).
Would recommend to move to the 7925 which offers 802.11a, which is also quite a bit more rugged than the 7920.
Offers Bluetooth for wireless headset communications as well.