At a prayer meeting,

At a prayer meeting, the disciples sing JAI-RAM JAI-RAM. The sound amplified by a loudspeaker comes back after reflection from a building at a distance of $80 \mathrm{~m}$ from the meeting. What maximum time interval can be kept between one JAl-RAM and the next JAI-RAM so that the echo does not disturb a listener sitting in the meeting. Speed of sound in air is $320 \mathrm{~m} \mathrm{~s}^{-1}$.