How to prove or disprove findings on echo ranging formula?

Question

Can someone please help me figure out if my answer is correct.

Question:
What is the echo time if I snare a drum in the hall outside the room which is 80 meters long. The average echo time was 10 milliseconds. Use Echo Ranging formula to prove or disprove my findings, remember this echo was heard in air.

My answer:
I wrote formula d= r x t
d= 160m ( because 80x 2) the sound must travel back
t= 10 ms = 0.01 seconds
c = 16000m/s ( answer)

Under ideal conditions, this appears to be wrong. As the speed of sound in air travels 344m/s in dry air (temperature of 20 °C (68 °F)). So either the time or the distance measurements are incorrect.

Answer 1

You must be using electronic equipment to measure such a short time. Perhaps this equipment displays only the time of the first echo, which might have come from some sound-reflecting surface at only 0.01*0.5*344 = 1.7 m distance, such as a nearby wall, or the ceiling or the floor. I've done similar experiments outdoors at a distance from a large brick wall, clapping my hands. The results were close to what the formula predicts. If the equipment has an analog amplitude-vs-time display, did you look for an additional echo, possibly a lot fainter, with about a half second delay? Possibly if there's limiting in such equipment, the nearer echo might have driven the gain too low to see the farther one. Can you hear a half-second echo? Maybe you should repeat the experiment outdoors, using a brick wall with not much other clutter around.