By system delay we mean the time it takes to send a short pulse through the system under consideration. It is also called ‘time of flight’ or ‘initial time delay’.
If measuring using a loudspeaker and a microphone, the system delay is given by the distance from the loudspeaker to the microphone.
The system delay in seconds is given by the formula:
Delay = Distance \ Speed of sound
For example, if the distance is 34 meter (100 feet), the delay is 0.1 seconds when the speed of sound is 340 m/s (1115 ft/s).
In many cases, e.g. if you are performing a vibrational measurement and the transducers are positioned near each other, the system delay is so small that it can be ignored.