Time Different of arrival between different Sensor Output

Figure 1

The above figure shows that when the sound source near the mic2 instead of mic1, sound at mic2 will receive earlier than mic1 which is counted a smaller micro seconds.

In fact, each analogRead takes around 100 microseconds, which may make a significant error. However, the speed of sound is 343.2 metres per second (1,126 ft/s). The sound would travel only 0.1126 feet during an analogRead() in 100 microseconds.

To implement the circuit hence to receive enough signal, I use four microphone modules which shows in the following.

Figure 2

Figure 3

However, in figure 3, there are some error appointed. Mic4 always acquire signal at the first time although the sound source near mic2.