When watching space rocket launches on TV, we typically do not hear sonic booms when they break the sound barrier for a few reasons:
Distance: Most space rocket launches occur from launch pads situated at a considerable distance from the viewing areas. By the time the sound reaches the viewers, it has significantly attenuated, making it too faint to be audible.
Camera Microphones: The microphones used to capture the audio for television broadcasts are often directional and focused on the launch pad or the immediate surroundings. The sound of a sonic boom, which travels outward in all directions, may not be adequately captured by these microphones.
Speed of Sound: The speed of sound in Earth's atmosphere is around 343 meters per second (about 1,125 feet per second). A rocket launched from the surface of the Earth can achieve speeds far greater than this, especially during the ascent phase. As the rocket moves away from the viewing area, the sonic boom generated by it may not reach the viewers in real-time.
Sonic Boom Altitude: Sonic booms are typically generated at higher altitudes, where the rocket is flying at supersonic speeds. The sound of the sonic boom may not propagate effectively through the lower layers of the atmosphere to reach the viewers on the ground.
Sound Suppression: Some rocket launch sites employ sound suppression systems to mitigate the intense noise generated during liftoff. Water deluge systems or other methods are used to dampen the acoustic energy, which can reduce the intensity of any sonic booms as well.
Broadcast Delays: Live TV broadcasts often have slight delays for various reasons, including the need for some censorship and editing. These delays might further reduce the chance of hearing any sonic boom sounds in real-time.
It's worth noting that sonic booms can indeed be heard during certain rocket launches, especially in the vicinity of the launch site or in areas with favorable atmospheric conditions. However, for the majority of televised space rocket launches, the sound of the sonic boom is not a prominent feature in the broadcast audio due to the factors mentioned above.