In space, there is no medium for sound to propagate, as sound requires a medium (such as air, water, or solid materials) to travel through. In the scenario you described with a metal rod, if you were in a vacuum or space environment and somehow managed to create vibrations or sound waves in the rod, those waves would not be able to propagate because there is no material medium to carry the vibrations.
However, if we were to consider a scenario in which the metal rod is in a different environment, like on Earth, and sound waves can propagate through the rod, the restriction in the center of the rod would indeed affect the sound intensity on the other end.
When a sound wave encounters a restriction or change in the medium, such as a narrowing of the rod, several things can happen:
Reflection: Some of the sound waves may get reflected back towards the source due to the change in the impedance of the medium at the restriction.
Diffraction: Sound waves can bend or diffract around the restriction, leading to changes in the propagation direction and potentially causing some sound energy to be redirected towards the other end of the rod.
Absorption: Depending on the material properties, some sound energy might get absorbed or dissipated within the restriction.
Attenuation: The presence of the restriction can result in a reduction in the amplitude (intensity) of the sound waves as they pass through it due to scattering and energy loss.
The degree to which the sound intensity is reduced on the other end of the rod will depend on various factors, such as the size and shape of the restriction, the material properties of the rod, and the frequency of the sound wave. Generally, for a well-designed system, the sound intensity would be reduced, but the exact reduction would depend on the specific details of the setup.