What will happen if the air filter of Mitsubishi engine is not installed tightly?

My car was not equipped with an air filter once, and the engine sound was different from the original one, and I felt that the power had changed. Later, after the 4s was installed, it was found that the sound was still different from before. When replacing the original air filter, it was still a little loose, and the intake end was always a little loose, but the engine end was quite tight. My conclusion is that air filtration must be suitable and can't be done!