Insulation materials is the use of reflection acoustic impedance in a loud voice, in the shadow of the insulation materials have little voice transmission. And sound-absorbing material is sound-absorbing structure and sound-absorbing media to cause infinite sound, that is, reduce the reflected sound waves. The use of both materials have different requirements, a simple swap can not only meet your technical requirements, and may have the opposite effect.
More actual some of example on need with acoustic built die of theory to analysis has, with acoustic of some related of equation solutions is. on took you said of's, if in concert hall in with has noise material, so was Concert Hall is to balance reflection acoustic and infinite far field, with appropriate of sucking sound material elimination not necessary of reflection sound, reached has purpose of reverb field. but if for with has noise material, that is put was to weakened of voice to reflection has back, caused has reverb field of change, Can you hear the music that is a lot of buzz, and always have. General sound-absorbing material in the concert hall is strictly according to the concert hall building structure and main functions correspond to the effects and requirements of the different frequencies of sound absorption and decreased. These are the main purpose of architectural acoustics.
Is true for the sound-absorbing material for railway side. First, I clarify, sound-absorbing material is not totally got no sound, but sound waves at certain frequencies of energy consumed. But others on the not absorption frequency of sound waves is the ability to move through the material. Railway noise frequency rich source of energy, if only using sound-absorbing materials in General, received effects are minimal, set behind the sound-absorbing material (usually residential area) there is a lot of noise. Sound-insulation materials are generally anti-material, it is almost entirely of fully reflect back to the incident sound wave.
Of course, in special design, sound-absorbing material for railway noise can be. Human auditory sensitivity to noise is on in several frequency bands, take advantage of this, you can set the acoustic absorption of these frequency bands on to achieve the effect of noise. Generally more likely to be pure anti-and the combination of the two. I do not engage in railway noise, don't know which they are, but the basic principle is sound-absorbing and reflecting. Rest is material specific to eliminate energy thing.