Acoutsic

Underlays will have some sound reduction, or acoustic properties, any carpet underlay will prevent some sound being transmitted. A real problem is where flooring is laid in a flat/apartment, and the people underneath can hear the constant movement of feet.  Sometimes in your contract, laminate flooring is not allowed.

 

The right underlay can help. There are a variety of types of acoustic underlay. Different sellers will either have their own brand, or similar products will be sold under different names. There are two types of sound reduction.​

Sound impact. This is where the underlay stops the sound hitting the carpet being transmitted too far. For example, the sound of moving furniture. Some underlays only help with sound impact. This is common with, for example, felt underlays.​

Sound absorbing, or airborne reduction. This is where the carpet underlay goes some way in absorbing some of the noise in the air. For example, the noise of someone snoring in one room won't be transferred to another. Airborne noise comes from common sound sources such as voices, TVs and radios.  
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The higher the Db number next to the specification of the underlay, the better. For example, number of 24 shows that the underlay reduces the sound by 24dB. However, this is quite a simple way of looking at it, as the true measurements are made at specific frequencies. Best to check the technical stuff with your supplier, to be sure.