In this case, I would like to take a look at how different materials absorb different frequencies. This will help you to understand how softer items, like upholstered furniture, might differ from doors and how doors differ from concrete. The numbers listed in this chart are the "absorption coefficients" of these materials.
To give you an idea of how it works, carpet, the first item on the list has an absorption coefficient of 0.01 for 125Hz frequencies. That means that it will only absorb 1% of a tone at a frequency of 125Hz. It will absorb 2% of a 250Hz tone, 6% of a 500Hz tone, 15% of a 1kHz tone, 25% of a 2kHz tone and 45% of a 4kHz tone.
It becomes easy to tell that some materials absorb a good percentage of some signals, but reflect a good percentage of other signals. Remember that any percentage of the signal that is not absorbed is reflected.
The reason we start learning echolocation using hard flat objects is because of the fact that, as you see below, things like glass only absorb 2-3% of most frequencies and are therefore very reflective, or responsive. As opposed to things like upholstery and people which absorb at least 25% of most frequencies, and up to half of some of the higher frequencies.