Sound absorption coefficients of materials

[Analogous]

Some soundwaves (from speakers will arrive directly to our ears but others will bounce (reflected) around the room walls, floor and ceiling to arrive late at our ears, distorted and lower in volume.

Each reflection point consumes a bit of the energy of the soundwave making it quieter – how much is determined by the surface’s material. Wood absorbs more sound than concrete. Glass more than tiles. (Surprise!)

Lower the frequency, the greater the volume of material needed to absorb it. A very low bass sound will pass through a concrete wall and be heard outside, but the high treble will not. Inside the room what is not absorbed by the walls, floor or ceiling is reflected back into the room.

Our brain subconsciously attempt to separate the direct sound from the indirect sound in order to make better sense of it all. But more reverb there is, the more work our brain has to do. So what the room is made of, what is in the room, all it’s surfaces will impact on the sound we hear.

Professional sound engineers say a good-sounding listening room should have a reverb time of 0.3 – 0.7 seconds in the midrange and treble, (300Hz – 4kHz). And that a small amount of reverb is considered a good thing. It adds some life to the music. But too much is definitely bad.

I found this linked to an article by Darko. Here is a list of materials and how their absorption coefficients vary with frequency:

https://acoustic.ua/st/web_absorption_data_eng.pdf

 

[Analogous]

I found this in one of Herb Reicherts reviews (https://www.stereophile.com/content/gramophone-dreams-40-denafrips-terminator-ares-ii )

“ … I assess today's digital products by their ability to recover all the ambient and reverberant information stored in recordings.

All non-anechoic spaces pulse with audible reverberant energy. The complex time and phase relationships of these interacting reverberations are what we use to locate ourselves in our environment and assess our immediate safety. With our eyes closed, audible reflected energy tells us we are in the bathroom not the garden. Most importantly, these intricate patterns of reverberant energy assure us—perhaps deceive us is a better word—into thinking that what we are experiencing is real.

Sound recordings have carefully calculated amounts of naturally occurring and electronically manufactured reverberation. Record producers use reverb to thicken up vocals and locate singers and instruments in acoustic space. Unfortunately, adding reverb is a dangerous proposition. Too much, and the singer loses density and moves too far back in the recording's spatial illusion. Too little, and the singer sounds fake, dry, and disembodied. With the right amount of reverb, the singer displays a lifelike, intimate density. (I am deliberately not mentioning microphone proximity or the grossly audible effects of dynamic compression.)

The biggest challenge for audiophile audio is the proper recovery of all of the reverb captured on a recording—but no extra! I have found that only the finest systems can do this. The less-than-finest systems either subtract reverberant information, as a result sounding dry, gray, and hard; or they add reverb-like distortions (such as second harmonics, phase shift, or microphonics), which make recordings sound wetter or more atmospheric than they actually are.

It's hard to say where recorded reverb ends and system-added "reverb" begins because no one really knows what reverb is on the recording. I think the best way to tell is: If the reverb you hear from your system sounds "whole and a part of" the resonant fingerprint of the recording as a whole, it is likely on the recording. Labels like ECM and 2L make this job easier by employing recognizable house-sound reverb. If the reverb you hear from your system seems different from the whole in form or texture, it is probably added distortion. For example, second-harmonic distortion fills in what would normally be empty spaces and clouds detail like a fog. It sounds limp and de-energized compared to what recording engineers use.

To put the importance of reverberant information in a larger biological context: I believe reverberation is the auditory equivalent of shadows in visual perception. Exactly like reverberant sound, the complex interactions of shadow-matrices supply the primary data that tells our brain where we are and that what we are experiencing is real. In concert with our other senses, shadows and reverberations are the dominant "facts" of our perceived reality.”