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Room Acoustics

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Postscript

Room Acoustics

Every room has a sound.

Soundwaves inside a room are reflected, absorbed and dispersed by the rooms boundaries, furniture, as well as people inside.

Different rooms sound different.

The sound of a given room is determined by its size, geometry and materials being used, respectively their acoustic behaviour.

1) Size

The raw size determines the resonant frequencies (cavity modes) of the room, which means that a couple of (low) frequencies will be louder than all other frequencies.

A subwoofer is a loudspeaker especially designed to excite cavity modes in a room.

You cannot change the resonant frequencies of a room, unless you change its size (volume).

2) Geometry

The geometry of a room determines the direction of sound reflections. Room geometry is defined by position and angle of walls, floor and ceiling as well as furniture or any object inside the room. You entering a room, change room acoustics in the moment of entering. The most common reflection is that between parallel walls.

3) Material

The material of which the room is made (walls ceiling, floor) as well as the material of furniture or other objects inside a room play a fundamental role in room acoustics. You could call it macro-acoustics.

Technically, a material's acoustic property is determined by its reflection behaviour:

    a) How much of incoming sound is reflected ? -> Absorbtion Coefficient.

    b) In what direction ? -> Dispersion / Diffusion Coefficient.

With the above issues in question a variety of books, software and scientific publications have evolved, all to explain and improve room acoustics for recording, playback or live performances.

So one could have the impression that this area of engineering is well covered. Actually IT IS well covered, but I think, the most important part is missing:



How does the Reflection sound ?

Traditional acoustics is all about size, geometry, absorbtion and diffusion.

It deals with making reflections and resonances go away by absorption and diffusion.

Generally it tries to make things go away.

But after all, the sound quality in a room is determined by the sound quality of the sound source and that of the acoustic reflection. Yes, after all we listen to the source and the reflection.



So Hey, how does the Reflection sound ?

Funny, acoustics don't seem don't deal with that.

You can dampen a bad sounding room as much as you want, it will not sound good. It may sound a little less bad, and a little more dull and this is what we see quite often. Acoustic engineers sometimes overdampen a room, because the reflections inside sound bad.

What makes a room sound good or bad ?

Every material has a vibrational character. When soundwaves are reflected by any material, the reflection is not only determined by the material's absorption- and dispersion-coefficients but moreso by its vibrational character.

Take for example the vibrational character of stone, and remember or imagine the sound of a stone-(cellar) room. How does is sound ? Cold and hard plus echo, I would say. Now cover the room with a wallpaper and imagine again how it sounds... a little warmer and a little softer with a little less echo. Now if you dampen the stone-room with absorber panels, you may well be able to remove the echo, but not the sound character of the reflection. The bad remaining sound may make you dampen more and more, until you find yourself in a dead room, that still sounds bad.

Now imagine a room completely covered with tiles or glass-windows. How would that sound ? Like most bathrooms I would say, lots of echo, distorted mids, bodyless... and not really enjoyable.

Now what about a room completely laid out with raw wood ? It will sound a lot warmer and softer and a lot more like well-being, not perfect... but better. Not yet transparent but also not irritating. Not brilliant but also not distorted. In a word: woody.



What is the Ideal Reflection ?

The ideal reflection is that which exactly matches the Mother-of-Tone character.

A room that is constructed or retrofitted to give the ideal reflection actually is a place of well-being.

Any sound source will be reflected with the highest possible transparence and the best possible sound quality.

There is no physical resistance against the Mother-of-Tone character, as it is the vibrational yardstick of our ears and bodies, against which all sounds are perceived and evaluated.

Joy is the absence of physical resistance, a room with a vibrational character that matches the Mother-of-Tone character actually is a place of ecstasy.



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