Studios and home theaters tend to need different approaches to room treatments but the acoustics are basically the same.

In room acoustics, where a loudspeaker is the sound source and there is a well defined listening position, the reflected sound forms a critical acoustic fingerprint for the listener. They are:

• Early or primary reflections
• Secondary reflections
• Diffuse field reflections

Direct sound waves reach the listening position first by virtue of the shortest path. The sound a person experiences is always a mixture of direct and reflected sound. The ratio between the two is dependant on the listeners distance to the loudspeaker.

Early reflections are the first reflections from room boundaries to arrive at the listening position. Our animated room graphic below shows what typically happens in small rooms. The first and loudest early reflections (in red) come from the side walls because that is the shortest reflected path between the loudspeaker and the listener. On the response chart the first loud spike represent these early reflections. Many more early reflections follow in decreasing amplitude reflected from transverse angles other room surfaces further away.

Secondary reflections arrive behind the early reflections. The second large spike on the chart represents secondary reflections from the rear and side walls. The brain uses information provided by secondary reflections to gauge the size of a space. The longer the delay between the impulse wave and secondary reflections the larger the room.

The brain knows that, having traveled further, secondary reflections are naturally weaker. This poses an acoustic problem for studios and home theaters. The close proximity of the rear wall can set up a situation where the secondary reflections arrive with as much or more energy than the early reflections. The brain tries to deal with the unnatural acoustic but eventual ear fatigue results.

Diffuse field reflections are a complex propagation of the acoustic energy between many room surfaces. The time interval between reflections is overlapping and the ear hears the multitude of reflection as a single wash of room reverb. This is shown on the chart as a dense field of low amplitude spikes. They are much weaker now, having bounced off of two or more surfaces, and eventually fade away altogether.

These diffuse reflections also carry information about the acoustic space to the brain. There is a natural attenuation of very high frequencies in the diffuse field time region because of the directional characteristic of high frequencies and their nature to be absorbed by soft materials. Since diffuse reflections have bounced off of more surfaces there is more opportunity for high frequencies to be absorbed.