There are two issues that need to be addressed:-
1. Early reflections: This affects mid and higher frequencies of the music predominantly. They consist of musical sound waves that are reflected off the walls, ceiling and floor. Hence they reach the ears later than the sound coming directly from the speakers. They are heard within 20 odd milliseconds later than the direct sound and hence perceived as part of the music. This phenomenon typically alters the tonal balance and smears the music either emphasising or attenuating particular frequencies. This phenomenon is called 'comb filtering'. Since this happens across wide band of frequencies which bounce off multiple planes and surfaces of different materials and reach the ears at different intervals with differing intensities, the accuracy of music gets affected significantly.
2. Room modes: This only affects low frequency content of the music. They consist of standing sound waves reinforced by the boundary walls of the listening room and result in uncontrolled and uneven bass response. This phenomenon results in boominess, uneven bass response, obscuring of midrange etc. Even this happens across wide band of frequencies getting reinforced/ cancelled off multiple planes before reaching the ears affecting the accuracy of music significantly.
I'm sharing some links to articles and videos which would give some insights on the following topics:
Acoustics basics:
RealTraps - Acoustic Basics
Early / First Reflection Points:
https://www.youtube.com/watch?v=B9u7k2V4YPw
Room Testing for Bass Trap Placement:
https://www.youtube.com/watch?v=-8OELPNnxWY
Setting up a Listening Room:
RealTraps - How To Set Up a Room
Comb filtering:
RealTraps - Comb Filtering
Modal Ringing and Resonance:
https://www.youtube.com/watch?v=aHkAFSZmMk4
Nonmodal peaks and nulls in a small room video:
RealTraps - Non-Modal Peaks & Nulls
Nonmodal peaks and nulls in a small room write-up:
RealTraps - Presentation Text
Creating a Reflection-Free Zone:
RealTraps - Creating a Reflection-Free Zone
