Several common questions are often asked related to loudspeaker sound reproduction, such as:
1. Why does a loudspeaker sound different when moved to another room?
2. Why does my new bookshelf loudspeaker sound terrible at home? They were great in the showroom!
3. Why does the loudspeaker sound muddy/bassy inside a room? It was great when I listened to it outside.
There are other questions, but readers can get the point from the examples above. Often a loudspeaker is being evaluated for how well it reproduces sound, but the room seldom comes into the discussion. This article discusses how loudspeakers and rooms interact.
Outdoor vs. Indoor Impulse response (IR) is the response of a system to an impulse, usually plotted in a time domain graph (amplitude vs. time). The input impulse has specific characteristics: it contains all frequencies, it has the same energy at all frequencies, and an infinitesimally short duration.
This perfect impulse is also called a Dirac function. It’s also good to understand that a loudspeaker is usually designed, measured and specified in a free space condition. The term free space condition simply means no reflections.
A true free space condition does not include any reflections, including floor reflection. Therefore a theoretical free space will be a sound source hanging in the air, far (greater than 10 m away) from boundaries.
When a sound source is created in confined in a room, sound will bounce from walls, floor, ceiling, and furniture, etc. Like a microphone, our ears hear all sounds in a room: direct sound and room reflections. The room reflections will affect the frequency response of the loudspeakers.
A common misunderstanding is thinking that electronic corrections such as EQ or other electronic processors can be used to fix/eliminate room reflections.
Acoustical distortions are best handled with acoustical treatments, finding better source/listener positions, selecting appropriate loudspeakers (for bigger rooms) and lastly, digital correction.