Definitions for "Flat Response"
A theoretical ideal for audio components, especially speakers, representing a frequency response that does not deviate from a flat line over the audible frequency spectrum when fed a flat-line test signal. While a flat response is ideal, it is impossible in real world listening due to not only the speaker itself but also its interactions with the room and various surfaces within the room. A speaker can often be moved and adjusted to achieve a flatter frequency response within a given room.
An output signal in which fundamental frequencies and harmonics are in the same proportion as those of the input signal being amplified. A flat frequency response would exhibit relatively equal response to all fixed-point frequencies within a given spectrum.
A componet has a flat response when all frequencies are equally emphasized. Having a flat frequency response is a desirable thing.