Frequency response is a measurement of a device’s magnitude and phase output in response to an input stimulus. It is usually measured in the range of human hearing, typically 20 Hz to 20kHz. A device or system exhibiting a flat response is more accurately reproducing an input through the output without enhancements in a particular area. In other words, a flat response means what comes in goes out. The flatter the response, the more pure the audio. A flat frequency response is important in devices such as loud speakers, monitors and microphones when audio accuracy is desired.
Having said that, a flat response may not necessarily sound “good” to all people depending on the situation – it’s very subjective. Variables such as personal preference, hearing deficiencies and even cultural factors can influence what sounds good to a person. For example, I will use my dual or triple models when I’m playing guitar or mixing music. But I prefer the enhanced areas of the quad driver when I’m listening to my favorite music.
At any rate, a flat response can be used as a good starting or reference point to dial in your preferred sound.
Phase is also an important but often overlooked component of good and accurate sound. Proper phase is what gives accuracy its depth, presence and sound stage. While a device may have a nice frequency response curve, if the phase of the speakers is not correct, it will not sound good. Often, problems with phase will give a muddy or muffled sound, especially at higher volumes.
Below are two monitors with similar frequency response curves. Figure 1 is out of phase but Figure 2 is in phase. The user would detect a noticeable difference in these two devices even though the frequency magnitude is the same.