7--Fletcher-Munson Curve
Humans don't hear all frequencies of sound at the same level. That is, our ears are more sensitive to some frequencies and less sensitive to other frequencies. In the early 1930's Dr. Fletcher and Dr. Munson, audio pioneers at Bell Labs discovered that the human ear hears differnetly at varioius loundness levels. At 130+ dB SPL we hear almost flat. But we hear lows and highs poorly at lower volumes (lower SPL) and it gets worse the softer the sound. To complicate matters further we all loose our hearing above 14,000 Hz as we age!
The important thing to understand about sound is the volume (in SPL) affects your perception of bass and treble response significantly. What sounds quiet one way, sounds different loud. The same thing is true for sources and microphones. A mic that sounds good at low level may sound terrible at high level! Fletcher-Munson also discovered that the dynamic range of the human ear was 120 dB!
Which Is Best Flat Or Shaped
Choosing the right response profile depends on the sound source and the surrounding environment where it is used. Wide, flat frequency responses are most appropriate for music where a wide range of frequencies are being produced---classical music, symphonies, violin solos, etc. But a flat microphone usually is not what experts pick for sources that have a more limited frequency response. A "shaped response" with a boost in the response in exactly the correct place, is usually the best sound for voices. Most microphones do not have this shaping, or rise in response, in the correct place of the response curve.
Two of the most popular dynamic mics in the world are prime culprits examples of this. You will see these stuck in front of guitars, amps, drums and worse--- pianos. The sound engineer has paid no attention to the fact these microphones have a terrible mid range peak in the wrong place. Couple this peak with the built in proximity effect and the instrument you are trying to amplify ends up sounding nothing like the original! Louder for sure but not pleasant to listen to. A popular dynamic on a snare drum has no "snap" and the snare actually become honky sounding because the microphone has a 3K response rise. This is over 30-yearold technology and its time things change.
After several years of experimenting and listening, the Heil Sound team discovered that most of the old line favorites have their frequency response in the wrong place. Just about every dynamic microphone has a mid-range response peak that is in the wrong place. The peak is too low in frequency and therefore adds a nasal, hollow sound to the source it tries to reproduce. As a consequence, these popular microphone have to be equalized heavily to sound proper. The large diameter Heil dynamic mics have placed a small rise in exactly proper frequency which gives it a perfect natural sound, without any equalization.
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