Total Harmonic Distortion THD
If everything works well, then your speaker THD curve will show nothing too abnormal and be at a low level. A good THD level to aim for as a speaker engineer is a distortion level of at least -40dB from your fundamental frequency, which equates to a distortion level of 1%.
As an audiophile, if you are concerned about THD and comparing speakers, then the lower the THD value the better.
Second-order or ‘even’ harmonics are even-numbered multiples of the fundamental frequencies and create a rich, pleasing sound.
Third-order or ‘odd’ harmonics are odd-numbered multiples of the fundamental frequencies, which give the signal an edgier, more aggressive sound.
THD+N = Total Harmonic Distortion + Noise
SINAD
-
120dB (>20 bits): Provably inaudible noise and distortion.
- 109dB—119dB (18 bits—20 bits): Well beyond 16-bit (CD) resolution.
- 96dB—108dB (16 bits—18 bits): Meets and exceeds 16-bit (CD) resolution.
- 85dB—95dB (14.3 bits—16 bits): Does not meet 16-bit (CD) resolution.
- <85dB (<14.3 bits): Performance is below the minimum lenient threshold defined in this thread.
THD+N <0.0001% Great 0.0001% - 0.0004% Well beyond 16-bit (CD) resolution 0.0004% - 0.0015% Meets and exceeds 16-bit (CD) resolution 0.0015% - 0.0056% Does not meet 16-bit (CD) resolution > 0.0056% Bad
Thresholds
Lenient
Dynamic range, linearity: 96 dB
THD, IMD (intermodulation distortion): -66 dBFS / 0.05%
Noise: -85 dBFS / 0.005%
SINAD: 85 dB
Crosstalk: -60 dBFS
Jitter: -110 dBFS, -100 dBFS around the main tone
Frequency response: ±0.5 dB
Channel balance: 1 dB
Output impedance: 2 ohms
Strict
Dynamic range, linearity, SINAD: 120 dB
THD, IMD, noise, crosstalk, jitter: -120 dBFS / 0.0001%
Frequency response, channel balance: ±0.1 dB
Output impedance: 0.16 ohms