Effect of 440kHz garbage on tweeter distortion?
Following my measurements on Hypex NC400 modules, I was curious if permanent output residuals of class D switching frequency, which I measured 943mVpp at 446kHz, would have any effect on measurable tweeter distortion. Especially taking into account that level of useful audio signal during listening at moderate or low volume would be well below the HF switching frequency residual.
So I prepared a test, where the power amp is driven from a sum of two signals, one comes from the sound card in audio band, the second one from sine generator GAG-810. The level of HF signal was set to get about 960mVpp/440kHz at power amplifier output, and audio signal level was set to get 220mVpp in 1st round and 440mVpp in the 2nd round of tests. The 440kHz HF frequency was switched on and off and measurements taken in both cases. The output was sent to Beyma T2030 tweeter and measured by Behringer ECM8000 microphone, in near field.
Conclusions
No significant effect of 440kHz HF frequency with 940mVpp amplitude was observed in acoustical measurements. Neither in frequency response, nor in distortion plots. My previous suspicion was not confirmed by measurements. Very small differences in harmonics plots are at the limit of repeatability of acoustical measurement.
As I have the setup still connected, please feel free to tell me your suggestions what more you would like to measure re this topic, if you have any.
Images
Measurement setup
Tweeter + microphone
Frequency responses from 5 measurements. Lower, at 220mVpp signal level, HF on/off. Higher, at 440mVpp signal level, HF on/off. HF on/off curves overlap in both cases. Y-axis in dB, but level not calibrated.
Distortion, signal level 440mVpp, HF off.
Distortion, signal level 440mVpp, HF on.
Following my measurements on Hypex NC400 modules, I was curious if permanent output residuals of class D switching frequency, which I measured 943mVpp at 446kHz, would have any effect on measurable tweeter distortion. Especially taking into account that level of useful audio signal during listening at moderate or low volume would be well below the HF switching frequency residual.
So I prepared a test, where the power amp is driven from a sum of two signals, one comes from the sound card in audio band, the second one from sine generator GAG-810. The level of HF signal was set to get about 960mVpp/440kHz at power amplifier output, and audio signal level was set to get 220mVpp in 1st round and 440mVpp in the 2nd round of tests. The 440kHz HF frequency was switched on and off and measurements taken in both cases. The output was sent to Beyma T2030 tweeter and measured by Behringer ECM8000 microphone, in near field.
Conclusions
No significant effect of 440kHz HF frequency with 940mVpp amplitude was observed in acoustical measurements. Neither in frequency response, nor in distortion plots. My previous suspicion was not confirmed by measurements. Very small differences in harmonics plots are at the limit of repeatability of acoustical measurement.
As I have the setup still connected, please feel free to tell me your suggestions what more you would like to measure re this topic, if you have any.
Images
Measurement setup
Tweeter + microphone
Frequency responses from 5 measurements. Lower, at 220mVpp signal level, HF on/off. Higher, at 440mVpp signal level, HF on/off. HF on/off curves overlap in both cases. Y-axis in dB, but level not calibrated.
Distortion, signal level 440mVpp, HF off.
Distortion, signal level 440mVpp, HF on.