We just discussed ultrasonic noise from Class D amps in a different thread but it would probably fit better here.
It seems people are concerned about Ultrasonic noise polution and I want to have a look into that. So it's about HF noise through your speakers from left over switching frequencies (and every design has some of that).
So I made a few quick measurements with an amp of mine based on Hypex NCore. HF peak is at 70kHz and up to 20uV there, summed from 10-90kHz it's about 600uV. 10-20kHz it's about 19uV (15uV(A)) - so the main part of this is actually HF from 20kHz to 60kHz.
So in my opinion that's absoutely no concern about! Actually you have to search hard for tweeters which will do anything at 70kHz (Bliesma T25B can do this).
But there are so many Class D designs out there - what are your experiences and measurements? How doe ICEpower and Pascal modules do in this regard? Or cheaper chip designs? Any measurements available?
It seems people are concerned about Ultrasonic noise polution and I want to have a look into that. So it's about HF noise through your speakers from left over switching frequencies (and every design has some of that).
So I made a few quick measurements with an amp of mine based on Hypex NCore. HF peak is at 70kHz and up to 20uV there, summed from 10-90kHz it's about 600uV. 10-20kHz it's about 19uV (15uV(A)) - so the main part of this is actually HF from 20kHz to 60kHz.
So in my opinion that's absoutely no concern about! Actually you have to search hard for tweeters which will do anything at 70kHz (Bliesma T25B can do this).
But there are so many Class D designs out there - what are your experiences and measurements? How doe ICEpower and Pascal modules do in this regard? Or cheaper chip designs? Any measurements available?
And some HF measurements from tweeters. Some designs do well at very high frequencies like ring radiators but level drops significant.
The graphs are labled which tweeters are measured, hope this is good to read...
600uV vs. 2,83V used here ... that's 73dB less as seen in this graph.
Sorry different scale:
The graphs are labled which tweeters are measured, hope this is good to read...
600uV vs. 2,83V used here ... that's 73dB less as seen in this graph.
Sorry different scale:
It will depend on the kind of amplifier, the building and the luck.
Single ended ones with RF integration filters are good in this aspect. BTL if the RF out of phase in both amplifiers and has both differential and common mode filters are better.
Those IC's now in use in TV sets without filters are really bad.
Also a good shielding is important. A metallic box (Faraday's shield) well closed and with well designed input, output and power lines are the best option.
Single ended ones with RF integration filters are good in this aspect. BTL if the RF out of phase in both amplifiers and has both differential and common mode filters are better.
Those IC's now in use in TV sets without filters are really bad.
Also a good shielding is important. A metallic box (Faraday's shield) well closed and with well designed input, output and power lines are the best option.
Here is an example from Stereophile.
Without the filter, 325mV of ultrasonic noise was present at each pair of loudspeaker terminals, with a center frequency of 396kHz.
https://www.stereophile.com/content/primare-a358-8-channel-power-amplifier-measurements
This amount of noise seems to be typical of Class D. I have no direct experience with Class D amplifiers.
Ed
Without the filter, 325mV of ultrasonic noise was present at each pair of loudspeaker terminals, with a center frequency of 396kHz.
https://www.stereophile.com/content/primare-a358-8-channel-power-amplifier-measurements
This amount of noise seems to be typical of Class D. I have no direct experience with Class D amplifiers.
Ed
That's really a lot. I'm wondering that this doesn't make problems with CE registration (or do they only start with 1MHz?)
On the other hand - 400KHz - no way your middle ear is moving at this frequency, that is mechanical not possible. And your cochlea has no receptors for such a frequency. And a tweeter ... is also not doing anything at 400kHz.
I would not worry about that in terms of hearing.
On the other hand - 400KHz - no way your middle ear is moving at this frequency, that is mechanical not possible. And your cochlea has no receptors for such a frequency. And a tweeter ... is also not doing anything at 400kHz.
I would not worry about that in terms of hearing.
Okay. I omit the word "ultrasonic" when I read the line. That amount of noise is not acceptable at any frequency.
Ed
Ed