I get the feeling that, since the white noise sounds very different AND the dips in the frequency graphs are different for both amps, he did not use the exact same mic position for both amps... These dips in the higher frequency are cause by destructive interference of sound waves coming from different directions (both refections and interference between the left and right channel). He seems to interpret them as a difference in frequency response between the amps but they are actually caused by a difference in mic position/height.
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Amplifier measurements may require improvement
- Thread starter Djano
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Another Junk video without clear methodology. There are many non-controlled parameters when measuring an amplifier over loadspeaker via microphone. The result says nothing. Maybe the Yahama amp graph version is bad too.
Hm, trying to understand your statement for more power at 40 Hz. If the speaker delivers less SPL at 40 Hz then more power is only possible either when the music material has loud bass content or an equalizer enhances the bass region. Otherwise loudspeakers have more impedance due to resonance at low bass and therefore draw less current. So the amplifier provides less power.I already run a test to cover what is happening here. From the review:
Look at the line in orange. it is the response at 20 Hz. See how it clips earlier. Almost every amplifier I have tested does the same thing. For a while I was noting the max power at 20 Hz.
Above is why I say you need more amplification power than you may think you do. This has nothing to do with Class D vs others. Simple fact that most music energy is at 40 Hz where speaker response is weak. So you need a lot of power to push that response to your ears.
- Thread Starter
- #63
This would be a huge methodological mistake. It seems obvious to me that the microphone should not be moved between tests.
I don't even see the point of moving it. Just plug in the other amplifier and rerun the test: why bother moving the microphone?
But, yes, it could be that...
@Holdt is right: @SimpleTheater needs to clarify this point.
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Ha, forgot about that stalker feature!
Nothing changed. Nothing was moved. Notice the only difference between the tests at the low range of frequency response was when pushed to 100+ dB. In the other tests they measured nearly identical. So this is an issue with the FOSI amp when pushed to its limits.
Please watch the video. 48 volt 5 amp ps.
Any chance you can measure the impedance of your speakers? It would be very helpful to see impedance and phase (and maybe calculate EPDR) to get a feel for how difficult of a load they present.
Would also be great to do the same sweeps and measure the voltage at the amplifier terminals as suggested by @pma. Ideally you would do this with a voltage divider into a soundcard so you can see a detailed plot of output voltage vs frequency.
Thanks for joining in the discussion!
Michael
ta240
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It is the old "we don't know what we don't know". What other 'aspects' aren't being tested that we haven't realized yet.
Reason for this was that the REW tests were done with a UMIC that didn't move, but that doesn't capture audio for the video. I was using both the camera's mic and a Blue Yeti for the video. Good catch btw.
Integrated Amplifier Comparison: $90 vs $9000
I continue to hear differences between amplifiers that might be expected to be inaudibly different. That is, for two high-SINAD systems that I'm not running into clipping, I hear differences. I also believe in measurements. My perspective has been consistent: "Everything that can be measured...
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This was the Fosi V3 versus bridged HypeX NC500.
I suspect that the Fosi V3 is more reactive with reactive loads. I did NOT see this problem on my similarly conducted experiment with a microphone, which doesn’t move (though I am physically in the room and physically move which can affect reflections potentially).
My null testing was perfect in the range described here. So this suggests two things
1) My test methodology was decent. If I grossly misrecorded the two amplifiers, you would not see any matching in the null test.
2) I only saw a 2 dB difference in the bass. Again, a really clean null comparison that can be argued that it may or may not be audible but is an accurate reflection of a difference in the performance of the amp. In this case, the Fosi put out MORE bass which might suggest that it is USING UP its power reserve.
3) There is no way to make sense of the midrange/treble in my test. Any real differences are also masked by test methodology. There could be differences. There might not.
In any regard,
1) there is no free lunch. If you want a transparent amp that doesn’t have any gotcha’s, the Benchmark AHB2 has stood the test of time. Cry once, buy once.
2) The Fosi is still a superb deal. I acknowledge some reader’s concerns about the geopolitics of adding tax revenue to the CCP, but even these small issues in performance from the stand point of how it will sound is more than reasonable for the price point. A $90 amplifier seems a lot trickier than a $90 DAC.
3) I am a big proponent of testing into reactive loads, although there is no one true standard that exists which creates the challenge for even magazines like Stereophile with their one simulated load that might not reflect today’s speakers.
Believe me, I'm not making a living on YouTube!
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Galliardist
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No. And there are a couple of iterations of the DC8Ti at that.
These speakers all appear to have a fairly low average impedance, and a fairly high sensitivity figure (presumably measured at 1kHz as normal).
The V3 starts to struggle at just below 40 Hz though. I don't feel that we need the exact measurements for this model to presume that the amp is not properly driving a speaker with low impedance in the bass here.
The Yamaha is rated 190W into 4 Ohms and 220W into 2 Ohms. These are Yamaha's figures but should be reliable. No way is the Fosi going to put out 220W into 2 Ohms even with the 48W power supply. Gain on the Fosi is apparently only 26 which may further limit its ability in this situation.
I don't see what the mystery here is at all.
- Thread Starter
- #76
The thread precisely discusses this. Feel free to read it. In fact, it seems to be measured. I only did not understand the measurments good enough
We still lack some data to confirm, but it seems very very very likely that there measurments sufficed to anticipate what happened
Unfortunately I'm not setup to do this.
- Thread Starter
- #78
I understand your concern with the time thing.
Just know that in the video description, there are timestamps for specific parts (Equipment used, etc.)
So, looking for a specific information should not take too much time.
I was able to come back to identify the speakers and do so in less than 20 seconds
Let me add that the ONLY reason this became an issue, which I detail in the video, was I was trying to do a simple level match of the FOSI v3 with a Yamaha amp. The fact that it couldn't break 80 dB was nothing short of astonishing to me since Amir tested this at 88 watts with the 5 amp 48v ps. But that's just at 1 khz. That's when I got out the old Yamaha receiver rated at 50 watts and it blasted past 80 to 93 dB (nothing was changed except the rca cable were swapped - no mic changes, nothing).
Using music, I could definitely get the meter to go well over 100 dB, but music isn't white noise, so in the real world it may not matter to you.
Using music, I could definitely get the meter to go well over 100 dB, but music isn't white noise, so in the real world it may not matter to you.
@SimpleTheater, do you have the WAV files of the sweep of the high SPL Fosi amp test? Would you be willing to share them?
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