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Post by patate91 on Aug 10, 2019 14:12:28 GMT
I was looking at THD specs and measurements and I wanted to check if I understand correctly. This is the kind of graph I found. If I understand correctly : at low power (W) there's more distortion. If yes I'm wondering why most manufacturers are not giving us this informations. I guess a lot of people are mostly using their amp below 1 w of Power. Edit Does the graph shows a typical amplifier's behavior?
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Post by Michael Lawrence on Aug 10, 2019 14:46:32 GMT
They're not hiding anything from you, you're just not correctly parsing what the data is showing you. THD+N includes noise floor in the spec. Noise floor is a constant, so as signal levels drop, noise floor is relatively higher, which is why the THD+N trace (stated in dB, which is relative) is higher for lower signal levels. Understanding the presented data can be half the battle in audio. For a lot more on that, check out my Intro to FFT Audio Analyzers webinar, particularly the first half. Hopefully that helps. m
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THD specs
Aug 10, 2019 14:58:30 GMT
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Post by patate91 on Aug 10, 2019 14:58:30 GMT
They're not hiding anything from you, you're just not correctly parsing what the data is showing you. THD+N includes noise floor in the spec. Noise floor is a constant, so as signal levels drop, noise floor is relatively higher, which is why the THD+N trace (stated in dB, which is relative) is higher for lower signal levels. Understanding the presented data can be half the battle in audio. For a lot more on that, check out my Intro to FFT Audio Analyzers webinar, particularly the first half. Hopefully that helps. m Juste to make sure I'm not saying that this Graph is hidding my something. Here's an exemple of what I think is hidding me something : 50 watts / channel RMS; 8 Ohms; 20 Hz – 20 kHz; <0.05% THD. Thanks for the link, I'll have a look for sure.
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THD specs
Aug 10, 2019 17:22:07 GMT
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Post by patate91 on Aug 10, 2019 17:22:07 GMT
@michael Lawrence : great video, I hope there will be more of them!.
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THD specs
Aug 10, 2019 18:30:12 GMT
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Post by patate91 on Aug 10, 2019 18:30:12 GMT
They're not hiding anything from you, you're just not correctly parsing what the data is showing you. THD+N includes noise floor in the spec. Noise floor is a constant, so as signal levels drop, noise floor is relatively higher, which is why the THD+N trace (stated in dB, which is relative) is higher for lower signal levels. Understanding the presented data can be half the battle in audio. For a lot more on that, check out my Intro to FFT Audio Analyzers webinar, particularly the first half. Hopefully that helps. m I'll try to rephrase what I said earlier with what I've learned from your video. Why manufacturers are using their lens on high power when we mostly use few watts? I mean distortions numbers should focus on what we are doing with our audio equipements?
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Post by Michael Lawrence on Aug 10, 2019 23:42:54 GMT
Well first of all, be careful with that generalization. While it's true that in a home listening environment, the amplifiers are generally operated at a relatively low level, in a live sound reinforcement environment, it's routine for the system to be driven to within a few dB of its maximum capability, which is why we spend a lot of time worrying about limiters and so on. So many power amps in professional situations will be driven to their full output, and that data is relevant.
Almost all forms of distortion in power amplifiers (with the exception of some forms of crossover distortion) get worse as level / load increases. So you can think of those ratings as a worst case scenario. It is a common industry norm to define a power amp's max output capability by noting the point at which it reaches 1% THD. That's when we consider it to be clipping, and where the specs come from. If you turn the input down, or increase the load Z, or both, you can expect THD to drop.
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THD specs
Aug 10, 2019 23:54:13 GMT
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Post by patate91 on Aug 10, 2019 23:54:13 GMT
Well first of all, be careful with that generalization. While it's true that in a home listening environment, the amplifiers are generally operated at a relatively low level, in a live sound reinforcement environment, it's routine for the system to be driven to within a few dB of its maximum capability, which is why we spend a lot of time worrying about limiters and so on. So many power amps in professional situations will be driven to their full output, and that data is relevant. Almost all forms of distortion in power amplifiers (with the exception of some forms of crossover distortion) get worse as level / load increases. So you can think of those ratings as a worst case scenario. It is a common industry norm to define a power amp's max output capability by noting the point at which it reaches 1% THD. That's when we consider it to be clipping, and where the specs come from. If you turn the input down, or increase the load Z, or both, you can expect THD to drop. I think it's ok with my point of view : what's important for pros is not the same as home users. I'm not a pro so when I'm looking to buy an equipment I'm looking for informations that I need for my use. Informations usefull for pros are not that much usefull for me. (in reality I'm not a good exemple since I like to learn so I want as much as possible, but anyway I'm sure you understand).
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Post by patate91 on Aug 11, 2019 0:08:47 GMT
Based on those informations I doubt that people, in a home use, needs a lot of power.
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THD specs
Aug 11, 2019 18:08:11 GMT
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Post by patate91 on Aug 11, 2019 18:08:11 GMT
What kind of THD+N can I expect with speakers with 97db sensitivity. I played with numbers on this web site myhometheater.homestead.com/splcalculator.htmlWith 0.005 W I get an SPL of 75db. My amplifier specs are : 50 watts / channel RMS; 8 Ohms; 20 Hz – 20 kHz; <0.05% THD. Signal to Noise Ratio (8 Ohm load): > 110 dB; ref rated power; (A-weighted).
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Post by Michael Lawrence on Aug 15, 2019 12:45:32 GMT
It depends heavily on the design of the loudspeaker (and to a lesser degree, the amplifier). Why not measure it?
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Post by rock on Aug 15, 2019 13:21:42 GMT
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THD specs
Aug 15, 2019 14:06:58 GMT
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Post by patate91 on Aug 15, 2019 14:06:58 GMT
It depends heavily on the design of the loudspeaker (and to a lesser degree, the amplifier). Why not measure it? I would have to measure at low SPL using REW? I guess it would be hard to Tell if it's the noise is from my house and street or the amplifier's noise floor. In the "real" world at low SPL it seems to be dead silent to me. But I it would certainly be fun to measure it.
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Post by Michael Lawrence on Aug 15, 2019 15:51:51 GMT
Yes, REW will measure THD as well as individual harmonics. The measurement noise floor can be lowered by using multiple sweeps in the measurement settings. Doubling the number of sweeps lowers the noise floor by about 3 dB because noise is (generally) uncorrelated between the measurements and will average to 0.
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