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Distorsion percentage, power or voltage?
Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. |
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Distorsion percentage, power or voltage?
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#6
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#7
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#8
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#9
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#10
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Distorsion percentage, power or voltage?
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). There is no more or less logic to doing it one way or the other, they are exactly equivalent. |
#11
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Distorsion percentage, power or voltage?
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). There is no more or less logic to doing it one way or the other, they are exactly equivalent. |
#12
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Distorsion percentage, power or voltage?
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). There is no more or less logic to doing it one way or the other, they are exactly equivalent. |
#13
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Distorsion percentage, power or voltage?
John Fields wrote in message . ..
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). There is no more or less logic to doing it one way or the other, they are exactly equivalent. |
#15
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Distorsion percentage, power or voltage?
John Fields wrote in message
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#16
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Distorsion percentage, power or voltage?
John Fields wrote in message
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#17
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Distorsion percentage, power or voltage?
John Fields wrote in message
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#18
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Distorsion percentage, power or voltage?
(Stewart Pinkerton) wrote in message ...
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. |
#19
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Distorsion percentage, power or voltage?
(Stewart Pinkerton) wrote in message ...
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. |
#20
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Distorsion percentage, power or voltage?
(Stewart Pinkerton) wrote in message ...
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. |
#21
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Distorsion percentage, power or voltage?
(Stewart Pinkerton) wrote in message ...
On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. |
#22
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:32:02 -0800, (Dick Pierce)
wrote: John Fields wrote in message . .. On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). --- Except that decibels describing the ratio of one power to another P1 is dB = 10 log ---- , while for voltages or currents it's _20_ times P2 the log of the ratio. -- John Fields |
#23
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:32:02 -0800, (Dick Pierce)
wrote: John Fields wrote in message . .. On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). --- Except that decibels describing the ratio of one power to another P1 is dB = 10 log ---- , while for voltages or currents it's _20_ times P2 the log of the ratio. -- John Fields |
#24
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:32:02 -0800, (Dick Pierce)
wrote: John Fields wrote in message . .. On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). --- Except that decibels describing the ratio of one power to another P1 is dB = 10 log ---- , while for voltages or currents it's _20_ times P2 the log of the ratio. -- John Fields |
#25
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:32:02 -0800, (Dick Pierce)
wrote: John Fields wrote in message . .. On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Precisely. ALL of the THD meters in existance are essentially voltmeters with filters. Going from the ancient and venerable General Radio 1936 or Hewlett-Packard 330, through the HP 334, through the Sound Technology 1700, Amber, Marconi and so on, they are ALL voltmeters that have a narrow-band notch filter in them. And, if you describe the ratio of the original to its distortion products in dB rather than in percentage, what do you care? A THD of 1% means the amplitudes differ by a factor of 100:1, their powers differ by 10000:1, but it's 40 dB in both cases. That's the entire point: A RATIO between two signals is EXACTLY the same whether you describe the RATIO of the voltage, the RATIO of the power or the LOGS of those ratios (assuming the impedance is the same in all cases, which is a prefectly reasonable assumption). --- Except that decibels describing the ratio of one power to another P1 is dB = 10 log ---- , while for voltages or currents it's _20_ times P2 the log of the ratio. -- John Fields |
#26
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:33:31 -0800, (Svante)
wrote: John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. --- When measuring _total_ harmonic distortion, the contribution of each of the individual partials is immaterial in that what's being determined is the contribution to distortion that _all_ of the harmonics due to the fundamental's presence contribute. Furthermore, even if the contributions of the individual partials were to be measured, their voltages would each be measured using a tuned voltmeter and then the process of determining their contribution determined mathematically. As a matter of fact, in order to measure the power directly, the normal load would have to be disconnected and a bolometer with precisely the same impedance as the load substituted for the load. Expensive and more than just a _bit_ awkward. -- John Fields |
#27
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:33:31 -0800, (Svante)
wrote: John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. --- When measuring _total_ harmonic distortion, the contribution of each of the individual partials is immaterial in that what's being determined is the contribution to distortion that _all_ of the harmonics due to the fundamental's presence contribute. Furthermore, even if the contributions of the individual partials were to be measured, their voltages would each be measured using a tuned voltmeter and then the process of determining their contribution determined mathematically. As a matter of fact, in order to measure the power directly, the normal load would have to be disconnected and a bolometer with precisely the same impedance as the load substituted for the load. Expensive and more than just a _bit_ awkward. -- John Fields |
#28
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:33:31 -0800, (Svante)
wrote: John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. --- When measuring _total_ harmonic distortion, the contribution of each of the individual partials is immaterial in that what's being determined is the contribution to distortion that _all_ of the harmonics due to the fundamental's presence contribute. Furthermore, even if the contributions of the individual partials were to be measured, their voltages would each be measured using a tuned voltmeter and then the process of determining their contribution determined mathematically. As a matter of fact, in order to measure the power directly, the normal load would have to be disconnected and a bolometer with precisely the same impedance as the load substituted for the load. Expensive and more than just a _bit_ awkward. -- John Fields |
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:33:31 -0800, (Svante)
wrote: John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. --- When measuring _total_ harmonic distortion, the contribution of each of the individual partials is immaterial in that what's being determined is the contribution to distortion that _all_ of the harmonics due to the fundamental's presence contribute. Furthermore, even if the contributions of the individual partials were to be measured, their voltages would each be measured using a tuned voltmeter and then the process of determining their contribution determined mathematically. As a matter of fact, in order to measure the power directly, the normal load would have to be disconnected and a bolometer with precisely the same impedance as the load substituted for the load. Expensive and more than just a _bit_ awkward. -- John Fields |
#30
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Distorsion percentage, power or voltage?
Svante wrote:
Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Several reasons: 1. 40 dB down is 40 dB down, whether you're talking about voltage or power, assuming constant load impedance. If the 2nd harmonic is 40 dB down, it means the voltage ratio is 1%, and the ratio of delivered power is 0.01%. A dB in voltage is a dB in power! 2. Audio amplifiers are voltage devices. The actual power delivered to the load depends on the load impedance. For example, let's say an amplifer has 1% 2nd harmonic distortion in voltage. How much power is delivered to the load at that 2nd harmonic frequency? The answer depends on the load impedance at that frequency. It is not unusual for a speaker's impedance to change substantially over an octave. So in this case, the power ratio may not be 0.01%. 3. The measuring equipment measures ratios of voltages. It does not measure power delivered to the load. |
#31
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Distorsion percentage, power or voltage?
Svante wrote:
Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Several reasons: 1. 40 dB down is 40 dB down, whether you're talking about voltage or power, assuming constant load impedance. If the 2nd harmonic is 40 dB down, it means the voltage ratio is 1%, and the ratio of delivered power is 0.01%. A dB in voltage is a dB in power! 2. Audio amplifiers are voltage devices. The actual power delivered to the load depends on the load impedance. For example, let's say an amplifer has 1% 2nd harmonic distortion in voltage. How much power is delivered to the load at that 2nd harmonic frequency? The answer depends on the load impedance at that frequency. It is not unusual for a speaker's impedance to change substantially over an octave. So in this case, the power ratio may not be 0.01%. 3. The measuring equipment measures ratios of voltages. It does not measure power delivered to the load. |
#32
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Distorsion percentage, power or voltage?
Svante wrote:
Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Several reasons: 1. 40 dB down is 40 dB down, whether you're talking about voltage or power, assuming constant load impedance. If the 2nd harmonic is 40 dB down, it means the voltage ratio is 1%, and the ratio of delivered power is 0.01%. A dB in voltage is a dB in power! 2. Audio amplifiers are voltage devices. The actual power delivered to the load depends on the load impedance. For example, let's say an amplifer has 1% 2nd harmonic distortion in voltage. How much power is delivered to the load at that 2nd harmonic frequency? The answer depends on the load impedance at that frequency. It is not unusual for a speaker's impedance to change substantially over an octave. So in this case, the power ratio may not be 0.01%. 3. The measuring equipment measures ratios of voltages. It does not measure power delivered to the load. |
#33
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Distorsion percentage, power or voltage?
Svante wrote:
Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Several reasons: 1. 40 dB down is 40 dB down, whether you're talking about voltage or power, assuming constant load impedance. If the 2nd harmonic is 40 dB down, it means the voltage ratio is 1%, and the ratio of delivered power is 0.01%. A dB in voltage is a dB in power! 2. Audio amplifiers are voltage devices. The actual power delivered to the load depends on the load impedance. For example, let's say an amplifer has 1% 2nd harmonic distortion in voltage. How much power is delivered to the load at that 2nd harmonic frequency? The answer depends on the load impedance at that frequency. It is not unusual for a speaker's impedance to change substantially over an octave. So in this case, the power ratio may not be 0.01%. 3. The measuring equipment measures ratios of voltages. It does not measure power delivered to the load. |
#34
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Distorsion percentage, power or voltage?
Svante wrote:
John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Only if the load impedance is constant over that frequency range. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#35
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Distorsion percentage, power or voltage?
Svante wrote:
John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Only if the load impedance is constant over that frequency range. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
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Distorsion percentage, power or voltage?
Svante wrote:
John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Only if the load impedance is constant over that frequency range. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#37
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Distorsion percentage, power or voltage?
Svante wrote:
John Fields wrote in message On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. --- It is _much_ easier to notch out the fundamental(s) and measure the voltage of the remaining component(s) than it is to measure their power. Then, knowing the voltage of the offending component(s) appearing across the load and the impedance of the load at the various frequencies at which distortion rears its ugly head, their contribution to the power being dissipated in/by the load can be easily calculated. Sure, but adding the partials a total amount of distortion would be much easier if the percentages were power percentages. 2% 2nd, 1% 3rd and 0.5% 4th harmonic would simply add up to 3.5%. Being voltage percentages one would has to do: sqrt(0.02^2+0.01^2+0.005^2)=2.3%. OK, nowadays, the computer would do this for us, so maybe it doesn't matter much. Only if the load impedance is constant over that frequency range. Certainly I would not argue that such a well-established standard should be changed, and I would probably have no success at all trying to do so, I just think it seems a bit akward and worth reflecting over. |
#38
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:40:26 -0800, (Svante)
wrote: (Stewart Pinkerton) wrote in message ... On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. Why does it matter? Why is the kilogram the standard for mass? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#39
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:40:26 -0800, (Svante)
wrote: (Stewart Pinkerton) wrote in message ... On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. Why does it matter? Why is the kilogram the standard for mass? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Distorsion percentage, power or voltage?
On 16 Jan 2004 14:40:26 -0800, (Svante)
wrote: (Stewart Pinkerton) wrote in message ... On 16 Jan 2004 06:40:38 -0800, (Svante) wrote: Harmonic distorsion is expressed as the ratio between the distorsion components and the fundamental. What surprises me is that it is the VOLTAGES that are compared (in the electrical case) not the POWERS. So if we have a second harmonic 40 dB down, the second harmonic distorsion is 1 %, not 0.01 %. (In this case the voltage of the harmonic is 1% of the fundamental, and its power is 0.01% of the fundamental) What is the reason for this convention? I'd think that power would be more logical. Think what you like, voltage is the standard. Yes I will think what I like, and I know voltage is the standard, that should be clear from my post. But I asked about the REASON for the standard. Why does it matter? Why is the kilogram the standard for mass? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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