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| Wrong wattage calculation on a review of an audio amp. |
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| BrianHG:
Wrong wattage calculation on a review of an audio amp. Help, did this guy calculate the wattages wrong or have I've been doing audio wrong my entire life... See his table at 10:50 where he lists the scope voltage reading in peak-to-peak and his calculated wattage... This is what I calculate: 72v p-p into 8 ohm = 36v / 8ohm = 4.5 amp. 4.5 amp X 36v = 162 watts peak. Or 162 watts peak * 0.707 = 115 watts RMS. A far cry from what the presenter listed as 81 watts. It is me that wrong with my 162/115 watts, or the presenter with his half peak power watts of 81? The rest of his figures all all off by the same amount... |
| themadhippy:
--- Quote ---It is me that wrong --- End quote --- could be, --- Quote ---72v p-p into 8 ohm = 36v / 8ohm = 4.5 amp. --- End quote --- yer calculating the rms voltage from the peak to peak voltage wrong. you forgot to divide multiple it by 0.707 |
| DonKu:
162 watts peak * (0.707)^2 = 80.98 watts RMS. |
| BrianHG:
--- Quote from: DonKu on January 02, 2025, 06:47:00 pm ---162 watts peak * (0.707)^2 = 80.98 watts RMS. --- End quote --- Really? Google: how to convert peak watts to true RMS watts Response: --- Quote ---To convert peak watts to true RMS watts, multiply the peak watts by 0.707. --- End quote --- Remember, the square root of 2 = 1.41421356237 and 1/1.41421356237 = 0.7071067812. You are not supposed to * by .707 to the power of 2, you are supposed to take the peak power and divide by the square root of 2, hence, 162/(sqr-root2) or 162/1.41421356237 = 115 watts, not 81 watts. True RMS wattage is not 50% peak wattage like with you 81 watt calculation. That is just plain wrong! 162 watts peak would mean a square wave at 72vp-p. 115 watts RMS would means a sine wave with 72vp-p. 81 watts would mean a square wave with 50% on duty cycle. Sine waves deliver more effective power than that. |
| TimFox:
The peak power for a sine wave is twice the mean power (rms power is a vulgar error). 72 V pk-pk = 36 V peak = 25.46 V rms. (25.46)2 / 8 = 81 W mean power. |
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