|
Bronze Member Username: DarkvirusMt. vernon, AR United States Post Number: 21 Registered: Dec-06 | --- The Situation --- I have a 2 channel amplifier, and I'm pushing a 2ohm DVC subwoofer with it. I'm trying to measure how much wattage is actually going to the subwoofer. I take a reading at what I think to be full power and measure 55 volts accross the Left Positive and the Right Negative, where it should be when its bridged, since running two 2ohm channels off a 2ch. amp is essentially running bridged 4ohm. (I think?). Using the formula for power (watts), I take 55 volts, and square it, then divide by 4 (since its 4 ohms of resistance), which gives me 756.25 watts. --- The Questions --- 1. Since this is twice the amount of power the amp is rated for, is it possible to do that? 2. Am I using the formula incorrectly, or using the wrong formula for wattage? 3. What is the actual wattage I'm seeing? --- Ending Notes / Summary To no surprise, when you divide 756.25 by 2, you get 378.125 watts, and the amp is rated for 380w MAX RMS power. I'm left to wonder which number is right. Input voltage was 12.7v DC, power wire resistance of 0.11ohms, ran 47hz test tone which gave 55.5v (+ or - .4v) over dual 2 ohm coils. |
|
Gold Member Username: Nd4spd18Northwest PA Post Number: 6794 Registered: Jul-06 | You can't measure amplifier output that way. |
|
New member Username: LoudazzaltimaBrooklyn, NY Post Number: 10 Registered: Mar-08 | I think u did it right cause at 4ohm with 55v u should have a amp readin of 13.5. Do u have a multi meter. That would really help. But I think ur right but what ur getting is the peak which is always double the rms |
|
Gold Member Username: Nd4spd18Northwest PA Post Number: 6798 Registered: Jul-06 | YOU CAN NOT MEASURE AMPLIFIER OUTPUT THAT WAY http://www.bcae1.com/measpwr.htm ^^^^ That is the ONLY way to do it |
|
Gold Member Username: N2audioLawrence, Ks USA Post Number: 1518 Registered: Mar-04 | ~700 sounds reasonable for a dynamic power measurement, but that doesn't tell you much about how it compares to any other ~400w rms amp. Getting a reasonably accurate amplifier power measurement requires knowing precisely the impedance the load is presenting to the amp. That is the step of the procedure few of us have the means to establish. |
|
Gold Member Username: SomedonniedudeIllinois United States Post Number: 1169 Registered: May-07 | "the peak which is always double the rms" Not true, every amp is different. For example compare kicker, rockford fosgate, and sony. They are rate their amps differently between RMS and Max power. (Sony is the only other example I could think of off the top of my head, so don't flame me lol) |
|
Bronze Member Username: DarkvirusMt. vernon, AR United States Post Number: 24 Registered: Dec-06 | First of all, I do have a DMM, it's how I was able to obtain these measurements (analog looks cool but just doesnt do justice). Secondly, considering the web link M.S. posted, I belive the "false wattage" shown by the amplifier is a result of box loading. Taking a voice coil and using its resistance should be the same thing. To take it one step further, using it in free air without a box will eliminate the box loading effect. After all, it's just resistance. In conclusion, I believe the link M.S. posted is very comprehensive and complete, however, it requires equipment that I dont have. I'm going to run several more tests. One where the terminals have no load on them, and bridge the amp to 4ohm and read the bridge. |
|
Gold Member Username: SomedonniedudeIllinois United States Post Number: 1184 Registered: May-07 | A VC will not work for the test, it says it word for word in the link. Even if you did have an appropriate resistor, you will still get only the max power at the load. You Need oscilloscope to see when the signal is no longer clean, meaning its no longer "RMS". |
|
Gold Member Username: SomedonniedudeIllinois United States Post Number: 1185 Registered: May-07 | A sub will not work for the test, it says it word for word in the link. Even if you did have an appropriate resistor, you will still get only the max power at the load. You Need oscilloscope to see when the signal is no longer clean, meaning its no longer "RMS". |
|
Gold Member Username: Nd4spd18Northwest PA Post Number: 6850 Registered: Jul-06 | No way to do this without a scope and resistors. End of story........ |