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How much power??!


jnasty

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Hey guys so I just picked up the dd1 and set my gains to distortion.. amp is an arc audio 4000se. I also had my dmm hooked up as well and got a reading of 72.8v before distortion. does this mean my amp puts out 5,299w at 1ohm?? Is this a cheap way to "dyno" my amp? I'm highly doubtful this amp makes that much power but HELL, I'll be happy if it does.. 

Vehicle: 2002 Ford Escape

Electrical: 275A Singer, 160ah XS/Yinlong lithium, 2,000farad XS Supercaps

Head Unit: Apple iPad Hi-Res Passthrough Topping d10s

Speakers: {ACTIVE} - (4) Arc Audio RS 6.0, (2) Arc Audio RS 4.0 & (2) Arc Audio RS 1.0

Sub Stage: (2) TC Sounds LMS Ultra 5400 18" 

Amplifiers: ARC Audio - (4)4200SE(comp modded, (2)4000SE 

Processing: Helix DSP Pro W/ Dash Mounted Director 

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I can give you a half (ass) answer. I should have realized this point earlier, but sadly I did not...

The output of your amp is AC, so when you try to do calculations like V^2/Z or I^2*Z, you're getting VA not Watts. See my attachment. You need to know the power factor of the amp output to get a true measure of real power (Watts). Then W = V*I*pf or (V^2*pf)/Z or I^2*Z*pf, but only at the point in time you measured. If that measurement is fairly constant over a range of time in a given condition, then the average power in that condition is what you calculated.

power_triangle.png

 

But we aren't given power factor are we?? How are you all getting real power measurements besides for buying an expensive ass PQA?

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I do want to add one thing though:

The lower the harmonic distortion of the amp, the better the power factor is, and thus the more the real power part dominates the measurement you're taking with a (hopefully true RMS) DMM. You can get an idea of real power delivered using a good DMM on a good amp, but it will always be less. On a reactive load like a speaker, you will always have some reactive component, and every amp will have some measure of harmonic distortion.

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Was wondering this too, would clamping the speaker wire and getting an amp reading then multiply that by voltage going into amp to get watt output the sub is seeing?

Sundown NSV4 18"  +  Sundown SALT-4 Baby

MechMan Elite 370a  +  XS3100 - XP3000

SHCA 1/0 OFC(blue+  SMD Fuse Holders(blue)

Pioneer AVH-2440NEX  SHCA Pro RCA 

 

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If you can find one, get an AMM-1 if you want to clamp unless you have access to a TL with clamps

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No, they are just realtime clamps. both can even capture what your rising to.

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Well looking at AMM-1 website, it does say power factor and real power measurement.

But I was talking with a colleague and it turns out you can make it super easy by using a scope. Probe the voltage and use a clamp probe on the current, then take a reading at the frequency and volume of interest. Instantaneous power will be the voltage at one point in time multiplied by the current at the same point in time. This is useful because we know power draw varies with frequency, so we're only looking at very specific operating points anyway (worst case power draw). Doing this eliminates the need to know power factor.

As a side I think you can calc the power factor by cosine of the phase between the voltage and current waveforms. I'm pretty sure that will vary by frequency too though. 

One more point. Clamping power is one thing, but the actual SPL is the real measure of your system. Power draw is typically lower when SPL is highest because the SPL is coming from mechanical and enclosure resonances as opposed to high power draw. 

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8 hours ago, Dragonsyph said:

I wish the AMM 1 wasent 400 bucks, would be nice device to have.

Same as most of the SMD products, they aren't insanely expensive but are a bit pricier than they should be. They're marketed towards people that want the most-used features in an easy to understand interface and don't mind dropping the extra cash. You can pick up a Rigol scope and a BNC current clamp for 400 and have the added benefit of seeing the signal on the screen, among other things. Just need to have some electronics knowledge to calculate things.

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