posted
For those of us without fancy test equipoment like I'm sure we all want, if you wanted to get a decently accurate power estimate of what your amp is putting out, would it be fairly close to get a measured in box woofer impedence plot, as in from LMS or the Woofer tester, then just hook a good DMM across the speaker terminals while playing the sub and use the AC volts to plug into the power equation? I know you are supposed to use a resistive load for testing, but super high power resistors are kind of hard to find, then you would have to reconfigure if you wanted to try a different frequency where the impedance was different.. Thanks
posted
Ya know, that's actually a pretty good Q. Lets consider this for a moment. You have a woofer, in a box, tuned to whatever freq. And you also have a test tone setup to play said freq. Why then, whould it not be at least ball park acurate to measure said amp with a DMM. Not for the sake of the amps actual power, but for the sake of the power your actually getting from said amp. This of course brings another intresting Q. Considering in box impedance, along with the fact that the each woofers resistance slopes differently according to freq, you could, at the very least, measure at which point (freq dependant) that your amp is putting out the most power in your said application. Which, in reality, is the only measurement that matters. But then again, I've spent all summer drinking, and my brains a little fried....
[ 08-15-2001: Message edited by: Snot ]
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Posts: 1082 | From: Former BS Moderator <IMG SRC= | Registered: Mar 2000
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posted
Buzz- You could get a semi-accurate clamp on current meter for about the same price as "the woofer tester".. And using a DMM and a clamp on ammeter would be as accurate or probably more so than your method, I would guess..
But, yeah, if you had methodology to know the impedance, then you could use your method.. however, so many things will affect the impedance...
ShadowStar
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Posts: 2579 | From: Somewhere In the Northeast | Registered: May 1999
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posted
Couldn't you plot the driver impedance in-box and then derive the power output from that?
I mean if your sub puts out 1000 watts at 2 ohms, and your impedance at, say, 55 Hz is 32 ohms, the amp should be putting out 62.5 watts... Which seems simply too low to me so maybe that wouldn't work.
Adam
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posted
Buzz, Yes you can. you divide the voltage by the impedance to get the current. Square the current and multiply it by the RESISTANCE of the coil. This will give you the power in Watts. the voltage squared divided by the impedance will give you the apparent power or magnitude of power in Watts and vars(the reactive part of power).
A side note: the impedance and resistance does change with power. not much though. It is dependant on the size of the port mostly, as well as the temperature of the coil. so if you do a large burp, check the dc resistance imediatly after. The best thing is to get a GOOD clamp-on and measure the current your getting into the subs. Thats what moves them.
Posts: 1269 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
I want the woofer tester to do impedance charts as well as get sub parameters so I will probably purchase it anyway, but let me see if I can summarize this- So you electrical pros think that the better method would be to get a clamp on meter to use with the DMM and use P=I*E over using the measured voltage and in box impedance using P=V^2/R, correct? Thanks for the input everyone!
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