Hi
I want to connect a 3800W@8ohms audio amplifier to 4.3kOhms load.
Is the output power of the amplifier for 4.3kohms about 7W???
These are the same thing, derived from V = I*R and P = V*I.
Most amplifiers are built for constant voltage output, and as long as output current is within rated limits, the amplifier will work fine. It's probably fine to put a 4.3kohm load on it...but more to the point is, why?
Tim
-- Deep Fryer: A very philosophical monk. Website @
The assumption is power from a sine wave. If so, you should get that 4.3k resistor a toasty 7Watts.
I wonder about that power spec??? I've heard marketing plays with stuff like:
*Music power *Peak power *Average power *Instantaneous power *Pulse power *Power at a spec %thd *Total power *Power supply power *Burn out powerD from BC British Columbia Canada.
You left out the most important marketing gimmick of all "instantaneous peak power at the wall plug" the turn-on thump.
No wayy.... :P The surge power to charge the reservoir caps..?? Geezz.. :P
IIRC another marketing power spec is what I call 'full load power'. That's where the power spec is at,say..,1 ohm but the amp is typically used at 8 or 4 ohm load.
D from BC British Columbia Canada.
Yeah, then my cute BS Yamaha amp, with 6 ohm output. Can't hit full power at 8 ohms, can't hook up 4 ohms, never seen a 6 ohm speaker. Whatever.
-- Cats, coffee, chocolate...vices to live by
It means only that they tested the amp with 6 Ohm resistive load. The popular misconception is that the speaker resistance at DC is its impedance. The speaker impedance is very much reactive and dependent on the frequency; so the trivial calculations for the power and the current vs drive voltage may be wrong by several times.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
How about short-circuit current times open circuit voltage?
-- Keith
Loudspeaker Impedance Curve
"Vladimir Vassilevsky" a écrit dans le message de news:Yw5pj.5414$ snipped-for-privacy@newssvr14.news.prodigy.net...
I don't aggre with that. The annouced impedance of a speaker is the minimum of its impedance between its resonance and the inductive part.
Unless it is an ebay amp.
I bought one rated at 1000Watts that put out about 100 watts !!!
So there is the ebay rating too....
I did a 5 second Google search to find an example of some marketing foolery with audio amp power.
On the spec link. Power: 500Watts/ch at 14.4VDC at 1khz (2 channels) Maximum current draw is 15A Stereo mode load impedance is 2 to 4 ohms. Bridged mode load impedance is 4 to 8 ohms.
15A max current draw???? wtf??? 14.4VDC * 15A = 216Watts total! How the crap do you get Pout=1000W when the amp fuse blows at Pin=216W (assuming fused at 15A).1000Watts bridged on 4 ohms?? Does a matching 4 ohm speaker exist with as much power as my microwave oven??? I was surprised to find a 900W subwoofer.
But read the fine print. " The power capacity is determined according to AES2-1984 standard. Program power is defined as the transducer's ability to handle normal music program material."
I suspect the trail then goes into the land of 'music power'. :P
D from BC British Columbia Canada.
Merely 1kWt? I developed car amplifiers rated at 10kWt of continuous power :)
A woofer rated at 1kWt is rather typical. But, that 1kWt rating assumes that the woofer behaves like a resistor of 4 Ohms. The actual heat dissipation in the woofer is several times less due to the reactance.
Vladimir Vassilevsky DSP and Mixed Signal Consultant
I can't imagine the speaker Z being significantly reactive at low frequencies. Do you think a 4 ohm 1000W woofer can handle a 63Vrms 20Hz sine wave continuously? I'm guessing not. This is not musical and I think the spec is 'music power'.
D from BC British Columbia Canada.
power
that
in
Indeed it is very reactive, especially for the tuned port systems.
At least for the duration of several minutes. This is how they test it. The
20Hz excitation creates severe mechanical stress for the speaker.Vladimir Vassilevsky DSP and Mixed Signal Consultant
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power
that
in
Phase curve is often missing. Please take a look at this:
Vin
"vincent.thiernesse" a écrit dans le message de news:47a5e237$0$833$ snipped-for-privacy@news.orange.fr...
microwave
dissipation
other examples:
HP1
absolute value:
HP2
absolute value:
obviouly the phase cannot swing over +/- 90° and in my example it doesn't exceed +/- 45°
phase swing over the resonnance is as big as absolute value overshoot.
we could expect that the phase reaches +90° at high frequencies but you have to consider skin effect or capacitve effet in the coil.
@+
Vincent
1000 watt-tons certainly sounds like a lot of power.
Seems like one would want a bit higher efficiency, though I also suspect one wouldn't want anything close to 1000W of sound in a room either. OTOH, I suspect that you've missed the point.
-- Keith
... snip
An ideal, efficient transducer would absorb 1 KW without heating, just transforming electrical energy into mechanical energy. Of course, real transducers are not 100% efficient, so some heating is expected.
On the other hand, the resistive part of the input impedance is a measure on how well energy is converted instead of stored. And it does not get warm :) Again, this is in the ideal case...
Pere
If you apply 63Vrms to a typical 4 Ohm subwoofer (that is supposed to be
1kW), it will drain at the order of 200VA of power. From that 200VA about 10W is converted to the sound, and the rest goes into the heating of the voice coil.Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
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