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Old 17th July 2003, 04:51 PM   #1
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Default Limit power to 80watts RMS from 180-20,000Hz

Whats the best way to go about this? my friend has a pair of 6 * 9 car speakers rated at 80watts rms... he says they are good for that from about 180Hz up... I wanna feed them 80watts and see what happens.... impedence is about 4ohms... what sort of current is that anyway?? does that mean the voice coil has to disipate 80watts of heat? lol hmm
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Old 17th July 2003, 05:18 PM   #2
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Hi Skinny,

Where have you been? We’ve missed you.

The power rating on speakers, particularly auto speakers, doesn’t mean a whole lot. It is telling you that if they are 4ohm (it varies) speakers, and you put 80W of power to them, you’ll be put about 4-1/2A through the speaker, and that's the most you power you should use. P = I x I x R That said, I wouldn't try to see where the limit is unless you don’t want the speaker and you’re not particularly fond of the amp you’re driving the speaker with.
Rodd Yamashita
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Old 17th July 2003, 05:33 PM   #3
trwh is offline trwh  United Kingdom
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Built a couple of these with high brightness orange LEDs encapsulated in epoxy resin pointing at LDRS, and they work fine.

Take a look at an amp I built with a limiter here:

Good luck,
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Old 17th July 2003, 05:47 PM   #4
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I think this question is a little bit academical. Picture this: You are in the bathroom and play at an avarage level of 80 watts. How long can you stand it without ear protection?

If the speakers can take 80 watts or I'm convinced that they sound crap before this. They sure don't sound wonderful at max power.

Conclusion: Don't turn up volume more than it starts to sound bad (= real loud!)
/Per-Anders (my first name) or P-A as my friends call me
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Old 17th July 2003, 06:13 PM   #5
PRR is offline PRR  United States
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> I wanna feed them 80watts and see what happens.... does that mean the voice coil has to disipate 80watts of heat? lol hmm

You mean, you are going to feed a 80 Watt sine-wave? Then the heat in the voice coil is only 79 watts. A good watt will come out of the speaker as sound energy.

At 50Hz, a 6x9 is good for more like 0.1 acoustic watts so probably 10 electric wats before it slaps itself silly. Yes, 180Hz is not a bad cut-off for a hard-working 6x9.

It is absurd to think a 1-inch or 1.5-inch coil is going to take 80 watts RMS for long. It will get mighty hot. Used to be the glue would melt. With modern epoxy, instead the coil holds together up to temperatures where the copper resistance rises. The coil may be 3Ω cold, but may go up over 6Ω without melting the glue. With conventional constant voltage amps, input power and efficiency both drop, so output level sags after a second or so.

What, you do not listen to sine waves? If you listen to music, an 80 watt amplifier in light clipping will deliver maybe 8 or 10 watts of average heating power in the coil.

But this is all crap. If the box says 80 watts RMS, it can probably stand normal use with an 80 watt amplifier.
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Old 17th July 2003, 07:47 PM   #6
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place a bipolar 100uf cap in series with them you will get a good 6db roll off...I do that with all my systems
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Old 18th July 2003, 12:47 AM   #7
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Thats just it.... they won't take 80watts RMS, but my "friend" seems to think they will take it continuous... his reason for this judgement is that him amp has VU meters on it and they say they will.... I sorta wanted the pleaseure of watching his expression as they popped... lol ahh well.. better not... they cost him $70 for the pair...
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