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How to find out RMS of car mp3 player
For example my pioneer spec says,
Maximum power output ....... 50 W 4
Continuous power output ... 22 W 4 (50 Hz to 15 000
Hz, 5% THD, 4 W load, both
channels driven)
Does it mean it has 50 w RMS per channel or 22w RMS.
Car Audio Head units rated at 50wX4 RMs generally output only 22wx4 RMS in normal conditions (= "Continuous power output"). Basically, when you have music playing, the HU is really capable of feeding only 22w RMS per channel (that too, at full crank, with a fair amount of distortion). While playing segments of music that become really loud for a few seconds (beats/crescendos etc), the HU can just manage to output 50wRMs per channel for a few milliseconds with the volume knob cranked up all the way, just before clipping. In other words, "maximum power" is mostly nonsense if you're into listening to music from the HU. This is a very rough explanation, but I guess you will understand
"50w RMS per channel" is basically a claim the marketing guys slap onto the HU to make us think we're getting more than we're actually getting. Just like all those *hahahahaha* PMPO figures.
And most of the car amps, RMS is mentioned seperately
Thay says
100w RMS *4 at 2 ohms, 50w RMS *4 at 4 ohms.
Do i need to buy 2ohms speaker or 4 ohm spekers which performs better?
but Some of the CAR AMP syas only watts , how to arrive RMS per channell at this case?
1. In the case where the RMS figure is mentioned, there is a rough way to check how accurate the claim is. Look at the rating of the fuse on the amp. If there is more than one fuse, add up the ratings of all the fuses. Multiply this rating with 6 for class A/B amps and by 10 for class D amps. The result is the approximate total of the
maximum output in RMS of the amp (all channels together).
For example, my Class A/B 4-channel amp has two 30amp fuses. So total = 30 x 2 = 60amps. 60amps x 6 = 360. So the amp is putting out approximately a total of 360w RMS at the maximum. Or 360/4 = 90wRMS per channel.
Please understand that this is only a rough and ready rule. It looks at the output that the amp is likely to give you in real world conditions (you rarely get above 12v to 12.5v from a regular automotive battery in real world conditions). And it takes a somewhat conservative look at the amp rating, but it gives a figure you can base a purchasing decision on.
There is a slightly more detailed method that goes by the typical voltage we can expect from a car battery and the typical efficiency of Class A/B amps and Class D amps. I can mention that method also, if you'd like me to -- it is a method that gives a slightly more encouraging picture about the amp's output. I prefer the more conservative approach
2. In the case of the RMS figures with the impedance mentioned (the ohms figure), it is simply to give you an idea of the power the amp will feed speakers of different impedance. If you hook up 2ohm speakers to the amp, it will feed 100w per channel (maximum). If you hook up 4ohm speakers to the amp, it will feed 50w per channel (maximum). Speakers with the higher impedance typically sound better (when paired with an amp feeding them power at that higher impedance), and they also put a lower load on the car electricals. So I personally always prefer 4ohm speakers, and I always prefer to wire DVC subs also in such a way that they present a 4ohm load to the amp (even at the cost of lower power being fed).
3. If the amp documentation and the package give only the figure in watts (no RMS or PMPO mentioned), I'd personally stay away from that brand. The lack of information is most likely intended at misleading the buyer. Esp. when the figures mentioned are like 1200watts for a Rs.10K amp. *snicker, snicker*. To get a rough idea of the amp's capability, I'd go by the fuse rating method I've mentioned above to calculate the amp's actual maximum output.
