Duda (altavoces) Yamaha MusicCast RX-V483

Para que se entienda mejor (porque crea confusión) aquí lo explica:

The sensitivity of a loudspeaker is the sound pressure between 125 Hz (250 Hz) to
4 kHz (8 kHz) at a specific distance - when you have a constant voltage - measured in dB per watt and meter. 2.83 volts = 1 watt into an 8 ohm load (nominal impedance) at a distance of
1 metre. Mostly it is the voltage of constant 2.83 volts at the distance of 1 meter, at 8 ohms nominal impedance. Herewith is the power P = V ² / R = 2.83² / 8 = 1 watt. With a 4 ohms loudspeaker you generate 2 watts. To get the reference value of 1 watt, you have to subtract from the sensitivity 3 dB.
It is not the efficiency you get here, it is the sensitivity.
The very small value of the efficiency is never shown by a manufacturer. Usual values for HiFi speakers and studio monitors are between 0.2 % and maximum 2 % − that is an efficiency of 0.002 to 0.02.
There is no connection between the efficiency and the sound quality.

There is an international standard that defines sensitivity, and it specifies that sensitivity be referred to SPL @ 1m for 2.83V input. The actual measurement can be made at any distance and input level, but must be calculated back to 1m and 2.83V equivalent. A 4-ohm speaker will under these conditions appear to have an advantage, and many manufacturers take unfair advantage of this. This is why it is also required to quote nominal impedance, so that one can see that if the nominal impedance is low then the speaker will in fact be drawing more power from the amplifier and hence the amplifier will have to be able to deliver this. Not all manufacturers follow the industry standards in every instance of published specifications, so the consumer needs to pay close attention and read the fine print.

Esto quiere decir que la sensibilidad de un altavoz se publica como si la impedancia fuera 8 ohmios (aunque el altavoz sea de 4). Hay que tener en cuenta las 2 cosas (sensibilidad e impedancia que indica el fabricante).

El fabricante anuncia una sensibilidad (por ejemplo 90 dB) pero también indica el dato de impedancia y si es menor que 8 nos está diciendo "ojo que en realidad el altavoz está chupando más potencia".

Por otro lado está la eficiencia que es lo que realmente se aprovecha, lo que se transforma en sonido. La que no se aprovecha se transforma en calor.