NAD Power Output Confusion? What does it all mean?


OK, Im confused.... It takes more power to drive a 4 ohm speaker, yet the power ratings on say the NAD T762 are much higher wpc output for the 4 ohm than the rating for the 8 ohm???? Does that mean the effeciency of the receiver is higher with the 4 ohm speakers, and what the heck do they mean after the power rating when they say "respectivly"

OK, I can understand that. Lets start at the beginning so that we don't skip a step and add to your confusion.

It is not true that all 4 ohm speakers need more power, per se. You are confused by the fact that several prominent 4 ohms speakers are also very power hungry. They need a lot of current. But the bottom line is that a 4 ohm rating does not, in and of itself, require a lot more power. For example, if you look at what are often called Micro Stereos or Executive Stereos (like the Denon DM-30S or the Onkyo CS-210) they have little speakers that have a 4 ohm rating, but they are connected to little receivers capable of only 20 wpc into 4 ohms. So you have been given the wrong impression that 4 ohm speakers need more power. In reality, the proper statement is that some 4 ohm speakers are power hungry and need a lot of current.

Now current is not the same thing as "watts" although many people think the two are the same. Current is measured in amps, not watts. High quality receiver/amp manufacturers usually will give a specification showing how many amps the amplifier is capable of, e.g., an NAD 752 is capable for 45 amps and I think a H/K 525 is capable of 40 amps. However, few receiver manufacturers will issue a specification for current (amps) because the specification would be embarrassing (their unit would look as wimpy as it really is) and it isn't necessary for the generic 8 ohm speaker with a sensitivity of 92 db/watt/meter, which is what most speakers are these days.

Also realize that a rating in ohms is testing the impedence (resistance) of the speaker. The higher the impedence (resistance), the lower the power that is available to that speaker. Turned around, it is equally true that if impedence (resistance) is lowered, the available power is greater. So it is really true that a good amp that is stable at 4 ohms has a lot more power for 4 ohms than it does at 8 ohms.

As for what is meant by "respectively", I assume you are talking about the receiver's power ratings where it is rated into perhaps 8, 6, and 4 ohms (or, in the case of NAD, they rate it into 8, 4, and 2 ohms) and then they list three power numbers, so that the first power value applies into 8 ohms, the second power rating applies to the second impedence rating, etc.

I hope this helps.

In addition to what Hawk says the problems are that 8 ohms and 4 ohms are either an average resistance measurement of the speaker over the frequency range, or a resistance measurement taken at a particular frequency. So while 8 ohm speakers can often drop to 4 ohm or so at certain frequecies and rise to 18 ohms at others, an 8 ohm speaker on average presents itself as a more stable resistance to the amp/wire combination.

The lower the ohms, the closer the resistance comes to the resistance (impedance) of the speaker wire. Under normal circumstances this isn't very critical with good amplification, but when using fairly long runs of speaker wire it starts to present a much larger problem, unless you keep using much fatter (thicker gauge) wire.

So a 4 ohm speaker often drops to 2 ohms and sometimes less. This can present a far less stable circumstance to the amp/wire/speaker load combination.

Thanks for clearin that up Hawk and G-Man

This has to be an error. but there are 5 stores saying all the same price


Yes, unfortunately, it was an error! I went to order one and entered my zip code to calculate all charges. Only then did a full description show up. One was for an S200 lightning grounding strip (manufacturer unspecified). Two others were for a Canon S200 camera and the last one was also an S200 (manufacturer unspecified-but I think it too was for the Canon camera). Dang! I thought I was going to get an NAD amp for $54.95. I'm so bitter!
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