Speaker impedence and amp power ratings

Overdose

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Feb 8, 2008
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I've just been spending a fair amount of time looking into a one box streaming system and being new to music streaming, have many questions, but this particular one is related to the amplifier section of such a box.

Two of the most attractive units to me so far are the Marantz M-CR603 and Denon CEOL and both seemed to fit the bill, but looking closer, I noticed that the power ratings are into 6 Ohms and 4 Ohms loads respectively.

Why do manufacturers not test to a standard load or even publish several different load ratings? 60W power handling into 6 Ohms is obviously not the same as 60W into 4 Ohms. Also is there any way to get some idea of the capability of the amplifier to drive alternative speakers and how would you go about making sure that the speakers are an even match and not going to give the amp a hard time?
 

ID.

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There will be others who are far more knowledgeable about this than me, but one thing is that speaker impedance varies, so the ohms quoted are usually nominal. AFAIK even an 8ohm speaker may drop to 4 when dealing with certain frequencies.

Amps often list at least the watts into 8 and 4 ohms as these seem to be most standard for speakers. A good amp (one that can provide good current) will double its watts into 4 ohms, but not all amps do this, or need to. Generally the watts into lower impedance will increase as the speakers draw more current from the amp.

As a general rule, 4ohm speakers are harder to drive because many cheaper amps can't supply the current they need, so I'd be a little wary of using 4ohm speakers with cheaper/less powerful amps. Interesting that the CEOL quotes into 4 ohms. Maybe they wanted to make it sound more powerful? Maybe it is made to drive 4 ohm speakers, but I doubt it as the matching speakers are apparently 6 ohms. Certainly the Marantz's quoted watts into 6ohms would be higher into 4 ohms (and the CEOL's quoted wattage for 4Ohms would be lower into 6 ohms).

Edit: after looking at the manuals the CEOL can apparently drive speakers from 4-16ohms, while the Marantz recommends 6-8 ohm speakers.
 

Overdose

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Feb 8, 2008
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Thanks for the reply.

That's the problem I see with these units. The manufacturers quote power ratings, but there is no information to indicate any flexibility, but then there is always going to be a compromise in this area when space for the required power supplies will be limited due to the size of the box it all squeezes in to.
 
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Anonymous

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What's more important is the THD+N (total harmonic distortion plus noise) figure at the quoted power rating, also if it is for a single channel, two channel or for AV receivers 7 channels driven. It is easy to bolster power figures if you push the amp to 10% THD+N. Look for power ratings taken at 0.1% or lower, and with all channels driven (quoting for a single channel means half the load on the power supply).

Strictly speaking the power figure should be taken at exactly 230V AC as well, since higher values will give higher power for the same THD level...
 

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