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Same watts at 8 and 4 ohms?

I'm in the market for an integrated amp and trying to sort through tech specs. My understanding of the tech aspects of hi-fi gear is limited. Looking for some clarity in regard to watts-per-channel specs.

It is my understanding that wpc at 4 ohms is typically 1.5x -2x the wpc at 8 ohms.

But I'm seeing a number of respectable mid-fi integrateds with the same wpc for both 8 and 4 ohms. The NAD 388 is one and I think this is true for several of the Cambridge Audio units at a similar price point ($1500-$2000).

The NAD features make a point of saying " 4-ohm stable for use with a wide range of speakers". 

Would appreciate any insight to what these specs mean and what 4 ohm stable really means to me. My speakers are 4 ohm speakers.

Thanks,

George
n80
djones51
4,947 posts
 
With NAD it’s their power supplies and the way they rate. They use 4 Ohm all channels driven over full 20hz-20khz spectrum at certain distortion. They should also show a dynamic rating which will vary by Ohm. For the C388 it’s 250 8 Ohm, 350 4 Ohm and 400 2 Ohm. 4 Ohm speakers need more power from the amplifier than 8 Ohm, the main thing is good power supply in the amp. 
djones51
4,947 posts
 
I have 86dB sensitive speakers but they are easy to drive the impedance doesn’t dip below 5.7 Ohm  so it’s somewhat about impedance. I can play these speakers at deafening levels and not tax my 200 W at 8 Ohm integrated amp.
twoleftears's avatar
twoleftears
5,324 posts
 

Where's @georgehifi when you need him?

NAD and McIntosh are engineered differently, so conventional expectations do not apply.  This may be a good thing or a bad thing.

If well engineered a conventional Class A/B amp should double or nearly double into 4ohms.

Other classes of amp bring different expectations.

But it's really an extensive and complicated subject.

Better to ask about specific brands/models.

lowrider57's avatar
lowrider57
5,418 posts
 
My speakers are 4 ohm speakers.
What speakers do you own; brand and name of model?

The most important detail in determining amount of power to drive a speaker is impedance. And the way to research a speaker is to view the impedance curve which shows how much resistance the speaker has across the frequency spectrum. Most curves can be found online. 


atmasphere's avatar
atmasphere
12,128 posts
 
@n80

Here's the deal:

With most speakers its expected that the amp will 'voltage drive' the speakers (note that I said 'most'- not all speakers behave this way!).


Now if an amplifier 'voltage drives' the speakers, IOW is a 'voltage source', the power it makes into 4 ohms will be double that of 8 ohms, with a marketing exception: it may not do that at full power. So if you are driving the amp alternately into 4 and 8 ohms, right up to nearly its rated power the 4 ohm power levels will be double that of the 8 ohm levels. But right about that point of full power this phenomena stops as the power supplies and/or output devices can't support that power doubling for that last 3dB.

And that last 3dB has little to do with how the amp sounds or for that matter, how it performs on the bench. The amps you mentioned have no worries acting as a voltage source in this conversation BTW.


It does suggest that a corner was cut somewhere, but in the grand scheme of things a relatively small corner, since 3dB simply isn't that audible to the human ear in terms of sound pressure! OTOH, that first watt is far more important as most of the time that will be where the amp is used most and it is entirely unaffected by this sort of thing.

Now if you really want that doubling of power right up to full power into 4 ohms, be my guest but you will be spending a bit more for that last 3dB, and if you happen to own 8 ohm speakers it won't do you a bit of good. My advice is listen to the amp and see if you like it, if so take it home and see if you like it there, if so, fuggettaboudit and enjoy the music :)
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