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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
cakyol's avatar
cakyol
940 posts
 
Ideally, a power amp should be able to deliver twice as much power at half the impedance. The way it can achieve this is if:

1) Its power supply can meet the demand (probably the most important criteria).
2) Its output stage/heatsinks are designed to dissipate the demands of the extra power.
3) It is still stable with the higher load (less impedance).

So, if it is NOT able to do it, most likely one or more of the above is suspect. Most of the time, it is the power supply inadequacies (item 1 above).

dave_b's avatar
dave_b
3,159 posts
 
Amp should double.  More power is better.  Class A or A/B best.  Heavy is good.  All the aforementioned has never lead me astray!
atmasphere's avatar
atmasphere
11,857 posts
 
Ideally, a power amp should be able to deliver twice as much power at half the impedance. The way it can achieve this is if:
This statement is false, on account of the fact that list following it is not what is needed. What is important here is that the amp is able to act as a voltage source and to that end, it does not have to double power as the load impedance is halved- at full power. Any amp that has an output impedance low enough will effectively double power as impedance is halved, with the exception of when the amp nears clipping. That is the only time that doubling power might be an issue, and only important if you have a low impedance load and you really for some reason need that last 3dB, which is not a very audible increase to the human ear.

This 'doubling down' thing is mostly marketing and **waaaaay** overplayed.
cakyol's avatar
cakyol
940 posts
 
atmasphere,

You are right in saying that the internal impedance of an amplifier must be way less than the speaker impedance, in order to deliver power indirectly proportional to the speaker impedance. I took that as a given, since that is the case with most amps these days. However, if the supply line starts collapsing under the extra load, it will never be able to deliver the extra power, no matter what other parameters are tweaked.
georgehifi's avatar
georgehifi
10,312 posts
 
This statement is false
This ’doubling down’ thing is mostly marketing and **waaaaay** overplayed.
This is the false statement, and is the typical statement of amp manufacturers that can’t double down with their amps.

However, if the supply line starts collapsing under the extra load, it will never be able to deliver the extra power, no matter what other parameters are tweaked.
Not just the supply, but the whole output stage as a well.

Use this comparison analogy
A 3000w Behringer https://djcity.com.au/product/behringer-nx3000-power-amp-with-smart-sense/?gclid=EAIaIQobChMIsLTX0viJ6wIV3sEWBR0v2w9eEAQYASABEgK3DvD_BwE
Verses
Old 25w ML2 monoblocks, https://img.usaudiomart.com/uploads/large/2229206-5c605986-mark-levinson-ml2.jpg
Both into a pair of the worst speaker loads known, the Wilson Alexia, but still very efficient at 90db, just a horror load.

To a given volume level the 25w ML2 will walk all over the 3000w Behringer for sound quality, control, image and depth.

Cheers George
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