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
I think that what Ralph is saying is that doubling power into 4 ohms is only necessary if you drive the amp to its full output. 

If your amp puts out 150 watts into 8 ohms and 200 into 4 ohms, it will drive your speakers just fine if you only need 100 watts into the 4 ohm frequencies to drive them as loud as you want to listen to them.

Is that right, @atmasphere ?

Playing your speakers (and most speakers) with 100 watts into 4 ohms would be really loud.  I think any of the amps you're looking at will drive your speakers satisfactorily.  So, as Ralph said, try to listen to the amps and pick the one that sounds the best to you.


n80 But I’m seeing a number of respectable mid-fi integrateds with the same wpc for both 8 and 4 ohms.
Severely current limited either on purpose for damage protection (maybe by autoformer) and/or by bad design, these amps are not ideal to have with 4ohm nominal or less speakers
Because 4ohm nominal speakers can go down even lower than 4ohms, maybe 2ohm, and even lower again as seen by the amp if there is >-50 negative phase angle involved at those low impedance’s.
Good place to learn, study Stereophiles speaker bench testing, usually the first 3 or so paragraphs with graphs will give you far better insight than just words do here.

Classic example is the 90db efficient Wilson Alexia, which is manufacturer spec’d at 4ohm nominal, yet tests show it goes down to 1.6ohm in the bass and has some -45 degrees phase angle which they say calculates to and presents as 0.9ohm! EPDR (equivalent peak dissipation resistance) as seen by the amp in that bass area.

This is heavy reading 3 pages, so skip it if you want.
https://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2


If watts is all that matters with no current ability, we all own these 3000w $400 Class-D Behringers, and we wouldn’t need an "Amplifier" forum section in Audiogon
https://www.storedj.com.au/behringer-nx3000-ultra-lightweight-3000w-class-d-power-amplifier

These 25w yess!! just 25w ML2 Mark Levinson monoblocks would slay the 3000w Behringer into the Wilson Alexia’s to a given level.
https://www.hifido.co.jp/photo/05/504/50446/c.jpg
https://img.usaudiomart.com/uploads/large/2229202-mark-levinson-ml2.jpg


Cheers George
You guys are teaching me a lot but not making it any easier.


I'm just waiting for the magic word on the perfect $2000 integrated to match with a pair of $6000 speakers.  ;-)

@twoleftears I think those have been recommended but I can't remember if I have checked them out. But I will.

@tomcy6 These speakers will rarely be played at more than 50% volume if that.

@georgehifi I have a Levinson, well, Madrigal, dual monaural amp for my Aerial 7Bs and it is huge and heavy. No way the wife is going to allow a pair of monoblocks in there. She can't wait for me to get the Classe' and the Bryston out.
Your speakers don't look like they would be difficult to drive. They only reccomend and amp of 50 watts or higher. I haven't seen measurements of the 6t but stereophile has the 7t looks like it stays mostly between 4 and 8 Ohms. 

Frequency Response 35 Hz to 25 kHz ±2 dB, -6 dB at 30 Hz
Sensitivity 90 dB for 2.83 volts at 1 meter on axis
Impedance 4 ohms, 3 ohms minimum, low reactance
Power Requirements 25 watts minimum, >50 recommended
Woofers Dual 5.9″ (150 mm) with cast magnesium frames, special papyrus blend cone. copper pole sleeve, dual magnets, 1.25″ coil, long and linear Xmax
Midrange 4.8″ (123 mm) with cast magnesium frame, special papyrus blend cone. copper pole sleeve, dual magnets, 1.00″ copper clad aluminum coil
Tweeter 1″ (25 mm) with thick machined aluminum plate, soft ring-dome design with machined wave guide, dual-magnets, 1.00″ coil, copper pole sleeve
Crossover Fourth order acoustic Linkwitz-Riley, 600 Hz and 4,000 Hz crossover frequencies, 2 physically separate networks
n80 OP
I’m not saying to get the ML2’s, it was used as an example of what does drive speakers.

Your 7B’s drop to 3ohms around 150-200hz not too bad but still needs needs a bit of power there.
But! they are specified as 86db by Aerial, but actually tested by Stereophile at only 84db!!
I would look for a >100w-8ohm amp that can do tested doubling those watts into 4ohms and you should be fine.

Or you can get the $400 3000w Behringer and listen to that, probally not for long.👎

Cheers George