Value of an amp doubling wpc 8ohm vs 4ohm

[Gump]

I know this has been discussed before but I did a search and it's a hard subject to explain to a computer because I couldn't find anything.

How important is it for an amp's wpc to double from 8ohm's to 4 ohm's? Is it really that big of a deal? And I'm talking pure SQ here.

Specifically: Does an amp with 200wpc at 8ohms and 400wpc at 4 ohms sound significantly better than an amp that puts out 200wpc at 8 ohms and only 300wpc at 4 ohms?

How much should this weigh in judging the quality of an amp?

I am currently evaluating the Anthem P5 amp as well as the ubiquitous Classe 5200. The Classe comes fairly close to doubling wpc while the Anthem is 325wpc at 8 ohms and 500wpc at 4 ohms. (I won't insult you by doing the math for you here).



Educate me wise ones!!!

[Karma]

HI Gump,
The short answer is that there is no short answer. Without getting into a complicated explanation, yes it is important but it's not always obvious. The ability for an amp to double up is largely a measure of two things:
1. The current delivery capability of the power supply and,
2. The ability of the amp to dump heat.

Doubling is an indication of the power supply to maintain its voltage under the varying loads that the typical loudspeaker presents to the amp. Ideally, the power supply voltage will not vary at all when the speaker demands more current. If it does vary, intermodulation distortion (IM distortion) increases. IM is the most egregious type of distortion; much more sonically harmful than harmonic distortion.

Thus, doubling keeps IM low under dynamic real world conditions at the edge of the amps power performance envelope. While the concept is expressed as a simple spec, its real significance is how the amp performs dynamically with real speaker loads (remember, any given speakers impedance varies all over the place often 300% or more) and real music passing through the system.

Yes, it is important. It is a mark of quality (and cost!). Also, this particular discussion only makes sense in the context of solid state designs.

Sparky

[grit]

I'll toss in a thought - It really depends on the speakers you're powering. My Aerial's are a difficult load to drive, and are very close to being a 4 ohm speaker. So for my application, it makes a big difference. Most speakers really have a range of resistance that varys with the frequency they are producing.

BTW, that Classe; if you look at the stats closely for the x200 series, you'll notice that for the 2200, the power almost (if not exactly doubles. My guess is the reason the 5200 does not double is because you are driving 5 channels at once. If you use it for only 2-channel (eg, stereo listening), it probably will almost exactly double.

[peterS]

it has everything to do w/ regulated vs unregulated power supplies
there are strong opinions on both ends of the spectrum for which offers better "sq"

at lets say 8 ohms unregulated will increase/ decrease its rail voltage directly proportional to the voltage it is receiving (ie 120 v) obviously this is far more important in car audio where voltage and current are always an obstacle to overcome
lowering the impedance on a unregulated supply will cause voltage sag... ie power output will not double when impedance is cut in two

a regulated amp will always maintain its rail voltage to maintain the same power output
the cost is two fold, one it will have a lower rail voltage per given design (or it will cost more to match the output of unregulated) and it draws more current when the input voltage drops.... (the later takes on more importance in car audio when amperage is in the hundreds!)
both add to $/watt in board design and heat dissipation

there of course are many amps that are somewhat regulated, or not "stiffly" regulated
as with many compromises this is probably the best solution for most

the only instance i could justify a stiffly regulated amp in home use is probably a speaker with a wicked impedance curve.... i have heard that the martin logan summits fall into this category.... would need to be quite the amp

[Karma]

HI Peter,
In my experience, the "B+ and B-" power supplies, that is those that supply power to the output devices are not regulated on the vast majority of amplifiers even those that can double. I mean by that that a formal regulator is not involved at all. Rather, voltage is maintained by reducing resistance in the power supply, very large filter capacitors (a transient signal issue only), using very large high current capacity rectifiers, and large gauge power wiring. The power transformer does the trick by using large diameter wire in the windings and are wound to reduce magnetic losses. These power supplies are very expensive to build and the transformers are huge.

Formal regulators have their own problems and are not a silver bullet which is why they are not generally used especially in high power specified amplifiers.

Do you know something different?

Sparky

[ThomasW]

Sparky is correct.....

There are probably a 1/2 dozen or so home audio amps on the planet with regulated power supplies . And regulated power supplies aren't related to an amp's ability to double down.

Suffice to say that unless one is buying certain VERY high end Levinson, Halcro, or Linn, etc, you aren't getting a regulated power supply.

Personally I do buy amps that 'double-down', that way there's little worry about what speaker you hookup.

[peterS]

HI Peter,
In my experience, the "B+ and B-" power supplies, that is those that supply power to the output devices are not regulated on the vast majority of amplifiers even those that can double. I mean by that that a formal regulator is not involved at all. Rather, voltage is maintained by reducing resistance in the power supply, very large filter capacitors (a transient signal issue only), using very large high current capacity rectifiers, and large gauge power wiring. The power transformer does the trick by using large diameter wire in the windings and are wound to reduce magnetic losses. These power supplies are very expensive to build and the transformers are huge.

Formal regulators have their own problems and are not a silver bullet which is why they are not generally used especially in high power specified amplifiers.

Do you know something different?

Sparky

i am sure there are many inbetween
i am sure that many manufacturers that boast of regulated supplies are actualy utilizing the above (at least in car audio) as it is a big deal to some to 'get more power' when bridging

[Karma]

HI Peter,
Please don't take this wrong. I'm not trying to out argue you. I promise. But we should get the facts straight.

Car audio is an entirely different beast and should not even be in this converstion. A car battery is about as perfect as a DC supply can get. It's ability to deliver a constant voltage that is independent of current is impressive. The limitation is the power wiring as you probably know. Because of a batteries low voltage, the current through the power wiring can be very high; hundreds of amps in the case of a high power amplifier under the right signal conditions. In this case, the regulators are a necessary but not an ideal solution because the regulators themselves are not ideal.

Furthermore, all accessory automobile power amps use DC to DC converters to achieve the voltages necessary to produce high power. The converters may well include regulators in an attempt to negate the resistance effects of the power wiring. But the battery itself is actually far better than the regulators.

I believe we are talking about hi fi home amplifiers that plug into the wall. I doubt that any car amp can compete with the amps we discuss on this forum from any point of view except power ratings. I suggest that we keep this discussion real and on track.

Sparky

[peterS]

HI Peter,
Please don't take this wrong. I'm not trying to out argue you. I promise. But we should get the facts straight.

Car audio is an entirely different beast and should not even be in this converstion. A car battery is about as perfect as a DC supply can get. It's ability to deliver a constant voltage that is independent of current is impressive. The limitation is the power wiring as you probably know. Because of a batteries low voltage, the current through the power wiring can be very high; hundreds of amps in the case of a high power amplifier under the right signal conditions. In this case, the regulators are a necessary but not an ideal solution because the regulators themselves are not ideal.

Furthermore, all accessory automobile power amps use DC to DC converters to achieve the voltages necessary to produce high power. The converters may well include regulators in an attempt to negate the resistance effects of the power wiring. But the battery itself is actually far better than the regulators.

I believe we are talking about hi fi home amplifiers that plug into the wall. I doubt that any car amp can compete with the amps we discuss on this forum from any point of view except power ratings. I suggest that we keep this discussion real and on track.

Sparky

to clarify i only see the merit and the mention of a regulated power supply in car audio so i used them as an example, i just dont see how it makes any difference in the a/c realm... if someone knows otherwise im all ears
fyi car audio operates off of the alt (14.8v) dipping into the battery (12.8v) is to be avoided . furthermore the 2V drop does have significance

you are pretty off base on your assumptions on the quality of amplifiers, there is definitely a niche ( brax, zapco, audison, tru, etc) but a cars acoustics and noise floor negate/ limit any 'sq' gains imo

i think we would both agree that an external power supply would be a far better investment than any form of regulation, correct?

[Karma]

HI Peter,
I would love to get into a discussion of the relative merits of home hi fi and car audio. I think it would be very interesting but this thread is not the place to do so. I don't know if such a discussion has a place on this forum.

Regulators do have a place in amplifier design. Maybe in the future they will find a place in home audio. Class D amps are finally maturing and being produced for home audio. So are switching power supplies. Like you, I don't see a good reason why regulators are not used more on the high power supply lines but they are not. Right now they are rare. Out of the thousands of home audio amplifiers I fixed when I ran my repair shop I did not see one! They are commonly used for the lower power supply voltages. I don't have the reasons why. Maybe someone else can tell us.

Sparky

[peterS]

HI Peter,
I would love to get into a discussion of the relative merits of home hi fi and car audio. I think it would be very interesting but this thread is not the place to do so. I don't know if such a discussion has a place on this forum.

Regulators do have a place in amplifier design. Maybe in the future they will find a place in home audio. Class D amps are finally maturing and being produced for home audio. So are switching power supplies. Like you, I don't see a good reason why regulators are not used more on the high power supply lines but they are not. Right now they are rare. Out of the thousands of home audio amplifiers I fixed when I ran my repair shop I did not see one! They are commonly used for the lower power supply voltages. I don't have the reasons why. Maybe someone else can tell us.

Sparky

to the contrary, i dont see why they would be necessary in home audio... id guess its either because the voltage drops in the ac world do not translate into audible differences in output or in extreem cases where it does pose a problem external power suplies can be used

[ThomasW]

Here's a little snip from another discussion that deals with this question...

We don't see regulated power supplies for home amplifier output stages for several reasons.

First, is that with the high current involved, regulation becomes expensive, as the regulation devices need to handle just as much or more current/power as the amplifier output devices.

Second, power supply regulation stabilizes rail voltage by holding it at a level below the normally available rail voltage, so that it will limit 'headroom' and available dynamic power. That's not to say that you will lose dynamic performance in terms of how dynamic the content is, but rather that you will lose dynamic output level capability in an absolute, peak power kind of sense.

Third, for the money spent on regulating that power supply, you can often divert that to greater improvements in other parts of the amplifier, either in increasing the power supply's capacity, or using nicer/more parts in other circuits.

[Karma]

HI Thomas,
There seems to be no question that cost trade offs are involved. I suspect that the required quality and complexity of the regulation circuits make the proposition difficult. Even so, the technology does exist as evidenced by commercial bench power supplies which are definitely high performers under complex load conditions.

It is interesting that while the idea of rail regulators have been around for a long time, they have not penetrated the market in any significant numbers.

Sparky

[whoaru99]

....
Suffice to say that unless one is buying certain VERY high end Levinson, Halcro, or Linn, etc, you aren't getting a regulated power supply.

Perhaps the newer Levinsons do, but my good old No. 23 does not have regulated rail supplies - at least not according to the manual.

I think this old dog does it by sheer massive power supply; 2.52kVA worth of transformers and 144,000uF capacitance. The old dog can hunt though!!

As mentioned, the importance comes with low impedance speakers. I'm using Studio 100's that have a decent efficiency and are rated at 8 Ohms, but in the same breath, are somewhat hard to drive because of a fairly wide impedance dip below 4 Ohms all the way down to about 2.5 Ohms around 90-100Hz. This is where the amp can make a very significant difference in how well a speaker performs.

[Karma]

HI whoaru,
I also have a Levinson No. 23 amp. I use it in my main system to drive my dual Kinnergetics SW800 subwoofers, one sub per amp channel. These are 4 ohm speakers. The amp does a great job delivering 400 very stiff watts per channel into the 4 ohm load and never showing any signs of stress. This is a perfect example of an amp doubling its power as the load decreases by half.

When going full tilt the power draw modulates the table lamp next to my listening chair with the bass. This is not good and a little scary. At some point it needs to get a dedicated service. It is a wonderful amp.

Initially I used the No. 23 to drive my Martin Logan CLS IIA electrostatics. The CLS is famous for being a difficult drive with their impedance going as low as 1 ohm at high frequencies. Very few amps can do the job well. The No. 23 did not even brake a sweat.

Sparky

[Gump]

Excellent information, gentlemen. Much food for thought.
It sounds like the speaker load is an important variable in this equation. I've got B&W 803D's. I'm now convinced I'll have to give more importance to the load doubling capabilities of any amps I'm considering buying if I want to get the best out of them, especially while driving them at more demanding levels.

I appreciate the educational info.

Sparky, How can I get my lamp to do that? ......in case I put on any old 70's cd's and want that "disco" lighting effect. :rofl:

[peterS]

^ i dont think you have to worry
the impedence of those speakers should be very smooth

[whoaru99]

803D min impedance 3.65 Ohms @ 99Hz...

[Kobus]

So in trying to understand the basics better!

An amps specs is 200wpc 8 ohms - 330wpc 4 ohms.

So the bass at the 4 ohm level will be a dB softer than what it should have been.

Is this correct.

Kobus

PS: I know it is a simplistic view, ignoring IM distortion as Karma mentioned, but is it also correct. (BTW, what is IM distortion)

[whoaru99]

Don't know what the answer to that is...

[peterS]

803D min impedance 3.65 Ohms @ 99Hz...

i was refering to the phase of the impedence graph

[peterS]

So in trying to understand the basics better!

An amps specs is 200wpc 8 ohms - 330wpc 4 ohms.

So the bass at the 4 ohm level will be a dB softer than what it should have been.

Is this correct.

Kobus

PS: I know it is a simplistic view, ignoring IM distortion as Karma mentioned, but is it also correct. (BTW, what is IM distortion)

vs 400w yes
can your ear distinguish between 1 db?- highly debatable