Are amplifier specs a problem?

[Matthew J Poes]

A friend cued me into this article:
https://www.audioholics.com/audio-amplifier/ftc-consumer-audio

And I took a read and posted some comments. I think its a really interesting article, but not because of the FTC portion of the issue. Namely, I think amplifier ratings/specs are a problem generally.

First, I don't think the average consumer understands those specs all that well, and I think manufacturers take advantage of that.

Second, I think new amplifiers, namely Class D amplifiers, have changed things a bit. These things oscillate, on purpose. That isn't a problem, but the filter (or lack there of) can create problems on the output. It doesn't always filter all the noise out (well ok, it never really does). They have higher distortion at high frequencies than other amplifier types, and sometimes its problematically so. They rely on assumptions about the speakers that can make them a bad match for speakers that are not particularly reactive, such as planar drivers, air-motion tweeters, etc. For example a filterless sigma-delta modulated Class D amplifier and a direct connection to an air-motion tweeter with nothing more than a resistor and capacitor may not be very good friends.

Now more than ever, manufacturers are starting to fool around with all of this. Gene calls out Onkyo for their newly inflated amplifier specs, which have actually been noted as illegal (apparently they have been reported to the FTC). With Class D amplifiers becoming more popular I also expect to see more of this, as it isn't hard to design an amplifier that might measure as 50 watts per channel in a full bandwidth all channels driven scenario and 100 watts as a single channel at 1khz. Further many companies are playing terrible games with the impedance in question, testing at 6 ohms was common, but I've now seen some amps show only specs into 4 ohms, 2 ohms, etc. Numbers that aren't of much use to most consumers with more typical speakers.

 

[Tony V.]

I don't think most consumers care any more about specifications or what they mean. We are a dying breed of individuals and we are not what is driving the industry unfortunately.

It would be a surprise to see many young people in the boutique hi fi store buying high end gear. Most go to bestbuy or buy on line not ever even hearing a single sound from the speakers or looking at the specifications. When I was on the other forum I did some comparisons and receivers with larger power supplies had the ability to drive the internal amps much closer to their advertised specifications. Now with some going with class D amps this might not be the case as digital amps require much less power. The issue is that entry level receivers as well as most mid level ones have class A/B amps and they don't benafit from decent size power supplies.

 

[Wayne A. Pflughaupt]

Prime examples of this issue have popped up at Audioholics recently.

One fellow was complaining that his speakers sounded “lifeless” after switching from a Yamaha RX-Z9 to an RX-A3070. Power ratings between the two don’t differ enough to make a difference (170 W for the Z9 and 150 W for the 3070, both at 20-20 kHz @ 0.015 % and 0.6 THD).

However, the Z9 weighs 26 lbs more than the 3070, which suggests the former has a more robust power supply (Sound and Vision tests confirmed that the Z9 could put out a hefty 165 watts @ 8-ohms @ 1 kHz with all channels driven, and 207 watts at 4-ohms). The strange thing was that the party was using Klipsch speakers, which typically are an easy drive for any amplifier.

The second case was more obvious and problematic. The forum member had switched from a Denon AVR-3805 to a Denon AVR-X2300 and was complaining that he got noticeably higher volume levels from the 3805. The 3805 was rated for 120 watts @ 8-ohms, 20 Hz – 20 kHz @ 0.05 THD. By comparison, the X2300W is rated for 125 watts @ 6 ohms, 1 kHz @ 0.7 THD.

It’s easy to see that all the 2300 spec parameters – rating at 6-ohms; rating at 1 kHz instead of broadband 20 Hz – 20 kHz; rating at a higher THD – are designed to inflate its power specification. If it had been rated with the same benchmarks as the 3805, I’ll bet its wattage specification could easily be half that of the 3805.

Regards,
Wayne A. Pflughaupt

 

[ddude003]

That is a very good question Matt... As I understand it there is no "standard way" to bench test and acquire the specs across the industry... No UL, so to speak, for the OEMs... And remember there are Specs and then there are Benchmarks... It takes a real Geek to sort things out...

In my own experience there has alway been something to be said about hurling watts of power thru pounds of copper (read large, quality, output transformers and autoformers)... Everyones ears are different...

 

[ddude003]

Wondering if there is an industry standard of watts per channel per pound of copper ;^)

 

[tesseract]

Due to the Japanese spec-racing wars, the FTC did put the clamp down a couple of decades ago. There could have been more done, and perhaps should be now, but at the time their action was sufficient.

Oscillation is one of the reasons I use MIT cabling (dons flamesuit). Sounds like my planars (and ribbons) might be happy with that? These cables are also said to filter back EMF, which may or may not be necessary.

 

[ddude003]

Due to the Japanese spec-racing wars... a couple of decades ago...

That sounds like the "gentleman's agreement" for the 1990's J-spec sports cars... I've still got one of those I drive on weekends... 8^)

I have/had a lot of friends that are bench tech EEE's that have put more than one of my, or their, preamps and amps on some pretty exotic test equipment and shook their heads in disbelief at the hard truth of those so called specs... That being said, specs are just a guide as to what may be possible... A "system" is only as good as its weakest component... And a "system" real world benchmark is what your ears hear and in turn brain decodes into aural nirvana or not...

As for my thoughts on cables... Maxwell suggests that _all_ things transmit and receive... It makes sense to keep that in mind when configuring a "system"...

 

[AudiocRaver]

When someone says "this amp sounds beetter to me than that one," or plays louder, or whatever, my first thought is to dig into the conditions of the comparison and reduce variables. There migiht be differences, and there might be measurable differences that are not obvious from specs - or even covered in the specs. Standsards can help, and can sometimes hurt if a manufacturer can not spec something that clearly shows a competitive advangabe but is restricted by a standard from saying it.

 

[ddude003]

="Sounds like my planars (and ribbons) might be happy with that? These cables are also said to filter back EMF, which may or may not be necessary."

Thank you... Your comment of back emf has me wondering how much back emf is produced by an electrostatic panel vs planars vs a ribbon vs a std voice coil type speaker and the effect on the feedback designs in amps and Wide Band Damping Factor specs and of course output transformers and autoformers...

 

[Tony V.]

When someone says "this amp sounds beetter to me than that one," or plays louder, or whatever, my first thought is to dig into the conditions of the comparison and reduce variables. There migiht be differences, and there might be measurable differences that are not obvious from specs - or even covered in the specs. Standsard can help, and can sometimes hurt if a manufacturer can not spec something that clearly shows a competitive advangabe but is restricted by a standard from saying it.

So true, user error is also a big factor here in setup. I can't recall how many times I've responded to questions on forums and find out that the setup was done incorrectly or the mic was placed wrong.

 

[dc2bluelight]

Oscillation is one of the reasons I use MIT cabling (dons flamesuit). Sounds like my planars (and ribbons) might be happy with that?

This is 2018. If an amp is so unstable as to break into oscillation due to a reactive load, it's either broken or designed wrong. Ditch the amp in either case.

These cables are also said to filter back EMF, which may or may not be necessary.

Ok, well you do have your flame suit on...
What you should filter for is back-MBS, not back EFM. If cables filter back EMF they also filter forward EMF, and you do not want that.

 

[AudiocRaver]

I am sure you know this, but for the benefit of all...

EMF stands for Electromotive Force, or voltage. It is a general term that can refer the "good" voltage (audio frequency) that drives your speakers and can refer to the "bad" voltage that interferes with something else, like your amplifier output stage. As interference, it is often called Electromagnetic Interference. or EMI, usually high-frequency interference, above audio frequencies, and into the RF range.

While Dennis's post might have been a tad more specific, it was not incorrect, according to accepted definitions.

I have never heard of back-MBS, and a Google search turns up nothing I could find having to do with audio or electronics. Could you please explain what it is for us? Thanks.

And while we appreciate all accurate and useful information,, including polite corrections where appropriate, no flame suits are needed around AV NIRVANA, we do not tolerate flaming in any way, shape, or form, even in jest. Thanks for understanding.

 

[dc2bluelight]

I am sure you know this, but for the benefit of all...

EMF stands for Electromotive Force, or voltage. It is a general term that can refer the "good" voltage (audio frequency) that drives your speakers and can refer to the "bad" voltage that interferes with something else, like your amplifier output stage. As interference, it is often called Electromagnetic Interference. or EMI, usually high-frequency interference, above audio frequencies, and into the RF range.

Actually, EMI is the result of some form of coupling of an undesired signal. The coupling could be inductive, electrostatic (capacitive) or actually connection (conduction). That signal could take several forms, EMF is one of them, but so we don't get mired in terminology...EMF is measured in Volts, and is in the vernacular, "voltage".

While Dennis's post might have been a tad more specific, it was not incorrect, according to accepted definitions.

I have never heard of back-MBS, and a Google search turns up nothing I could find having to do with audio or electronics. Could you please explain what it is for us? Thanks.

You needed to apply +3dB sense of humor. M=Marketing.

And while we appreciate all accurate and useful information,, including polite corrections where appropriate, no flame suits are needed around AV NIRVANA, we do not tolerate flaming in any way, shape, or form, even in jest. Thanks for understanding.

Ouch. So 3dB of sense of humor might be a lot to ask, I guess.

I personally have an extremely low tolerance for audio mythology, and simply cannot take audiophoolery seriously. So when it comes up, there's a strong likelihood of a snarky quip out of me rather than just firing both barrels. Sometimes I don't have the time to sit and type out a full explanation (and explaining your joke is always a barrel of fun) but will always come back later and demystify if necessary. But if it's not appropriate to take even a little exception to something that is without scientific merit, or if what I posted is considered a "flame" around here, just let me know now so we can make this easy.

The "correction", if that's what it seemed like, is in the marketing hype of cables that proclaim that you can somehow passively filter back-EMF independently from...well...EMF. The concept of back-EMF in a system involving speakers is EMF that opposes the original cause, the current that moved the voice coil, caused by the movement of the coil on what is essentially a spring, through a magnetic field. The problem is that both the EMF from the amp and the back-EMF from the speaker are AC signals appearing on the same conductors at the same time. There is no separating them passively or actively. Once causes the other and they co-exist as a result. You can measure the effects, but that's about it. Wire cannot filter back EMF, no conductor can, which makes at least part of his post incorrect according to all definitions of the mechanisms. It's marketing Blue Smoke, hence my (apparently quite lame) quip about back-MBS. You can lump it in with directional cables, cable conditioning, risers, the whole messy lot. But marketing it is. And I have no issue with marketing so long as there's a shred of truth in there to provide actual value.

Sorry, Dennis. Sorry Mr. Raver. We good?

 

[tesseract]

@dc2bluelight - You understand that this is a filtered cable we are discussing and not just wire?

Read my post carefully. I made no claims, other than protection from oscillation (Spectral Audio has proven this is could be necessary) which, being an audio reviewer, is a protection I don't mind having.

Perhaps you could aim this at the people actually making the claims and give MIT a call? Starting another thread about what you might find out would be welcome!

 

[AudiocRaver]

Yes we are. Beg pardon if I over-reacted. Thanks for the explanation.

 

[AudiocRaver]

Sense of humor is always welcome, when applied in unquestionably friendly terms. Flaming is so prevalent in the internet world that I have a tendency to stomp on sparks so that I will not have to call in a fire truck later on. "Only you can prevent forest fires."

'Nuff said. We are good.

 

[dc2bluelight]

@dc2bluelight - You understand that this is a filtered cable we are discussing and not just wire?

Yup, they would have to be.

Read my post carefully. I made no claims, other than protection from oscillation (Spectral Audio has proven this is could be necessary) which, being an audio reviewer, is a protection I don't mind having.

I responded to both the oscillation issue and this: "These cables are also said to filter back EMF". As to oscillation, why do you think you need protection? Of course it could be necessary, but the solution is a better amp design. Oscillations are never present in isolation from other issues. If it oscillates, ever, it's designed wrong or broken. You can choose to put a band-aid on it if you like, but that doesn't change the design.

Back EMF has been addressed.

Perhaps you could aim this at the people actually making the claims and give MIT a call? Starting another thread about what you might find out would be welcome!

Well, sorry about that. I figured I'd respond here because I thought forum members were sort of "friends"...sort of...and I do care about friends and people in general. I've already read the MIT site. I don't know what would make anyone think they'd welcome communication from an engineer who takes issue with their 'science', and applies actual truth in audio. That unproductive. I don't care at all that they make $10K speaker cables, it bothers me greatly that people buy them when every issue they "address" can be dealt with better and cheaper elsewhere with a total system design approach.

I have no idea how to tell if a contribution to a thread would be welcome or not, but I'm getting the idea pretty fast. Good think I found this out now before power cables came up!!

Again, guys...so sorry to offend. I'll give you all the room you want.

 

[tesseract]

"I have no idea how to tell if a contribution to a thread would be welcome or not, but I'm getting the idea pretty fast. Good think I found this out now before power cablescame up!!"

Power cables? There really is no reason for snark, nor a need to play the victim. Your insight is welcome here, just leave negativity at the door when you come in, please.

Once again, my personal choice in amplification is not the concern. It is other amps that come my way that might be.

Let's steer this thread back onto topic.