|   What's up with power ratings? | grampi44
Nov 9, 2003 1:52 PM | | There was a time when the industry had a standard for power ratings and you knew by reading the specs on a receiver what you were getting. The manufacturers, or maybe their marketing departments, have seemingly found a way around the standards.
It used to be if receiver A and receiver B were both rated at 100 watts per channel, with each channel driven into 8 ohms from 20-20Khz @ .008% THD, these two receivers were equal in terms of power output. Now days, these specs don't tell you much anymore. You have to know which receivers have high current power supplies, and which ones don't. For example, I just replaced a Sony receiver with a Denon receiver. The Sony was rated at 5 X 100 watts, while the Denon is rated at just 5 X 80 watts, yet the Denon pushes a very noticeable amount more power than did the Sony. I'm guessing this is because the Denon has a higher output power supply than the Sony had.
I guess my point is the industry needs to come up with a new standard so consumers know where they stand BEFORE they make a purchase. The way it is now is misleading to the consumer. There's nothing more sickening than listening to someone else's Harmon Kardon receiver, with just 55 watts per channel, blow away your Pioneer receiver rated at 100 watts per channel. |
| re: What's up with power ratings? | jackz4000
Nov 9, 2003 3:09 PM | | True. I have a 1987 Kenwood Receiver rated at 100 RMS, both channels driven at 1 kHz, at 8 ohms, 20-20,000Hz with 0.008% total harmonic distortion. Very clean, for the price. Talked to one of the techs at Kenwood. He told me that today its all just a numbers game with most manufacturers in regard to amps and power. For marketing, the numbers are tweaked. They scrimp a bit. A friend who has an audio electronics lab told me the exact same thing, although the high end producers keep the ratings honest. I have noticed some brands rate at 4 or 6 ohms lately, just gotta move those units at a certain price-point. Higher THD #'s. With HT coming on strong--lotta units to move. More for less. |
| re: What's up with power ratings? | mtrycrafts
Nov 9, 2003 7:20 PM | | b You have to know which receivers have high current power supplies, and which ones don't.
Why? How will you know or tell?
b The Sony was rated at 5 X 100 watts, while the Denon is rated at just 5 X 80 watts, yet the Denon pushes a very noticeable amount more power than did the Sony.
How did you determine this? Did you do extensive testing with instruments? What was the continuous RMS rating od each? One channel, two channel driven or all driven at the same time?
You cannot tel by listening.
b I'm guessing
Yes you are.
b I guess my point is the industry needs to come up with a new standard
There is a standard in place. It doesn't cover all channels driven if it is multi channel but they do test in stereo mode.
b There's nothing more sickening than listening to someone else's Harmon Kardon receiver, with just 55 watts per channel, blow away your Pioneer receiver rated at 100 watts
Maybe it doesn't blow it away but is a false perception. |
| re: What's up with power ratings? | grampi44
Nov 9, 2003 8:10 PM | | My statement saying you have to know which receivers have high current power supplies and which ones don't was to make the point that because there are no standards in place to give you this info, you need to find it out on your own. The type of power supply makes a huge difference in just how much power a receiver will put out. The industry needs to establish a rating that gives the consumer some indication of how much current a paticular unit's power supply provides.
How did I determine the Denon had more power than the Sony? I listened to both units, through the same speakers, with the same source materials. The Denon played louder, clearer, and handled the transients (provided more headroom)with much less strain than did the Sony; a clear indication the Denon makes more power. No test instruments needed.
I've listened to a lot of receivers and I can tell you the quality of the power output of receivers such as Pioneer, Kenwood, Sony, JVC, ect., doesn't compare to that of the H/K's, Denons, and Onkyos, even when forementioned receivers are rated at twice the power. It isn't perceived, it's real. |
| re: What's up with power ratings? | Quagmire
Nov 9, 2003 8:28 PM | | You mentioned "headroom" in your post... actually Dynamic Headroom is a useful spec in determining the quality of the power supply. The greater the rating the more available power the receiver or amp has for those demanding transients. Also, RMS ratings down to 4 ohms is a useful spec, although few receivers rate the amp section down to 4 ohms it's not uncommon for good quality power amps to do so. There again, many good power amps provide seperate power supplies for each channel - one of the better reasons to consider the seperates route.
Q |
| re: What's up with power ratings? | mtrycrafts
Nov 10, 2003 9:51 PM | | b although few receivers rate the amp section down to 4 ohms
But some will give you the dynamic ratings into it, or lower loads. |
| re: What's up with power ratings? | mtrycrafts
Nov 10, 2003 9:50 PM | | b you need to find it out on your own.
And how do you do this? Buy some test gear?
b The type of power supply makes a huge difference in just how much power a receiver will put out.
Yes, and is reflected in the specs and bench testing from credible reviewers.
b The industry needs to establish a rating that gives the consumer some indication of how much current a paticular unit's power supply provides.
Irrelevant. The industry has standards on how to rate amps to drive different loads continuously. That is all you need.
b How did I determine the Denon had more power than the Sony? I listened to both units, through the same speakers, with the same source materials.
Not possible.
b The Denon played louder, clearer, and handled the transients (provided more headroom)with much less strain than did the Sony; a clear indication the Denon makes more power.
Not possible.
b No test instruments needed.
Wrong.
b I've listened to a lot of receivers and I can tell you the quality of the power output of receivers such as Pioneer, Kenwood, Sony, JVC, ect.,
I suppose you did your listening double blind so you were not biased?
b doesn't compare to that of the H/K's, Denons, and Onkyos, even when forementioned receivers are rated at twice the power. It isn't perceived, it's real.
Nonsense. You have no basis for this but your unreliable listening. Useless. |
| re: What's up with power ratings? | 3db
Nov 11, 2003 12:56 PM | | The Sony was rated at 5 X 100 watts, while the Denon is rated at just 5 X 80 watts, yet the Denon pushes a very noticeable amount more power than did the Sony.
How did you determine this? Did you do extensive testing with instruments? What was the continuous RMS rating od each? One channel, two channel driven or all driven at the same time?
You cannot tel by listening.
Really?? Interesting that thru listeneing that you can't determine which amp has more power reserves. Playing louder while giving cleaner sound means what exactly?: given the speakers are the same. |
| re: What's up with power ratings? | mtrycrafts
Nov 11, 2003 11:38 PM | | b Playing louder while giving cleaner sound means what exactly?: given the speakers are the same.
Playing louder when, exactely? Between 80watts and 100 watt peaks? A fraction of a dB? In peak performance? |
| re: What's up with power ratings? | 3db
Nov 12, 2003 5:12 AM | | Playing louder when, exactely? Between 80watts and 100 watt peaks? A fraction of a dB? In peak performance?
If amp A plays cleaner and noticeably louder than amp B then I would say that Amp A is more powerful than Amp B. But this would also lead me to conclude that Amp A is underated in terms of power with respect to Amp B. Which amp is properly specced is anyone's quess. I would tend to give that nod to Denon over the other model mentioned (too lazy to look it up ). It would also show me which receiver has the more robust power supply. |
| re: What's up with power ratings? | mtrycrafts
Nov 16, 2003 8:02 PM | | Well, not totally correct.
b If amp A plays cleaner and noticeably louder than amp B then I would say that Amp A is more powerful than Amp B.
If, then yes.
b But this would also lead me to conclude that Amp A is underated in terms of power with respect to Amp B.
Yes, or that amp b is speced at different distortions?
b Which amp is properly specced is anyone's quess.
That is why one should read test specs from multiple sources.
Going back to the 80 vs 100, that dB may or may not be audible, at some sensitive frequency bands, barely:) Unless:
the listening test was unreliable, the specs are way off in favor to the 80watt unit. |
| Power supplies, "dynamic headroom" and other stuff... | Kursun
Nov 10, 2003 12:28 PM | | One way to see that an amp has a good power supply and output stage is to see that it doubles its power output with each halving of load (speaker) impedance. If it has an oversized power supply, its supply voltage will be well regulated and won't drop low with demanding loads. On the other hand, the output stage should be oversized too as low impedance loads will require high currents to be passed.
I don't agree with Quagmire... "Dynamic headroom" is a specification that has nothing to do with quality. A cheap amplifier with soft and ill-regulated power supply will output more power under short term requirements but not continuously or into complex loads. A good oversized amplifier will have 0 (Zero) db "dynamic headroom".
I once had seen a Sony HT receiver specification sheet... It was rated 100W (for a given frequency range and distortion figure) into 8 ohms. But it was rated 40W into 4 ohms! We could get much better information about HT amplifiers if they were forced to specify the the continuous output into 4 ohms. But we shouldn't ever forget that, "we get what we pay for". |
| Power supplies, "dynamic headroom" and other stuff... | grampi44
Nov 10, 2003 12:54 PM | | Good post. Be cafeful with that "we get what we pay for" stuff. Sony could decide to start pricing their stuff 4 times higher than what it is now, but that wouldn't make it any better. |
| "we get what we pay for", Roger Waters, and other stuff... | Kursun
Nov 10, 2003 2:02 PM | | That stuff is really the heart of the matter, you know that...
I am no hi-end'er. Back in the 2-ch days I had considered $400-500 is reasonable sum of money for a 2-ch integrated. Now most people expect to pay $300-500 for a receiver with 7-ch amplification, all sorts of DA/AD decoding, video switching,etc.
As Roger Waters of Pink Floyd fame has said (Amused to Death) "This species has amused itself to death". We are probably more to be blamed than manufacturers, who actually seek nothing but to amuse us for cheap.
We poor members of this species have placed wrong importance on stuff like "brand image", etc. The truth was always at our hand (or somebody else's...):
"We get what we pay for!" |
| Your statement about DH don't look right. | Smokey
Nov 10, 2003 3:31 PM | | You said in your previous post:""Dynamic headroom" is a specification that has nothing to do with quality. A cheap amplifier with soft and ill-regulated power supply will output more power under short term requirements but not continuously or into complex loads. A good oversized amplifier will have 0 (Zero) db "dynamic headroom".
Dynamic Headroom got everything to do with amp quality. A cheap amp can provide continuously into a load, but it cannot provide short powerful bursts known as Dynamic headroom. For example, a 10 watt amp can get as loud as 100 Watt amp due to their RMS (continuously) ratings since it doesn't take too many watts for a speaker to get loud. But a 10 watt (or cheap) amp can not provide short burst of power (that can reach up to 200 watt) to a load, but probably a 100 watt amp can if it have ample Dynamic Headroom.
It is not amplifier's continuos (RMS) rating that determine its quality, but rather its DH rating. So a good size amplifier does not have zero Dynamic headroom, but rather DH in the range of 2-3 dB. If an amplifier have zero DH, the short power burst are clipped resulting in higher THD (Total harmonic distortion) and listening fatigue.
A good amplifier should have RMS rating of 100 watt, and DH rating of 2-3 dB :) |
| *** I'm sorry but You are Wrong, very Wrong!!! *** | Kursun
Nov 11, 2003 10:32 AM | | Dynamic Headroom is a phrase coined by non-engineer hi-fi people, mainly British What Hi-fi and Hi-Fi Choice magazines.
It's very easy to produce an amplifier that has high dynamic headroom. Just replace the power transformer of a high quality amplifier with a cheap weak power transformer, but one with a slightly higher output voltage. If the power supply drops by SQRT(2) under continuous operation you'll get an amplifier that has 3db "dynamic headroom". A high quality amplifier, I repeat has 0 db dynamic headroom.
Here are some link that will provide some food for thought for you:
http://www.alphadigitaltech.com/pdf_files/Dynamic%20Headroom.pdf
"The term Dynamic Headroom was invented by manufacturers who's equipment was designed with too little power supply capacity.... Above-average amplifiers (that have larger power transformers and larger filter capacitors) may have Dynamic Headroom in the range of 0.1 to 1.5 db."
http://sound.westhost.com/power.htm
"If the power supply is regulated or has considerable excess power capacity, the continuous and music power ratings will be almost identical. The difference was (at one time) measured, and was called "dynamic headroom". Few amps have a dynamic headroom of better than 1 or 2dB, and the greater the headroom, usually the cheaper the power supply for the rated power." |
| RMS, DH and THD ratings all go together hand in hand. | Smokey
Nov 11, 2003 2:01 PM | | If you read the disclaimer under your second link (can't open the first link), it said the article is slightly toungue-in-cheek- which mean it shouldn't be taken too seriously.
And after reading the following sentence from that link:"..and the greater the headroom, usually the cheaper the power supply for the rated power", I see why it is tongue-in-cheek because that sentence is basically wrong.
One main thing that was left out of picture in your link was THD (Total Harmonic Distortion) ratings. It is true that some boomboxes have excessive peak power rating, but if you look at their THD%, it will be in excess of 1% and most likely 10%. Which mean you are not hearing peak power, but distortion. And that is the down side by using cheap power supply. It is real easy to have high peak power (or RMS) rating, but it is hard to offer it at low THD% percentages (below 0.3%). And if you have excessive THD, it is not called Dynamic headroom anymore, but distortion.
And your statment, "A high quality amplifier, has 0 dB dynamic headroom.", is basically wrong in concept. Unless we are talking about high power amps such as Carver where its RMS power rating is around 200-300 watts, then having a quality amplifier with zero DH is asking for trouble. If you have no DH above 100 watt where most of music peaks occur, then the amplifier is clipping which mean distortion. So quality amplifier is measures by how it can deliver high short term (DH) power, rather than continuos (RMS) power. With low THD% of course :) |
| that's your choice. | Kursun
Nov 11, 2003 2:43 PM | | Some people actually prefer "soft" type power supplies as amplifiers with that type of power supply can give shorts bursts of relatively higher power. But this type of amplifiers are not successful at powering hard to drive loudspeakers. An amplifier with well regulated oversize power supply gives cleaner power at all power levels and better damp the speakers.
This is a matter of choice, if you prefer "soft" type cheap power supplies this is your choice.
The truth is if 100W is not enough for you, than you should buy a more powerful amplifier, not look for more DH.
Try to get at my first link too. There are more goodies for you there. Don't you have Adobe Acrobat installed? |
| Alot of... | Quagmire
Nov 11, 2003 2:48 PM | | ...good information here, Kursun. And you know, that's what this forum should really be about. I don't mind being corrected at all... let me be the first to say that you are RIGHT and that I am WRONG. I would only add that in my opinion, most amps, particularly those found in mass market receivers are not that "powerful" and that the dynamic headroom rating of an amp can at least give some idea of how the amp might react to dynamic requirements beyond its nominal rating.
If I understand the information you provided, amps with low dynamic headroom had better be "very powerful" because once they are driven much beyond their RMS rating they will be into clipping. Also, I do have to say that I think some manufacturers do manage to provide their amps with useful dynamic headroom without sacrificing quality. Products with seemingly low WPC ratings like some offerings from NAD, Rotel, and Adcom spring to mind. I've had a little Adcom GFA 535 amp (60 wpc) for years now, which I believe was a Nelson Pass design, and it has held it own very well against receivers rated at 100 wpc or more.
Thanks for the links and the info, maybe you can educate us further on this topic.
Q |
| Thanks for the compliment. | Kursun
Nov 12, 2003 10:37 AM | | Several factors come to my mind that may make the sound of an amplifier seem higher than its rated power:
* If its power supply is robust, it will produce higher power into lower impedance and hard to drive speakers (which introduce lots of capacitance, inductance, back-emf and phase shift due to its high order passive crossover).
* Some brands probably under-rate their products on purpose, as a marketing tactic, to gain market recognition and brand image. (I don't think a decent brand needs such misleading tactics, though you are being deceived on the opposite direction.)
And last but not least:
* An amplifier producing somewhat higher distortion, psycho-acoustically will seem to produce more power than an amplifier with pristine, distilled water clarity sound. Noise is always louder.
Also,
like mtrycrafts, I think the ear, though a fascinating instrument by itself, is not a very accurate SPL meter. |
| Credit where credit is due... | Quagmire
Nov 12, 2003 11:40 AM | | Interesting points:
So if I may summarize what you're saying on this issue...
Amplifiers which are built with ample power, represented by a higher value RMS rating, need not rely on so called "reserve power" which may be indicated by high dynamic headroom numbers. Is this even close? If so, then what in your opinion would need to be a minimum RMS rating for an amp or receiver to qualify as being powerful enough? It would seem that there must be some minimum because an amp with zero headroom will begin clipping as soon as that minimum is breached. Do you see any way that amps rated below this minimum could employ some useful means of gaining headroom without sacrificing quality?
Q |
| Good questions Q. | Smokey
Nov 12, 2003 1:19 PM | | And I got a question for you. You said:"Do you see any way that amps rated below this minimum could employ some useful means of gaining headroom without sacrificing quality?"
Are you saying that to gain headroom, we have to sacrifice quality?? |
| Good questions Q. | Quagmire
Nov 12, 2003 7:18 PM | | "Are you saying that to gain headroom, we have to sacrifice quality??"
No, I think that's Kursun's position. I think he makes some good points, although I'm not entirely convinced. That's one reason I wanted him to expound on this a little. So often these issues get boiled down to absolute statements such as "ALL amps with high dynamic headroom ratings have weak power supplies." or "ALL amps with high RMS values are good amps.". I don't buy into that. Even in the links that he provided you'll find many words like "usually" and "many" instead of "always" and "all". But I do think he was right in challenging my assertion that a higher dynamic headroom rating is indicative of a good power supply. I now see how it is possible for manufacturers to achieve a high value with regard to this spec without including a good power supply. I just happen to think that it may be possible to accomplish both - a good strong power supply with decent dynamic headroom.
Q |
| Good questions Q. | Kursun
Nov 13, 2003 10:03 AM | | A special case for amplifiers with large Dynamic Headroom would be class G and class H amplifiers. These amplifiers have at least two power supplies: one high current/low voltage, the other low current/high voltage. The second power supply supplies the higher voltage for short peaks.
Though these design concepts have generally been used for inexpensive equipment or pro-audio, there is no reason why it shouldn't be used for higher quality home equipment. In fact Marantz MA-500 and MA-700 are two good examples of this design.
On the other hand a manufacturer who designs and builds a no expense spared amplifier wouldn't design an amplifier with a built-in power supply voltage drop. He would just put in the best transformer and output transistors. A class G or H amp just saves the manufacturer from using oversize transformer, output transistors and heatsinks.
As for the words "usually" and "many" instead of "always" and "all"..., that you mention in your post... Well, this is probably the understated way engineers like to talk. They don't like to talk big, very much unlike politicians... |
| I thought....... | Smokey
Nov 13, 2003 3:59 PM | | ..that good amplifiers had to keep output voltage rail constant despite change of loads?
Having two power supply to provide high current/low voltage and low current/high voltage would go against that concept, wouldn't you say? |
| Good questions Q. | mtrycrafts
Nov 16, 2003 8:10 PM | | b I think he makes some good points, although I'm not entirely convinced.
Do a googole search. There are numerous other links to explain dynamic headroom. While most seem to say that very high dynamic numbers, 6 dB is an indication of a poor power supply, you don't need to select an amp that has almost nothing, fractions of a dB. Up to 3dB is good what I gathere. |
| Good questions Q. | Kursun
Nov 17, 2003 1:34 PM | | Sorry I am late answering. Last week and this week I had to do a lot of out of town traveling...
Consider the two examples below:
(1) AMP A: (with soft and inexpensive type power supply)
Maximum output specification:
Continuous output: 250W@8 ohm - 340W@4 ohm - not recommended into 2 ohms
Dynamic output: 300W@8 ohm - 380W@4 ohm - not rec.into 4 ohm
(2) AMP B: (with hard and expensive type power supply)
Maximum output specification:
Continuous output: 250W@8 ohm - 500W@4 ohm - 1000W@2 ohm
Dynamic output: 250W@8 ohm - 500W@4 ohm - 1000W@2 ohm (same power under continuous and dynamic conditions)
You can see the problem with AMP B: Though it is built as a 1000W amplifier and is capable of outputing very high currents, it is used only as a 250W amp most of the time (such a waste!); whereas AMP B can actually rise to 300W under dynamic conditions.
What I am proposing, as an ideal amp, is to take AMP B (rather than AMP A) and transform it to class G, so that its specification will turn in to something like this:
(3) AMP C: (with hard and expensive type power supply + class G operation)
Maximum output specification:
Continuous output: 250W@8 ohm - 500W@4 ohm - 1000W@2 ohm
Dynamic output: 1000W@8 ohm - 2000W@4 ohm - 4000W@2 ohm
Class G and H has been used mainly on the $200-$300 amplifiers to provide the most bang for the buck. My third example above can be built as a high quality alternative. I wonder if you'll agree with me. |
| Summary... | Kursun
Nov 12, 2003 2:04 PM | | Your summary is quite accurate...
Yes you do not need to rely on so called "reserve power". If you do not have enough power, this just means you need an amplifier with higher power.
An amplifier with robust power supply will provide better tracking at low impedance regions of the speakers, as it doubles its output power with each halving of load impedance. An amplifier with soft type power supply will deliver its worst performance at this critical condition, just when needed, because it will not deliver the high currents required into low impedance loads.
Second part of your summary requires quite advanced evaluation.
The worst/best case an amplifier with great DH can provide probably is about 3db. It's not really much compared to the dynamics a music piece can contain. Luckily/unluckily, recorded music is heavily compressed, though with the advent of higher quality formats things may change and the importance of headroom may increase.
I do not know any radical technique of gaining headroom without sacrificing quality. Fast recovery from overload is probably one important factor. McCormack used distributed power supply filtering concept on their DNA (Distributed Node Amplifier) amplifiers. They avoided using one centralized and massive power supply capacitor with relatively sluggish behavior, and used many smaller valued, higher quality capacitors that are distributed around various stages and output transistors. One massive capacitor is harder to re-charge instantaneously during close to overload levels. This is a good idea, one towards gaining headroom without sacrificing quality, but is not radical. |
| Thanks for the compliment. | mtrycrafts
Nov 16, 2003 8:06 PM | | b Also,
like mtrycrafts, I think the ear, though a fascinating instrument by itself, is not a very accurate SPL meter.
Ah, a passing comment. Great, thanks :) |
| Price point is what they build for n/t | jackz4000
Nov 10, 2003 4:10 PM | | 1 |
| re: What's up with power ratings? | Woochifer
Nov 10, 2003 10:49 PM | | The key is that these standardized power ratings that you bring up are the FTC ratings, and they are required ONLY for stereo and monoblock receivers/amps. The FTC tests not only required a standard output test, but it required that the receiver/amp sustain that output. I read a few years ago that the FTC test is not required for multichannel receivers. And with the market now solidly shifted to 5.1, 6.1, and "7.1" receivers, this type of loophole opens the door for all kinds of ridiculous specs to get tossed around.
When you look at these multichannel power ratings, keep in mind that very few of them are done with all channels driven simultaneously. Some of them are done with only one channel driven. And with no standard test that must be used to report power output, manufacturers can use a variety of different test parameters to get the output that they want to advertise. I've seen power output ratings measured at 1 kHz into 4 ohms and over 20% distortion using one channel. Obviously, this is not comparable to an all channels driven test using a wideband frequency test, 8 ohms resistance, and before distortion levels increase. Yet, unsuspecting consumers might look at a spec sheet or an ad and assume that amps tested under those very different conditions are comparable just because the output numbers are similar.
Sound & Vision's not normally a magazine that I recommend, but they are a good resource for test bench results. One of their tests uses the more demanding FTC standard in an all channels driven output. With this test, you often see receivers that claim 100 watts x 5 or 6 channels outputing only about 20 watts/channel with all channels driven. Yet, there are others that output more than 70 watts/channel. These types of discrepencies are a lot more revealing than the noncomparable numbers you see on a lot of spec sheets or advertising. Unfortunately, in recent issues I've seen S&V using a less demanding all channels driven test (don't remember if they lowered the resistance or used a single frequency test), so the output numbers they've been posting more recently are not as far below what their advertising says.
In your Sony versus Denon example, most of Sony's ads emphasize the 6 ohm 1kHz output, while Denon has tended to favor the 8 ohm 20Hz-20kHz output (although more recently I've seen them using the 6 ohm output more). The power supplies were probably comparable, but the tests used in their power output claims probably were not. As others have noted though, unless you do some objective measuring, there are too many variables to really assert that one receiver is more powerful than another just by listening. Just note that you like one better than the other, and enjoy your listening. |
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