Amplifier power output - RMS vs Peak as it applies to home theater soundtracks - Page 2 - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #31 of 42 Old 07-17-2013, 07:00 AM
AVS Addicted Member
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,381
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 747 Post(s)
Liked: 1161
Quote:
Originally Posted by OllieS View Post

Quote:
Originally Posted by DonH50 
The power supply does not sag as much for short peaks as it does for steady-state sinusoidal signals (often used during testing). As a result, typical receivers do not lose as much power in the real world as steady-state multichannel testing would indicate.

Do you have any evidence that suggests this or are you just making assumptions? I would love to see some cold hard data on this.

One source of such evidence is the AVR spec sheets. They contain numbers for both steady state power and power for short peaks. The former is always less than the latter.

While is it possible to measure many amplifier performance parameters with dynamic signals including real world musical recordings, I don't know of any reviewers that actually do so. It would be counter to the interests of their advertisers whose business is based on heavy metal.
arnyk is offline  
Sponsored Links
Advertisement
 
post #32 of 42 Old 07-17-2013, 11:58 AM
AVS Special Member
 
A9X-308's Avatar
 
Join Date: Mar 2008
Location: Australia; now run by adults.
Posts: 5,273
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 86 Post(s)
Liked: 71
Quote:
Originally Posted by OllieS View Post

Do you have any evidence that suggests this or are you just making assumptions?
It's really basic electrical engineering.
A9X-308 is offline  
post #33 of 42 Old 07-17-2013, 12:13 PM
 
arnyk@pcavtech's Avatar
 
Join Date: Nov 2008
Location: grosse pointe woods mich
Posts: 33
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
Quote:
Originally Posted by A9X-308 View Post

It's really basic electrical engineering.

Right. Short term peaks are supplied by power from the power supply''s filter capacitors. These charge up during quiet passages and get partially drained during peaks. The maximum power that the amplifier can provide without clipping is limited by the voltage in these capacitors. The worst case is when you do bench tests with steady sine waves which are like a peak that never ends.

Building a power amp with a huge power transformer is mostly for the benefit of bench tests with sine waves. Building one with huge capacitors can help at very low frequencies. An AVR that is used with a subwoofer to amplify music will perform well with music even though it won't take your breath away on test bench when you test it with sine waves and won't be very impressive to look at when you open up the chassis and look at the size of its parts.
arnyk@pcavtech is offline  
post #34 of 42 Old 07-17-2013, 12:19 PM
AVS Special Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 6,084
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 159 Post(s)
Liked: 262
Quote:
Originally Posted by OllieS View Post

Quote:
Originally Posted by DonH50 
The power supply does not sag as much for short peaks as it does for steady-state sinusoidal signals (often used during testing). As a result, typical receivers do not lose as much power in the real world as steady-state multichannel testing would indicate.

Do you have any evidence that suggests this or are you just making assumptions? I would love to see some cold hard data on this.

Cold hard data for what? That power supplies sag less for short than long pulses, the difference between music and sine wave testing, real-world crest factors, or ???

Look at most any AVR data sheet and compare multichannel (all channels driven) to stereo output ratings if you want an idea how power supply sag affects power output. For multichannel data, look at various threads on AVS and elsewhere that show how much power is running in each channel during a typical movie scene or whatever. Or dig up that old AES paper that presents the peak-to-average power ratio in music if that's what you are questioning. My assumptions are based on data, but I do not have the data at hand and am too lazy to dig for it since I have known it for decades. Just call me a typical engineer (though actually I look up job-related stuff all the time, won't do to have a system fail because I missed or mis-remembered something, though I do remember pi to enough places to keep me out of trouble).

There were a bunch of studies in the 80's on this general subject, probably spurred by the CD and realization that all of a sudden 0 dB really was the limit of a digital system and hard clipping commenced immediately, no soft saturation like in tapes (where different manufacturers interpreted 0 dB differently but invariably there was 3 - 6 dB of headroom above 0 on the Vu meters).

There was a lot of step and pulse testing back then as well. I remember TAS and Audio used to show step responses, looking for overshoot/ringing and sagging on HF and LF square waves. I don't have the "cold hard data" at hand but there was a huge debate about whether very stiff supplies that clipped quickly were better, or softer supplies that offered more headroom. I think the bottom line, then and now, was to have enough power on tap so that clipping was insignificant. Does not mean no clipping, just that things clipped at a point over sane listening levels. Sane is in the ears of the listener, of course.

Back then, the IHF drove a new test procedure requiring a 1/3-power, 1-hour preconditioning test to help weed out over-spec'd amps. A lot of amps really struggled with that test, mainly because of thermal management issues. I wish there were standardized multichannel tests, and better test loads defined to better reflect real-world speakers, but I am not aware of any. Of course, audio is not my career, just a hobby, so I have not kept up.

I suppose the answer is "no, just my assumptions" since I don't have any of those studies at hand. Feel free to ignore them or do your own research and draw your own conclusions (assumptions, whatever). There are a lot of good data and articles out there I simply haven't time to pursue. I have been chastised for being too technical and not technical enough, guess I must be doing OK if both sides are vexed. smile.gif But, I have a day job, and this is supposed to fun, after all.

HTH - Don

p.s. Thanks for covering for me, Arny and A9X-308.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is online now  
post #35 of 42 Old 07-17-2013, 01:13 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
This short article explains how capacitors charge and discharge:

Slew rate and slew rate limiting

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #36 of 42 Old 07-17-2013, 02:02 PM
AVS Addicted Member
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,082
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 753 Post(s)
Liked: 434
Quote:
Originally Posted by DonH50 View Post

The issue is music, typically having a much higher peak-to-average ratio than a sine wave, does not stress the power supply as hard. That is, a pure sine wave has a pretty constant average power and low crest factor (peak-to-average ratio). Music with the same average power ratio has much higher peaks. The power supply does not sag as much for short peaks as it does for steady-state sinusoidal signals (often used during testing). As a result, typical receivers do not lose as much power in the real world as steady-state multichannel testing would indicate.
Well, real-world does not include speakers that act like resistors. In that sense, bench tests that use such dummy loads (which is the "standard") can overestimate the power that the unit produces. There was a very good AES paper that was posted in the other thread that documents this very well. Complex waveforms also require higher peak power than simple tones.

Bottom line is that this is a complex topic. We don't get to simplify it was was done and say that real life is always simpler than bench test results. It may not be.

Amir
Founder,
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"Insist on Quality Engineering"

amirm is offline  
post #37 of 42 Old 07-18-2013, 01:13 AM
AVS Addicted Member
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,381
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 747 Post(s)
Liked: 1161
Quote:
Originally Posted by amirm View Post


Well, real-world does not include speakers that act like resistors.

No, they are generally reactive loads over at least part of the normal audio range. One of the worst cases generally occurs in the octave of two above the bass roll-off.

http://www.stereophile.com/content/infinity-primus-360-loudspeaker-measurements



You can see a good real world example of this in the 100-400 Hz range. It dips below 4 ohms. This speaker starts its bass roll off around 100 Hz:



I happen to have a pair of the current version of this speaker (Primus P363) which has similar impedance and response characteristics.

I have clipped out a Yamaha RXV 371 (mainstream bottom end AVR) and a Denon AVR 1913 (middle of the road) into these speakers. No lasting effects.
Quote:
In that sense, bench tests that use such dummy loads (which is the "standard") can overestimate the power that the unit produces.

The point being made here is that back in the bad old days SS amplifiers were built using output transistors that were capable and durable with resistive loads, but could be overstressed with reactive loads. When this problem ("Secondary Breakdown") caught early designers unawares, the amplifier output devices would fail and the amplifier would be permanently damaged and required a whole new set of output and driver transistors, as well as perhaps a few resistors. Been there done that.

This problem was quickly identified, and protective circuits were added that would cause the amplifier to effectively clip before it destroyed itself. This clipping would take place at far lower output voltages than would be expected from bench testing with power resistors. The Crown DC 300 is an example of an early amplifier that was subject to premature clipping. One common speaker that the original DC 300had problems with was the AR-3 which was rated at 4 ohms. Another common amplifier that had fewer problems with premature clipping (but could still have problems with some speakers that were worse than the AR-3) was the Dyna 400.

Problems with premature clipping were circumvented by adding more output transistors. One amplifier that implemented this approach was the Dyna 416 which was basically a Dyna 400 with another output transistor in parallel with each output transistor in the Dyna 400.

There were speakers, particularly the legendary Infinity Kappa 9, that had absolutely ridiculous impedance curves. Notice the dip below 1 ohm from 20 to 40 Hz:



that led to the production of amplifiers with ludicrous numbers of output devices in parallel such as the Threshold 4E. I owned one of these babies and it was absolutely bodacious with low impedance and highly reactive loads. Although rated at only about 125 wpc it was capable of more than 400 wpc at 2 ohms and could easily blow power line fuses on the test bench. I put in a 30 amp circuit!



Kappa 9s and speakers like them have pretty well disappeared from the market because they only work well with a limited number of amplifiers. Speaker manufacturers only make money when audiophiles actually keep the speakers and don't return them right away.



NHT was one of the new age speaker manufacturers that started paying attention to impedance curves. Many of their flagship loudspeakers actually have impedance curves that stay at or above their rated impedance:

Output devices with improved resistance to secondary breakdown were then developed which eliminated the need for doubled-up or tripled or quadrupled output devices. Some come in typical plastic packages which completely obfuscates their outstanding current handling and resistance to secondary breakdown. They are not prohibitively expensive.
Quote:
There was a very good AES paper that was posted in the other thread that documents this very well.

No doubt not from the current edition of the Journal because this is a solved problem.
Quote:
Complex waveforms also require higher peak power than simple tones.

That's my point! ;-)

Amplifiers are still tested by audio ragazines with sine waves and resistive loads, even though they are actually used with music and loudspeaker loads which is a completely different thing.
arnyk is offline  
post #38 of 42 Old 07-25-2013, 12:45 PM - Thread Starter
Advanced Member
 
Nyal Mellor's Avatar
 
Join Date: Aug 2010
Location: SF Bay Area, California, USA
Posts: 935
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 35 Post(s)
Liked: 73
Quote:
Originally Posted by amirm View Post

Well, real-world does not include speakers that act like resistors. In that sense, bench tests that use such dummy loads (which is the "standard") can overestimate the power that the unit produces. There was a very good AES paper that was posted in the other thread that documents this very well. Complex waveforms also require higher peak power than simple tones.

Bottom line is that this is a complex topic. We don't get to simplify it was was done and say that real life is always simpler than bench test results. It may not be.

Can you link the other thread?


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
. We specialize in the design and creation of high performance listening rooms, home theaters and project studios for discerning audio/video enthusiasts.
Nyal Mellor is offline  
post #39 of 42 Old 07-26-2013, 01:54 AM
AVS Addicted Member
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,381
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 747 Post(s)
Liked: 1161
Quote:
Originally Posted by Nyal Mellor View Post

Quote:
Originally Posted by amirm View Post

Well, real-world does not include speakers that act like resistors. In that sense, bench tests that use such dummy loads (which is the "standard") can overestimate the power that the unit produces.

This appears to be a half-truth. Tests with resistive load can either underestimate or overestimate an amplifier's performance with loudspeakers. With modern amplifiers and speakers, underestimates are the most likely.
Quote:
There was a very good AES paper that was posted in the other thread that documents this very well.

Complex waveforms also require higher peak power than simple tones.

This also appears to be a half-truth. Tests with pure tones can either underestimate or overestimate an amplifier's performance with music. With modern amplifiers and speakers, underestimates are the most likely.
Quote:
Bottom line is that this is a complex topic. We don't get to simplify it was was done and say that real life is always simpler than bench test results. It may not be.

Can you link the other thread?

Probably: http://www.avsforum.com/t/866797/the-official-jbl-owners-thread

The AES article is probably: Benjamin, "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994 (available from www.aes.org). It has some of the same flaws listed above.

There is a somewhat flawed summary/exposition of the AES article online at http://www.stereophile.com/reference/707heavy It also has some of the same flaws listed above.
arnyk is offline  
post #40 of 42 Old 07-26-2013, 10:47 AM
AVS Addicted Member
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,082
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 753 Post(s)
Liked: 434
Quote:
Originally Posted by Nyal Mellor View Post

Can you link the other thread?
Here it is: http://www.avsforum.com/t/1478651/watts-and-current. It is a fairly good mirror but more detailed version of the discussion here. Post 154 has the AES paper that I referenced: “Peak Current Requirement of Commercial Loudspeaker Systems.” You need to buy the paper but the abstract has the summary: http://www.aes.org/e-lib/browse.cfm?elib=5198&rndx=838817

There is also a nice discussion about tube amplifier power vs solid state on WBF Forum. Since you are a member there you know where to find it but for others, click on the first link in this google link: https://www.google.com/search?rlz=1C1SNNT_enUS374US375&q=site%3Awhatsbestforum.com+%22constant+power%22+mep&oq=site%3Awhatsbestforum.com+%22constant+power%22+mep&gs_l=serp.3...56615.58259.0.58803.4.4.0.0.0.0.100.316.3j1.4.0.ernk_timecombined...0.0..1.1.20.serp.APj489QDET8. And then read the thread on "constant power."

Amir
Founder,
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"Insist on Quality Engineering"

amirm is offline  
post #41 of 42 Old 07-26-2013, 10:54 AM
AVS Addicted Member
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,082
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 753 Post(s)
Liked: 434
With respect to deleted comments above, please go to post #149 in the WBF thread where I provide an example of a speaker that presented a dead short at higher frequencies even though its stated "nominal" impedance is not that. Said speaker damaged one amp and forced protection on others even at very low wattage amps. Granted, this is an old speaker and the driving amps were tube but the point remains that speaker *can* present more difficult loads to an amplifier than a simple resistor. This is why we say "impedance" as opposed to resistance. Impedance is frequency specific and hence, no single number can ever represent it in such cases.

Amir
Founder,
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"Insist on Quality Engineering"

amirm is offline  
post #42 of 42 Old 07-27-2013, 06:19 AM
AVS Addicted Member
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,381
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 747 Post(s)
Liked: 1161
Quote:
Originally Posted by amirm View Post

With respect to deleted comments above, please go to post #149 in the WBF thread where I provide an example of a speaker that presented a dead short at higher frequencies even though its stated "nominal" impedance is not that. Said speaker damaged one amp and forced protection on others even at very low wattage amps. Granted, this is an old speaker and the driving amps were tube but the point remains that speaker *can* present more difficult loads to an amplifier than a simple resistor. This is why we say "impedance" as opposed to resistance. Impedance is frequency specific and hence, no single number can ever represent it in such cases.

This speaker appears to be a good example of bad design. Its quite clear that the rediculous impedance curve is at least partially traceable to a high level treble control that appears to be part of the speaker. IOW, its completely intentional.

Building hyper robust amplifiers to overcome badly designed speakers is like adding a massive sprinkler system to a house made out of oil paper.

The idea that an electrostatic speaker would need a treble boost network runs counter to years of (false) propaganda claiming inherent superiority for electrostats at high frequencies.

There is a reason why electrostatic speakers have not gone mainstream despite decades of promotion and development and that is the fact that they have no inherent performance advantages and cost more to provide equal performance if they can even provide equal performance which is often not true.

In short, with electrostats you can easily end up paying more money for poorer quality sound.
arnyk is offline  
Reply Audio theory, Setup and Chat

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off