How Many Watts am I using?

[highfigh]

It's going to be highly dependent on content and the speakers in question. If you listen to a lot of rock music, you'll be lucky to have a 6 dB dynamic range.

For the majority of medium-sized living room setups listening well below reference level, 100wpc is more than adequate. In the majority of circumstances, people need a lot less power than they think.

100W in most rooms is loud as he!! but if the music calls for a 20dB peak, 100W of amplifier power can run short and it is possible to find music that is so dynamic, but it tends to be from a couple of decades ago.

 

[ski2xblack]

It seems to boil down to different approaches.

"Too much is just enough" approach, accommodating for peak power levels, to avoid clipping, ever. Clean watts are cheap.

"Practical" approach, taking into account that we don't perceive transient clipping, but otherwise having sufficient power to avoid audible clipping. It's practical, but it's this approach that yields all sorts of real, audible differences between amps, particularly middling AVRs, as far as how they clip and recover from clipping conditions.

"Whimsical" audiophile approach, based on marketing nonsense.

 

[Bucknekked]

A lot of threads start with a request on “what should I do?” or “what should I buy?” and after a number of suggestions they peter out when the OP either bolts for the door or trundles off and makes a purchase. In a lot of threads, we never know exactly what happened or what was the aftermath of a purchase.

In this thread, it started out as a request for “how many watts am I burning” to get an idea of just how much of my current 75WPC Denon AVR I am actually using. Since I have new 4 ohm speakers coming, it was a topic of concern because my AVR is 8 years old and I didn’t know whether or not it was up to a 4 ohm load.

After lots of fine questions, suggestions, and other points of audio esoterica, the trend went from “probably don’t need anything” to “well, it’s possible you might want to upgrade”. That’s all I needed to hear. With help from some of AH’s finest minds, I went in search of a new amplifier for my music.

My choice is a Denon x4200W AVR. Most of you are familiar with Denon and if you want a real review there are a lot of those available. I thought rather than trying to write an audiophile quality review I would just share some of my experiences with the new box instead. Most of you already know I have an aversion to purple prose so it seemed like the only safe and genuine thing to do.

I'm going to break this up to in bite sized pieces. Long posts freak some people out.

 

[Bucknekked]

WHY CHOOSE AN AVR? WHY NOT.......
With all the choices available, why choose an AVR? The AVR choice was made quite simply based on connectivity. My original mindset was separates : pre-amp and monoblocks. Reality stuck its ugly head in the door and shouted “how are you going to hook up your music?” Crap. The whole shopping expedition was derailed by connections: AVR’s connect to anything and everything. Pre-amps and others make it harder. Modern in this case wins out over traditional.

AN AVR ISN’T GOOD ENOUGH
I have seen this line of thought a lot on AH: Why should anyone serious about music for a music only system compromise and get an AVR when pre-amps / amps or integrated amps are far superior? In a word (two words) : they’re not. New AVRs like the x4200W can run in DIRECT or PURE DIRECT modes which turn off literally everything else in the box except the pre-amp connections and the power amplifiers in use. The amps rock as well as anything else in a dedicated case.

WHY THAT PARTICULAR BOX?
I chose Denon because I have had several trouble free generations of Denon AVRs. No issues. No failures. No annoying problems. How many things can you say that about? The great minds on AH helped me decide on the x4200W verses others based on what I need in the amplifier section and what was available in a price performing deal.

REFURB VS NEW VS BIG BOX
A x4200w at retail is $1,499. Refurbed at accessories4less is $749 with a manufacturers 1 year warranty. I’m not interested in big box stores so I didn’t even make the obligatory trip and stand around with kids trying to sell me their wares. There are sites in NYC that do $1,199. I chose accessories4less at $749 because many AH folks have tried them and I didn’t see a real downside to at least trying. Amazon has them as a purchase option so how much more protection do you need?

My first refurb box died within 24 hours of arrival. It would just shut off and lie there dead and refuse to do anything for 12 hours or so. A couple of those temper tantrums and I called accessories4less and they paid to ship the box back and paid to ship me a replacement unit. The second unit arrived looking fresh as a daisy and its running perfectly.

 

[Bucknekked]

INSTALLATION OBSERVATIONS
AVR’s can seemingly be complicated to install. With a “setup” button on the remote control and an onscreen menu on the attached flat panel display, its ez peazy. No problems, no hassles and its working perfectly. I can’t say enough about how easy Denon has made setup over my 8 year old model. No comparison.

HOW DOES THE MUSIC SOUND? IS IT DIFFERENT?
Is it different sounding than my 8 year old AVR? I can tell a long and winding story about my comparisons between the two AVRs, my expectation bias, and all that claptrap. In a few words: honestly, except the new box will go louder better than the old one, there’s no telling them apart with music. I guess that means I am an audiophile failure: I can’t claim to hear the difference between two sources.

ANYTHING STICK OUT ABOUT THE NEW BOX?
Something does stick out about the new box over the old : HDMI . My old box was HDMI 1.4a and the new box is HDMI 2.0xxx something or other. They behave differently in a couple of significant ways. I use HDMI to connect my music sources to keep it all digital and clean. It was one of the deciding factors in buying an AVR.

The new box behaves differently in that when I turn off the AVR, my music source (a Mac Mini connected to the AVR with HDMI) continues to have an onscreen display on the attached flat panel TV as the console for the Mac Mini media server. Apparently, in the new Denon AVR, the HDMI will still pass the computers video signals to the flat panel even when the AVR is powered off. My old Denon would not do that: turn off the AVR and the video signal to the TV from the computer would shut off as well. That’s a positive improvement.

Its also a negative improvement as well because in the new setup if one doesn’t power up and power off the HDMI connected devices in a given order the Mac Mini computer can become confused. I managed to confuse it. The observable problem is that the Mac Mini will only see the receiver as an Airplay device. Press play on a song and it sends it to the receiver as an Airplay song and the receiver then changes in to Airplay mode and the whole process gets slowed down and its irritating as hell. Its a years long known problem by Apple. It doesn’t have a “fix” per se. They tell you to power up and power down your devices in order (receiver 1st, TV last) and the problem goes away.

 

[Bucknekked]

OVERALL IMPRESSIONS
My overall impression with the Denon x4200w is overwhelmingly positive. It looks great. It sounds great. It has every connection under the sun. Its sets up easily and even the remote isn’t bad. (not backlit: a pet peeve) . Accessories4less was a great route to a good deal (YMMV and all that for refurbed stuff).

My hats off to the AH members who helped give me advice. The advice was consistently positive in nature and helpful. Lots of dearly held opinions of course, but nobody crossed the line and told me I was going to hell if I didn’t buy what they recommended. The process of asking for information and “what if’s” worked very well during the last month or so. I enjoyed the learning experience and the purchase. Now I’m enjoying having that cool looking box on the shelf making great music.

Now if we can just get those Salk Songtowers finished I can stop pacing around the house.

 

[lovinthehd]

The new box behaves differently in that when I turn off the AVR, my music source (a Mac Mini connected to the AVR with HDMI) continues to have an onscreen display on the attached flat panel TV as the console for the Mac Mini media server. Apparently, in the new Denon AVR, the HDMI will still pass the computers video signals to the flat panel even when the AVR is powered off. My old Denon would not do that: turn off the AVR and the video signal to the TV from the computer would shut off as well. That’s a positive improvement.

.

Great points in general in your several posts. In this regard, though, are you sure you don't have HDMI Pass Through enabled in the avr?

 

[MrBoat]

I'm shocked. I was waiting to see Outlaw, QSC or Emotiva. I don't think he's done yet, folks. Remember that this is the guy that equates subwoofers with NHRA.

 

[Bucknekked]

I'm shocked. I was waiting to see Outlaw, QSC or Emotiva. I don't think he's done yet, folks. Remember that this is the guy that equates subwoofers with NHRA.

In my house there are many rooms................future upgrades...........

 

[yepimonfire]

100W in most rooms is loud as he!! but if the music calls for a 20dB peak, 100W of amplifier power can run short and it is possible to find music that is so dynamic, but it tends to be from a couple of decades ago.

It's loud as hell if you're listening to highly compressed music, for movies it's just enough to reach reference level at a distance of 8 feet using speakers rated at 90 dB @ 2.83v 99% of us don't listen at reference level, which is why I say 100w is a lot more power than most of us need. I'm going to assume most of us probably keep the knob between -10dB and -20dB for movies. At -10dB, with an 87dB bookshelf sitting 9 feet away, a solid 50 watts will suffice. Even if someone has a large dedicated theater with the farthest seat being 20' from the front, 100w into a 91dB floor stander is still enough to play at -10dB with a peak per channel of 95dB.

Wattage isn't the only factor obviously, some speakers are going to be current hungry across certain ranges due to crazy phase angles or impedance dips. You can't just chalk it up to "if I put 100w into this speaker, I will get this SPL, if my receiver can do 100wpc minimum continuous, there will be no distortion". 100w at what frequency, impedance, and voltage? If you've got something like a Paradigm Reference Studio 100, at 104hz it drops down to 2.5 ohms. a 100wpc receiver might have voltage rails capable of delivering 30v, but the power supply might crap out when asked to deliver the 12 amps required to drive the two channels at 100w. This is why THX Ultra 2 certification requires amplifiers to be able to swing a minimum 18A peak across all channels. This is something an external amplifier or receiver with a better power supply would be better equipped to deal with.

Plenty of classical music has a dynamic range of about 30dB, also there's always this

 

[highfigh]

It's loud as hell if you're listening to highly compressed music, for movies it's just enough to reach reference level at a distance of 8 feet using speakers rated at 90 dB @ 2.83v 99% of us don't listen at reference level, which is why I say 100w is a lot more power than most of us need. I'm going to assume most of us probably keep the knob between -10dB and -20dB for movies. At -10dB, with an 87dB bookshelf sitting 9 feet away, a solid 50 watts will suffice. Even if someone has a large dedicated theater with the farthest seat being 20' from the front, 100w into a 91dB floor stander is still enough to play at -10dB with a peak per channel of 95dB.

Wattage isn't the only factor obviously, some speakers are going to be current hungry across certain ranges due to crazy phase angles or impedance dips. You can't just chalk it up to "if I put 100w into this speaker, I will get this SPL, if my receiver can do 100wpc minimum continuous, there will be no distortion". 100w at what frequency, impedance, and voltage? If you've got something like a Paradigm Reference Studio 100, at 104hz it drops down to 2.5 ohms. a 100wpc receiver might have voltage rails capable of delivering 30v, but the power supply might crap out when asked to deliver the 12 amps required to drive the two channels at 100w. This is why THX Ultra 2 certification requires amplifiers to be able to swing a minimum 18A peak across all channels. This is something an external amplifier or receiver with a better power supply would be better equipped to deal with.

Plenty of classical music has a dynamic range of about 30dB, also there's always this

100W into speakers that provide 90dB/W/M comes to 110dB- tell me that's not loud and explain why it's not loud. Add a second speaker receiving equal power and providing the same output and you add 6dB. Add the room's reflections and it adds again.

My comment was about 100W being loud- it is. An amp capable of 100W that's not operating at that level is totally irrelevant because that's not 100W- it's whatever level the signal demands at a particular setting on the volume control at that time. A system with 5 main speakers will be loud, even if the total power output is 100W- picking one impedance dip on one speaker at one frequency is hardly representative of all systems, so I'm not sure why you included that.

 

[yepimonfire]

100W into speakers that provide 90dB/W/M comes to 110dB- tell me that's not loud and explain why it's not loud. Add a second speaker receiving equal power and providing the same output and you add 6dB. Add the room's reflections and it adds again.

My comment was about 100W being loud- it is. An amp capable of 100W that's not operating at that level is totally irrelevant because that's not 100W- it's whatever level the signal demands at a particular setting on the volume control at that time. A system with 5 main speakers will be loud, even if the total power output is 100W- picking one impedance dip on one speaker at one frequency is hardly representative of all systems, so I'm not sure why you included that.

It's not 110dB at 3m. It came up to about 101dB based upon the peak spl calculator. Of course, that's a single speaker, that's still crazy loud, I certainly wasn't arguing that it wasn't. I was just stating that it's sufficient for -5dB below reference level movie watching, in a medium sized room which is still too loud for most people. Yes, other speakers add 3dB, but like ive stated in this thread before, using a relative volume control will tell you the peak spl of a single speaker. If you listen at 0dB, each channel has a maximum peak of 105dB at 0dbfs. At -15dB, 90dB per channel. As for speakers being current hungry at certain frequencies, the Paradigm isn't the only one, though it's a worst case example. A good deal of speakers will dip down to 4 ohms across some of the frequency range, which places a lot more demand on the power supply. Whether or not the power supply can handle the extra current is dependent on the receiver. The point I was trying to make was that wattage isn't the only factor, you can generally get an idea of how well a receiver can handle impedance drops by looking at its 6 ohm and 4 ohm ratio to its 8 ohm ratio. Outside of flagship receivers, most 100w receivers fail to deliver 200w into 4 ohms at the same voltage because the power supply can't keep up with the current demands. This problem gets worse with lower powered receivers and with 5-7 channels being driven, since a majority of midfi receivers are only going to be able to deliver about 70% of their rated 2ch output ACD. Looking at it purely from the perspective of watts, one could say that a 50wpc receiver is plenty loud for a medium sized room, but that only works if the speakers impedance is flat from 20hz to 20khz and the power supply is capable of delivering enough amperage to drive all 5 channels to 50w.


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[PENG]

It's not 110dB at 3m. It came up to about 101dB based upon the peak spl calculator. Of course, that's a single speaker, that's still crazy loud, I certainly wasn't arguing that it wasn't. I was just stating that it's sufficient for -5dB below reference level movie watching, in a medium sized room which is still too loud for most people. Yes, other speakers add 3dB, but like ive stated in this thread before, using a relative volume control will tell you the peak spl of a single speaker. If you listen at 0dB, each channel has a maximum peak of 105dB at 0dbfs. At -15dB, 90dB per channel. As for speakers being current hungry at certain frequencies, the Paradigm isn't the only one, though it's a worst case example. A good deal of speakers will dip down to 4 ohms across some of the frequency range, which places a lot more demand on the power supply. Whether or not the power supply can handle the extra current is dependent on the receiver. The point I was trying to make was that wattage isn't the only factor, you can generally get an idea of how well a receiver can handle impedance drops by looking at its 6 ohm and 4 ohm ratio to its 8 ohm ratio. Outside of flagship receivers, most 100w receivers fail to deliver 200w into 4 ohms at the same voltage because the power supply can't keep up with the current demands. This problem gets worse with lower powered receivers and with 5-7 channels being driven, since a majority of midfi receivers are only going to be able to deliver about 70% of their rated 2ch output ACD. Looking at it purely from the perspective of watts, one could say that a 50wpc receiver is plenty loud for a medium sized room, but that only works if the speakers impedance is flat from 20hz to 20khz and the power supply is capable of delivering enough amperage to drive all 5 channels to 50w.


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I generally agree with all your points, except the very last sentence. If you listens to 5 channel music, unless it is 5 channel stereo, you shouldn't have to worry about 50W into all 5 channels simultaneously except for very short duration. Most conventional power supplies found in, for examples, NAD, D&M's and Yamaha's mid to high end models, can handle such short duration demands nicely.

if you search S&V bench tests for Denon 3000 and above series AVRs you will likely find that they can provide >2X200W at 0.1% THD into 4 ohms. The only Digm 100 that has dips to 2.5 ohms is the V3, then again, for that narrow range of frequencies, the power supply's peak output capability can handle it without audible clipping and compression. With all due respect, I don't think a lot of those reviewers, even JA, are EEs specialized on the Power side and may not know much about transformer's performance characteristics. You can measure the peak current output of an AVR easily and be amazed with their peak current capability without hearing any sign of clipping/distortions. Some reviewers tend to overrate the so called power hungry thing frequently but it is not a bad thing that they do, because it is obviously better safe than sorry. The fact is, well designed power transformers, even the tiny ones (under 1kVA) used in audio amplifiers, should have excellent overload capability especially for short duration of ms to a few seconds. That, combined with properly sized caps mean there is no issues with providing double the rated current required for peaks and the occasional impedance dip moments. Phase angle is not (it is for the designer) a factor in terms of current demand calculations for loudspeaker loads, though it has to be factored in when considering the amps ability to deal with heat and perhaps stability issues.

 

[yepimonfire]

I generally agree with all your points, except the very last sentence. If you listens to 5 channel music, unless it is 5 channel stereo, you shouldn't have to worry about 50W into all 5 channels simultaneously except for very short duration. Most conventional power supplies found in, for examples, NAD, D&M's and Yamaha's mid to high end models, can handle such short duration demands nicely.

if you search S&V bench tests for Denon 3000 and above series AVRs you will likely find that they can provide >2X200W at 0.1% THD into 4 ohms. The only Digm 100 that has dips to 2.5 ohms is the V3, then again, for that narrow range of frequencies, the power supply's peak output capability can handle it without audible clipping and compression. With all due respect, I don't think a lot of those reviewers, even JA, are EEs specialized on the Power side and may not know much about transformer's performance characteristics. You can measure the peak current output of an AVR easily and be amazed with their peak current capability without hearing any sign of clipping/distortions. Some reviewers tend to overrate the so called power hungry thing frequently but it is not a bad thing that they do, because it is obviously better safe than sorry. The fact is, well designed power transformers, even the tiny ones (under 1kVA) used in audio amplifiers, should have excellent overload capability especially for short duration of ms to a few seconds. That, combined with properly sized caps mean there is no issues with providing double the rated current required for peaks and the occasional impedance dip moments. Phase angle is not (it is for the designer) a factor in terms of current demand calculations for loudspeaker loads, though it has to be factored in when considering the amps ability to deal with heat and perhaps stability issues.

It depends on the movie, if the movie is a dialogue heavy drama/comedy with very little action, sure, for most action movies, that's not the case. I have a couple of movies audio tracks pull off into flac, I will grab a screen shot of the content of each channel loaded up into my DAW.

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[highfigh]

It's not 110dB at 3m. It came up to about 101dB based upon the peak spl calculator. Of course, that's a single speaker, that's still crazy loud, I certainly wasn't arguing that it wasn't. I was just stating that it's sufficient for -5dB below reference level movie watching, in a medium sized room which is still too loud for most people. Yes, other speakers add 3dB, but like ive stated in this thread before, using a relative volume control will tell you the peak spl of a single speaker. If you listen at 0dB, each channel has a maximum peak of 105dB at 0dbfs. At -15dB, 90dB per channel. As for speakers being current hungry at certain frequencies, the Paradigm isn't the only one, though it's a worst case example. A good deal of speakers will dip down to 4 ohms across some of the frequency range, which places a lot more demand on the power supply. Whether or not the power supply can handle the extra current is dependent on the receiver. The point I was trying to make was that wattage isn't the only factor, you can generally get an idea of how well a receiver can handle impedance drops by looking at its 6 ohm and 4 ohm ratio to its 8 ohm ratio. Outside of flagship receivers, most 100w receivers fail to deliver 200w into 4 ohms at the same voltage because the power supply can't keep up with the current demands. This problem gets worse with lower powered receivers and with 5-7 channels being driven, since a majority of midfi receivers are only going to be able to deliver about 70% of their rated 2ch output ACD. Looking at it purely from the perspective of watts, one could say that a 50wpc receiver is plenty loud for a medium sized room, but that only works if the speakers impedance is flat from 20hz to 20khz and the power supply is capable of delivering enough amperage to drive all 5 channels to 50w.


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Multiplying the power by 100x adds 20dB. Do the math. Add more speakers with each outputting 50W and it's still loud.

 

[yepimonfire]

First two minutes of Fantastic Beasts and Where to Find Them, meters measure in dBfs, there's is just as much content in the surrounds as there is in the front L/R, with the center carrying the most content of all 5 channels, LFE removed because it is irrelevant in this discussion. All 5 channels are driven at about the same level for an entire two minutes, which I wouldn't call a very short peak. The common assertion that it's very rare to see all channels driven at the same level for more than a short peak is nothing more than a myth. This is probably the fifth movie I've analyzed like this, and each time, all channels are frequently driven at similar levels, the only time this isn't the case is when a scene is strictly dialogue with no music.

Multiplying the power by 100x adds 20dB. Do the math. Add more speakers with each outputting 50W and it's still loud.

And sitting nine feet away causes an 8.8dB loss due to dispersion, putting me back at my original number given of 101.2dB. Speaker sensitivity ratings are measured at 1m. I'm not arguing that it isn't loud enough, I'm talking about peaks in volume found in movies and some music. Most of us are lucky to use more than a few watts listening to music at an average volume of 80dB, but during an intense scene in a movie that headroom becomes valuable.

 

[PENG]

First two minutes of Fantastic Beasts and Where to Find Them, meters measure in dBfs, there's is just as much content in the surrounds as there is in the front L/R, with the center carrying the most content of all 5 channels, LFE removed because it is irrelevant in this discussion. All 5 channels are driven at about the same level for an entire two minutes, which I wouldn't call a very short peak. The common assertion that it's very rare to see all channels driven at the same level for more than a short peak is nothing more than a myth. This is probably the fifth movie I've analyzed like this, and each time, all channels are frequently driven at similar levels, the only time this isn't the case is when a scene is strictly dialogue with no music.

And sitting nine feet away causes an 8.8dB loss due to dispersion, putting me back at my original number given of 101.2dB. Speaker sensitivity ratings are measured at 1m. I'm not arguing that it isn't loud enough, I'm talking about peaks in volume found in movies and some music. Most of us are lucky to use more than a few watts listening to music at an average volume of 80dB, but during an intense scene in a movie that headroom becomes valuable.

Thank you for the video. The resolution is poor so I could not see it clear enough to say if all 5 channels are at levels so high as to call for 50W per channel for the 2 minute duration. I could however, see that the L and R channels did appear to average around the more or less same level and peaked together most of the time too, but definitely not channel 4 and 5. I don't understand why we are seeing it so differently. Again, to me the levels varied most of the time and channel 4 and 5 did appear to be much lower, though the resolution is too low to see how much lower in terms of dB SPL. By the way, for power transformers, 2 minutes is indeed a "very short" duration. As an example, a typical transformer protections fuse may not begin to melt for about 2 minutes with 2X the rated current, or 12X for about 100 ms.

I have measured the voltages and currents, in both average and peaks (not fast enough for the absolute peaks) for a movies including spider man, LOTR etc., so I know at least in my room, I will not approach 50W average, not even close, peaks for split seconds, yes definitely. I don't believe in myths, not me.

 

[yepimonfire]

They were about the same. The only one that was significantly louder was the center.

If you've measured and found you never need a full 50w then that's all you need. All I'm saying is strictly based on numbers, at reference level all channels must be capable of 105dB peaks with an average program level of 85dB as a standalone entity, the LFE channel should be capable of 115dB. If you listen below reference level you can subtract whatever number from that level (i.e. 95dB for -10dBfs). From there you can plug the distance and sensitivity measurements of ONE speaker into the peak spl calculator and figure out whether or not the amplifier is up to the task. Yes, adding speakers makes it louder, but that doesn't change the requirements for a single speaker.

A majority of amplifiers are rated for 120% of their RMS power for peak power into the same load, so if the amplifier can do 100w RMS into 8ohms, then it can do 120w peak. Manufacturers never publish how long a peak is, so I have no idea if that's 20 seconds or 2 minutes. As I've previously stated, most amplifiers found in receivers are only going to be able to put out 70% of their rated rms power when all channels are driven. Obvious, not all channels are driven simultaneously all of the time, I'm coming up with these numbers based on the absolute worst case scenario, that being all 5/7 channels driven at 0 dbfs at full bandwidth down to 80hz at a desired volume level relative to reference level. If I plan for enough headroom to achieve that, then I can be absolutely certain I will never run out of headroom.

I know on a few occasions using a 60wpc receiver I've hit audible clipping during intense passages demanding full power into all channels at about -10dBfs, this even being in a small room, so planning for extra headroom is better than not.

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[PENG]

They were about the same. The only one that was significantly louder was the center.

If you've measured and found you never need a full 50w then that's all you need. All I'm saying is strictly based on numbers, at reference level all channels must be capable of 105dB peaks with an average program level of 85dB as a standalone entity, the LFE channel should be capable of 115dB. If you listen below reference level you can subtract whatever number from that level (i.e. 95dB for -10dBfs). From there you can plug the distance and sensitivity measurements of ONE speaker into the peak spl calculator and figure out whether or not the amplifier is up to the task. Yes, adding speakers makes it louder, but that doesn't change the requirements for a single speaker.

A majority of amplifiers are rated for 120% of their RMS power for peak power into the same load, so if the amplifier can do 100w RMS into 8ohms, then it can do 120w peak. Manufacturers never publish how long a peak is, so I have no idea if that's 20 seconds or 2 minutes. As I've previously stated, most amplifiers found in receivers are only going to be able to put out 70% of their rated rms power when all channels are driven. Obvious, not all channels are driven simultaneously all of the time, I'm coming up with these numbers based on the absolute worst case scenario, that being all 5/7 channels driven at 0 dbfs at full bandwidth down to 80hz at a desired volume level relative to reference level. If I plan for enough headroom to achieve that, then I can be absolutely certain I will never run out of headroom.

I know on a few occasions using a 60wpc receiver I've hit audible clipping during intense passages demanding full power into all channels at about -10dBfs, this even being in a small room, so planning for extra headroom is better than not.

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I fully agree in worst case scenario one needs to plan to have at least 20 dB (I prefer 30) higher than the highest average spl one normally listens to. That's why some of us keep suggesting people to use the online spl need calculator linked below instead of the Crown Audio one. There are a couple more that are even better but harder to find. I also agree 50WPC is only good for small rooms and sensitive speakers when peaks requirements are factored in, to avoid clipping occasionally. As I said I only disagree with your last sentence in that previous post, and now I realize it is just a slight disagreement because we do agree on worst case scenario basis. I just won't say the other claim about surround channels draw less or even much less (on average/most of the time) is a myth because it is mostly true, but false in some cases. Maybe we are now down to semantics on that point.

http://myhometheater.homestead.com/splcalculator.html

 

[highfigh]

And sitting nine feet away causes an 8.8dB loss due to dispersion, putting me back at my original number given of 101.2dB. Speaker sensitivity ratings are measured at 1m. I'm not arguing that it isn't loud enough, I'm talking about peaks in volume found in movies and some music. Most of us are lucky to use more than a few watts listening to music at an average volume of 80dB, but during an intense scene in a movie that headroom becomes valuable.

And again, you're ignoring the reflections. Unless your speakers are far from the walls, floor and ceiling or their dispersion is narrow, the walls will affect the SPL.

I'm not arguing that having extra power is useful- I'm arguing that 100W IS loud, especially when more than one channel is operating.