Amplifier wattage a useless figure in home theatre - AVS Forum
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post #1 of 183 Old 04-07-2014, 03:33 AM - Thread Starter
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Hi,

As per my research 105 db is the reference level of sound in home theatres.

So with speakers of 90db sensitivity we can reach this figure with just 32 watts of amplifier power at 1 metre with just one speaker (see table below)


Watts Power
1 90
2 93
4 96
8 99
16 102
32 105
64 108
80 108.75
96 109.5
128 111
256 114

Taking into consideration that

1. Decibel level decreases by 3db by doubling the distance

2. Decibel level increases by 3db by doubling the number of sources with same power.

1 speaker shall produce 99 db at 3m from the source with 32 wat amplifier. However, that 7speakers (3 front, 2 sides and 2 rears) shall produce107.25db.

Speaker DB
1 99
2 102
4 105
5 105.75
6 106.5
7 107.25


Am I missing something here?


Thanks Hussain
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post #2 of 183 Old 04-07-2014, 04:36 AM
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Not too far off. It's pretty hard to figure the SPL loss over distance because everybody's room is different. 3 db may be good for your room, I don't know. It's too much loss for my reflective room. The calculators use an anechoic factor of 6db for each doubling of distance but I don't think that is very helpful. In my room, which is reflective, My average use is less than a watt per channel with peaks at 10 to 15 watts measured. The biggest spike I ever recorded was 18 watts during an explosion in a movie. My speakers are 87 db sensitive and I sit 11 feet away. I don't listen at reference level but I think 32 watts would handle my system or nearly so if I did.

I've only made my measurements at one main speaker. I don't have any way to measure all speakers working at once because I use voltage and current measurements to calculate the power dissipation. Rarely does a sound track drive all the speakers simultaneously and never for very long. I would probably just ignore that part of your calculation. In my room, I lose 2 db from 11 feet away so the 32 watts from your calculation would produce around 103 db. 103 db would drive me out of the room. That is uncomfortably loud for me. That's why I never go to movie theaters.

I would quibble a little with the title of the thread but would certainly agree that amplifier power is not a very important thing in home audio.
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post #3 of 183 Old 04-07-2014, 04:48 AM
 
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Here is a calculator for it. It doesn't account for room gain and adds 3db head room which is a good thing. Depending on your room and layout would determine the gain. I think the wattage figure would be between your calculation and the calculator. I also do not think the gain from multiple speakers is figured when determining wattage needed.
http://www.crownaudio.com/how_much_power.htm

http://www.crownaudio.com/elect-pwr-req.htm
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post #4 of 183 Old 04-07-2014, 04:59 AM
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Try this calculator http://myhometheater.homestead.com/splcalculator.html

"I realize that somebody playing free music isn't as commercial as a hamburger stand. But is it because you can eat a hamburger and hold it in your hand and you can't do that with music? Is it too free to control?" - Don Van Vliet (aka Captain Beefheart) discussing commercial success in the music biz


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post #5 of 183 Old 04-07-2014, 05:08 AM - Thread Starter
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Originally Posted by FMW View Post

Not too far off. It's pretty hard to figure the SPL loss over distance because everybody's room is different. 3 db may be good for your room, I don't know. It's too much loss for my reflective room. The calculators use an anechoic factor of 6db for each doubling of distance but I don't think that is very helpful. In my room, which is reflective, My average use is less than a watt per channel with peaks at 10 to 15 watts measured. The biggest spike I ever recorded was 18 watts during an explosion in a movie. My speakers are 87 db sensitive and I sit 11 feet away. I don't listen at reference level but I think 32 watts would handle my system or nearly so if I did.

I've only made my measurements at one main speaker. I don't have any way to measure all speakers working at once because I use voltage and current measurements to calculate the power dissipation. Rarely does a sound track drive all the speakers simultaneously and never for very long. I would probably just ignore that part of your calculation. In my room, I lose 2 db from 11 feet away so the 32 watts from your calculation would produce around 103 db. 103 db would drive me out of the room. That is uncomfortably loud for me. That's why I never go to movie theaters.

I would quibble a little with the title of the thread but would certainly agree that amplifier power is not a very important thing in home audio.

True, My calculations are based upon science of sound waves travelling in open space and does not take into account room reflections/absorbtion.
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post #6 of 183 Old 04-07-2014, 05:10 AM - Thread Starter
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Originally Posted by ttlnb View Post

Here is a calculator for it. It doesn't account for room gain and adds 3db head room which is a good thing. Depending on your room and layout would determine the gain. I think the wattage figure would be between your calculation and the calculator. I also do not think the gain from multiple speakers is figured when determining wattage needed.
http://www.crownaudio.com/how_much_power.htm

http://www.crownaudio.com/elect-pwr-req.htm

I would appreciate if you can tell me what is amplifier headroom means in noob terms and why do we need it.
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post #7 of 183 Old 04-07-2014, 05:11 AM - Thread Starter
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Originally Posted by lovinthehd View Post

Try this calculator http://myhometheater.homestead.com/splcalculator.html
This calculator gives the same results.
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post #8 of 183 Old 04-07-2014, 05:21 AM
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It can do multiple speakers...

"I realize that somebody playing free music isn't as commercial as a hamburger stand. But is it because you can eat a hamburger and hold it in your hand and you can't do that with music? Is it too free to control?" - Don Van Vliet (aka Captain Beefheart) discussing commercial success in the music biz


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post #9 of 183 Old 04-07-2014, 06:18 AM
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Quote:
Originally Posted by hussain View Post

Quote:
Originally Posted by ttlnb View Post

Here is a calculator for it. It doesn't account for room gain and adds 3db head room which is a good thing. Depending on your room and layout would determine the gain. I think the wattage figure would be between your calculation and the calculator. I also do not think the gain from multiple speakers is figured when determining wattage needed.
http://www.crownaudio.com/how_much_power.htm

http://www.crownaudio.com/elect-pwr-req.htm

I would appreciate if you can tell me what is amplifier headroom means in noob terms and why do we need it.

Headroom is the difference between absolute maximum possible undistorted level (usually just below clipping), and the maximum level that is actually used.

Think of it as the difference between the maximum speed limit where you drive, and the top speed of your car.

Strictly speaking your car's top speed under the worst conditions (up hill, into the wind, maximum load, etc.) need not be more than the maximum speed limit. However most cars will better that by some amount.

A few reserves are nice so that your current decision is not cast in stone. However the claim that great amounts of headroom improve sound quality is false.
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post #10 of 183 Old 04-07-2014, 06:31 AM
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A few reserves are nice so that your current decision is not cast in stone. However the claim that great amounts of headroom improve sound quality is false.


Quote:
Just added a Rotel 1095 (thanks to BlueNose) to my Onkyo 3008 to power my MA GX300s GX350 GX100s using these interconnects Neutrik Van damme single RCA phono to phono cable NYS373 - NYS373 | eBay.

Never expected so much improvement, resolution dynamics bass and best of all effortless headroom, sound seems to envelop you adding depth and clarity, picking out more instrument nuances/voice tones, even at reasonable volume levels.

Movies should be a blast this weekend:)
But also remember all amps sound the same:)

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post #11 of 183 Old 04-07-2014, 06:45 AM
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Originally Posted by hussain View Post

I would appreciate if you can tell me what is amplifier headroom means in noob terms and why do we need it.

Headroom is unused amplifier power. Reserve power.
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post #12 of 183 Old 04-07-2014, 06:54 AM
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Where some AVR's fail is the more channels driven the advertised power drops off and thats why bench tests are important also some fall short when the impedance drops below 8 ohms so while they may look close on the specs they may be miles apart once loads are present also the current marketing seems to want to advertise WPC at 1% distortion rather than.01.
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Originally Posted by oztech View Post

Where some AVR's fail is the more channels driven the advertised power drops off and thats why bench tests are important also some fall short when the impedance drops below 8 ohms so while they may look close on the specs they may be miles apart once loads are present also the current marketing seems to want to advertise WPC at 1% distortion rather than.01.

Yup I tried a Kef Model 200 Reference with a Yamaha 5xx series (70W for center) Bloody awful. Congested sound. Upgraded to single channel on a proper 60W per power amplifer..much much better.

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post #14 of 183 Old 04-07-2014, 07:04 AM
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Quote:
Originally Posted by fatbottom View Post

Quote:
A few reserves are nice so that your current decision is not cast in stone. However the claim that great amounts of headroom improve sound quality is false.


Quote:
Just added a Rotel 1095 (thanks to BlueNose) to my Onkyo 3008 to power my MA GX300s GX350 GX100s using these interconnects Neutrik Van damme single RCA phono to phono cable NYS373 - NYS373 | eBay.

Never expected so much improvement, resolution dynamics bass and best of all effortless headroom, sound seems to envelop you adding depth and clarity, picking out more instrument nuances/voice tones, even at reasonable volume levels.

Movies should be a blast this weekend:)
But also remember all amps sound the same:)

Two words: sighted evaluation. People tend to hear what they want to hear.
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People tend to hear what they want to hear.

Correct, like yourself you hear what you want to hear. lol

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Originally Posted by oztech View Post

Where some AVR's fail is the more channels driven the advertised power drops off and thats why bench tests are important

Bench tests have their place and God knows I've bench tested enough amps for three or more people over the past 55+ years. However bench tests just generate numbers and interpreting those numbers is not trivial. There are even some non-obvious factors related to bench test numbers: LOTS!

There is a gigantic asymmetry between bench tests and actual use when it comes to "All Channels Driven" (ACD) measurements and actual use.

Actual use is with music or drama, not sine waves. Sine waves stress amplifiers several times more than music does. A key parameter is called Crest Factor (CF) which is the ratio between peak and average power. For sine waves CF is 3 dB. For music CF is always at least 6 dB for the worst case, and if you get into the real world of listening to music its up to 20 dB or more. Highly compressed music has a CF in the range of 10 dB.

What this means is that if I design an AVR to to ACD tests on the test bench I would have to put in from twice to 10 times as much power transformer and heat sinks as well as other parts as would be required for an amplifier that was designed to amplify music.
Quote:
also some fall short when the impedance drops below 8 ohms

I know of no mainstream (Denon, Marantz, onkyo, Pioneer, etc.) AVRs that have any difficulty driving loudspeaker loads that go down below 4 ohms. The average impedance of speakers is maybe 150% of their rated impedance. So bench tests with 8 ohm resistors put that much more stress on the amp than real world 8 ohm speakers.
Quote:
also the current marketing seems to want to advertise WPC at 1% distortion rather than.01.

I've seen that happen in the detailed portions of spec sheets but I again know of no mainstream examples. In fact all good solid state amplifiers can be reasonably be expected have less than 0.05% THD just below clipping. I've seen this be true even when the amp was speced at 10% THD!

Manufacturers fudge power ratings to push the amp into a little bit of clipping to produce most of the specs we see. The power goes up a little. BFD.
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Quote:
People tend to hear what they want to hear.

Correct, like yourself you hear what you want to hear. lol

The joke is probably on you because unlike a lot of the posturing that goes on around here, most of the definitive things I say are directly or indirectly based on DBTs which are a kind of lie detector. They are especially effective when I'm telling lies to myself.
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post #18 of 183 Old 04-07-2014, 07:37 AM
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Originally Posted by fatbottom View Post
Quote:
Just added a Rotel 1095 (thanks to BlueNose) to my Onkyo 3008 to power my MA GX300s GX350 GX100s using these interconnects Neutrik Van damme single RCA phono to phono cable NYS373 - NYS373 | eBay.

Never expected so much improvement, resolution dynamics bass and best of all effortless headroom, sound seems to envelop you adding depth and clarity, picking out more instrument nuances/voice tones, even at reasonable volume levels.

Movies should be a blast this weekend:)
But also remember all amps sound the same:)
 

I would like to have the link to this post. Thank you

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post #19 of 183 Old 04-07-2014, 09:01 AM
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Thats why I still like the THX Select and Ultra ratings on AVR's because its been tested to play at a certain volume to fill a said size room with certain settings and although there are AVR's that will do this without the certification how would the average consumer know this removes all doubt.
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post #20 of 183 Old 04-07-2014, 09:22 AM
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Originally Posted by oztech View Post

Where some AVR's fail is the more channels driven the advertised power drops off and thats why bench tests are important also some fall short when the impedance drops below 8 ohms so while they may look close on the specs they may be miles apart once loads are present also the current marketing seems to want to advertise WPC at 1% distortion rather than.01.

Just a couple of points. The first relates to amplifier power with all channels driven. Note that it is only an issue if the power falls so much that it becomes unable to drive the speakers without distortion. Since most receivers are overpowered for normal home audio applications, this drop in power is normally not enough to be an issue. Secondly, it is rare for all speakers to be driven at the same time at high volume. When this occurs in movie soundtracks it is usually for explosions and they last only a few seconds. Most consumers think they need 300 watts per channel when, in fact, they never use more than about 20 watts per channel.

You talked about moving from a test load to a real load but you assumed the real load would be harder to drive. it is the opposite. The real load is easier to drive than the resistive load because it varies in level and frequency constantly.

Your last issue relates to full power distortion. The manufacturers massage the ratings to suit marketing goals. Audiophiles like you seem to think amplifier power is a critical factor so they do what they can to maximize it. If they rate power at 1% distortion, then the .01% distortion point might be less than 1 db lower (not even an audible difference.}. In order to satisfy you they would probably do well to provide both numbers but understand that their target customer is less knowledgeable than you so it would just confuse him.

Finally impedance ratings for amplifiers are made at full power. The rating would drop as power rating drops. Since we rarely if ever use full power, the fear about lower speaker impedances is overblown in the audiophile community. While speaker impedance can be a problem, it isn't except in exceptional situations. I drive 4 ohm speakers with a bottom of the line AVR every day in my bedroom system. Incidentally all speakers vary impedance with frequency so all of them have swings in impedance that go below and above the nominal rating. It is not just typical. It is universal.

So in a nutshell, amplifier power ratings are developed based on what the company wants to say. If they wanted to say other things, they would simply adjust the power rating. Amplifier power is not a major factor in home audio. Amplifier power ratings are even less a factor.
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post #21 of 183 Old 04-07-2014, 09:23 AM
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Correct, like yourself you hear what you want to hear. lol

This from someone who has never done a bias controlled listening test describing someone who has done many many of them.
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post #22 of 183 Old 04-07-2014, 09:25 AM
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Thats why I still like the THX Select and Ultra ratings on AVR's because its been tested to play at a certain volume to fill a said size room with certain settings and although there are AVR's that will do this without the certification how would the average consumer know this removes all doubt.

Most of them don't know what THX means. I think you might have a hard time finding a receiver that doesn't meet THX standards. The manufacturers, most of whom are losing money on AV receivers, don't want to pay the fees for the certification.
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post #23 of 183 Old 04-07-2014, 09:41 AM
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Most of them don't know what THX means. I think you might have a hard time finding a receiver that doesn't meet THX standards. The manufacturers, most of whom are losing money on AV receivers, don't want to pay the fees for the certification.
Not true or we would not have threads with overheating AVR's and protection modes turning on they are not all on the same page from the same mfg .
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post #24 of 183 Old 04-07-2014, 10:12 AM
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Not true or we would not have threads with overheating AVR's and protection modes turning on they are not all on the same page from the same mfg .

I don't read many. Some are certainly due to use error - lack of ventilation, short circuits on the speaker connectors etc. But there is no question that that there are exceptions to what I said. I think most receivers can handle THX, however, as I said.
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post #25 of 183 Old 04-07-2014, 12:18 PM
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Granted with most mfg.'s stated a required ventilation distance at the sides and top there are posters that will ignore that and then complain when they have problems but I see where some will buy a mid level ( not going to bash a brand in particular the majority know who they are) and try to run their low efficient speakers set to large in a large room at high levels then the heartache begins.
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Yes the bench test is harder on the AVR than most speakers but if it passes that with flying colors you know your speakers will be just fine.
I am aware of impedance differences with frequency variations and so is the AVR when pushed hard enough been there done that.
I wish the equipment still had a viewable VU or LED meter so most could see the dynamics where for the most part it cruises along at 5 watts then the crescendo or explosion hits and it needs or wants 100 watts classical music is famous for this.
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post #27 of 183 Old 04-07-2014, 12:55 PM
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Originally Posted by oztech View Post

Granted with most mfg.'s stated a required ventilation distance at the sides and top there are posters that will ignore that and then complain when they have problems but I see where some will buy a mid level ( not going to bash a brand in particular the majority know who they are) and try to run their low efficient speakers set to large in a large room at high levels then the heartache begins.

It is all just a matter of degree. It is possible stress any amplifier. My point was that, in normal home audio situations, the amplifiers aren't a big issue. Yes there are exceptions and yours may be one. Personally, I've never stressed a home audio amplifier. That would include the 12 watt mono amplifier I used in the mid 1950's to the 25 watt per channel integrated I use in my two channel system upstairs.

I have stressed all kinds of them in pro audio applications including the 450 watt per channel (into 4 ohms) amp that drives my stage piano system into two EV sound reinforcement speakers.
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post #28 of 183 Old 04-07-2014, 01:14 PM - Thread Starter
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Guys,

This is high tech discussion, but have few things to add.

1. I cross matched onkyo/integra power supply consumption rating with all channel driven test in reviews. Almost all were able to deliver 72-75 percent of their max power supply consumption to speakers e.g. Onkyo 1009 with power supply of 830 watts was able to give out 86.2 watts per channel at .01 distortion when seven speakers were driven.

2. Keeping above figure in mind with 90 db speakers, lets assume that at reference level only the front three are driven at full power while the rest of four speakers are at zero power. To deliver 105 db by just front three speakers we shall need just 48 watts per channel.

3. Even with 3db headroom we need 96 watts X 3 channels. That's is a total of 288 watts

4. Now at 72 percent efficiency we just need receiver with power supply consumption of about 400 watts which is almost every receiver in the market.


So lets put this debate to rest. Watts for home theatre are completely irrelevant .
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post #29 of 183 Old 04-07-2014, 02:44 PM
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post #30 of 183 Old 04-07-2014, 03:04 PM
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This post is for you fatbottom.
http://www.avsforum.com/t/1526197/amplifier-wattage-a-useless-figure-in-home-theatre#post_24577848

Thank you

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