As always with subjects of this type it is too easy to get overwhelmed by the detail and complexity of the situation but the reality is this;
If you have speakers of average sensitivity in a 'normal' size domestic room and play at reasonable levels then a 50 watt amplifier is propably going to be fine, but step outside those parameters and all bets are off.
Thats about right however, 2m is not typically, even in my small romm Im 3m away and if firng down the room it would be 4-5m, you hav eto double the power for each metre. Also 89db is quite sensitive, for floorstanders that maybe the mean but stand mounts are more likely to be 87db, that is rated at 8Ohms, watch out for 4Ohms speakers that are more difficult to drive. Some popular speakers are around 85db or less like Kef LS50s and B&W CM1s, LS3/5A are only 83Ohms. .
The rating of amplifiers is for a continuous output (100w for example) however most amplifiers will produce much higher power than this for short periods (milliseconds) which is all that is required to cover musical peaks, (The average power required is usually pretty low) and this is why amplifiers seem underpowered on paper, but work fine in the real world.
Hope this helps
As always the answer is a little more complex. Assuming your amplifiers are 100watts rms (to the usual criteria) they will have a peak power on a sine wave of √2 x 100 or a little over 140 watts. A music signal is very different, musical peaks can be very brief and a lot of amplifiers can handle peaks of several times their rated output, but in some cases this can put a significant drain on the amplifier power supply.
An amplifier that is being asked to handle such peaks consistently can suffer from a drop in their voltage rails as the capacitors in the power supply become drained, so your 100watt amplifier may actually clip peaks on a music signal that are less than the 100watt rating of the amplifier significantly so if the PSU capacitors are modestly sized and/or slow to charge.
This is just another example of the complexity of how a hi fi system works under real, dynamic conditions and one of the reasons why the rms output of an amplifier is a largely useless specification, unless perhaps you want to indulge in a little recreational arc welding.
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Indeed. We may, for instance, listen to the news on our systems with the amp pushing out only a few milliwatts which illustrates how logarithmic our hearing is. It would be interesting reading up on any research done that asks a good number of subjects "How much do you think is twice as loud?" to see what the variation was.
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Half power has been mentioned as used with frequency response measurements but that refers to power or amplitude, not loudness. The level difference of 10dB seems to be the agreed amount - not 3dB I'd thought it was.
There doesn't seem to be a lot of agreement so far. Several different 'definitive' answers.
I'm not yet convinced that "twice as loud" or "half the volume" are quantifiable. I can get to grips with "equal loudness" as a valid perception but "double" or "half" is like saying the bath water is now "twice as hot" as it was before. It's not an absolute like saying "I'm now sitting twice as far from my speakers".
It does make perfect sense to refer to a doubling of loudness to definable quantity such as power for the convenience of measurement but is arbatory rather than absolute. Length seems like an absolute primary quantity but it is now defined by the speed of light & a time interval rather than the intuitive to understand physical metal bar with markings 1m apart!
You need to research the difference between loudness, which is an entirely subjective notion and level, sound preassre level to be precise, which is a quantifiable, measurable unit just like a metre.
I'm not sure of the absolute figures, but I understand (I think) the general principals:
- A "small" increase in the sensitivity of a speaker has a much more dramatic (logarithmic) effect on loudness from a given amp Wattage
- The impedance of the speaker combined with the current reserves of the amp, can also have a dramatic effect
- The room plays a big part
- The different type of distortion that Valve and SS amps have, allows Valves to make more of their given power
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The constant unsureness is the answer to the question: "How many decibels (dB) are doubling a sound"? or "What is twice the sound?" Answer: Doubling means the "factor 2". What does doubling of a "sound" mean? Doubling the (sound) intensity is obtained by an increase of the (sound intensity) level of 3 dB. Doubling the sound pressure is obtained by an increase of the (sound pressure) level of 6 dB. Doubling the loudness feeling is obtained by an increase of the (loudness) level of about 10 dB
That's the point I'm making - loudness is surely subjective? Of course SPL, amplitude & power are definable quntities so can be compared & computed or codified if you will. Twice or half are very difficult to pin down when it come to perceived stuff like loudness but some folk are giving figures such as 10dB as an absolute ratio rather than referencing it a known quantity like if we add a second source of equal loudness (or SPL or power or amplitude into a known impedance) & call the perceived increase a doubling of loudness which in power terms would be a 3dB increase (as an example).
You need to be careful, loudness and (sound pressure) level are not interchangeable terms, as Fletcher said to Munson.
Once again without getting overly complex, SPL is a measure of the compression of air, a defineable and measurable function.
The point being made is that hi-fi equipment (and systems) do not always behave the way common sense would suggest and that the moment you step away from decent systems reproducing music at modest levels some very odd things start to happen. Moderate listening levels do use a very modest amount of power, hence the 'First watt' argument much loved by single ended afficionados.
Just trying to to give non technical enthusiasts a reminder that what you hear is not always what you think it is and that differences in the performance of components may not be caused by by the things you think they are.
With this twice as loud thing, it's a bit like how much more light is twice as bright? Or how much harder do you have to hit your thumb with a hammer for it to hurt twice as much? The 10db twice as loud figure is a rough guide.
90 dbs is loud. 100dbs is very loud. 110 dbs is ear-distortingly loud. 120 dbs is physically painfully loud.
Or how much harder do you have to hit your thumb with a hammer for it to hurt twice as much?
Not very hard..........I believe it's a logarithmic scale.
So let us play a quality modern recording with a dynamic range of 60dB, remember a CD has a theoretical 96db range.
No such thing.
Most CDs have a DR below 20, many below 10.
There is a good list here...
The highest they have tested on any track is 34.
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My first reaction to "twice as bright" was to think the answer was dead easy but it is referenced to adding a second light source of equal intensity - in other words is referenced to measureable quantities rather than being perceptually accurate. Most double-glazed windows half the amount of light coming through them which just seems plain wrong - it can't be that much loss but it is! Measuring lumination & illumination is very different if related to each other. One has to be equally careful with definitions as with sound!
Thanks for that frog, interesting post and link.
At a recent music festival most of the bands, groups, ensembles, orchestras had a dynamic range of less than 30 dbs once they started playing. The band with the biggest dynamic range played their version of Fat Boy Slims' Praise You. This peaked at 108dbs when all one hundred odd musicians were playing together and went down to about 50 dbs during note decay on a chime bar solo. So that was a dynamic range of about 58dbs. I would have loved to have made a recording of this performance on digital and reel to reel and then tried to play it back at the same volume...
I wonder how that range was tested. A "normal conversation" is commonly listed as being 60 dB, so at a festival you wouldn't even hear the band if they dropped to 50.
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