I was sorta bored today so I measured the AC voltage across the speaker outputs of my amp playing at the loud side of comfortable listening. Did y’all know that (in my case) it only takes 170-250mV RMS to fill the/my room…? Over 8 ohms that would be 0.25 / 8 = 0.03 amps. That makes 0.25 * 0.03 = 0.008 watts… So either I am totally wrong or completely surprised… By the way: while taking the measurements I used 1000Hz and ear protection…
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Try correlating that with speaker efficiency/room size/listening distance and a dB meter.
For most the ‘loud side of comfortable listening’ where you’d think about ear protection is about 90 dB. Average speaker efficiency is roughly 87 dB/w/m. And typical American living spaces are around 2800 cubic feet (say 8ft x 15ft x 25ft) where you’d be sitting about 15 feet from the speakers. So room gain/listening distance would cost roughly 10 dB. Final result with two speakers would require 10 dB of gain or 10 watts.
In a small bedroom room gain/listening distance would cost roughly 3 dB, so with two speakers 2 watts would be needed.
Thanks for thinking with me @jlm, here are some specifics:
- My home build speakers are roughly 88db efficient.
- Room size is 33ft long, 25ft wide (avarage) and 9ft high.
- This is what I mean with “loud side of comfortable”…
- Listening distance is 12ft.
Check your meter. 65 dB is NOT loud but does help to explain that low wattage calculation. I’m a big believer in the first watt, but your number is too low.
73.7 AVG 80.5 MAX
It’s an iPhone Six so that’s not the problem… #basta Hahaha…
I’m not kiddin’, this is the level that I listen to when I’m alone at the house or my wife is upstairs, being drunk (again).
I have 89db/w/m speakers, and a listening chair 3m from the speakers. Calculation for anechoic conditions shows that I should need 0.5wpc to generate 80db, my maximum tolerable sound level. Actual measurement showed that I really only needed a third of a watt per channel, owing to the reinforcement of room reflections. That would mean that my 80wpc amp should be grossly overpowered. Factor in the broadcasting standard that average level should be -23db down on absolute peak, and the amp is about right. Since seldom listen over 70db I could get away with a less powerful one in practice.
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So it looks like we’re in the first watt zone… For the sake of complacency: the rest we need for dynamics… 
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I have seen the phrase “pressurizing the room” Is that a real term and what does it mean. Also, how does the word dynamics relate to it. Finally, can you provide a definition for dynamics.
Thank you very much,
Chas
I really don’t have a clue what you’re talking about Chas…
This strikes me as incredibly low. One thing you might want to check is whether your multimeter actually gives you correct AC readings at 1kHz. They might assume something closer to 60Hz and just be off with the sampling, etc. Do you have a function generator or some other way of generating a 1kHz signal with known voltage to test?
The other issue is that a pure 1kHz tone is going to have a lot less energy than music, which contains many frequencies, especially lower ones.
The simplest way to test both here would be to try a 100Hz tone instead to see what reading you get. I’d guess it’s going to be much higher.
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Jazz has on average 15 dB maximum peaks, classical up to 30 dB. Both produce 105 dB peaks in live performances. Thus there is a real need for additional watts. Note that the risk of pushing a small amp too hard (especially a solid state amp) is clipping the amp which can burn up driver voice coils.
“Room filling” is a sonic phenomenon where it seems that sound is “everywhere” in the room, not just coming from “over there” where the speakers are located.
Dynamics are the instantaneous variations of sound pressure (volume) levels. Dynamics are characterized as macro (large/exciting) or micro (tiny/detail oriented).
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When people speak of pressurizing or loading a room they typically mean the music is loud enough it reacts with the room, especially the bass. Each room possesses a fundamental resonant frequency which you can sense/hear if there is enough sufficient acoustical energy.
@rkosara already hit that point…
(One thing to take into consideration: measuring 1KHz will not give you an adequate power consumption compared to e.g. symphonic or rock music (using the whole listening spectrum). So when leveling a 40Hz or 80 Hz sine wave to get to 70 or 80 db (A-weighted) the power needed will be higher. Trying it again with pink noise might be interesting.)
When I made my measurements I chose a passage of chamber music where the sound level was substantially constant for a period, and then made voltage measurements for each speaker connection.
But let’s assume I am a factor of 100 times wrong: I am still at 0.8 watts…
Yes, that’s the accuracy of that meter in that range. You just used a 1KHz test tone, and that will use less power than e.g. pink noise, which covers the whole range from 20Hz to 20KHz.
Anyhow, it’s fascinating that the first Watt indeed is the most important - and that doubling the watts will result only in a 3 dB increase in loudness while to have a sound twice as loud (10 dB) you need to increase the power ten times.
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