How to calculate how many watts are speakers using ??

b0ka95

Novice Member
So I got question and, it's a interesting one.

So whenever looking at speakers specs, you can see numbers like for example 89db for sensitivity, meaning your speakers will be generating 89db of volume at 1 meter distance using 1 watt.
So is this really true?
When I'm watching a movie my receiver is cranked at around 65-70% and volume is around 80-85db, it's pretty damn loud :D
Does this mean that I need to push my receiver even harder to get that 1 watt of power to my speakers?
My receiver btw is Denon X540 (70W per channel).

Any answer will be greatly appreciated since I am really curious about this one.
Thanks in advance!
 

BlueWizard

Distinguished Member
Curious ... Why?

You judge sound by the sound, not the position of the Volume Control Also, if you are play at 65% to 75%, unless you have a digital volume control, that is far louder than 85db. At about 65% to 75% my Stereo is running at 100db or more.

Though again, it depends on the volume control. If this is an AV Receiver, and 65% means about 1/3rd below 0db, that's one thing. But if it is a digital volume control with a read out on the display, then that is about right. If it is an analog volume control, 65% to 75% is VERY Loud.

Most systems average a fraction of a watt up to a watt or two. The extra voltage and power are used for transients and peaks.

If you have a volt-meter, you can measure the voltage at the speaker terminals, and you can - best guess - the working power with this formula =

P = E²/R

Where "E" is the Voltage, and "R" is the nominal Resistance of the speaker.

So, if you measure an average of 5 volts, and the speakers are rated at 8 ohms, we have -

P = 5² / 8 = 25 / 8 = 3.125 Watts

Not really precise, but it is good enough to get a general indication of the power.

But the real thing to do is just turn the amp up until it sounds good and accept it. It doesn't matter what the underlying details are ... as long as you like how it sounds.

Also, Speaker Sensitivity is 1w/1m. Do you sit 1 meter away? Technically you have to subtract 6db every time the distance from the speaker doubles. Though functionally in most rooms it work out closer to 3db.

So, 89db at 1 meter ...83db at 2 meters ...76db at 3 meters which is close to the typical listening distance in most homes. Though in functional reality, it is likely to be more like 80db at 3 meters.

The Sensitivity Rating of a speaker, doesn't mean much once you've bought the speakers. That rating exists so speakers can be fairly compared, and informed buying decisions can be made. But one you have them it serves no purpose. It is not like that is an ideal volume or anything. It just allows speakers to be compared.

There is a controversy around Sensitivity ratings. Should all speakers be fed the same Voltage? Or should all speakers be fed the same Power? That only works precisely at 8 ohms. If you want the same power to each speaker ,whether 4 ohms, 6 ohms, or 8 ohms, you have to feed those speakers different Voltage. If you want the same voltage fed to each speaker, then they will receive different amount of power. So, you frequently see Sensitivity rated at 2.83v/1m. That is 1 watt at 1 meter IF the speaker is 8 ohms.

I'm in the camp that say each speaker should receive the same Voltage because a give voltage corresponds to a given position on the volume control. The reality is that Amp are Voltage devices. They feed speakers a Voltage, and then the Speakers consume Power in proportion to their impedance. The signal feed to speakers is a Voltage Signal an it corresponds to a fixed position on the volume control. So ...voltage for me. But there are probably just as many people in the Power camp.

That probably doesn't answer your question, but that's about the best I can do.

Steve/bluewizard
 
Last edited:

Paul7777x

Distinguished Member
Steve said it all. I’ll only add that if you’re concerned about your power consumption in cash terms, then forget about it.

Even at near full whack 12hrs a day, it’s at worst, a few quid a month.
 

Ugg10

Distinguished Member
There are a number of online calculators about, this one is fairly typical.

Peak SPL Calculator
 

dannnielll

Well-known Member
So I got question and, it's a interesting one.

So whenever looking at speakers specs, you can see numbers like for example 89db for sensitivity, meaning your speakers will be generating 89db of volume at 1 meter distance using 1 watt.
So is this really true?
When I'm watching a movie my receiver is cranked at around 65-70% and volume is around 80-85db, it's pretty damn loud :D
Does this mean that I need to push my receiver even harder to get that 1 watt of power to my speakers?
My receiver btw is Denon X540 (70W per channel).

Any answer will be greatly appreciated since I am really curious about this one.
Thanks in advance!
It is a very reasonable question but the answer is that there is no easy relationship between the knob position on the amplifier and the sound or acoustic energy from a loud speaker. There is even more difficulty in determining the acoustic energy at any distance away from the speaker, as this is room properties and frequency dependent. It can be done, and requires calibrated microphones and good experience in mechanical engineering .. Acoustics is a subset of mechanical.
Most of the amplifiers and AVRs which display a dB scale can do so because the internal signal voltages at the input to the final stage of power amplification are being feed via a digital potentiometer ,and they are just displaying the command it is getting . The electrical power output or maximum power capable from the amplifier is determined by the power supply voltage and current capability of the power supply. Thus a standard front end circuit, by a manufacturer could be feeding a number of different powered output stages and 0dB could represent 40, 60 100 watts of electrical power into a load of 8 ohms .But as has been pointed out not all speakers are 8 ohms ,and no speaker is at 8 ohms over its entire frequency range.

The only thing you can take for granted is that a 3dB increase represents a doubling in electrical power.
Next the speaker assembly which converts electrical power into mechanical vibrations,can be designed over an enormous range of efficiencies. .. The horn configuration being the most efficient and various planar speakers the lowest efficiency. There are tradeoffs regarding frequency response, agility, accuracy etc ,with high efficiency speakers losing quality for efficiency. .. those un intelligible public address systems are usually horns. The best the speaker manufacturers can say is that at a power input of 1 watt electric power, they can generate a SPL of 90 dB for a microphone set one meter and on axis in front of the device.
Now SPL is based on the perception of sound,and assumes that 0 dB is the smallest audible sound.. a pin dropping . On that basis 120 dB is the loudest sound,at the threshold of pain and anything louder will cause severe hearing loss. To make it even more confusing , some amplifiers say their maximum power is 3 dB and use a negative scale for lower volume.
 
Last edited:

andy1249

Distinguished Member
So whenever looking at speakers specs, you can see numbers like for example 89db for sensitivity, meaning your speakers will be generating 89db of volume at 1 meter distance using 1 watt.

Thats a very specific measurement for a very specific purpose.
You see all kinds of misunderstandings and extrapolations from this very specific measurement to real world situations which are largely nonsense.

That measurement is done with a 1khz sine wave.
No one listens at 1 meter and no one listens to 1khz sine waves.

The measurement tells you nothing about actual listening because that is dynamic across the range of hearing as is the impedance across the speaker load for the frequency range applied to it.

Calculating instantaneous power for all those frequencies at all those impedances during any passage of music in real time based on that simple calculation would tax a supercomputer.

Power fluctuates wildly during any passage of music.
The important thing is that your amp has the overhead capacity to deal with it.
Thats all.
 

BlueWizard

Distinguished Member
As you can see, as we interpret it, you question is far more complex that I suspect you initially thought it was.

For Full Orchestral Music, here is the Power Spectrum -

powerdistribution-oct-sm-jpg.486612


I suspect peak power is not where you thought it would be. Notice that relative to the Peak Power, high frequencies are 1/5th to 1/20th of that peak.

Also, though the spec isn't always given, speaker do have a Maximum Output Level, this is purely mechanical. The speakers can only move just do far, and as such can only push air just do hard.

Here is one example - Klipsch Cornwall-III - 102db Sensitivity - Max SPL 119db -

https://f072605def1c9a5ef179-a0bc3f...ct-specsheets/Cornwall-III-Spec-Sheet-v03.pdf

When you reach 120db, the cone can no longer move farther forward, and starts to compress the sound much like an amp reaching its voltage limit and clipping.

Generally, though the Max SPL spec is not always given, most speaker top out around 105db to 110db. Keep in mind to go from 100db to 120db takes 128 TIMES THE POWER. That is, the Power Doubles 7 times to cover that span.

And that brings up another point, Power is NOT Linear. 10% of the top end is massively more power than 10% on the bottom end.

In the example above (100db to 120db), this is how the power breaks down assuming we start at 1 watt.

100db = 1w
103db = 2w
106db = 4w
109db = 8w
112db = 16w
115db = 32w
118db = 64w
121db = 128w

You can see how each modest increase in volume at the high end cause a massively greater jump in power, than the same increase on the low end. From 100db to 103db the Power increases by 1 watt (from 1w to 2w). But for the same change in volume at 118db to 121db, the power increases by 64w (64w to 128w). This is with an extremely high efficiency speakers.

Here is a speaker with a more common Sensitivity -

90db = 1w
93db = 2w
96db = 4w
99db = 8w
102db = 16w
105db = 32w
108db = 64w
111db = 128w
115db = 256w
118db = 512w
121db = 1024w

90db Sensitivity for a Stereo Hi-Fi speaker would be considered on the efficient side. So, in this case to move from the same 118db to 120db, there is a 512w INCREASE in Power (512w to 1024w).

That last little turn of the Volume Control cause a huge cascade in the power output. That is how people blow speakers. You try to squeeze that last little bit from the speaker -BAM!- the power doubles and your speakers is blown. Though to be fair, you would have to be Massively Loud to start with - painfully loud.

It should be clear from this how a speaker can be loud at 1 watt but still require substantial power to hit higher peaks in the sound output. Those surging peaks are functionally like increasing the volume control for the duration of that short peak.

You are cruising along at a steady 1 watt for a movie, the -BAM!- the Death Star blows up and the power peaks at 105db or about 32w with a 90db speaker. But if you happen to have speakers rated at 87db, then the power is 64w, and if you happen to have speakers rated at 84db, then it requires 128w to achieve a peak of 105db.

Generally a AV Receiver Surround System is calibrated so 0db on the read-out is 85db relative to a standard calibration tone, and calibrated in such a manner, it allows for 20db of headroom. So, 85db + 20db = 105db. That is the typical peak output of a movie (105db). Though the Subwoofer can peak at 115db.

Don't know if that helps, but there it is.

Steve/bluewizard
 
Last edited:

lindsayt

Active Member
The easiest way to get an OK measurement is to buy or borrow a calibrated sound meter. Sound meter apps for phones aren't accurate enough.

Play some music or a movie at whatever volume you wish. Stand with your sound meter 1 metre directly in front of your speakers. See what db reading it gives you.

If you know the sensitivity and nominal impedance of your speakers you can work out how many watts your amplifier is feeding to your speakers.

If you have 89 db sensitive speakers that are 8 ohms and the sound meter tells you that the sound at any instant was 89 dbs at 1 metre in front of your speakers then your amplifier was delivering 1 watt. If the speakers are 4 ohms it was 2 watts.

In this example, for every 3 dbs above or below 89 dbs you need to double or half the power. So that, for example 98 dbs would be 8 watts and 99 dbs would be 10 watts for 89 db, 8 ohm speakers.

I find 99 dbs at 1 metre from my speakers rather generously loud when I'm sitting 5 metres from my speakers.

For late night listening there are times when my amplifier is feeding my speakers power levels of the order of micro watts to milli-watts for transient peaks - which is quite mind boggling.
 

andy1249

Distinguished Member
If you know the sensitivity and nominal impedance of your speakers you can work out how many watts your amplifier is feeding to your speakers.

Speaker efficiency is a metric that only measures the actual percentage of electrical power that the speaker converts to acoustic power.

Electrical power in the amp vs acoustic power from the speakers are not the same.
There are heavy losses

Edit ...Typical efficiencies for cabinet speakers are around 1 to 3 percent in transducing electrical power to acoustic power, most of the electrical power is dissipated as thermal and kinetic energy.
So for example, at a typical 1% efficiency , to get the 1 watt acoustic power that is the reference for the SPL measurement , you require 100 watts of electrical power in the amp.
 
Last edited:

Ugg10

Distinguished Member
If you know the sensitivity and nominal impedance of your speakers you can work out how many watts your amplifier is feeding to your speakers.

If you have 89 db sensitive speakers that are 8 ohms and the sound meter tells you that the sound at any instant was 89 dbs at 1 metre in front of your speakers then your amplifier was delivering 1 watt. If the speakers are 4 ohms it was 2 watts.

Out of interest does this work when you are not measuring with a 1khz sine wave i.e. music or pink noise, because as far as I am aware each of the drivers have a frequency/impedance curve that although nominally 8ohm may range from as low as 2ohm up toas high as 50 ohm depending on the frequency (the higher values typically at the resonant frequency for woofers). Even a complete speaker will have a frequency / impedance curve which designers try to make as flat as possible (typically) but again may fluctuate.
 

BlueWizard

Distinguished Member
Out of interest does this work when you are not measuring with a 1khz sine wave i.e. music or pink noise, ....

1khz Sinewave and Pink Noise are going to be steady signal and that will make it easier to get an accurate reading on the output level.

Music on the other hand is dynamic, and the meter and you reading the meter are going to have to best guess average the reading, which is less accurate.

because as far as I am aware each of the drivers have a frequency/impedance curve that although nominally 8ohm may range from as low as 2ohm up to as high as 50 ohm depending on the frequency (the higher values typically at the resonant frequency for woofers). Even a complete speaker will have a frequency / impedance curve which designers try to make as flat as possible (typically) but again may fluctuate.

If you use full spectrum Pink Noise, you will get a pretty accurate reading using the Nominal Impedance of the speaker.

However if you use a specific frequency, there is a way to determine the approx speaker impedance at that frequency.

Get a power resistor, say 8 ohms, put it in series with the Speaker, and send a 1khz tone (or whatever frequency you are interested in), and measure the voltage across the known value Resistor and the Speaker.

The ratio of the Voltages is in proportion to the ratio of the impedance. For example, if you measure 5v across the 8 ohm resistor and 4v across the speaker, then the speaker impedance is -

4v/5v = x/8ohms
x = (4/5)8
x = 6.4 ohms at that specific frequency

As can be seen from the Graph I am providing, Speaker Impedance peaks at the Rated Resonance Frequency of the speakers, and dips to its lowest on either side of that peak.

Here is the Dayton Audio Classic 8" woofer -

https://www.parts-express.com/pedocs/specs/DC200-8 8_ Classic Woofer 8 Ohm Specification Sheet.pdf

The blue line on the graphs is the impedance of the speaker are various frequencies. Keep in mind a woofer like this would probably crossover at about 500hz to 1khz, so the higher end impedance would not come into play.

The Peak is about 47hz at 30hz (Free Air Resonace). The lowest are at 150hz and on the low end around 5hz at about 6.5 ohms.

This is a 8" woofer with a nominal impedance rating of 8 ohms.

However, because the output of speakers are acoustically measured for the Sensitivity Rating that is Acoustic Power, the actual Sound Level you hear for a standard input. So, you can get a fair reading by scaling the power up and down relative to the SPL you are measuring.

Steve/bluewizard
 

lindsayt

Active Member
Out of interest does this work when you are not measuring with a 1khz sine wave i.e. music or pink noise, because as far as I am aware each of the drivers have a frequency/impedance curve that although nominally 8ohm may range from as low as 2ohm up toas high as 50 ohm depending on the frequency (the higher values typically at the resonant frequency for woofers). Even a complete speaker will have a frequency / impedance curve which designers try to make as flat as possible (typically) but again may fluctuate.
Yes it does work - sort of - and that's why I said that it was the easiest way to get an OK measurement.

If you know the impedance curve of your speakers, or at least the minimum impedance of the bass drivers you can take that ohm value together with a rough guess at the main frequencies you're listening to, to arrive at a more accurate figure than just using the nominal impedance.

You could also make an allowance for sound meters having a DIN weighting as well as most of them getting less sensitive below 80 hz.

But as a ballpark figure, combined with a tape measure and the sensitivity and impedance specs of the speakers, sound meters are the cheapest and easiest way to measure the power the amplifier is sending to your speakers.


Edit and the problem with using pink noise or sine waves in the context given in the opening post in this thread is that they are artificial noises. It's very difficult for the brain to equate the loudness of a sine wave or pink noise to the loudness of music or a movie for a given power level.
A sine wave played at 1 watt from the amplifier to the speakers is a very annoying and piercing sound. Music played at amplifier power levels ranging from 1 milliwatt to 10 watt peaks will be less annoying even though the peak power level is 10 times higher.
 
Last edited:

lindsayt

Active Member
Speaker efficiency is a metric that only measures the actual percentage of electrical power that the speaker converts to acoustic power.

Electrical power in the amp vs acoustic power from the speakers are not the same.
There are heavy losses

Typical efficiencies for cabinet speakers are around 1 to 3 percent in transducing electrical power to acoustic power, most of the electrical power is dissipated as thermal and kinetic energy.
So for example, at a typical 1% efficiency , to get the 1 watt acoustic power that is the reference for the SPL measurement , you require 100 watts of electrical power in the amp.
Your post is taking this thread off-topic.

Every calibrated sound meter I've ever seen has given a measurement of loudness (sound pressure) in dbs.

For the purposes of this thread - there is no point in paying any attention to the acoustic power in Watts, because we have no way of easily measuring it in watts.

What we do have is a cheap and easy way to measure the sound 1 metre in front of our speakers in dbs.

From that measurement, if we have the most commonly quoted specifications for speakers (eg 89 dbs/[email protected] metre & 8 ohm nominal impedance), we can easily work out how many watts of electrical power our amplifiers were feeding our speakers (as a ballpark figure).
 

andy1249

Distinguished Member
From that measurement, if we have the most commonly quoted specifications for speakers (eg 89 dbs/[email protected] metre & 8 ohm nominal impedance), we can easily work out how many watts of electrical power our amplifiers were feeding our speakers (as a ballpark figure).


Im right on topic and No you cant.
The 1 watt reference for the db measurement is acoustic watts not electrical watts in the amplifier.
You cannot calculate amp electrical watts from a db measurement ,only acoustic watts.
That is one of the nonsensical extrapolations I mentioned in this thread.

Equating acoustic watts from a db measurement to electrical watts in an amp is wrong.
Think about it?
That would mean the speaker was a 100% efficient transducer.
100% efficient transducers are impossible.

Standard speakers, i.e. what most of us have, are 1% transducers.
Horn designs are as efficient as 3%
Some exotic Piezo designs are as efficient as 25%
No matter what speaker type you have , electrical watts in the amp are significantly larger, up to 100 times the “acoustic watt” calculation you get from a db figure.
 
Last edited:

lindsayt

Active Member
andy1249, the 2 most commonly quoted specifications for speakers are the nominal impedance and the efficiency / sensistivity in dbs/2.83v @ 1 metre.

What do you think the 2.83v in these specifications indicates?

It indicates 2.83 volts.

Can you please explain to me how you think that 2.83 VOLTS is an indication of acoustic power and not electrical voltage?

Acoustic power is NOT electrical. It doesn't have a voltage. Acoustic power is made up of a pressure per square metre. It is this pressure per square metre that the sound meter microphone is measuring and then converting back to electrical power to give a reading in dbs (decibels).

Measuring the sound in dbs with a calibrated sound meter with a knowledge of the most commonly quoted speaker specifications is entirely right for getting a quick, easy indication of the amount of power the amplifier is delivering to the speakers.

I am not and never have equated electrical watts from the amplifier to acoustic watts in the air on a 1 to 1 ratio.

I do equate electrical watts from the amplifier to dbs at 1 meter in front of the speakers by the simple conversion factors of the efficiency and impedance specs of the speakers.


Let me give you a specific example.

I have 2 speakers: Heybrook HB1's and EV Patrician 800's. Their specs are:
HB1's: 8 ohm nominal impedance, 89db/2.83v a 1 metre
EV Patrician 800's: 16 ohm impedance in the midrange dropping to 5.5 ohms in the bass (lets call it 8 ohm nominal impedance for simplicity for a ball park figure), 102db/2.83v @1 metre.

If I play some music on the HB1's and measure peaks of, for example, 70dbs, I know that if I turn my system off and leave the volume where it is and connect the EV's and play the same recording, I will get peak measurements of 83dbs.

I also know that when the manufacturer (or even better an independent source like Stereophile magazine) put 2.83 volts into my speakers they got measurements of 89 dbs at a distance of 1 metre for the HB1's and 102 dbs for the EV's. And from their measurements I can know how much electrical power my amplifier is delivering to my speakers for any given db reading on my calibrated sound meter.

This means that the EV's are about 20 times more efficient at converting electrical power into acoustic power at 1 metre in front of them than the Heybrooks. When you look at the engineering of the 2 speakers you can see why. Compression drivers and horns for the midrange vs conventional cone and dome. Huge bass driver in a corner horn enclosure vs pretty small mid-bass driver in a small sealed box.

According to this website:
Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs speaker sensitivity 1 watt = 2,83 volt box chart - sengpielaudio Sengpiel Berlin

my HB1's are 0.5% efficient at convert electrical power to acoustic power at 1 metre in front of them, whilst the corner horn EV's are 10% (rather higher than the 3% you said they'd be capable of).

For the purposes of determining the power the amplifier is feeding the speakers, the efficiency as a percentage is entirely off-topic as sound meters do not give readings in percentages, they give them in dbs.
 

andy1249

Distinguished Member
andy1249, the 2 most commonly quoted specifications for speakers are the nominal impedance and the efficiency / sensistivity in dbs/2.83v @ 1 metre.

What do you think the 2.83v in these specifications indicates?

It indicates 2.83 volts.

Can you please explain to me how you think that 2.83 VOLTS is an indication of acoustic power and not electrical voltage?

Acoustic power is NOT electrical. It doesn't have a voltage. Acoustic power is made up of a pressure per square metre. It is this pressure per square metre that the sound meter microphone is measuring and then converting back to electrical power to give a reading in dbs (decibels).

Measuring the sound in dbs with a calibrated sound meter with a knowledge of the most commonly quoted speaker specifications is entirely right for getting a quick, easy indication of the amount of power the amplifier is delivering to the speakers.

I am not and never have equated electrical watts from the amplifier to acoustic watts in the air on a 1 to 1 ratio.

I do equate electrical watts from the amplifier to dbs at 1 meter in front of the speakers by the simple conversion factors of the efficiency and impedance specs of the speakers.


Let me give you a specific example.

I have 2 speakers: Heybrook HB1's and EV Patrician 800's. Their specs are:
HB1's: 8 ohm nominal impedance, 89db/2.83v a 1 metre
EV Patrician 800's: 16 ohm impedance in the midrange dropping to 5.5 ohms in the bass (lets call it 8 ohm nominal impedance for simplicity for a ball park figure), 102db/2.83v @1 metre.

If I play some music on the HB1's and measure peaks of, for example, 70dbs, I know that if I turn my system off and leave the volume where it is and connect the EV's and play the same recording, I will get peak measurements of 83dbs.

I also know that when the manufacturer (or even better an independent source like Stereophile magazine) put 2.83 volts into my speakers they got measurements of 89 dbs at a distance of 1 metre for the HB1's and 102 dbs for the EV's. And from their measurements I can know how much electrical power my amplifier is delivering to my speakers for any given db reading on my calibrated sound meter.

This means that the EV's are about 20 times more efficient at converting electrical power into acoustic power at 1 metre in front of them than the Heybrooks. When you look at the engineering of the 2 speakers you can see why. Compression drivers and horns for the midrange vs conventional cone and dome. Huge bass driver in a corner horn enclosure vs pretty small mid-bass driver in a small sealed box.

According to this website:
Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs speaker sensitivity 1 watt = 2,83 volt box chart - sengpielaudio Sengpiel Berlin

my HB1's are 0.5% efficient at convert electrical power to acoustic power at 1 metre in front of them, whilst the corner horn EV's are 10% (rather higher than the 3% you said they'd be capable of).

For the purposes of determining the power the amplifier is feeding the speakers, the efficiency as a percentage is entirely off-topic as sound meters do not give readings in percentages, they give them in dbs.

Sorry but you are totally wrong.
You are making an incorrect assumption and you are mixing your units.

Keeping it simple.
The 2.83 volts is simply the reference signal level.

Speakers output sound pressure.
If you measure the speakers published db level at 1 meter that means you have 1 acoustic watt from your speaker and at typical 1% efficiency that would be 100 electrical watts in the amplifier.

At 0.5% efficiency that would be 200 electrical watts in your amp.
At 3% efficiency that would be 33 electrical watts in your amp etc.
That is how it works.

Electrical watts are always significantly higher than the acoustic watts from the db measurement.
You have confused the two watt units and made nonsense extrapolations like “ microwatts and milliwatts” in your amp. (Post # 8)
For late night listening there are times when my amplifier is feeding my speakers power levels of the order of micro watts to milli-watts for transient peaks - which is quite mind boggling.


Once you understand the difference between the units it is no longer “ mind boggling” and you will get why amp manufacturers dont mention microwatts or milliwatts in their specs.
 
Last edited:

dannnielll

Well-known Member
This sequence of posts seems to me to be a points scoring competition (there is another term ,involving distance which I will avoid ), since it is evident both players know more or less what they are talking about.
The electrical power going into a speaker is of course the instantaneous product of current by voltage and is measured in watts.. preferably by a true rms power meter. (4 terminal device) It can be measured in Watts ..and if one is sure that the impedance remains constant at say 8 ohms, simplified to a voltage or current measurement. Thus the 2.8 v rms into a load of 8 ohms yields 1 watt.of Rms power.

The acoustic measurement is a power flow across a surface area and is measured as watts per metre Sq . Any microphone measurement is at a single point in space. To cconver this to speaker transducer efficiency it must be integrated over a sphere of the radius of size the distance the calibrated microphone is from the speaker. And centred on the speaker However as the speaker is probably .. (invariably ) a non isotropic emitter, that calculation is non trivial.. In any off axes position the power flux is reduced..Therefore the acoustic flux would need to be measured at a multitude of different positions, on the same locus... Not a trivial task
The reading on a calibrated sound meter will be ultimately Watts/ m sq. But may be displayed as a dB acoustical reading. ..Of which there are a few,one of which is skewed to match human ear sensitivity.
 

andy1249

Distinguished Member

lindsayt

Active Member
Sorry but you are totally wrong.
You are making an incorrect assumption and you are mixing your units.

Everything that I have said in this thread is 100% correct.

Keeping it simple.
The 2.83 volts is simply the reference signal level.
You appear to be failing to grasp the significance of the 2.83 volt part of the 89 dbs/2.83v @ 1 metre speaker specification.

Speakers output sound pressure.
If you measure the speakers published db level at 1 meter that means you have 1 acoustic watt from your speaker and at typical 1% efficiency that would be 100 electrical watts in the amplifier.
This statement makes no sense whatsoever.

If I measure my speaker's published db efficiency I have to feed my speakers an AC signal with a frequency of 1 khz at a voltage of 2.83 volts from a signal generator. I then have to place a sound meter, 1 metre in front of my speaker. This sound meter will give me a reading in dbs. In the example of my HB1's the reading that I get will be 89 dbs. This is far less than 1 acoustic watt.

According to this page:
Sound power - Wikipedia
1 acoustic watt would measure at 120 dbs on a sound meter.
That's higher than the vast majority of domestic speakers can produce, even at a distance of 1 mm.

According to you and that wiki link, if I measure my Heybrook speakers at the 1 acoustic watt level you are claiming, I will be listening to my speakers at a volume that will have broken them!


At 0.5% efficiency that would be 200 electrical watts in your amp.
At 3% efficiency that would be 33 electrical watts in your amp etc.
That is how it works.
You appear to have gotten your understanding of the manufacturer's specs the wrong way round!

When they do the tests to arrive at the efficiency headline specification they feed 1 electrical watt into 8 ohm speakers and 2 electrical watts into 4 ohm speakers. During these tests they will be getting something like 0.005 acoustic watts from ordinary speakers.

Electrical watts are always significantly higher than the acoustic watts from the db measurement.
You have confused the two watt units and made nonsense extrapolations like “ microwatts and milliwatts” in your amp. (Post # 8)

Once you understand the difference between the units it is no longer “ mind boggling” and you will get why amp manufacturers dont mention microwatts or milliwatts in their specs.
Yes of course electrical watts are significantly higher than acoustic watts in a hi-fi system. Speakers are inefficient transducers.

However, human ears are incredibly sensitive to nano watt levels of acoustic power.
According to that Wiki page, a quiet conversation has an acoustic power level of 10 to the minus 9 watts! Multiply that by 200 to get electrical watts and there are times when I am listening to my system at micro watt electrical power levels.

I think it's quite mind boggling that the human ear can hear a ticking watch which has an acoustic power of ten to the power of minus 10 watts!
 

andy1249

Distinguished Member
According to that Wiki page, a quiet conversation has an acoustic power level of 10 to the minus 9 watts! Multiply that by 200 to get electrical watts and there are times when I am listening to my system at micro watt electrical power levels.

Wrong db reference level on the header on the right hand side.
You need to shift four steps down till we are talking about the same db reference, i.e. watts per meter.
Dbs are a ratio, specifying your reference level is important.
Note where 1 watt is on that table compared to specified reference of 1 watt for speakers.
So you are orders of magnitude out.

As for the rest of your post, I guess I owe you an apology.
I honestly thought you were making a simple mistake regarðing units and thats all.

From that post its clear you dont understand a great deal ( or are actually just points scoring ) and either way I,m done with this.
 
Last edited:

lindsayt

Active Member
Wrong db reference level on the header on the right hand side.
In that case, can you please provide a link to a reputable source anywhere on the internet that gives a table of dbs measured by a calibrated sound meter against acoustic watts or acoustic watts per meter?

I am not aware of anyone in the audio industry that refers to in room volume levels in terms of acoustic watts, or acoustic watts per meter, or acoustic watts per meter squared. Everyone that I've come across - apart from you andy1249 - refers to in room volumes in terms of dbs. When measuring sound volumes, everyone I've come across has used sound meters / microphones calibrated to the same reference levels. So that, for example a reading of 90 dbs on the Stereophile testing equipment will be the same loudness as 90 dbs on my sound meter (for a 1 khz test tone).

Here's a link to a recent Stereophile speaker measurement page. It's typical of the measurements that they do.
Audio Physic Step Plus loudspeaker Measurements
Please note that they always refer to in room volumes in terms of dbs and not in terms of acoustic watts nor acoustic watts per meter.



You need to shift four steps down till we are talking about the same db reference, i.e. watts per meter.
Who says I need to shift four steps down to arrive at the acoustic watt level? Are you saying that that wiki entry is incorrect and that you are correct? On what basis should I take you as an authority over wiki? Would you like to write to wiki to explain how they are wrong?

Please provide a link to a table that you are happy with that cross references acoustic watts or acoustic watts to dbs.

"Watts per meter"? In posts #9, #14, #16, you used the units of acoustic watts. Now you are using the unit of acoustic watts per meter. Please make your mind up which units you want to use.



Dbs are a ratio, specifying your reference level is important.
Yes and that's why all commercially available calibrated sound meters are calibrated to the same reference level.

Note where 1 watt is on that table compared to specified reference of 1 watt for speakers.
So you are orders of magnitude out.
I didn't write that wiki entry.


As for the rest of your post, I guess I owe you an apology.
I honestly thought you were making a simple mistake regarðing units and thats all.

From that post its clear you dont understand a great deal ( or are actually just points scoring ) and either way I,m done with this.
Thank-you for the apology.

No thanks for saying that you think that it's clear that I don't understand a great deal. When I do understand perfectly well how the OP can find out roughly how many watts his amplifier is sending to his speakers for the minimum of time, effort and cost.
 

dannnielll

Well-known Member
Like I said a P****contest. !.

Sound Pressure • terms • definitions • units • measurements ...

Sound Pressure is the difference between the pressure caused by a sound wave and the ambient pressure of the medium the sound wave is passing through.

Sound Pressure is a sound field quantity, not a sound energy or sound power quantity.
Sound Pressure Definition IEC 801-21-20, root mean square of the instantaneous sound pressures over a given time interval, unless specified otherwise

Sound pressure is measured in pascals, symbol Pa. However the immense range of human hearing, 0.00002 pascals up to 200 pascals, means the pascal is not practical for everyday use. Fortunately the sound pressure level in decibels, detailed below, neatly solves this problem.
Sound Pressure Level (SPL) = 20 log (p/po) dB, where p is the sound pressure in pascals and po is the reference sound pressure of 0.00002 pascals = 0 dB in air ≡ to the threshold of hearing at 1KHz
Some typical Sound Pressure and Sound Pressure Levels
Sources at 1 m Sound Pressure SPL re 20 μPa
Rifle 200 Pa 140 dB
Threshold of pain 20 Pa 120 dB
Pneumatic hammer 2 Pa 100 dB
6 dB = twice or half the pressure 1 Pa 94 dB
Street traffic 0.2 Pa 80 dB
Talking 0.02 Pa 60 dB
Library 0.002 Pa 40 dB
TV Studio 0.0002 Pa 20 dB
Reference Sound Pressure 0.00002 Pa 0 dB
Sound Pressure Level is a sound field quantity and uses the 20 log factor so, as a rule of thumb:

6 dB = a factor of 2 in sound pressure (double or half the sound pressure)
10 dB = a factor of 3 in sound pressure
20 dB = a factor of 10 in sound pressure

Sound Pressure Level Definition IEC 801-22-07, logarithm of the ratio of a given sound pressure to the reference sound pressure in decibels is 20 times the logarithm to the base ten of the ratio.

● Note 1 : unless otherwise specified, the reference sound pressure is 20 μP for airborne sound and 1 μPa for sound in mediaother than air.
● Note 2 : unless otherwise specified, the sound pressures are understood to be expressed in root-mean-square values.
See also our sound pressure level calculations article

Related Terms - listed alphabetically
Average Sound Pressure see effective sound pressure
Band Sound Pressure Level Definition IEC 801-22-12, level of the sound pressure produced within a specified frequency band.

● Note: the band may be specified by its lower and upper cut-off frequencies, or by its geometric centre frequency and bandwidth. The width of the band may be indicated by a modifier such as one octave band (sound pressure) level, one-half octave band level, one-third octave band level.
Effective Sound Pressure is the root-mean-square of the instantaneous sound pressure.
Effective Sound Pressure is also known as the average sound pressure.

See also • the Effective Value Definition IEC 103-02-03

Equivalent Continuous Sound Pressure Level Definition IEC 801-22-11, logarithm of the ratio of a given root-mean-squaresound pressure, during a stated time interval, to the reference sound pressure. Average sound pressure level in decibels is 20 times the logarithm to the base ten of that ratio.

● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa. Also known as the time-average sound pressure level.
Equivalent continuous sound pressure level should not be confused with
Equivalent continuous sound level. To compare these definitions directly click here

To make it more interesting... The Pascal is a unit of pressure, and watts is a unit of power the relationship between them is.

Derived Unit Measures,Formal Definition,
newton (N) force kg·m·s-2
pascal (Pa ) pressure kg·m-1·s-2
joule (J ) energy or work kg·m2·s-2
watt (W ) power kg·m2·s-3

To save you the work of doing the conversion...
The actual average threshold of hearing at 1000 Hz is more like 2.5 x 10-12 watts/m2 orabout 4 decibels, but zero decibels is a convenient reference. The threshold of hearing varies with frequency, as illustrated by the measured hearing curves.. in other words a power level of 1 picowatt / m2 is defined generally as the lowest intensity sound that humans can hear, at the most sensitive frequencies in the lower Kilohz range. When one realises that the ear lug is only about a 2 cm in diameter,the actual power which gets into the ear is really really tiny.
Finally if one had a device generating an SPL of 1watt/ m sq of acoustic power level at a distance of 1 m, it would be at the threshold of pain ,and assuming it was non directional (isotropic) the area of the sphere is 4 pi metre sq so the total acoustic power outputted is 4pi Watts
 
Last edited:

BlueWizard

Distinguished Member
Discussing Electrical Power vs Acoustical Power is a nice little side track, but it doesn't address the question.

How to calculate how many watts are speakers using ??

I suspect he means how many watts speakers are CONSUMING, but a nitpicking point.

First we are not comparing Electrical Power and Acoustical Power, we are comparing Electrical Input vs SPL Output from the Speakers. And to make that comparison we have a reference point - [email protected]/1m or [email protected]/1m.

SPL (Sound Pressure Level or Loudness) will chance consistently within the normal working range of the speaker. In will increase or decrease by 3db every time the power is double or halved.

So, that seems to be everything we need to estimate the Amp Power simply by measuring the SPL output of the speaker.

Or as I originally suggested, simply measure the voltage at the Speaker terminals for a given measured SPL output of the speaker. Not completely accurate, but it should give you a general idea.

For a general idea of the Power, either of the suggested methods will work. However, if he want very precise measurement, then he will need some electronic test equipment. That need not be excessively expensive, but it is also not free.

Also, he would need to determine if he needs Dynamic Measurements or Static Measurements. By that I mean with Music Playing, or with steady Test Tones?

If you know the rated Sensitivity of the speaker, then with music or a movie playing, if you measure the SPL Loudness, you can easily make a best guess at the Amplifier Power.

Or, from a fixed point in the room, if you measure typical listening level, then measure louder listening level, using the Speakers Sensitivity, you can again estimate the increase in Amp Power. You can probably use a Smart Phone for making this measurement. They are typically not accurate relative to absolute measured SPL, but they should be reasonably accurate in measuring a change in SPL level.

For example, a Smart Phone will be consistently inaccurate. That is to say, it might read 95db when the absolute SPL is actually 100db. So, in accurate in that sense. Bit if you take two measurements at difference volume levels the difference is likely to be accurate.

Let me explain it a different way. Let's say the Smart Phone always measures 10db off. So the actually sound is 75db but you measure 65db, then you bump to volume to 85db, and the meter reads 75db. The absolute value is not accurate, but the 10db difference between the two readings is. And from many measurement, absolute level is not as important as the difference between two levels. So in this sense a Smart Phone could be used to make the determination under consideration in this discussion. And actual SPL Meter would be better, but you could make due with a Smart Phone.

Steve/bluewizard
 

lindsayt

Active Member
Bluewizard, have you ever tried measuring the voltage at your speaker terminals whilst it is playing music or a film?

I have, with my multimeter. It was a waste of time. My multi-meter is OK for measuring DC voltages. For example: batteries. It's also fine for measuring steady state AC voltages, eg the the 50hz mains voltage.

Music and movies are neither DC nor steady state AC. My multi-meter can't cope with that type of signal.

If I had some sort of fancy oscilloscope type set up I'd be in business. But how much would such a set-up cost? Maybe this would do the trick for about £200?
Leader LS8050 Dual Time Base, Delayed Sweep Oscilloscope | eBay

Maybe I should buy it and hire it out to audio enthusiasts for £10 plus shipping costs per week-end?
 

dannnielll

Well-known Member
Bluewizard, have you ever tried measuring the voltage at your speaker terminals whilst it is playing music or a film?

I have, with my multimeter. It was a waste of time. My multi-meter is OK for measuring DC voltages. For example: batteries. It's also fine for measuring steady state AC voltages, eg the the 50hz mains voltage.

Music and movies are neither DC nor steady state AC. My multi-meter can't cope with that type of signal.

If I had some sort of fancy oscilloscope type set up I'd be in business. But how much would such a set-up cost? Maybe this would do the trick for about £200?
Leader LS8050 Dual Time Base, Delayed Sweep Oscilloscope | eBay

Maybe I should buy it and hire it out to audio enthusiasts for £10 plus shipping costs per week-end?
The problem is the your digital multimeter is not designed for the task.... The standard DMM is actually a DC voltmeter movement taking 3 samples per second and in the range 0 to 1.999volts. The switches select various resistors to change scales. AC measurements switch in a diode and a capacitor circuit with a time constant of about 0.5seconds. ..so it measures a dc average voltage and scales it as RMS. It only has a frequency response slightly above 120 hz.
Proper measurements require a high speed multiplying circuit, used to square the voltage, summing these values ,and averaging that. .. and displaying the Square Root of this ...a True RMS measurement.
What I would have done,and would have discussed with students would be to run a scope at a slow time base and look at the width of the of the trace
AC millivolmeters ,based on using proper a proper audio amplifier, feeding a high speed diode bridge ,was another method...
 

The latest video from AVForums

Star Wars Andor, Woman King, more Star Trek 4K, Rings of Power & the latest TV, movies & 4K releases
Subscribe to our YouTube channel

Latest News

Focal launches Bathys noise-cancelling wireless headphones
  • By Ian Collen
  • Published
Formovie Theater UST projector hits the UK
  • By Ian Collen
  • Published
Sonus faber unveils new flagship Arena speaker series
  • By Ian Collen
  • Published
Sharp showcases its upcoming 4K TV and audio line-up
  • By Ian Collen
  • Published
HiFi Rose announces all-in-one RS520 audio streamer
  • By Ian Collen
  • Published

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom