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In Reply to: RE: Efficiency and Sensitivity are not the same thing! posted by neolith on May 08, 2017 at 15:58:14
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Nope.Sensitivity is, and always has been, expressed in 1W/1m.
"Efficiency" is often used to describe sensitivity while taking into account impedance. (Sensitivity compensates for impedance). This is not really what actual efficiency is... efficiency is really an expression of electrical power in compared to acoustic power out.
A tweeter that is 90db 1W/1m sensitive is 0.6% efficient
A prosound woofer that is 97db 1W/1m sensitive is 3% efficient.The rest goes into heat (I^2*R coil losses and overcoming frictional forces of the mechanical system, which also results in heat).
I always refer to this calculator page for efficiency.
http://www.sengpielaudio.com/calculator-efficiency.htm
Although 32 and 16 ohm speakers were once very common, 8 ohms became a common "nominal" impedance for speakers for many decades. As such, the voltage used for efficiency is 2.83V, as this voltage when applied to an 8 ohm nominal load gives 1 Watt.
P = (V^2) / R
P = 2.83^2 / 8
P = 8 / 8
P = 1WInterestingly, this means an 8 ohm speakers will have the same value for efficiency and sensitivity!
When you apply 2.83 volts to a 16 ohm speaker you get
P = (V^2) / R
P = 2.83^2 / 16
P = 8 / 16
P = 0.5WWhen you apply 2.83 volts to a 4 ohm speaker you get
P = (V^2) / R
P = 2.83^2 / 4
P = 8 / 4
P = 2WEfficiency takes into account the speakers impedance in so far as how it impacts power. Sensitivity compensates for this by adjusting the input voltage to keep input power constant.
I could be wrong, but I think this is a common usage of the word "efficiency" when it's technically incorrect. In reality, it's really sensitivity with and without using the 8 ohm reference for power. Sensitivity 1W/1m and sensitivity 2.83V/1m.
1W/1m = let's adjust voltage to have a common 1W input.
2.83V/1m = let's apply 2.83V and allow power to vary with impedance.Since amplifiers are voltage sources, the 2.83V/1m has real-world applications, where sensitivity really speaks more to the speakers actual *efficiency*.
As such, a 2 ohm speaker can be less efficient than an 8 ohm speaker but still produce higher SPL at 2.83V. This is because you get 4W at 2 ohms and 1W at 8 ohms with 2.83V applied.
Cheers,
Presto
Edits: 05/09/17 05/09/17 05/09/17
Your opening sentence ("Sensitivity is, and always has been, expressed in 1W/1m.") is incorrect.
Sensitivity is in fact 2.83 Volts at one meter.
In every other way your post is correct.
Efficiency as a measurement standard went out some years ago (1980s), to be replaced by sensitivity. But you still see it used all over the industry. There is continuing confusion on the topic.
The history of it goes back to the 1950s, when EV and MacIntosh began to push for a voltage source amplifier standard. Prior to that time, all speakers had to have level controls for the midrange and tweeter as the actual voltage response of the amplifier to be used was unknown (IOW they were not there to adjust to the room). By adopting a voltage source as a reference, the controls could be eliminated. But the older efficiency standard held on well into the 1980s and is still used today.
"Sensitivity is, and always has been, expressed in 1W/1m."Okay, that might well be incorrect. Here, let's try this:
"Sensitivity, in my travels through domestic speaker specifications, has almost always been expressed in 1W/1m"
They will also say "1m SPL@2.83V". It's rare to see them cite 4V for 16 ohm drivers or 2V for 4 ohm drivers even though if they give 1W/1m as those are exactly the applied voltages. I've seen a lot of specs in pro-sound circles for four ohm driver which are at 2.83V / 1m. 2.83V vs. 1W can't be the same if you say "The 8 ohm version is 3db less sensitive than the 4 ohm version". If you use voltage as the reference, there is a 3db difference. If you use power (1W) as a reference they will have the same sensitivity, if all other design details besides coil impedance are observed.
This is why the *word* sensitivity (at 1m) can't mean 2.83V *and* 1W at the same time unless it's an 8ohm nominal driver or system.
This is why I thought they reserved "sensitivity" for 1W/1m and perhaps threw people off calling 2.83V/1m/8 ohms sensitivity as well.
I wonder if life would be easier if we said "1m power sensitivity in 1W/1m" and "1m voltage sensitivity in 2.83V/1m"
EV has SPL at 10 feet with, what was it, four volts applied?
From the EVM12S 12" mid-woofer specification sheet:(EIA Standard SE-103 Section SE3).
The thing is, it's easy to get 1W/1m from the 10 foot measurement - just increase the SPL per the inverse square law for the SPL at 1m instead of 10 feet. (It's already at 1W).
If the person seeing the spec knows what it is and can compare apples to apples with other drivers/systems he's okay. For everyone else, it's not surprising there is confusing surrounding the terms and their application.
Cheers,
Presto
Edits: 05/10/17 05/10/17
We're pretty much on the same page except that first bit.
Okay, that might well be incorrect. Here, let's try this:
"Sensitivity, in my travels through domestic speaker specifications, has almost always been expressed in 1W/1m"
That's a bit closer, which is to say that individual manufacturers are making the same mistakes that many consumers do, which is that they freely mix the two terms.
Whenever you see the '1W/1m' thing expressed as 'sensitivity' that is the manufacturer screwing up. These days, many of them are so young they don't even know there was a prior measurement standard.
So... what are the *correct* terms?
We know what SPL 2.83V/1m and SPL 1W/1m means technically...
What are the terms for EACH.
They are not the same by definition although they will yield the same result for an 8 ohm nominal device.
The best descriptions I have come across is:
2.83V/1m -> Voltage Sensitivity
1W/1m -> just "Sensitivity" but perhaps should be "power sensitivity"
Cheers,
Presto
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Ralph ;
" These days, many of them are so young they don't even know there was a prior measurement standard."
Careful Sir...your wrinkles are showing !!!
LOL .
Couldn't resist !
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