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Post by Axis on Jul 24, 2016 15:04:34 GMT -5
How is efficiency and nominal impedance tied to each other ? Is a 4 ohms compared to 8 ohms speaker more or less sensitive ?
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DYohn
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Post by DYohn on Jul 24, 2016 16:27:47 GMT -5
How is efficiency and nominal impedance tied to each other ? Is a 4 ohms compared to 8 ohms speaker more or less sensitive ? First off, sensitivity and efficiency are not the same thing. Sensitivity is the db SPl produced at specific frequencies at 1 watt power level and measured at a specific distance on axis from the loudspeaker. Efficiency is in general how effectively a loudspeaker converts electrical energy into mechanical energy. The terms are often used interchangeably by consumers but that's really incorrect. Sensitivity is a specification, efficiency is a gross measure of how much power is required to attain some target output level. Impedance is directly related to efficiency in that lower nominal impedance systems can attain higher dbSPl with less power input. Note that impedance changes dramatically with frequency, so all speakers are more efficient at some frequencies and less so at others. Impedance is not related to a loudspeaker's sensitivity rating as it is a fixed power and frequency and whatever is required to get to that power is used. Note also to beware of sensitivity ratings given at "2.83V". This is the voltage level necessary to attain 1 watt at 8 ohms, but at 4 ohms it generates 2 watts and makes those sensitivity results invalid (but often used by shady companies to make their speakers look better on paper.) |
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Post by Axis on Jul 24, 2016 16:42:14 GMT -5
How is efficiency and nominal impedance tied to each other ? Is a 4 ohms compared to 8 ohms speaker more or less sensitive ? First off, sensitivity and efficiency are not the same thing. Sensitivity is the db SPl produced at specific frequencies at 1 watt power level and measured at a specific distance on axis from the loudspeaker. Efficiency is in general how effectively a loudspeaker converts electrical energy into mechanical energy. The terms are often used interchangeably by consumers but that's really incorrect. Sensitivity is a specification, efficiency is a gross measure of how much power is required to attain some target output level. Impedance is directly related to efficiency in that lower nominal impedance systems can attain higher dbSPl with less power input. Note that impedance changes dramatically with frequency, so all speakers are more efficient at some frequencies and less so at others. Impedance is not related to a loudspeaker's sensitivity rating as it is a fixed power and frequency and whatever is required to get to that power is used. Note also to beware of sensitivity ratings given at "2.83V". This is the voltage level necessary to attain 1 watt at 8 ohms, but at 4 ohms it generates 2 watts and makes those sensitivity results invalid (but often used by shady companies to make their speakers look better on paper.) So with these Specs of the T1 these figures for Efficiency: 88 dB are not the same as often seen with a Sensitivity Spec for a speaker ? Example: speaker sensitivity 92 db at 1 watt at 1 meter. I still wonder why these speakers are 4 ohms or rated at 4 ohms. Car Audio speakers were just about always 4 ohms and some Home speakers are 4 ohms but it is not the norm from all the specs I have looked at for Home speakers over the years. I believe sometimes designer will do this for a certain reason. I believe Emotiva has had other speakers in the past that were 4 ohm. Airmotiv T1 Specs from Emotiva Product page. Efficiency: 88 dB (2.83V/1m). Power handling: 150W continuous / 300W peak. Nominal impedance: 4 ohms. Frequency response: 37 Hz - 28 kHz (+0/-6 dB). |
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DYohn
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Post by DYohn on Jul 24, 2016 17:01:14 GMT -5
Those specs tell me the actual sensitivity rating of that loudspeaker is 85db.
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Post by Axis on Jul 24, 2016 17:04:00 GMT -5
Those specs tell me the actual sensitivity rating of that loudspeaker is 85db. Thanks  |
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Post by gzubeck on Jul 28, 2016 1:09:52 GMT -5
How is efficiency and nominal impedance tied to each other ? Is a 4 ohms compared to 8 ohms speaker more or less sensitive ? With most speaker manufacturers if they have two versions of 4 ohm and 8 ohm speakers with the 4 ohm one usually 1 db more sensitive. That means an 88 db speaker at 8 ohm is usually around 89 db for 4 ohm. |
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Post by yves on Jul 28, 2016 14:39:12 GMT -5
How is efficiency and nominal impedance tied to each other ? Is a 4 ohms compared to 8 ohms speaker more or less sensitive ? With most speaker manufacturers if they have two versions of 4 ohm and 8 ohm speakers with the 4 ohm one usually 1 db more sensitive. That means an 88 db speaker at 8 ohm is usually around 89 db for 4 ohm. The logical relationship between efficiency and nominal impedance has a name. It is called "fantasy". www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity |
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Post by gzubeck on Jul 29, 2016 1:04:31 GMT -5
With most speaker manufacturers if they have two versions of 4 ohm and 8 ohm speakers with the 4 ohm one usually 1 db more sensitive. That means an 88 db speaker at 8 ohm is usually around 89 db for 4 ohm. The logical relationship between efficiency and nominal impedance has a name. It is called "fantasy". www.audioholics.com/loudspeaker-design/loudspeaker-sensitivityIt only really matters if you want to use it in a design and need to pad a tweeter to match the multiple woofers. So if there is a 1 db difference in an MTM design it would now be 2db difference. Also, the load the amplifier sees is important depending on whether it's a parallel or series layout. I just wanted to give the original poster my personal observation that given the same exact speaker but designed for different resistances there's a small bump of around 1db given manufacturers specs. So if you want the same exact speaker but different loads there will be a very small difference. |
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Post by yves on Jul 29, 2016 4:55:59 GMT -5
It only really matters if you want to use it in a design and need to pad a tweeter to match the multiple woofers. So if there is a 1 db difference in an MTM design it would now be 2db difference. Also, the load the amplifier sees is important depending on whether it's a parallel or series layout. I just wanted to give the original poster my personal observation that given the same exact speaker but designed for different resistances there's a small bump of around 1db given manufacturers specs. So if you want the same exact speaker but different loads there will be a very small difference. It won't be 2 dB. That's because, all else being equal, the difference between using a single woofer and using dual woofers is always ~3 dB so if there's a 1 dB difference in an MTM design it would now be ~1 dB difference because else you would be comparing apples and oranges. |
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Post by gzubeck on Aug 2, 2016 21:45:33 GMT -5
It only really matters if you want to use it in a design and need to pad a tweeter to match the multiple woofers. So if there is a 1 db difference in an MTM design it would now be 2db difference. Also, the load the amplifier sees is important depending on whether it's a parallel or series layout. I just wanted to give the original poster my personal observation that given the same exact speaker but designed for different resistances there's a small bump of around 1db given manufacturers specs. So if you want the same exact speaker but different loads there will be a very small difference. It won't be 2 dB. That's because, all else being equal, the difference between using a single woofer and using dual woofers is always ~3 dB so if there's a 1 dB difference in an MTM design it would now be ~1 dB difference because else you would be comparing apples and oranges. You are correct that there would be a +3 db increase if you use two woofers. What does this have to do with mild difference in a 4ohm and an 8 ohm speaker? Both dual speakers will have a +3 db increase! It's constant for both there. But if you use a 4 ohm speaker there will be +2 db difference. |
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Post by yves on Aug 3, 2016 2:10:12 GMT -5
It won't be 2 dB. That's because, all else being equal, the difference between using a single woofer and using dual woofers is always ~3 dB so if there's a 1 dB difference in an MTM design it would now be ~1 dB difference because else you would be comparing apples and oranges. You are correct that there would be a +3 db increase if you use two woofers. What does this have to do with mild difference in a 4ohm and an 8 ohm speaker? Both dual speakers will have a +3 db increase! It's constant for both there. But if you use a 4 ohm speaker there will be +2 db difference. +2 dB difference in what? Distortion level?  |
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Post by sme on Aug 4, 2016 2:56:16 GMT -5
The way I usually use the terminology *sensitivity* and *efficiency* is as follows:
To understand the distinction, you must first understand something about *impedance*. An amplifier is a voltage output device. The voltage provided by the amp is the same as the signal that is sent to the speakers. Impedance (among other things) describes how much power a speaker will consume when the amp provides a particular voltage. Impedance changes with frequency. Most speakers have one or more impedance peaks where resonances are present. At frequencies where impedance is high, the speaker is consuming relatively less power for a given input voltage. The *nominal impedance* is a made up number to roughly describe how high the impedance is outside the peaky areas.
Sensitivity is the SPL output at 1 meter of the speaker for a given *voltage* input from the amp under a standard set of measurement conditions, typically either anechoic or half-space (installed flush into a very large rigid wall). Sensitivity varies with frequency. The shape of sensitivity vs. frequency is also the frequency response of the speaker. Frequently, the sensitivity is measured using a signal whose voltage would cause 1 watt to be consumed if the impedance were equal to the *nominal impedance*. For an "8 ohm" speaker, the signal level would be 2.83V. For "4 ohm" it would be "2V", but some manufacturers will still report 4 ohm nominal speakers measured at "2.83V" also. Sensitivity is important in speakers because amplifiers have a maximum voltage they can output without clipping.
Efficiency is the SPL output at 1 meter of the speaker for a given *power* consumed by the speaker (mostly turned to heat in the coil) under a standard set of measurement conditions. (See above.) Efficiency also varies with frequency, but it's curve has a different shape than the sensitivity or frequency response. Efficiency depends on both sensitivity and impedance. Even if sensitivity is high, efficiency may not be high if the impedance is real low because the speaker's still sucking down a lot of power. Efficiency is important in speakers for two reasons. First, the vast majority of power consumed by the speaker is converted into heat in the voice coil. Heat is detrimental to the performance of drivers, even when it's nowhere near enough to cause failure. The second reason is that the ability of an amp to sustain its maximum voltage deteriorates as it is asked to deliver more power. Otherwise, you'd always get double power in 4 ohm as you do into 8 ohm.
Let me now repeat that impedance, sensitivity, and efficiency all change with frequency. However, manufacturers typically only publish single values. This is very unfortunate because there are many ways of aggregating impedance, sensitivity, and efficiency data for multiple frequencies into a single number. There is no consistency in the methods used. Terminology is also frequently used in a confusing way. Some manufacturers will publish the sensitivity of a 4 ohm speaker as a number of dB/1W @ 1 meter that was actually measured with a 2.83V test signal and then chose the SPL value where the response peaks. Never mind the fact that the 4 ohm nominal speaker might have significant dips that are even lower. I've even seen manufacturers fudge-in a "room gain" value to make their numbers even bigger. It's a pretty ugly deal out there, and you really can't trust these manufacturer numbers without at least clarifying their methodology and ideally by comparing to third party data or just doing the measurements yourself.
A couple more minor points. First, impedance, sensitivity, efficiency are generally measured using low level signals where the speaker is hopefully behaving linearly. However, in real speakers, these properties will change to some extent or another depending on the content with the changes becoming more severe and unpredictable as they are pushed harder. Second, speakers behave as temporary energy storage devices. Only some of the power that gets transferred from the amp to the speaker is actually consumed by the speaker. The power which is not consumed by the speaker is returned to the amp at another point in the cycle. As I understand it, class AB amps are not able to re-use this power. Instead, it gets dissipated in the amp output devices. This can be a substantial cause of heating inside the amp and can cause problems in amps that can't dissipate the heat fast enough. Efficiency, however, is only concerned with how much power gets consumed by the speaker for a given level of output. To understand how much power gets dissipated in the amp requires looking at the impedance phase angle as well.
Hopefully that sums it up.
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Post by sme on Aug 4, 2016 3:01:10 GMT -5
Much more important to audible distortion than mass is voice coil inductance. Yes, inductance is critical. There's a reason I'm using mid/bass drivers with vanishingly low inductance. |
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Post by yves on Aug 4, 2016 8:46:46 GMT -5
The way I usually use the terminology *sensitivity* and *efficiency* is as follows: To understand the distinction, you must first understand something about *impedance*. An amplifier is a voltage output device. The voltage provided by the amp is the same as the signal that is sent to the speakers. Impedance (among other things) describes how much power a speaker will consume when the amp provides a particular voltage. Impedance changes with frequency. Most speakers have one or more impedance peaks where resonances are present. At frequencies where impedance is high, the speaker is consuming relatively less power for a given input voltage. The *nominal impedance* is a made up number to roughly describe how high the impedance is outside the peaky areas. Sensitivity is the SPL output at 1 meter of the speaker for a given *voltage* input from the amp under a standard set of measurement conditions, typically either anechoic or half-space (installed flush into a very large rigid wall). Sensitivity varies with frequency. The shape of sensitivity vs. frequency is also the frequency response of the speaker. Frequently, the sensitivity is measured using a signal whose voltage would cause 1 watt to be consumed if the impedance were equal to the *nominal impedance*. For an "8 ohm" speaker, the signal level would be 2.83V. For "4 ohm" it would be "2V", but some manufacturers will still report 4 ohm nominal speakers measured at "2.83V" also. Sensitivity is important in speakers because amplifiers have a maximum voltage they can output without clipping. Efficiency is the SPL output at 1 meter of the speaker for a given *power* consumed by the speaker (mostly turned to heat in the coil) under a standard set of measurement conditions. (See above.) Efficiency also varies with frequency, but it's curve has a different shape than the sensitivity or frequency response. Efficiency depends on both sensitivity and impedance. Even if sensitivity is high, efficiency may not be high if the impedance is real low because the speaker's still sucking down a lot of power. Efficiency is important in speakers for two reasons. First, the vast majority of power consumed by the speaker is converted into heat in the voice coil. Heat is detrimental to the performance of drivers, even when it's nowhere near enough to cause failure. The second reason is that the ability of an amp to sustain its maximum voltage deteriorates as it is asked to deliver more power. Otherwise, you'd always get double power in 4 ohm as you do into 8 ohm. Let me now repeat that impedance, sensitivity, and efficiency all change with frequency. However, manufacturers typically only publish single values. This is very unfortunate because there are many ways of aggregating impedance, sensitivity, and efficiency data for multiple frequencies into a single number. There is no consistency in the methods used. Terminology is also frequently used in a confusing way. Some manufacturers will publish the sensitivity of a 4 ohm speaker as a number of dB/1W @ 1 meter that was actually measured with a 2.83V test signal and then chose the SPL value where the response peaks. Never mind the fact that the 4 ohm nominal speaker might have significant dips that are even lower. I've even seen manufacturers fudge-in a "room gain" value to make their numbers even bigger. It's a pretty ugly deal out there, and you really can't trust these manufacturer numbers without at least clarifying their methodology and ideally by comparing to third party data or just doing the measurements yourself. A couple more minor points. First, impedance, sensitivity, efficiency are generally measured using low level signals where the speaker is hopefully behaving linearly. However, in real speakers, these properties will change to some extent or another depending on the content with the changes becoming more severe and unpredictable as they are pushed harder. Second, speakers behave as temporary energy storage devices. Only some of the power that gets transferred from the amp to the speaker is actually consumed by the speaker. The power which is not consumed by the speaker is returned to the amp at another point in the cycle. As I understand it, class AB amps are not able to re-use this power. Instead, it gets dissipated in the amp output devices. This can be a substantial cause of heating inside the amp and can cause problems in amps that can't dissipate the heat fast enough. Efficiency, however, is only concerned with how much power gets consumed by the speaker for a given level of output. To understand how much power gets dissipated in the amp requires looking at the impedance phase angle as well. Hopefully that sums it up. The thing that has summed it up for me a very long time ago was that you are better off learning how to steer clear of white van kinds of numbers. forums.audioholics.com/forums/threads/what-does-a-speakers-sensitivity-mean.83847/ |
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