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Sensitivity <=> Fidelity ?

post #1 of 15
1/27/13 at 6:52pm
Thread Starter 
I'm in the process of making a speaker selection, though frankly my speaker knowledge is admittedly limited. A friend of mine is a physicist, and also a pretty good and experienced musician. It's his opinion that sensitivity is the most important spec for determining speaker fidelity. The argument goes that for a given amount of power going into the speaker, all that power needs to come out. If it's not coming out at the intended frequency (which you measure via a sensitivity measurement), then the power must be coming out at other, nearby frequencies / harmonics that are not intended, i.e., you have distortion. This seems like a good argument, yet I've read elsewhere that sensitivity has little to do with fidelity -- that it's just a measure of the efficiency of the speaker.

Anyone care to take a side?
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post #2 of 15
1/27/13 at 6:58pm
It doesnt directly relate to fidelity. If all else is equal, higher sensitivity is preferred, but all else will never be equal smile.gif
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post #3 of 15
1/28/13 at 6:39am
Quote:
Originally Posted by aligborat View Post

I'm in the process of making a speaker selection, though frankly my speaker knowledge is admittedly limited. A friend of mine is a physicist, and also a pretty good and experienced musician. It's his opinion that sensitivity is the most important spec for determining speaker fidelity. The argument goes that for a given amount of power going into the speaker, all that power needs to come out.
Sensitivity and fidelity have absolutely no connection. Your friend's field of study is clearly not acoustical engineering, while IME musicians don't know any more about how speakers work than the average consumer.
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Anyone care to take a side?
This is an engineering question, there are no sides, only facts.
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post #4 of 15
1/28/13 at 7:16am
Thread Starter 
"Sensitivity and fidelity have absolutely no connection. Your friend's field of study is clearly not acoustical engineering, while IME musicians don't know any more about how speakers work than the average consumer."

Great! So what's the counterargument then? Where does the energy go, if not into the intended frequency?
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post #5 of 15
1/28/13 at 8:35am
Quote:
Originally Posted by aligborat View Post

Where does the energy go, if not into the intended frequency?
Heat.
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post #6 of 15
1/28/13 at 8:50am
Thread Starter 
Thanks -- for what it's worth, this was my counterargument to my friend as well, but for whatever reason he wasn't really buying it.
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post #7 of 15
1/28/13 at 9:53am
Quote:
Originally Posted by aligborat View Post

Thanks -- for what it's worth, this was my counterargument to my friend as well, but for whatever reason he wasn't really buying it.
That reason would be that he doesn't know what he's talking about. biggrin.gif
That doesn't mean he might not be quite competent in his chosen field, or be a good player. But like all scientific disciplines you won't understand acoustical engineering unless you study it, even if informally.
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post #8 of 15
1/28/13 at 10:24am
The only time I look at a speakers sensitivity rating is when I'm trying to drive them with something very low powered. These days, unless you're driving something with tube amps, power is plentiful for most home applications. The two measurements are in no way correlated. There are some beautiful, high fidelity planar speakers which have low sensitivity. Have your friend listen to a pair of Maggies!
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post #9 of 15
1/28/13 at 12:02pm
Quote:
Originally Posted by spincycle79 View Post

The only time I look at a speakers sensitivity rating is when I'm trying to drive them with something very low powered. These days, unless you're driving something with tube amps, power is plentiful for most home applications. The two measurements are in no way correlated. There are some beautiful, high fidelity planar speakers which have low sensitivity. Have your friend listen to a pair of Maggies!

Try playing Maggies at reference from 4m away. Their fidelity won't hold up as well. Perhaps the OPs engineer friend is talking about listening at higher volumes where distortion and compression kicks in. I don't know.

Well within the power handling capabilities, I don't think the two are related.
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post #10 of 15
1/28/13 at 12:16pm
Speaker sensitivity is a function of the overall SPL the speaker produces when fed a certain current. It has nothing to with how accurate the SPL is.

Having said that, it takes less power to produce SPL at higher frequencies than lower frequencies and my experience with highly sensitive speakers is they get their higher rating because they overplay the higher frequencies relative to the lower frequencies. I'm sure there are great highly sensitive speakers that don't do this and are more efficient for other reasons, but I haven't heard any.
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post #11 of 15
1/28/13 at 3:46pm
Quote:
Originally Posted by aligborat View Post

I'm in the process of making a speaker selection, though frankly my speaker knowledge is admittedly limited. A friend of mine is a physicist, and also a pretty good and experienced musician. It's his opinion that sensitivity is the most important spec for determining speaker fidelity. The argument goes that for a given amount of power going into the speaker, all that power needs to come out. If it's not coming out at the intended frequency (which you measure via a sensitivity measurement), then the power must be coming out at other, nearby frequencies / harmonics that are not intended, i.e., you have distortion. This seems like a good argument, yet I've read elsewhere that sensitivity has little to do with fidelity -- that it's just a measure of the efficiency of the speaker.

Anyone care to take a side?

I am very surprised that a physicist would say this. Tell him that if the efficiency is 1% (a typical value), then the other 99% of the power can't possibly go to making sound at other frequencies. It's mostly lost to heat. However, horn-loaded speakers tend to have lower distortion because they have higher efficiency and smaller cone motion leads to the same SPL. But most so-called horn-loaded speakers are only horn-loaded at the tweeter. If you want an example of a high efficiency fully horn-loaded speaker and sub, look at a Klispch La Scala or Klipschorn with a horn-loaded sub such as Bill's Tuba HT, or a tapped horn design.
Edited by psgcdn - 1/29/13 at 6:23am
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post #12 of 15
1/28/13 at 3:49pm
Quote:
Originally Posted by Bill Fitzmaurice View Post


This is an engineering question, there are no sides, only facts.

I think you should start structuring your sentences in the style of your avatar. Like so:

"An engineering question, this is. No sides there are, only facts."

Yes. Yessss.
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post #13 of 15
1/28/13 at 6:13pm
Quote:
Originally Posted by psgcdn View Post

I am very surprised that a physicist would say this. Tell him that if the efficiency is 1% (a typical value), then the other 99% of the power can't possibly go to making sound at other frequencies. It's mostly lost to heat. However, horn-loaded speakers tend to have lower distortion because they have higher efficiency and smaller cone motion leads to the same SPL. But most so-called horn-loaded speakers are only horn-loaded at the tweeter. If you want an example of a high efficiency fully horn-loaded speaker and sub, look at a Klispch La Scala or Klipschorn with a horn-loaded sub such as Bill's Tube HT, or a tapped horn design.

Yep, there are multiple ways a physicist or engineer competent in this field would view the question, including what you say. Another very simple way to disprove his claim is ask him to look at a plot of harmonic distortion components versus the fundamental for a speaker operating in its linear region. How much power is in the harmonics compared to the fundamental? Usually no more than a few percent -- it's visually evident. So if you were to "move a couple percent of power in the harmonics" back into the fundamental, the speaker goes form being low sensitivity to high sensitivity? Don't think so. He clearly didn't know what he was talking about.
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post #14 of 15
1/28/13 at 6:40pm
Thread Starter 
"So if you were to "move a couple percent of power in the harmonics" back into the fundamental, the speaker goes form being low sensitivity to high sensitivity? Don't think so."

This seems like a solid argument to me.

It's possible that I'm not doing his argument justice, and that it was indeed meant as a question regarding performance near peak power and/or at high SPL.
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post #15 of 15
1/29/13 at 6:32pm
Quote:
Originally Posted by aligborat View Post

"So if you were to "move a couple percent of power in the harmonics" back into the fundamental, the speaker goes form being low sensitivity to high sensitivity? Don't think so."

This seems like a solid argument to me.

It's possible that I'm not doing his argument justice, and that it was indeed meant as a question regarding performance near peak power and/or at high SPL.

I've never seen sensitivity measured anyway other than at a couple of volts input across the terminals, which results in an output ranging from low 80s - 100-ish dB at 1 meter. So I'm not sure it has any relevance being measured at the maximum acoustic output of the speaker.

The only way you could possibly describe sensitivity as a quality measurement of a speaker's performance is if it's extremely low, the amplifier you're using is more likely to clip to produce max output....so it's more of a system issue.
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