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buzzy
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Speaker efficiency - theoretical question

So we've all studied the interesting graphics of the off-axis dispersion of a speaker. Performance can vary. It made me wonder about a somewhat theoretical question, though the issue that raised it was a practical one.

Suppose you have two speaker models. Both measure the same efficiency [edit: as measured by sensitivity] under standard testing (at a fixed point, x distance away, for a given power input). But one has better off axis response. (Let's assume it's true horizontally and vertically, as well as at various frequencies, etc.)

Doesn't that mean the speaker with greater off-axis response is actually generating more total output, in order to achieve higher response off axis? If you could sum the output around a whole or half or quarter of a sphere, or something relevant, wouldn't the sum for the speaker with greater dispersion be more in total? (And yes, the standard measurement is attractive because it's just that - standard - and relatively simple and repeatable - but let's not get into the difficulty of summing the total output of a speaker just yet!)

Granted, most of the difference will be in the mid and upper frequency range, given the way low frequencies behave, so maybe in power terms it's not a huge difference.

Though for omnipolar speakers and perhaps bi/dipoles, the difference in total might be more significant, as the conventional way of measuring efficiency might not be the best measure of what those speakers are designed to do.

So given the way efficiency is usually measured, at a single point, it might not be a good index of output into a real world room that may have multiple listeners at multiple listening locations.

Thoughts?

Jan Vigne
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Re: Speaker efficiency - theoretical question

If I begin with a faulty assumption then take out this fact and don't allow that number into the equation but restrict it to just the ideas I want, will I be right?

Possibly. If we ignore the real world and insist on only what we want to see, we might be able to figure out the number of times you could possibly be correct.

And so on and so on.

However, you're ignoring too many things that occur in most speakers to actually make your point relevant. For one thing, electrical sensitivity is not the same as efficiency. The numbers you see in the "Measurements" section are for electrical sensitivity and result in figures spec'd as SPL which would be stated in decibels. Efficiency would be given as a per centage. A common consumer audio speaker system will have efficiency numbers at less that 5%.

The sensitivity measurement largely ignores the amount of power actually required to drive the speaker system and focusses on input voltage only. When you read the explanations of the first few graphs in Stereophile's measurements procedure, you'll see the explanation of how difficult the speaker will be for most amplifiers to drive. This is what you should pay attention to. This measurement/assessment is vaguely related to electrical sensitivity but ignores in room gains made by dispersion.

More energy put into the room will result in higher SPL's whether you're considering dipoles, monopoles or simply the dispersion patterns of a muliple driver system. If you're looking for a point to use against multiple driver systems, this uneven dispersion resulting in irregular frequency response at the listening position would be one to consider. This is why the measurement you want to look at is taken in the near field so as to ignore the contribution of the room which is unpredictable from listener to listener.

buzzy
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Re: Speaker [sensitivity] - theoretical question

Yes, I was referring to the standard sensitivity test, more so than efficiency in the literal sense. So you may have added that point of clarification for any others who are as stubbornly obtuse as yourself; though I can't recall every running across anyone even remotely close to you on that count.

Similarly, one would want to be certain to factor in the power going in, not just the voltage. As some tests even seem to do.

The point was, acoustical energy is coming out of a speaker, for a given power in; the standard measurement seems to be a rather limited measure that may be mis-characterizing speaker differences.

Though of course if one is comparing relatively similar speaker designs that may not be a significant factor.

And again the standard sensitivity measurement does have some very important virtures in terms of standardization, repeatability, and simplicity.

Jan Vigne
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Re: Speaker [sensitivity] - theoretical question


Quote:
So you may have added that point of clarification for any others who are as stubbornly obtuse as yourself; though I can't recall every running across anyone even remotely close to you on that count.

Oh, did I forget to say welcome to the forum after only your second post? How insensitive of me.

Exactly what "theory" are you inquiring about?

CharlyD
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Re: Speaker efficiency - theoretical question

Found an interesting article on the topic of Sound Power here.

Welshsox
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Re: Speaker [sensitivity] - theoretical question

Wow

Im a member of lots of forums on diffrent topics from cooking to watches to hifi

What makes this forum so agrressive ? everyone is entitled to an opinion and healthy discussion and debate is great. Whats with the attacks though ?

Im technically responsible for a systems group that designs world class safety systems in the harshest environments imaginable, when i run into people who get so aggressive about relatively small technical issues its either because a) they are technically challenged or b ) they have small dicks

Which catagory do you fall into buzzy ?

Alan

tom collins
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Re: Speaker [sensitivity] - theoretical question

Welsh: I concur with you completely. In the BMW motorcycle forum I participate in, there will occasionally come up a rant against arch-enemy Harley Davidson. Generally, the older members have heard it all before and will quash it right near the beginning. Although it probably sounds silly, people get very worked up about such things and from a practical point, those posts serve no purpose.
In this forum, we have some very knowledgable folks, some of which must hold the ee degree, and others with a great deal of empirical experience. There does not seem to be the same aversion by older group members to the "banter" in this forum. It just seems to be a characteristic and I think the arguers as well as the audience enjoy it too much to stop.
The Entry Level is the area that in which the "banter" is restricted (rightly so). To the group's credit, I've seen some members go to extraordinary lengths to answer a newbee's question there without sarcasm.
I think the more experienced members, especially the ones with physics or ee degrees, get their hackles up over people expressing opinions, some opinions formed from vast experience, as fact and it often ends up being an ee against someone with lots of experience. The problem is that often, unless you have an advanced degree, it is difficult to tell the difference in theories. One fault of the system is that often there is no one right answer and some posters do not acknowledge this in their postings and advocate vociferously for their point of view.
I have an advanced degree, just not the right one to participate meaningfully in these discussions, so i generally just flip through them.
Just my take on the forum after about a year.

Tom

cyclebrain
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Re: Speaker efficiency - theoretical question


Quote:
So we've all studied the interesting graphics of the off-axis dispersion of a speaker. Performance can vary. It made me wonder about a somewhat theoretical question, though the issue that raised it was a practical one.

Suppose you have two speaker models. Both measure the same efficiency [edit: as measured by sensitivity] under standard testing (at a fixed point, x distance away, for a given power input). But one has better off axis response. (Let's assume it's true horizontally and vertically, as well as at various frequencies, etc.)

Doesn't that mean the speaker with greater off-axis response is actually generating more total output, in order to achieve higher response off axis? If you could sum the output around a whole or half or quarter of a sphere, or something relevant, wouldn't the sum for the speaker with greater dispersion be more in total? (And yes, the standard measurement is attractive because it's just that - standard - and relatively simple and repeatable - but let's not get into the difficulty of summing the total output of a speaker just yet!)

Granted, most of the difference will be in the mid and upper frequency range, given the way low frequencies behave, so maybe in power terms it's not a huge difference.

Though for omnipolar speakers and perhaps bi/dipoles, the difference in total might be more significant, as the conventional way of measuring efficiency might not be the best measure of what those speakers are designed to do.

So given the way efficiency is usually measured, at a single point, it might not be a good index of output into a real world room that may have multiple listeners at multiple listening locations.

Thoughts?

Interesting question, one that I deal with at my job but have never thought about relating to audio.
In the radar industry we provide X amount of watts to an antenna. Our antenna has a specified amount of gain. This gain is not a real gain measured as an increase in output power, but instead a gain relative to a power density measured relative to a omniderectional source. Crap, let me try again. Both an antenna and a speaker produce a certain amount of output power. How that power is directed (focused)determines its gain. A narrower focus of the energy, creates a higher amount of gain. At the expense of the amount of energy off axis.
But then again efficiency in a speaker also takes in to account crossover losses and speaker losses.

Ajani
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Re: Speaker [sensitivity] - theoretical question


Quote:
To the group's credit, I've seen some members go to extraordinary lengths to answer a newbee's question there without sarcasm.

Unfortunately that doesn't seem to be the case with this thread. The original poster posed a theoretical question and received (what appears to be) a sarcastic response. He then got offended and responded rudely.

linden518
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Re: Speaker [sensitivity] - theoretical question

Ajani, I do agree with you. The response to the poster's question was needlessly condescending, I thought, especially considering that Buzzy seemed genuinely interested in the topic. It's never a great feeling to have sincerity be crushed by sarcasm, especially for a new member coming into the forum. But on the whole, though, as a group, the forum members are unusually helpful. I can attest to that b/c when I came in to this forum in December, many members rose to the task & steered me into the right direction & I'm still grateful for that...

Jan Vigne
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Re: Speaker [sensitivity] - theoretical question


Quote:
The response to the poster's question was needlessly condescending ...

To begin with, I see buzzy has now edited his op to read, "Suppose you have two speaker models. Both measure the same efficiency [edit: as measured by sensitivity] under standard testing (at a fixed point, x distance away, for a given power input)."

So, a little clarification can go along way even if it is applied after the mistake is pointed out to the poster.

However, the op includes the following phrases;

1) "Suppose you have two speaker models. Both measure the same efficiency [edit: as measured by sensitivity] under standard testing (at a fixed point, x distance away, for a given power input). But one has better off axis response. (Let's assume it's true horizontally and vertically, as well as at various frequencies, etc.)"

If we have one speaker that does not measure the same as the other, wouldn't it be safe to assume we have two different speakers on hand?

Buzzy still confuses efficiency and sensitivity even after his edit.

Power is not the measurement device for sensitivity, voltage input is.

"Let's assume" leads me to believe buzzy wants to have this set up exactly as he wants it and not as it might be.

The modifier " ... at various frequencies, etc." does the same.

What is the "etc." buzzy wishes us to ignore?

2) "Doesn't that mean the speaker with greater off-axis response is actually generating more total output, in order to achieve higher response off axis?"

No, not with that assumption, it does not.

3) "If you could sum the output around a whole or half or quarter of a sphere, or something relevant, wouldn't the sum for the speaker with greater dispersion be more in total?"

Or something relevant?! What does that mean? If I were summing the output around a sphere, I wouldn't be taking the measurement buzzy is apparently trying to find.

Would the sum be "more"? Who knows, no other properties are stated and none can be assumed. That is why the on axis measurement is taken as it is. This measurement technique is not some half baked idea attempted for the first time.

In room measurements describe more closely what buzzy wants to achieve. If he isn't close to knowing that, I cannot be blamed.

I pointed out his error to which I received what I considered to be a rude response. Buzzy has three posts so far and has made numerous errors in this one. Am I supposed to know he "knows" all this stuff he apparently cannot get right by dint of his two other posts which escaped me?

4) "(And yes, the standard measurement is attractive because it's just that - standard - and relatively simple and repeatable - but let's not get into the difficulty of summing the total output of a speaker just yet!)"

And here are more modifiers of an errant thought. Has buzzy not just asked us to consider the summed outputs? Now we should ignore them? Which ouptuts would buzzy prefer we include and which should we discard for the sake of buzzy's argument?

5) "Granted, most of the difference will be in the mid and upper frequency range, given the way low frequencies behave, so maybe in power terms it's not a huge difference."

Well, yes, granted in terms of power, "power" has nothing to do with any of the measurements buzzy seems to be referring to. All buzzy had to do was insert the word "voltage" where he repeatedly used "power" and he would have been much closer to his dream.

7) "Though for omnipolar speakers and perhaps bi/dipoles, the difference in total might be more significant, as the conventional way of measuring efficiency might not be the best measure of what those speakers are designed to do."

Are you going to make me explain how many errors are made or repeated in that sentence?

8) "So given the way efficiency is usually measured, at a single point, it might not be a good index of output into a real world room that may have multiple listeners at multiple listening locations."

There really is no way to interpret buzzy's intent here other than to ask him what he's been smoking. Efficiency is not a measurement related to being taken at a single point. If buzzy knew what speaker efficiency really meant, he wouldn't even come close to assuming it has anything to do with "multiple listeners at multiple listening locations" unless he might want to discuss the behavior of horns a bit. The reference to "efficiency" would still be fairly oblique at that point and seem to have nothing to do with buzzy's attempt at disseminating information.

All in all, the only thing buzzy managed not to mangle was, "Thoughts?", though that would surely get him a poor grade on a term paper since "thoughts" cannot be made into a stand alone question.

Given what I had to work with, gentlemen, I still feel my answer was reasonable.

linden518
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Re: Speaker [sensitivity] - theoretical question

Jan, I think you're missing my point. Whether Buzzy had relevant claims or not - that's not at issue here. As always, your points are well argued & not many would doubt the kind of audio knowledge that you have. But we had a new poster come in with a "theoretical" question, and wanted a sincere answer or a debate. Again: the point isn't whether or not his ideas were well grounded.

But your reply started like this: "If I begin with a faulty assumption then take out this fact and don't allow that number into the equation but restrict it to just the ideas I want, will I be right?

Possibly. If we ignore the real world and insist on only what we want to see, we might be able to figure out the number of times you could possibly be correct."

You're basically portraying him as a fool who ignores the real world, and that's what I found to be condescending and rude, the tone of it. If I were him, I would have been offended, too. Of course you could have engaged in a debate with him, point out the errors, but couldn't you have done so without portraying him as a dunce first? He was new here, and as a long-time member of this forum, you could have at least extended a bit of civility to him.

Jan Vigne
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Re: Speaker [sensitivity] - theoretical question

We'll have to disagree. I started by pointing out the numerous errors in the op without calling them any more than wishful thinking. Buzzy wanted to debate a "theoretical question". The point is you have to have the concepts correct to do so. You can't make exceptions to the rule here and ignore facts there if we're to get anywhere. As far as I knew, buzzy had more "if we ignore's" and "but let's not discuss this now's" in his box of postulations. Well, if you make an exception for everything that makes what we're discussing factual, then we can't have much of a debate, can we?

I explained where the errors had been made. I feel my response was not condescending. If buzzy felt I was calling him a "dunce", then both he and you mistook my intent. Which do you feel is more condescending, a teacher who explains where your thoughts left the tracks or one who simply hands out the "F"?

linden518
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Re: Speaker [sensitivity] - theoretical question

Jan, as I've said, I have no qualms with you explaining to someone about where the errors might have been made, as you see them. It's the way you've done it. You say I mistook your intent, and I sincerely hope so, actually, because what you wrote - the part I quoted - really comes off as you portraying the new member as a clueless person who ignores the real world. I don't think such rhetoric was necessary; you could have just pointed out the errors - as you saw them - w/o that kind of statement. The original poster found it offensive, the newish member Ajani also saw the sarcasm in it as unnecessary, and I'd have to agree, too, in this case.

That final question seems kind of weirdly arrogant, too, IMO: "Which do you think is more condescending, a teacher who explains where your thoughts left the tracks or one who simply hands out the 'F'?" The answer, for me, under this context, is: both. This is a forum. Why should anyone be a teacher in the first place, didactically leveling out judgments & ultimatums? Here, too, I hope I'm misinterpreting your metaphor and hope that you don't see yourself as this 'teacher' correcting people's ways.

Jan Vigne
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Re: Speaker [sensitivity] - theoretical question


Quote:
Here, too, I hope I'm misinterpreting your metaphor and hope that you don't see yourself as this 'teacher' correcting people's ways.

If you begin with one wrong assumption and then ignore the next idea presented ...

That is meant to be neither condescending nor arrogant, just a statement of fact. You are seeing what you want to see. Buzzy acknowledges he was wrong - though he still remains wrong.

linden518
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Re: Speaker [sensitivity] - theoretical question

I was actually commenting more about your following comment: "If we ignore the real world and insist on only what we want to see, we might be able to figure out the number of times you could possibly be correct."

This in effect implies that the only place that Buzzy can be right is... well, nowhere. Once again, let's leave aside for a minute the issue of right & wrong. I keep insisting that's not the point, and you keep mentioning it. The point is showing a bit of courtesy to the newcomer, it's that simple. And implying that there's no chance on earth - literally - that he could be right is not exactly the way of making him feel welcome, sarcasm intended or not. You might not have had malicious intent, Jan, but that kind of statement can come off as being pretty malicious. It did to a several people who have read it, and it seemed that way to me, too. That's all I'm saying. Again: I don't care who's right or wrong, argument-wise...

KBK
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Re: Speaker [sensitivity] - theoretical question

My take on it is that I don't mind winding up Jan and having him tear-ass into Ethan..but easy on the rest of us, there, Jan.

Ergonaut
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Re: Speaker [sensitivity] - theoretical question


Quote:
Yes, I was referring to the standard sensitivity test, more so than efficiency in the literal sense. So you may have added that point of clarification for any others who are as stubbornly obtuse as yourself; though I can't recall every running across anyone even remotely close to you on that count.

Similarly, one would want to be certain to factor in the power going in, not just the voltage. As some tests even seem to do.

The point was, acoustical energy is coming out of a speaker, for a given power in; the standard measurement seems to be a rather limited measure that may be mis-characterizing speaker differences.

Though of course if one is comparing relatively similar speaker designs that may not be a significant factor.

And again the standard sensitivity measurement does have some very important virtures in terms of standardization, repeatability, and simplicity.

Hi Buzzy

I think we in this thread need to agree on a scientific principle...

"You cannot destroy energy - you can only convert it".

Just for a moment suppose you could see sound, the wavelengths are produced in light. Onthe one speaker the light is bright but going in a forward direction only over a small range of angles --- the other over a large range of angles but dimmer.

One speaker is producing the same energy but is very directional. The other is producing the same energy but diverged over many more angles than the former.

In fully characterising the divergence of energy in a fully rounded test of a speaker whether testing free air response of a unit or characterising a complete system, the polar diagram provides this data.

The energy output of two speakers can be the same but the actual delivery into air at sea level is different.

One over fewer angles where the intensity per unit area is high and the other over many angle where the intensity per unit area is smaller.... but as you say appears to have a better off axis response.

Is this where your question was heading?

But I come back to my other point -- you cannot destroy energy -- they are producing the same energy and so if they were placed into an "Integrating sphere" the radiometer would measure the same flux for both.

ChrisNC
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Re: Speaker [sensitivity] - theoretical question

I think you got the question answered there with:

"You cannot destroy energy - you can only convert it".

I think (correct me if I am wrong), the question would be when using multiple measurement points (the distance from the speaker in x,y, and z axis) would the sum of the SPL be the same? I think they would not because of the room reflections as you get further from the front of the speaker.

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