I was reading a thread on this forum today, and the author dismissed a loudspeaker because the efficiency was "only" 95dB. For the past few months I've been doing a lot of loudspeaker measurements, and I've basically reached the point where I don't care at all about efficiency. Here's why:
Basically, I am focused on low distortion and high displacement now. I don't care if a speaker has an efficiency of 80dB or an efficiency of 100dB, as long as distortion and displacement are controlled.
For instance, I have measured $15 computer speakers which can put out 100dB of clean sound with an efficiency of 85dB, because they have high excursion and underhung motors. At the same time, I've measured $100 prosound drivers that struggle to generate 100dB at 100hz, because they're severely displacement limited.
Am I misguided? Or is efficiency really that important?
- There are many high efficiency speakers which sound good, but I personally believe it's because they have low distortion, not high efficiency.
- Distortion and xmax are related; in general, it goes up with xmax. One of the reasons that prosound drivers sound good is that they use drivers with much greater surface area, which lowers excursion.
Basically, I am focused on low distortion and high displacement now. I don't care if a speaker has an efficiency of 80dB or an efficiency of 100dB, as long as distortion and displacement are controlled.
For instance, I have measured $15 computer speakers which can put out 100dB of clean sound with an efficiency of 85dB, because they have high excursion and underhung motors. At the same time, I've measured $100 prosound drivers that struggle to generate 100dB at 100hz, because they're severely displacement limited.
Am I misguided? Or is efficiency really that important?
Different applications mean different outputs. When you say clean sound, did you measure this - distortion can appear in strange ways that aren't always noticable.
Have you read this? Power Handling Vs. Efficiency
The point where you're looking for >100dB efficiency is when you either have very little power, or like it extremely loud. For low distortion, high displacement, you'll probably want lots of very large drivers, not moving very far. As you have (correctly, IMHO) stated, distortion increases with Xmax.
I'd say efficiency can be a deciding factor - if you had 2 drivers, one at 82dB 1W/1m, and one that did 92dB/1W/1m, all other things equal, you'd pick the higher efficiency, simply because it means less distortion from your amp.
HTH
Chris
You're ignoring one parameter to focus on others. Why?
What you need to specify is:
-frequency response
-polar response
-max output level
-power compression
-distortion
When you then make a few design choices like transducer type and size, all other requirements can are then defined such as efficiency, excursion, power handling, etc. Or you may find you made a bad choice and cannot arrive at your design goal, so you need to change that first design decision.
For example, I could use a speaker that had very low distortion but was very low efficiency and required large amounts of power to reach a reasonable output level. It would likely have large amounts of power compression. If you compared that to a speaker that reached the same output level with much less power input, it would very likely have less power compression and sound more dynamic. This speaker would be more efficient.
What you need to specify is:
-frequency response
-polar response
-max output level
-power compression
-distortion
When you then make a few design choices like transducer type and size, all other requirements can are then defined such as efficiency, excursion, power handling, etc. Or you may find you made a bad choice and cannot arrive at your design goal, so you need to change that first design decision.
For example, I could use a speaker that had very low distortion but was very low efficiency and required large amounts of power to reach a reasonable output level. It would likely have large amounts of power compression. If you compared that to a speaker that reached the same output level with much less power input, it would very likely have less power compression and sound more dynamic. This speaker would be more efficient.
Ok, my rambling will be totally unscientific here. I've read on this forum at least 2 authors insisting that beyond 103 dB at 1m across the band you will subjectively have a different sound presentation, with everything being more "fast", responsive, more dynamics and so on and so forth.. This seems to be valid no matter the path chosen to reach this target, be it horns or direct radiators in parallel.
disclaimer: deep down I believe this is related to distortion and power compression as well. Maybe this 103db is some kind of a subjective threshold?
disclaimer: deep down I believe this is related to distortion and power compression as well. Maybe this 103db is some kind of a subjective threshold?
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"Oh no, not again..." - name that movie.
I recall going through all this back in the 1980s, due to the trend of making drivers with better and better frequency response and control of cone modes, which had ever decreasing efficiency due to the damping methods and cone materials used to achieve the performance. The end result was drivers that "couldn't get out of their own way", they needed so much power to achieve dynamic peaks that, even with big Krells etc to drive them, they couldn't reach realistic levels on large scale works. They sounded clean, but not dynamic. There's been a gradual return since then to paper cones, plus the availability of modern exotic fibres.
You appear to be suggesting that provided a driver meets your required distortion and SPL targets, you don't care how much power it requires to do it. But there's more to it than horsepower, as any car enthusiast can tell you. It's not just how fast it can go, but how quickly it gets there.
Applying that to speaker drivers, and assuming the distortion requirement is met, means you should look for high Bl, low moving mass, and large area. This combination is most often available in a (relatively) high efficiency driver.
I recall going through all this back in the 1980s, due to the trend of making drivers with better and better frequency response and control of cone modes, which had ever decreasing efficiency due to the damping methods and cone materials used to achieve the performance. The end result was drivers that "couldn't get out of their own way", they needed so much power to achieve dynamic peaks that, even with big Krells etc to drive them, they couldn't reach realistic levels on large scale works. They sounded clean, but not dynamic. There's been a gradual return since then to paper cones, plus the availability of modern exotic fibres.
You appear to be suggesting that provided a driver meets your required distortion and SPL targets, you don't care how much power it requires to do it. But there's more to it than horsepower, as any car enthusiast can tell you. It's not just how fast it can go, but how quickly it gets there.
Applying that to speaker drivers, and assuming the distortion requirement is met, means you should look for high Bl, low moving mass, and large area. This combination is most often available in a (relatively) high efficiency driver.
I run a mobile disco so efficiency is very important.
My amp already weighs a ton to drive the efficient speakers so I really dont want t ohave to double the amps weight to get a decent sound.
Thats a rear facing 18 inch speaker with forward facing outputs at the top and bottom !
It sounded good but was far too heavy for my disco so I put the driver in a simple box with a port.
Doesn't it depend on how one defines "distortion," though? My problem with the low-efficiency (say, under 85dB/w/m) speakers I've heard is that they suffer from severe dynamic compression when used over the course of a long piece of music. Higher efficiency speakers generally seem to suffer less from power compression in my experience, though that experience is skewed by the fact that I've not played with much cheap or poorly designed PA type stuff. My guess is that it's just because there's less heat generated, though better thermal management could also account for differences.
If you add in power compression, I think it's fair to say that there are three things that are important: distortion, displacement (which I think of as more cone area, less throw, though ideally lots of both), and heat management.
If you add in power compression, I think it's fair to say that there are three things that are important: distortion, displacement (which I think of as more cone area, less throw, though ideally lots of both), and heat management.
It's just a question of what kind of argument you want to have...
Ideally. There's a big word. Ideally we'd engineer everything with no waste of power. That's because any way you cut it, a waste of power is a waste of power. It's intrinsically undesirable.
A 100% efficient speaker would have perfect reproduction, by definition, so it remains a goal for reasons other than the elimination of waste of power. It's intrinsically desirable.
Efficiency is a major component of elegance which you ignore to the peril of more than just performance.
w
Ideally. There's a big word. Ideally we'd engineer everything with no waste of power. That's because any way you cut it, a waste of power is a waste of power. It's intrinsically undesirable.
A 100% efficient speaker would have perfect reproduction, by definition, so it remains a goal for reasons other than the elimination of waste of power. It's intrinsically desirable.
Efficiency is a major component of elegance which you ignore to the peril of more than just performance.
w
As a number, no efficiency is not important any more than the gain of an amplifier is. But I don't think it's that simple. What gets ignored when we discount efficiency is all that heat that gets dumped into the voice coil at lower efficiency levels and what effects it has. Turns out that high efficiency is highly correlated with high thermal capacity (bigger voice coils, megnets, etc.) - this is a double benefit because not only is there less heat to disipate but there is a greater capacity to handle it. The net result; the higher efficiency loudspeaker is inherently less sensitive to thermal modulation, also know as greater dynamics.
Personally I completely discount the importance of "nonlinear" distortion in a loudspeaker, but I do not discount the audible effects of thermal modulation. Given that position I would have to define efficiency as essential, not because I really care what the number actually is, but because of what a high efficiency design does for me in other regards.
Please note that I am talking about thermal modulation which is different than power compression. Related, yes, but not the same thing. Power compression is what happens long term and thermal modulation is the short term aspect of the problem. They can be quite different.
Yeah, but thats what I dont understand
If a woofer takes about 800watt continious before any "losses", how can 20watt or 50watt cause any problems
I have always thought it was the opposite, that such a woofer SOUNDS "compressed" if it doesnt get #enough# power
Could it be that some added EQ will feed it with the required power, thus sounds much better, with EQ
I believe its a common misunderstanding that a big woofer doesnt need much power because of its high sensitivity
Fore sure a 4" voicecoil needs lots of power
And, if it doesnt demand that much power, because we dont play it as loud as intended, we may need to help it, and beat it with some EQ POWER
Tho, a 15" with light cone, high Fs, and 1" voicecoil may work just fine with much less power
If a woofer takes about 800watt continious before any "losses", how can 20watt or 50watt cause any problems
I have always thought it was the opposite, that such a woofer SOUNDS "compressed" if it doesnt get #enough# power
Could it be that some added EQ will feed it with the required power, thus sounds much better, with EQ
I believe its a common misunderstanding that a big woofer doesnt need much power because of its high sensitivity
Fore sure a 4" voicecoil needs lots of power
And, if it doesnt demand that much power, because we dont play it as loud as intended, we may need to help it, and beat it with some EQ POWER
Tho, a 15" with light cone, high Fs, and 1" voicecoil may work just fine with much less power
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And how many db SPL sensitivity will it need to be to reach 100% efficiency ? unendless sensitivity ?
Or maybe just 0 to unendless linearity ?
Or both ?
Ehh, Ok
100% efficiency means no amps needed ?
I give up, I have no clew about 100% efficiency
Oh, what comes in comes out, right ?
But that means 0db sensitivity ?
Or maybe just 0 to unendless linearity ?
Or both ?
Ehh, Ok
100% efficiency means no amps needed ?
I give up, I have no clew about 100% efficiency
Oh, what comes in comes out, right ?
But that means 0db sensitivity ?
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Quote:Originally Posted by wakibaki
A 100% efficient speaker would have perfect reproduction
Hmmmm...... that's an interesting way to look at it.
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Bibo, ergo sum.
Yes, even if being highly concerned about efficiency often gets you a couple percent out of the input power and a couple percent distortion. Forseable technology is not going to get absolute fidelity by zero loss.
A 100% efficient speaker would have perfect reproduction
Hmmmm...... that's an interesting way to look at it.
__________________
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Bibo, ergo sum.
Yes, even if being highly concerned about efficiency often gets you a couple percent out of the input power and a couple percent distortion. Forseable technology is not going to get absolute fidelity by zero loss.
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