Get Beranek. Resign yourself to having to actually work some simple differential equations. It's not that hard, I promise.
While I'm thinking of it, there's also a fine little book from Harry Olsen that might serve as a stop-gap, "Music, Physics, and Engineering." It's more concerned with musical instruments, but the physics is all the same.
While I'm thinking of it, there's also a fine little book from Harry Olsen that might serve as a stop-gap, "Music, Physics, and Engineering." It's more concerned with musical instruments, but the physics is all the same.
According to a site :
"In a conventional cone type direct radiator loudspeaker, the acoustic impedance match with the air is poor at low frequencies requiring a large surface area to achieve high sound levels.
A bigger surface area will transfer more energy from cone to air than a smaller surface area and efficiency will also increase.
I looked at the "The Thigpen rotary woofer" operation and it says :
"The invention transducer acts against a comparatively large volume of air by dispensing with the cone or vibrating surface of a conventional loudspeaker. Rather than area, in this loudspeaker the impedance match with the air is proportional to the velocity of a vane moving through the air.
Which I found very interesting !
--Regards,
"In a conventional cone type direct radiator loudspeaker, the acoustic impedance match with the air is poor at low frequencies requiring a large surface area to achieve high sound levels.
A bigger surface area will transfer more energy from cone to air than a smaller surface area and efficiency will also increase.
I looked at the "The Thigpen rotary woofer" operation and it says :
"The invention transducer acts against a comparatively large volume of air by dispensing with the cone or vibrating surface of a conventional loudspeaker. Rather than area, in this loudspeaker the impedance match with the air is proportional to the velocity of a vane moving through the air.
Which I found very interesting !
--Regards,
I came across this explanation and to me it seems to make more sense now.
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/spk2.html (read the part where they talk about coupling loudspeakers to air".
--Regards,
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/spk2.html (read the part where they talk about coupling loudspeakers to air".
--Regards,
Vaughn,
Drivers are relatively efficient at converting electrical energy into mechanical energy (movement of the cone). Otherwise much better driver motors would be built. The big efficiency loss is converting the mechanical energy into acoustical energy. The impedance mismatch is between the relatively rigid cone, and, as previously mentioned, "soft squishy" air.
If you brought your stereo to the Dead Sea at 1300ft below sea level it will play a little louder than at the top of Mt Everest, because the air is thicker and more dense than at high elevation, and the impedance match between the cone and the air would be slightly better.
Another example mentioned previously is that water is a better impedance match than air. That's why you can hear so many very small sounds so well underwater, because the surface mechanically vibrating to stimulate sound underwater has a much better impedance match with water than it would with air.
Drivers are relatively efficient at converting electrical energy into mechanical energy (movement of the cone). Otherwise much better driver motors would be built. The big efficiency loss is converting the mechanical energy into acoustical energy. The impedance mismatch is between the relatively rigid cone, and, as previously mentioned, "soft squishy" air.
If you brought your stereo to the Dead Sea at 1300ft below sea level it will play a little louder than at the top of Mt Everest, because the air is thicker and more dense than at high elevation, and the impedance match between the cone and the air would be slightly better.
Another example mentioned previously is that water is a better impedance match than air. That's why you can hear so many very small sounds so well underwater, because the surface mechanically vibrating to stimulate sound underwater has a much better impedance match with water than it would with air.
I'm not sure of that.
Flux uniformity in the gap can still be improved, there are eddy currents which reduce efficiency, voice coil nonlinearities within the gap field, oh, and about 1% or thereabout of electrical energy is converted to mechanical and the rest is dissapated as heat.Unless I'm missing something, it doesn't seem to be efficient at all, or even relatively.
Horn loaded speakers, I think, are on the order of about 30 % efficient.--Regards,
So if I'm getting this right about the impedence match, air is not dense and the perfect impedence match to air would be air.
And so cones, because of their density, being a lot more dense than air, have a poor transfer of energy. But aren't speaker designers constantly trying to reduce cone mass as a possible answer to this ?
I know that it was said that cone mass isn't relevant for this impedence mismatch, but wouldn't a light cone have a better impedence match to air than a heavier one ?
--Regards,
And so cones, because of their density, being a lot more dense than air, have a poor transfer of energy. But aren't speaker designers constantly trying to reduce cone mass as a possible answer to this ?
I know that it was said that cone mass isn't relevant for this impedence mismatch, but wouldn't a light cone have a better impedence match to air than a heavier one ?
--Regards,
Vaughan said:
No, it's the rigidity, not the mass. Stir your finger around in a glass of water, and then do the same with a glass of air. The impedance match of your finger and water is better than your finger and air. Same thing with speaker cones....they don't stimulate air movement with much efficiency.
Vaughan said:
Ok, I'll try an intuitive explanation of the impedance mismatch with a little math:
The amount of energy transferred to "something" (for example the air) is
W=F*x
... or the energy equals force multiplied by the displacement.
Put the hand up in the air. Push the air away from yourself. Not much force from the air, is there? In fact, you can probably sense that most of the force is "consumed" by the mass of you hand.
So, accelerating the mass of your hand will consume much more energy than accelerating the air. This results in that most of the energy remains in the driver, and very little is transferred to the air as sound. The impedance mismatch is between the air (easy to move) and the mass of the cone/hand (hard(er) to move).
I could stop here, but there is another twist to the story, which probably is only important if a little doubt pop up in the head.
Mass cannot consume power. It can only store it. So there is no heat in the cone, but where does the energy go?
The answer lies in that almost all energy ends up in the voice coil. Whatever energy that is stored as velocity in the mass is consumed in the voice coil when the cone is decellerated. Then again, very little of the energy fed to the voice coil is fed to the cone, and most of it is converted to heat in the coil directly.
So there are actually two steps of mismatch
.
Vaughan said:Oh, just a wee question.
Is it because of the problems I cited before ? I'm sure this has something to do with the magnetic flux field in the radial gap. I could be wrong.
--Regards,
Hmm...
I suppose one could explain that in severl ways, but here is one, connecting to the other one:
Remember W=F*x?
Since the cone is oscillating back and forth, x never gets too large. It would be different if Xmax for the driver was very large (several meters) and if we fed the driver with DC. Then a constant force would accelerate the cone in one direction and the speed would build up, and so would x. Then F*x would become large. On the other hand, the coupling to the air is hopelessly low at low frequencies, so there would not be much sound anyway. Actually they balance one another. That is why a loudspeaker can have a flat response "in its mass controlled region".
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