I need help or advice in my understanding of how speakers work. I have read Vance Dickasons book and I have read a number of other books.
I have not read anything going indepth on this topic. This is a casestudy if anything. I want to reassure myself of what I know about the physics of driver operation and in general the physical workings of speakers.
I would appreciate it if the experts here on speaker design could please correct me when I'm wrong at any stage here. A speaker is designed to convert electrical energy into mechanical (or acoustical energy).
It's basically a coil of wire (voice-coil) around a former (a voice-coil former) that is designed to interact with a static magnetic field from a permanent magnet located behind the coil. But a voice-coil without current is useless and when a current flows through the voice-coil, it will create a force (because when two magnetic forces interact you get attraction and repulsion).
So the electromagnetic field is alternating. Electrons travel depending on the direction or orientation of the poles. The pole piece forms part of the motor and is designed to focus the magnetic field, to focus flux, and also to transfer some of the heat from the coil to the former where the heat is dissapated.
All these forces, magnetic forces are concentrated in the magnetic gap. A small air gap. So magnetic flux, the strength of the magnetic field takes place in this field. When both fields interact and force is generated, the diaphram, the cone that is connected to the voice-coil moves, and creates air. Presto.
Now to create a speaker with a stronger magnetic field, with stronger repulsion and attraction forces requires a bigger magnet and a coil with longer wire (more windings). A bigger diameter coil will mean better heat disappation and better power handling. A coil with more windings will be more efficient (meaning it will require less power to move at any given level).
If speakers are to have very high excursion capabilities, they require very long lengths of wire. And the more turns the coil makes, the more linear the response will be as long as the voice coil is within the gap area.
I know that cones need to be stiff for high excursions. But what is important for very high excursions are big coils and long wire lengths. Correct me if I'm wrong on that.
As soon as the coil turns are outside the gap, the motor strength (BL) goes down. BL is a measure of motor strength. So for the motor to be strong, or efficient, the voice coil must complete a number of constant turns within the gap where the magnetic field are generated.
Magnetic flux is determined by many things apparently. Not just big magnets and voice-coils, but pole-piece topologies also affect flux. Even the former to some degree will either subtract or add to the degree of flux inherent in the magnetic field.
Then there is a spider which controls the motion of the coil. It provides mechanical damping so that the voice-coil is well controlled. It also makes sure the voice-coil is centered in the gap area so that maximum flux is attained. With no suspension, the coil would just slam into the back plate.
Is this a correct understanding ? I know there are many other variables involved that I didn't mention. I think I'm well versed in this at the moment but I believe I have much room for improvement and understanding.
Thank you.
--Sincerely,
I have not read anything going indepth on this topic. This is a casestudy if anything. I want to reassure myself of what I know about the physics of driver operation and in general the physical workings of speakers.
I would appreciate it if the experts here on speaker design could please correct me when I'm wrong at any stage here. A speaker is designed to convert electrical energy into mechanical (or acoustical energy).
It's basically a coil of wire (voice-coil) around a former (a voice-coil former) that is designed to interact with a static magnetic field from a permanent magnet located behind the coil. But a voice-coil without current is useless and when a current flows through the voice-coil, it will create a force (because when two magnetic forces interact you get attraction and repulsion).
So the electromagnetic field is alternating. Electrons travel depending on the direction or orientation of the poles. The pole piece forms part of the motor and is designed to focus the magnetic field, to focus flux, and also to transfer some of the heat from the coil to the former where the heat is dissapated.
All these forces, magnetic forces are concentrated in the magnetic gap. A small air gap. So magnetic flux, the strength of the magnetic field takes place in this field. When both fields interact and force is generated, the diaphram, the cone that is connected to the voice-coil moves, and creates air. Presto.
Now to create a speaker with a stronger magnetic field, with stronger repulsion and attraction forces requires a bigger magnet and a coil with longer wire (more windings). A bigger diameter coil will mean better heat disappation and better power handling. A coil with more windings will be more efficient (meaning it will require less power to move at any given level).
If speakers are to have very high excursion capabilities, they require very long lengths of wire. And the more turns the coil makes, the more linear the response will be as long as the voice coil is within the gap area.
I know that cones need to be stiff for high excursions. But what is important for very high excursions are big coils and long wire lengths. Correct me if I'm wrong on that.
As soon as the coil turns are outside the gap, the motor strength (BL) goes down. BL is a measure of motor strength. So for the motor to be strong, or efficient, the voice coil must complete a number of constant turns within the gap where the magnetic field are generated.
Magnetic flux is determined by many things apparently. Not just big magnets and voice-coils, but pole-piece topologies also affect flux. Even the former to some degree will either subtract or add to the degree of flux inherent in the magnetic field.
Then there is a spider which controls the motion of the coil. It provides mechanical damping so that the voice-coil is well controlled. It also makes sure the voice-coil is centered in the gap area so that maximum flux is attained. With no suspension, the coil would just slam into the back plate.
Is this a correct understanding ? I know there are many other variables involved that I didn't mention. I think I'm well versed in this at the moment but I believe I have much room for improvement and understanding.
Thank you.
--Sincerely,
yea id say you have the right idea,
as far as increasing the excursion goes, the Xmax (voice coil overhang) will decrease the effiency of the speaker as there is coil outside the magnetic field. So this is a kind of lose lose situation.
ALL bass drivers have some of the coil outside the magnetic field to allow for more excursion because as soon as there is less wire in the field the speaker is no longer linear.
as far as increasing the excursion goes, the Xmax (voice coil overhang) will decrease the effiency of the speaker as there is coil outside the magnetic field. So this is a kind of lose lose situation.
ALL bass drivers have some of the coil outside the magnetic field to allow for more excursion because as soon as there is less wire in the field the speaker is no longer linear.
It depends on the signal. In any case, it's more relevant to talk about current flow instead of electrons.Vaughan said:
The coil is glued to the former, as far as I can tell, which means that the coil simply conducts heat directly to the former.
Moves air. 🙂
Not necessarily. Reduce the cross-sectional area of the coil gap and flux density increases. Using a larger magnet may not significantly increase flux. More windings works well in theory (not complete theory, I should think), but resistance increases also, so I'm not sure how that works.
It can't be that easy, otherwise all the higher-end drivers would do this.
Not necessarily.
How do you figure?
What's important for high excursion is linear BL vs excursion, among other things. The suspension system must also be designed to prevent damage at excessively high excursions.
Not sure what you mean.
How so?
454Casull,
If I don't know something then please correct me and explain where I'm going wrong. I need an explanation instead of a "not necessarily".
Thanks. I will try and answer your questions based on what I currently know about the subject.
The coil is glued to the former, as far as I can tell, which means that the coil simply conducts heat directly to the former.
So the pole piece does not transfer heat at all to the former ? There are no thermal transfer functions for the pole piece ? Strange.
Using a larger magnet may not significantly increase flux.
But flux will increase. A bigger magnet will give you a stronger magnetic field. More flux in the gap.
More windings works well in theory (not complete theory, I should think), but resistance increases also, so I'm not sure how that works.
Yes, but I was talking about longer wire not a thicker diameter. A bigger coil will be heavier and so will add resistance but will provide better power handling and better thermal dissapation.
It can't be that easy, otherwise all the higher-end drivers would do this.
So are you telling me that a voice-coil with more wire is not more efficient ? Are you forgetting BL ? L, length of wire in the gap ? One of the equations of motor strength besides flux density in the gap.
More wire should increase flux and increase BL. Perhaps you can explain why I'm wrong and provide an explanation.
Not necessarily.
This isn't helpful for me. I don't know what you mean by this. Longer wire means more turns, right ? More turns means longer excursions doesn't it ?
If I'm wrong please explain why.
How do you figure?
Because flux is concentrated in the magnetic gap. The strength (flux) of the field is concentrated in this gap. If the coil moves out of the gap, the number of turns in the gap decreases and BL goes down because the field symmetry is not uniform within the gap.
Thus the driver will be operating in a nonlinear fashion. Remember that if the signal is to be reproduced accurately, the voice-coil needs to move equally in the gap and the magnet field needs to be as symmetrical.
If the coil moves out of the gap it becomes nonsymmetrical hence the output will be nonlinear.
What's important for high excursion is linear BL vs excursion, among other things.
But what is actually required for high excursion ? Just the ability for high excursions ? Long lengths of wire and a great number of turns in the gap for linearity.
If one wants high excursion as well as a linear BL then the coil must move as many times as possible within the gap. Unless I'm wrong and you can explain why this is.
The suspension system must also be designed to prevent damage at excessively high excursions.
Definitely. But when we talk about cone exursions of 1", or 2", the coil is doing most of the work. This is why long lengths of wire is needed for long excursions right ? And big voice-coils are needed for high power handling.
And the less thermal compression the better.
Not sure what you mean.
What I mean't was that for the magnetic field to be symmetrical, the coil must move within the gap area where it is concentrated. BL is strongest within the gap. Outside the gap the BL goes down.
But the measurable distortion will be apparent before that occurs because the one-way linear exursion would have been reached.
How so?
Depends whether the former is conductive or nonconductive. If you are using aluminum, which is electrically conductive, it will cause eddy currents in the magnetic field. Which amounts to losses.
And the field will once again not be completely symmetrical. Different pole piece topologies also affect the magnetic field in different ways.
Nonconductive formers will give you slightly better flux compared to conductive because of the induced eddy currents that are part and parcel to using electrically conductive materials in a magnetic system.
Losses. I hope you can explain where I'm wrong. Perhaps some of the more experienced experts can chime in and can offer their advice and knowledge on this so that I can learn more.
--Sincerely,
If I don't know something then please correct me and explain where I'm going wrong. I need an explanation instead of a "not necessarily".
Thanks. I will try and answer your questions based on what I currently know about the subject.
The coil is glued to the former, as far as I can tell, which means that the coil simply conducts heat directly to the former.
So the pole piece does not transfer heat at all to the former ? There are no thermal transfer functions for the pole piece ? Strange.
Using a larger magnet may not significantly increase flux.
But flux will increase. A bigger magnet will give you a stronger magnetic field. More flux in the gap.
More windings works well in theory (not complete theory, I should think), but resistance increases also, so I'm not sure how that works.
Yes, but I was talking about longer wire not a thicker diameter. A bigger coil will be heavier and so will add resistance but will provide better power handling and better thermal dissapation.
It can't be that easy, otherwise all the higher-end drivers would do this.
So are you telling me that a voice-coil with more wire is not more efficient ? Are you forgetting BL ? L, length of wire in the gap ? One of the equations of motor strength besides flux density in the gap.
More wire should increase flux and increase BL. Perhaps you can explain why I'm wrong and provide an explanation.
Not necessarily.
This isn't helpful for me. I don't know what you mean by this. Longer wire means more turns, right ? More turns means longer excursions doesn't it ?
If I'm wrong please explain why.
How do you figure?
Because flux is concentrated in the magnetic gap. The strength (flux) of the field is concentrated in this gap. If the coil moves out of the gap, the number of turns in the gap decreases and BL goes down because the field symmetry is not uniform within the gap.
Thus the driver will be operating in a nonlinear fashion. Remember that if the signal is to be reproduced accurately, the voice-coil needs to move equally in the gap and the magnet field needs to be as symmetrical.
If the coil moves out of the gap it becomes nonsymmetrical hence the output will be nonlinear.
What's important for high excursion is linear BL vs excursion, among other things.
But what is actually required for high excursion ? Just the ability for high excursions ? Long lengths of wire and a great number of turns in the gap for linearity.
If one wants high excursion as well as a linear BL then the coil must move as many times as possible within the gap. Unless I'm wrong and you can explain why this is.
The suspension system must also be designed to prevent damage at excessively high excursions.
Definitely. But when we talk about cone exursions of 1", or 2", the coil is doing most of the work. This is why long lengths of wire is needed for long excursions right ? And big voice-coils are needed for high power handling.
And the less thermal compression the better.
Not sure what you mean.
What I mean't was that for the magnetic field to be symmetrical, the coil must move within the gap area where it is concentrated. BL is strongest within the gap. Outside the gap the BL goes down.
But the measurable distortion will be apparent before that occurs because the one-way linear exursion would have been reached.
How so?
Depends whether the former is conductive or nonconductive. If you are using aluminum, which is electrically conductive, it will cause eddy currents in the magnetic field. Which amounts to losses.
And the field will once again not be completely symmetrical. Different pole piece topologies also affect the magnetic field in different ways.
Nonconductive formers will give you slightly better flux compared to conductive because of the induced eddy currents that are part and parcel to using electrically conductive materials in a magnetic system.
Losses. I hope you can explain where I'm wrong. Perhaps some of the more experienced experts can chime in and can offer their advice and knowledge on this so that I can learn more.
--Sincerely,
This is very interesting, Vaughan, I have the loudspeaker cookbook and what you say is right on the money, you have basiclly explained what I read in 10 pages in less than 1 page...I also understand yours more
I also want to learn what Vaughan is asking for
I also want to learn what Vaughan is asking for
The coil is glued to the former, as far as I can tell, which means that the coil simply conducts heat directly to the former.
So the pole piece does not transfer heat at all to the former ? There are no thermal transfer functions for the pole piece ?
454: No, I didn't say that. The pole piece does absorb heat, but I had gathered the impression that you thought it was the only thing that "cooled" the voice coil, so to speak, but the coil is directly attached to the former.
Using a larger magnet may not significantly increase flux.
But flux will increase. A bigger magnet will give you a stronger magnetic field. More flux in the gap.
454: True. But flux density can also be increased by re-working the motor geometry. This method is more efficient than simply adding more magnet.
More windings works well in theory (not complete theory, I should think), but resistance increases also, so I'm not sure how that works.
Yes, but I was talking about longer wire not a thicker diameter. A bigger coil will be heavier and so will add resistance but will provide better power handling and better thermal dissapation.
454: For any given wire diameter, resistance is proportional to length. If you keep the diam. the same and make the coil longer, resistance increases.
454: There are drivers that are efficient and can handle large amounts of power, but power handling does not (not always) correlate to high efficiency. Also, thermal dissipation, or more accurately, [resistance to] power compression should not have anything to do with efficiency _in the short term_. As heat starts "soaking" throughout the motor, sensitivity decreases because resistance increases.
It can't be that easy, otherwise all the higher-end drivers would do this.
So are you telling me that a voice-coil with more wire is not more efficient ? Are you forgetting BL ? L, length of wire in the gap ? One of the equations of motor strength besides flux density in the gap.
454: No, I am not forgetting BL. But again, efficiency decreases as Re increases (as far as I can tell). As a side note, flux density is not separate, but is rather part of "BL" - the B is the flux density, usually expressed in Tesla(s), and BL is a factor in the sensitivity equation.
More wire should increase flux and increase BL. Perhaps you can explain why I'm wrong and provide an explanation.
454: See above.
Not necessarily.
More turns means longer excursions doesn't it ?
454: No. The number of turns in the coil is not necessarily related to excursion, though I now see what you're getting at. As you put more turns in the coil, the height of the coil increases, which increases excursion in an _overhung_ design, while it would decrease in an _underhung_ design. Also, the height of the coil (for a given number of turns) depends on whether it's single layer, double layer, triple, etc. (not that I know which configurations are more common)
How do you figure?
Because flux is concentrated in the magnetic gap. The strength (flux) of the field is concentrated in this gap. If the coil moves out of the gap, the number of turns in the gap decreases and BL goes down because the field symmetry is not uniform within the gap.
454: Yes, I understand now. You are correct; BL goes down when the coil moves out of the linear *field* - in an overhung design, there should always be some coil inside the gap.
the voice-coil needs to move equally in the gap
454: I don't understand.
What's important for high excursion is linear BL vs excursion, among other things.
But what is actually required for high excursion ? Just the ability for high excursions ?
454: The standard definition for max excursion is where BL decreases to 70% of BL at zero excursion. Anything that can increases it, works.
Long lengths of wire and a great number of turns in the gap for linearity.
454: Let's say we have 2 drivers. Both are conventional overhung designs. Both have a top plate thickness of 0.5", and a coil height of 1". Coil A is single-layer, while coil B is double-layer. As such, coil B will have twice as many turns inside the gap. Does this mean driver B has approximately twice the excursion?
If one wants high excursion as well as a linear BL then the coil must move as many times as possible within the gap.
454: Are you trying to say that there must be as high a number of turns inside the gap as possible?
The suspension system must also be designed to prevent damage at excessively high excursions.
Definitely. But when we talk about cone exursions of 1", or 2", the coil is doing most of the work. This is why long lengths of wire is needed for long excursions right?
454: Read up on XBL2.
And big voice-coils are needed for high power handling.
454: Almost always true, I think.
And the less thermal compression the better.
454: Yes.
Not sure what you mean.
What I mean't was that for the magnetic field to be symmetrical, the coil must move within the gap area where it is concentrated. BL is strongest within the gap. Outside the gap the BL goes down.
454: Let's get one thing straight - the symmetry of the flux depends ONLY on the motor geometry. Unless you're talking about the flux generating by the coil, in which case it MUST be symmetrical because of its shape.
But the measurable distortion will be apparent before that occurs because the one-way linear exursion would have been reached.
454: There is always measurable distortion. 😉
How so?
Depends whether the former is conductive or nonconductive. If you are using aluminum, which is electrically conductive, it will cause eddy currents in the magnetic field. Which amounts to losses.
454: Yes, losses do occur when using a conductive former, unless it is "broken". But does this actually weaken the field?
And the field will once again not be completely symmetrical.
454: I am not sure what you mean by symmetrical.
Different pole piece topologies also affect the magnetic field in different ways.
454: Yes. You should play around with FEMM; it's a wonderful learning tool. It's free, IIRC.
Nonconductive formers will give you slightly better flux compared to conductive because of the induced eddy currents that are part and parcel to using electrically conductive materials in a magnetic system.
454: Again, are you sure the flux in the gap actually decreases?
So the pole piece does not transfer heat at all to the former ? There are no thermal transfer functions for the pole piece ?
454: No, I didn't say that. The pole piece does absorb heat, but I had gathered the impression that you thought it was the only thing that "cooled" the voice coil, so to speak, but the coil is directly attached to the former.
Using a larger magnet may not significantly increase flux.
But flux will increase. A bigger magnet will give you a stronger magnetic field. More flux in the gap.
454: True. But flux density can also be increased by re-working the motor geometry. This method is more efficient than simply adding more magnet.
More windings works well in theory (not complete theory, I should think), but resistance increases also, so I'm not sure how that works.
Yes, but I was talking about longer wire not a thicker diameter. A bigger coil will be heavier and so will add resistance but will provide better power handling and better thermal dissapation.
454: For any given wire diameter, resistance is proportional to length. If you keep the diam. the same and make the coil longer, resistance increases.
454: There are drivers that are efficient and can handle large amounts of power, but power handling does not (not always) correlate to high efficiency. Also, thermal dissipation, or more accurately, [resistance to] power compression should not have anything to do with efficiency _in the short term_. As heat starts "soaking" throughout the motor, sensitivity decreases because resistance increases.
It can't be that easy, otherwise all the higher-end drivers would do this.
So are you telling me that a voice-coil with more wire is not more efficient ? Are you forgetting BL ? L, length of wire in the gap ? One of the equations of motor strength besides flux density in the gap.
454: No, I am not forgetting BL. But again, efficiency decreases as Re increases (as far as I can tell). As a side note, flux density is not separate, but is rather part of "BL" - the B is the flux density, usually expressed in Tesla(s), and BL is a factor in the sensitivity equation.
More wire should increase flux and increase BL. Perhaps you can explain why I'm wrong and provide an explanation.
454: See above.
Not necessarily.
More turns means longer excursions doesn't it ?
454: No. The number of turns in the coil is not necessarily related to excursion, though I now see what you're getting at. As you put more turns in the coil, the height of the coil increases, which increases excursion in an _overhung_ design, while it would decrease in an _underhung_ design. Also, the height of the coil (for a given number of turns) depends on whether it's single layer, double layer, triple, etc. (not that I know which configurations are more common)
How do you figure?
Because flux is concentrated in the magnetic gap. The strength (flux) of the field is concentrated in this gap. If the coil moves out of the gap, the number of turns in the gap decreases and BL goes down because the field symmetry is not uniform within the gap.
454: Yes, I understand now. You are correct; BL goes down when the coil moves out of the linear *field* - in an overhung design, there should always be some coil inside the gap.
the voice-coil needs to move equally in the gap
454: I don't understand.
What's important for high excursion is linear BL vs excursion, among other things.
But what is actually required for high excursion ? Just the ability for high excursions ?
454: The standard definition for max excursion is where BL decreases to 70% of BL at zero excursion. Anything that can increases it, works.
Long lengths of wire and a great number of turns in the gap for linearity.
454: Let's say we have 2 drivers. Both are conventional overhung designs. Both have a top plate thickness of 0.5", and a coil height of 1". Coil A is single-layer, while coil B is double-layer. As such, coil B will have twice as many turns inside the gap. Does this mean driver B has approximately twice the excursion?
If one wants high excursion as well as a linear BL then the coil must move as many times as possible within the gap.
454: Are you trying to say that there must be as high a number of turns inside the gap as possible?
The suspension system must also be designed to prevent damage at excessively high excursions.
Definitely. But when we talk about cone exursions of 1", or 2", the coil is doing most of the work. This is why long lengths of wire is needed for long excursions right?
454: Read up on XBL2.
And big voice-coils are needed for high power handling.
454: Almost always true, I think.
And the less thermal compression the better.
454: Yes.
Not sure what you mean.
What I mean't was that for the magnetic field to be symmetrical, the coil must move within the gap area where it is concentrated. BL is strongest within the gap. Outside the gap the BL goes down.
454: Let's get one thing straight - the symmetry of the flux depends ONLY on the motor geometry. Unless you're talking about the flux generating by the coil, in which case it MUST be symmetrical because of its shape.
But the measurable distortion will be apparent before that occurs because the one-way linear exursion would have been reached.
454: There is always measurable distortion. 😉
How so?
Depends whether the former is conductive or nonconductive. If you are using aluminum, which is electrically conductive, it will cause eddy currents in the magnetic field. Which amounts to losses.
454: Yes, losses do occur when using a conductive former, unless it is "broken". But does this actually weaken the field?
And the field will once again not be completely symmetrical.
454: I am not sure what you mean by symmetrical.
Different pole piece topologies also affect the magnetic field in different ways.
454: Yes. You should play around with FEMM; it's a wonderful learning tool. It's free, IIRC.
Nonconductive formers will give you slightly better flux compared to conductive because of the induced eddy currents that are part and parcel to using electrically conductive materials in a magnetic system.
454: Again, are you sure the flux in the gap actually decreases?
I am really interested in this topic. And I'm glad we are having these exchanges 454Casull. I am learning some things too. Apparently others are too.
I would very much like to continue discussing this if you are. I won't be able to post in this thread for the next few days but I hope to carry on soon.
Thank you for participating and I hope we can continue this discussion later. 🙂
Toast_Master,
This is very interesting, Vaughan, I have the loudspeaker cookbook and what you say is right on the money, you have basiclly explained what I read in 10 pages in less than 1 page...I also understand yours more
Wow. Thanks ! I am just trying to understand this as well as I can and I want to learn as much as possible (like everyone). But I am really flattered by your comments.
Thank you.
--Sincerely,
I would very much like to continue discussing this if you are. I won't be able to post in this thread for the next few days but I hope to carry on soon.
Thank you for participating and I hope we can continue this discussion later. 🙂
Toast_Master,
This is very interesting, Vaughan, I have the loudspeaker cookbook and what you say is right on the money, you have basiclly explained what I read in 10 pages in less than 1 page...I also understand yours more
Wow. Thanks ! I am just trying to understand this as well as I can and I want to learn as much as possible (like everyone). But I am really flattered by your comments.
Thank you.
--Sincerely,
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