I remember Mr. Brines talking about the relationship between moving mass, BL, and transient response. But is the same factor a way to predict the dynamic potential of a driver? For some now I have been operating on the assumption that it is, but I would like to know if there is any grounds for that or not. For example, looking at the Audio Nirvana 10" and 12" ferrite models, both units have approximately equivalent motors of 1400 and 1409g. But the 10" has 17g mms and a BL of 9 while the 12" has a moving mass of 28g and a BL of 8.86. This would lead me to assume that the 10" has greater dynamic potential as it is able to accelerate its 17 grams of weight more efficiently, producing more "slam." But, then again, maybe the 12" has greater slam potential by virtue of being so much larger.
Any value to making predictions such as these, or do Mms, BL, and other indicators fall short of hinting at how a driver will perform in real life?
Any value to making predictions such as these, or do Mms, BL, and other indicators fall short of hinting at how a driver will perform in real life?
Depends. You're refering to the nominal Newtonian acceleration factor which is taken (using SI units) as BL / Mms, giving an acceleration factor in meters per second per second per ampere. It's vaguely interesting from an academic POV, but in reality, it's all but meaningless. BL strictly should be written as B*L*i where i is the current in the voice coil. Thus, from that you can see that acceleration proportional to the amount of current you feed the drive unit. Simple as that. The ratio of raw motor power to mass is just another way of expressing efficiency.
'Dynamics' is an often misused term; technically it simply means the dynamic bandwidth of the drive unit, i.e. how much headroom it has available to handle large dynamic peaks in the material. FWIW, if you're concerned about this, you may find the Volume Displacement (Vd) figure of a drive unit, which is Sd*Xmax to be useful. That tells you how much air the raw driver can potentially shift in a linear fashion.
If you're concerned about transient response, this is pretty much a non-issue for wide-band / full range drive units. Since transient response is linked to the bandwidth the drive unit is able to cover (the transient part of the information occuring at higher frequencies) by definition, they all possess good transient response. A wide-band drive unit with poor transient response is essentially a contradiction in terms, unless it has an apalling frequency response, with large holes all over the place.
'Dynamics' is an often misused term; technically it simply means the dynamic bandwidth of the drive unit, i.e. how much headroom it has available to handle large dynamic peaks in the material. FWIW, if you're concerned about this, you may find the Volume Displacement (Vd) figure of a drive unit, which is Sd*Xmax to be useful. That tells you how much air the raw driver can potentially shift in a linear fashion.
If you're concerned about transient response, this is pretty much a non-issue for wide-band / full range drive units. Since transient response is linked to the bandwidth the drive unit is able to cover (the transient part of the information occuring at higher frequencies) by definition, they all possess good transient response. A wide-band drive unit with poor transient response is essentially a contradiction in terms, unless it has an apalling frequency response, with large holes all over the place.
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Really interesting Scott; thanks for the reply.
So then a Mark audio driver will have better dynamics than a similar-sized Fostex driver by virtue of having greater xmax, and thus more ability to handle dynamic peaks? (Setting aside the variable of cabinet design.)
I don't quite agree with that. MMS and BL should indicate how fast the cone can move. A light cone and strong motor means the cone can be easily accelerated, all else being equal. This means it can retrieve little details that may be otherwise lost on more heavier sluggish cone/motor combinations.
With regard to dynamic capability, IMO efficiency is a more indicative parameter. And finally, Xmax indicates how loud the driver can play after that first watt.
How does all this play out in the drivers being talked about? The ANs are extremely good at detail retrieval. In fact, I'm willing to be they are in Lowther class. They also do dynamics pretty well, but that is only down to their high efficiency. If you don't listen very loud, or have a small room, or listen to only simple music, the ANs have plenty of dynamics and plenty of detail retrieval. But as you turn up the volume, the limited Xmax presents itself. I'm crossing them over at 300 Hz, but on Led Zepp, at loud levels, they simply cannot handle it. Distortion is too high.
If you instead took a B&C 8", ala Geddes, that marries high efficiency with decent Xmax, it would do far better than the AN when it comes to absolute loudness. Of course, it doesn't have the extension of an AN.
Fostex and other high-eff full range drivers could be classified in the same category. They will have some small differences because of whizzers, dust caps, surrounds, etc. But their sonic signature will be the same.
The other class of drivers are the MAs and Jordans, low efficiency but huge Xmax. The Alpairs are very linear over their total Xmax and low distortion too. This is immediately obvious. But they certainly don't have the liveliness and naturalness of an AN/fostex/Lowther. To me, they sound less dynamic and less musical compared to the high-eff drivers. Of course, if simplicity of build is taken into account, the MAs are much easier to get good sound out of than the ANs/Lowthers that basically cry out for horns.
With regard to dynamic capability, IMO efficiency is a more indicative parameter. And finally, Xmax indicates how loud the driver can play after that first watt.
How does all this play out in the drivers being talked about? The ANs are extremely good at detail retrieval. In fact, I'm willing to be they are in Lowther class. They also do dynamics pretty well, but that is only down to their high efficiency. If you don't listen very loud, or have a small room, or listen to only simple music, the ANs have plenty of dynamics and plenty of detail retrieval. But as you turn up the volume, the limited Xmax presents itself. I'm crossing them over at 300 Hz, but on Led Zepp, at loud levels, they simply cannot handle it. Distortion is too high.
If you instead took a B&C 8", ala Geddes, that marries high efficiency with decent Xmax, it would do far better than the AN when it comes to absolute loudness. Of course, it doesn't have the extension of an AN.
Fostex and other high-eff full range drivers could be classified in the same category. They will have some small differences because of whizzers, dust caps, surrounds, etc. But their sonic signature will be the same.
The other class of drivers are the MAs and Jordans, low efficiency but huge Xmax. The Alpairs are very linear over their total Xmax and low distortion too. This is immediately obvious. But they certainly don't have the liveliness and naturalness of an AN/fostex/Lowther. To me, they sound less dynamic and less musical compared to the high-eff drivers. Of course, if simplicity of build is taken into account, the MAs are much easier to get good sound out of than the ANs/Lowthers that basically cry out for horns.
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MMS and BL should indicate how fast the cone can move. A light cone and strong motor means the cone can be easily accelerated, all else being equal.
Bl/Mms is sometimes called the acceleration factor. It's correlated to efficieny but it's a fallacy to believe it's correlated in any way to the quality of the reproduction of transients by the cone. With IBs, in the piston range, cones having the same emitting area and delivering the same output SPL at the same frequency are submitted to exactly the same acceleration. If the mass of the cones is the same, the force on the cone is the same and if the BLs are different, it is the current in the coils which is different. The cone "sees" the same force, it does not "know" that the BLs are different. Great drivers can have low or high ratios of Bl/Mms, it is not a quality criterion.
MMS and BL should indicate how fast the cone can move. A light cone and strong motor means the cone can be easily accelerated, all else being equal.
Bl/Mms is sometimes called the acceleration factor. It's correlated to efficieny but it's a fallacy to believe it's correlated in any way to the quality of the reproduction of transients by the cone. With IBs, in the piston range, cones having the same emitting area and delivering the same output SPL at the same frequency are submitted to exactly the same acceleration. If the mass of the cones is the same, the force on the cone is the same and if the BLs are different, it is the current in the coils which is different. The cone "sees" the same force, it does not "know" that the BLs are different. Great drivers can have low or high ratios of Bl/Mms, it is not a quality criterion.
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Efficiency is directly proportional to the square of the Bl product and inversely proportional to the cone mass (if I remember the formula correctly). Certainly, a lighter cone and stronger motor means greater efficiency, other things being equal. And what does more efficiency mean? Ability to play louder with less power? Yes. More headroom? Yes. Less power compression? Yes. And that to me generally means better sound. There are exceptions to the rule because there are a million different ways to make good sounding drivers.
If you look at nature, an increase in efficiency is generally accompanied by an increase in performance. That is not a hard rule, but it applies to drivers IMO. I've found that less sensitive speakers are the ones that sound dull, lifeless and are most certainly difficult to drive.
If you look at nature, an increase in efficiency is generally accompanied by an increase in performance. That is not a hard rule, but it applies to drivers IMO. I've found that less sensitive speakers are the ones that sound dull, lifeless and are most certainly difficult to drive.
It only means more headroom if you've got sufficient Xmax for a given application. You can have a reasonably high efficiency drive unit with almost no linear travel that will have less dynamic headroom than a slightly lower efficiency unit with far more linear travel.
Logical fallacy I'm afraid. Acceleration is proportional to the current in the voice coil. No current, no acceleration, however light the powertrain or powerful the magnet.
Logical fallacy I'm afraid. Acceleration is proportional to the current in the voice coil. No current, no acceleration, however light the powertrain or powerful the magnet.
Hi Ra7,
Less power compression?
In domestic conditions, no study shows power compression
If you look at nature, an increase in efficiency is generally accompanied by an increase in performance.
Do you have an example ? I can't see how concepts of efficiency and performance exist in nature.
Less power compression?
In domestic conditions, no study shows power compression
If you look at nature, an increase in efficiency is generally accompanied by an increase in performance.
Do you have an example ? I can't see how concepts of efficiency and performance exist in nature.
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Ok lets see here:
Force (F) = Mass (M) x acceleration (a)
or a = F/M.
In our case, F = B.l.i, where i is the current through the voice coil.
Therefore, a = B.l.i/M, where M can be assumed for the moment to be the mass of the cone. For a given current in the voice coil, the amount of acceleration produce does indeed depend on the magnetic flux density, length of the wire in the magnetic field and the mass of the cone.
I'm not so clear on whether greater acceleration equals better transient response. I can understand the logic of greater force exerted on a light mass will propel it faster than a smaller force on a heavier mass.
Scottmoose, your point that no current equals no acceleration is correct, but that's like saying no magnet equals no acceleration. We are assuming current to be constant in each driver being evaluated.
Force (F) = Mass (M) x acceleration (a)
or a = F/M.
In our case, F = B.l.i, where i is the current through the voice coil.
Therefore, a = B.l.i/M, where M can be assumed for the moment to be the mass of the cone. For a given current in the voice coil, the amount of acceleration produce does indeed depend on the magnetic flux density, length of the wire in the magnetic field and the mass of the cone.
I'm not so clear on whether greater acceleration equals better transient response. I can understand the logic of greater force exerted on a light mass will propel it faster than a smaller force on a heavier mass.
Scottmoose, your point that no current equals no acceleration is correct, but that's like saying no magnet equals no acceleration. We are assuming current to be constant in each driver being evaluated.
Yes, I'm aware it is correct. I would not have said it otherwise.
In which case they will conform to the laws of physics and accelerate at the same rate. You feed them a signal containing, say, a 100Hz tone, one will not be accelerating faster than the other. The drive unit with the lighter powertrain will be more efficient for a given motor power, but the acceleration of a powertrain is proportional only to the signal with which it is fed, it is not something of the drive unit's devising.
As for transient response, see my above post. The Fourier transform dictates that time and frequency are inherently linked, thus all wide-band / full range drivers inherently have to possess good transient response. This is not a matter for debate, it's a fundamental law of physics. The mass of the cone / powertrain / whatever you like to call it is irrelevant. You may wish to peruse this, at your leisure: http://www.adireaudio.com/Files/WooferSpeed.pdf
In which case they will conform to the laws of physics and accelerate at the same rate. You feed them a signal containing, say, a 100Hz tone, one will not be accelerating faster than the other. The drive unit with the lighter powertrain will be more efficient for a given motor power, but the acceleration of a powertrain is proportional only to the signal with which it is fed, it is not something of the drive unit's devising.
As for transient response, see my above post. The Fourier transform dictates that time and frequency are inherently linked, thus all wide-band / full range drivers inherently have to possess good transient response. This is not a matter for debate, it's a fundamental law of physics. The mass of the cone / powertrain / whatever you like to call it is irrelevant. You may wish to peruse this, at your leisure: http://www.adireaudio.com/Files/WooferSpeed.pdf
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Haven't we been here before? I am going to try exactly one more time and then I will never address this again.
The argument that BL and Mms are irrelevant to acceleration applies ONLY if BL and Mms are constant. This cannot apply when comparing driver A with driver B unless driver A and driver B have exactly the same BL and exactly the same Mms. Otherwise all drivers would have the same efficiency. If BL is smaller, i has less to push against. If Mms is smaller, i can push the cone farther faster.
"Acceleration factor" may be an ill chosen term and may indeed be directly proportional to efficiency, but BL and Mms are not independently irrelevant.
(Woofer "speed" BTW has little to do with the BLi/Mms issue. "Speed" is dependent on how well the woofer and/or mid reproduces the harmonic series of a bass note.)
Bob
Acceleration is proportional to current or the signal fed to "a" driver. For a given driver, yes, the flux density, length of wire and moving mass are fixed and constant. But they may not be the same in different drivers, and mostly they are not.
I just glanced through the paper. They call Bl and Mms constant, but again that is the case when considering the relationship of acceleration with transient response of a single driver. It is meant to showcase the characteristics of their drivers, with the low inductance. It does not apply to a comparison between different drivers with different cone masses and motors.
An analogy would be the combustion engine, where torque is proportional to say, the piston diameter. That is true for all engines, but that doesn't the engine will accelerate a two different cars at the same rate. That would depend on the mass of the car.
EDIT: I see Bob has already addressed the poor logic in that paper.
I just glanced through the paper. They call Bl and Mms constant, but again that is the case when considering the relationship of acceleration with transient response of a single driver. It is meant to showcase the characteristics of their drivers, with the low inductance. It does not apply to a comparison between different drivers with different cone masses and motors.
An analogy would be the combustion engine, where torque is proportional to say, the piston diameter. That is true for all engines, but that doesn't the engine will accelerate a two different cars at the same rate. That would depend on the mass of the car.
EDIT: I see Bob has already addressed the poor logic in that paper.
A drive unit is not a car. You feed a low mass & a higher mass drive unit (ensuring all else is in proportion) a signal containing, say, a 100Hz tone, then the former isn't going to be moving quicker than the latter. If it were, it would be producing something other than the signal with which it was fed.
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Two drive units producing 100 Hz tones will be moving (or accelerating, I'm not sure) at the same rate. But what we are interested in is what happens when we switch that 100 Hz tone to a 150 Hz tone. How fast can the two drive units stop producing 100 Hz and start producing 150 Hz. This is what is transient response in my mind. In an ideal system, this change would be instantaneous, but real drivers are far from ideal.
What I hear from a strong motor, light cone driver is that it can make this change quicker than a driver with a heavy cone/weak magnet.
I understand the theoretical definition of transient response and how it is governed by the upper BW limit - that's how fast the driver can move theoretically. If it has produce a higher frequency it has to be able to move faster. But I don't think that is what we are talking about here.
What I hear from a strong motor, light cone driver is that it can make this change quicker than a driver with a heavy cone/weak magnet.
I understand the theoretical definition of transient response and how it is governed by the upper BW limit - that's how fast the driver can move theoretically. If it has produce a higher frequency it has to be able to move faster. But I don't think that is what we are talking about here.
I understand the theoretical definition of transient response and how it is governed by the upper BW limit - that's how fast the driver can move theoretically. If it has produce a higher frequency it has to be able to move faster.
You will soon meet cone break-up and return of the inside the box pressure due "transparency" to the sound of light cones, both spoil the transient response.
If Bl/Mms was an important factor, we would have examples of far better transient responses of systems having light cones. I do not think we have many.
You will soon meet cone break-up and return of the inside the box pressure due "transparency" to the sound of light cones, both spoil the transient response.
If Bl/Mms was an important factor, we would have examples of far better transient responses of systems having light cones. I do not think we have many.
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