Read this a while ago, but just recently found it again:

http://www.yildiz.edu.tr/~ilkorur/WooferSpeed.pdf" rel="nofollow - http://www.yildiz.edu.tr/~ilkorur/WooferSpeed.pdf

There's a common misconception out there that heavy woofers must be "slow", and light woofers must be "fast". If a woofer A's moving mass is higher than woofer B's, then woofer A is probably going to be sloppy, or slow and inaccurate. Can't keep up with the bass line. Woofer A simply can't respond as fast as woofer B.  There's also this concept that the "acceleration factor" (BL/Mms) is an indicator of woofer speed/transient response. High BL, combined with a low Mms, should give great transient response, right? Well, on surface these might sound like logical assumptions. However, they are in fact incorrect! More to the point, moving mass has precious little to do with woofer speed or signal response! And we'll prove it...

In this paper, their tests are showing that Inductace (Le) has more of an effect on a drivers transient response than cone weight/motor speed. This is contrary to what I've heard, but I am no expert, what do you all think? 

Thoughts?

I used to upgrade Airsoft guns and there are a few things you can do to improve the speed of an electric gun. Now I know it is not directly the same, but I can see there are some pretty close resemblances. However if I am wrong, someone please explain.

The basic motor had relatively low power with thinner, fewer windings.

I used to buy motors that had thicker wire with less coils on the armature and much stronger neo magnets. It was easy to tell the difference in strength in the motors if you held the motor in one hand and spin the armature between thumb and forefinger of the other. The standard motor would continue to turn for maybe a couple of seconds, where as the better motors aimed at high torque it could actually be an effort to turn and as the armature is wound making it click as the sections confront the neo magnets. 

So using this logic as it is very similar. 

A good bass driver will have very strong magnets, with the strength per weight being better with neo magnets.

The length of windings and diameter of the wire will be specifically designed to the weight and properties of the cone. Combined with the diameter of the voice coil which will give more or less power in the piston.

It then follows, the higher the magnet strength combined with a specifically designed coil size/ wire size will determine the torque in the piston. It is this torque that will give you the 'speed' of the cone. With the higher ratio magnet to voice coil the higher the torque. At a given voltage. Obviously the higher the voltage the more power goes through the piston. 

As I understand it, the inductance ie the given amount of magnetic field , is dependant on various factors, if you take a simple large gauge wire and use that for a coil then the inductance will be much lower than if you use a smaller gauge with multiple windings. The windings in terms of length and gauge have to be selected upon the basis of their ability to handle the current and create a magnetic field. Inductance is directly related to force within the coils flux acting against the fixed magnet,the more windings, the more inductance, common sense would say that a lighter cone  would be more responsive given the same coil assembly otherwise any other view would appear to defy the laws of physics.

 

yeah I don't think it takes very much more than basic high school physics to understand that both parts will effect the result and the "speed" of the driver. 

A stronger magnet will push and pull harder, and so be able to move quicker given the same cone. 

A lighter cone will be easier to move so will move faster given the same magnet. 

And given stronger inductance in the coil, it will also react faster to the changes.

So a combination of all will decide ultimately how quick it sounds.

(Though obviously it becomes far more complicated than this as there are many factors to consider when deciding on your driver design. No point in having a super light cone that can move quickly if it tears up with the pressure of the speaker design. An no point in having a huge heavy magnet if it then affects the other t/s paramiters of the driver and takes it away from it's design goals. )

Now, my problem with the article is that he suddenly discounts a load of parameters that can't just be ignored for no reason. 

I haven't had time to really read the article properly and drill down into his graphs etc at the end, but from my quick skim h<span style="line-height: 1.4;">e seems to be saying that BL and MMS will have no effect on "speed", and doesn't really qualify it so we're left to assume he means between any driver. </span>

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<span style="line-height: 1.4;">He starts off well describing how having stronger motor force will give stronger acceleration of the driver etc. </span><span style="line-height: 1.4;">However then goes on to say because we're dealing with a "time" that we can just discount all of these things. The time is only part of the "speed".</span>

Lets compare it to his car analogy, and assume we've raced our quarter mile and want to slow down again. Now the drivers reaction time can be thought of as his "time" thing that the article speaks of. When the driver receives the signal to slow down, there will be a little delay in his reaction time and then he starts to push the breaks. and so yes one driver will likely react quicker than the other. But this isn't the only measure of how the car will slow down, that's just a measure of when it STARTS to slow down.

Imagine the driver that was slightly slower to react had a set of breaks on his car that were 3 times as good. Yes he may take a slight few milliseconds to react, but will still come to a stop much quicker overall because of his much better breaks. 

Or if they have the same breaks, but one car is a steel body and one carbon and aluminium and so much lighter. Again, the lighter one will stop quicker, even if the reaction time was slightly longer at the start.

So with out speaker, we can't just discount BL and MMS because it's not just how quickly it starts to change, its how quickly it makes the change overall based on the signal. 

If the driver is in the process of an inward movement and gets a signal to change to outward. Yes the reaction time it takes to realise this will have an effect, of course. And this is what the author of the article seems to argue. But then how quickly it decelerates and then accelerates in the other direction to complete this movement. It may start sightly quicker, but if it's a sloopy loose motor and takes ages to then reverse and go in the other direction, it'll sound slow. And it may start a fraction of a second later, but if it has a super strong motor and then completes the change quickly, it'll still sound fast. 

k

What I found with electric motors was, thinner windings with more of them yes gave ultimate higher speed. Less windings with a thicker wire gave faster acceleration/ deceleration. So response time was better. 

Obviously mag strength, coil size, cone composition, surround and voltage impact here.

The whole thrust of the argument is that an 18 is as linear as a 15 given the same power etc. As we know that the linearity is dependant on many things, one of which is cone size then the argument to me fails regardless of any other test.  In part though I think that the difference in perceived sound between an 18 and 15 is due to the physical cone size and angle of construction and how that relates to the size of the size of the sound pressure waves it is being forced to produce.?