[Roger A. Modjeski]

Did you know that the velocity of a cone driver actually increases as one goes down in frequency? Another way of saying this is that for a constant SPL the cone actually moves faster as one goes down in frequency. Sounds rather counter-intuitive doesn't it.

Let me know in the poll if this is news to you? Use a 4-15 inch driver for your thoughts in an infinite baffle or box, doesn't matter, and driven by a constant voltage oscillator.

You have to vote first to see the results and you can vote for several options.

1. The velocity of the cone doubles every octave we go lower.

2. The displacement (travel) of the cone quadruples every octave we go down.

3. The cone is moving 180 degrees out of phase with the battery polarity test. That is to say when the sine wave goes positive the cone moves in, not out as it did with the battery.

[Duke]

My understanding is that 1 and 2 are correct for constant SPL, assuming no cone breakup, and assuming we're talking about on-axis response instead of power response.  The acceleration on the cone  (change in velocity over time) goes in the other direction (increases with increasing frequency), if I recall correctly - which is why cone breakup sets in as we go up in frequency, rather than down. 

I don't know what battery polarity test you're referring to in 3. 

[konut]

Missing my option. I used to know this, but forgot. 

[Roger A. Modjeski]

My understanding is that 1 and 2 are correct for constant SPL, assuming no cone breakup, and assuming we're talking about on-axis response instead of power response.  The acceleration on the cone  (change in velocity over time) goes in the other direction (increases with increasing frequency), if I recall correctly - which is why cone breakup sets in as we go up in frequency, rather than down. 

I don't know what battery polarity test you're referring to in 3.

The velocity goes down with increasing frequency. Cone break up occurs simply because the cone flexes which has inspired cones that have flat fronts and filled with rigid foam.

The common battery test is to put the plus of a dry cell on the plus of the speaker and the cone should go out. However, above resonance the opposite occurs. Think about what happens with a weight on a spring in slow and fast motion (above and below the natural resonance of the combination.). That's a big hint to what is going on.

[Duke]

"The acceleration on the cone (change in velocity over time) goes in the other direction (increases with increasing frequency)"

This statement of mine is incorrect.  As long as the cone isn't in breakup, above resonance the acceleration is constant.

[Roger A. Modjeski]

"The acceleration on the cone (change in velocity over time) goes in the other direction (increases with increasing frequency)"

This statement of mine is incorrect.  As long as the cone isn't in breakup, above resonance the acceleration is constant.

YES...the acceleration is constant. That's the first step. The next step is what makes it constant and how this relates to the voltage applied to the speaker which is also constant?

[*Scotty*]

If the voltage is constant then the electromotive force available to the motor is also fixed, therefore the acceleration of the cone is also constant with frequency. The cone velocity will vary dependent upon how long the force is applied. Which explains why the velocity of the cone is lower with increasing frequency,the acceleration is applied over a shorter time period.
   From HyperPhysics
 Description of Motion in One Dimension Motion is described in terms of displacement (x), time (t), velocity (v), and acceleration  (a). Velocity is the rate of change of displacement and the  acceleration is the rate of change of velocity. The average velocity and  average acceleration are defined by the relationships:

A bar above any quantity indicates that it is the average value of  that quantity. If the acceleration is constant, then equations 1,2 and 3  represent a complete description of the motion. Equation 4 is obtained  by a  combination of the others. Cut and Pasted from Hyperphysics see link below http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#mot2 The interesting thing I have seen in impulse response graphs of tweeters is overshoot behavior that does not appear when the tweeter is reproducing sine-waves. I think I understand why it goes away when a sine-wave is applied to the tweeter but I would like to see someone elses take on why the over-shoot goes away. Scotty

[Roger A. Modjeski]

If the voltage is constant then the electromotive force available to the motor is also fixed, therefore the acceleration of the cone is also constant with frequency. The cone velocity will vary dependent upon how long the force is applied. Which explains why the velocity of the cone is lower with increasing frequency,the acceleration is applied over a shorter time period.
   From HyperPhysics
 Description of Motion in One Dimension Motion is described in terms of displacement (x), time (t), velocity (v), and acceleration  (a). Velocity is the rate of change of displacement and the  acceleration is the rate of change of velocity. The average velocity and  average acceleration are defined by the relationships:

A bar above any quantity indicates that it is the average value of  that quantity. If the acceleration is constant, then equations 1,2 and 3  represent a complete description of the motion. Equation 4 is obtained  by a  combination of the others. Cut and Pasted from Hyperphysics see link below http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#mot2 The interesting thing I have seen in impulse response graphs of tweeters is overshoot behavior that does not appear when the tweeter is reproducing sine-waves. I think I understand why it goes away when a sine-wave is applied to the tweeter but I would like to see someone elses take on why the over-shoot goes away. Scotty

This is TMI (too much information) and I want others to know it's not this complex. The answer is much simpler.  Fortunately the impedance in the range of interest is constant so a constant voltage produces a constant current. It's current that drives the motor and the cone.