That's true. In several years there is no shift in the resonance frequency.
And why does a lot of people come up with this, but not with the problem of thermal issues in the voice coil. At maximum output the electric damping is halved and the filters in a crossover an octave off (and okay that's the ultimate case). But with an "ideal" amplifier (Zo = 0 ohms), ideal cables (Z = 0 ohms) and an ideal or no passive crossover (Z = 0 ohms) a temperature rise of 16 ºC lowers the damping factor from infinity to 16 (and 32 ºC to 8, 64 ºC to 4, 128 ºC to 2).
Thermal issues destroy the tuning of your enclosure, port and crossover. And the frequency response of your driver.
By using high output impedance amplifiers you kill the resistive electromagnetic damping.
"The cone flap in the wind" is nonsense, as I stated there are other and better ways of damping.
And about electromagnetic damping...
Electromagnetic damping destroys the transients
The claim is that electromagnetic damping stops the cone faster, brings it faster to the rest position.
That’s true, but is that relevant? It’s not the position that gives the output.
The acceleration of the cone determines the output (not the speed or position)
- So, bringing the cone to a stop is counterproductive
- To stop the cone a force is needed
- When there is an excursion, there is a force applied in the oppositie direction. The force gives an acceleration and thus an (SPL) output
- This gives an output when the signal stops
Electromagnetic damping needs voltage-drive
For electromagnetic damping you need voltage-drive, a low output impedance.
- This introduces a phase shift by the inductance
- The current rises slower than the voltage (the current creates the output)
- This destroys the attack of a signal
Electromagnetic damping works always
Electromagnetic damping is not a brake, it works always (like driving with your E-brake -aka parking brake of handbrake- on):
- When you want to stop
- But also when you want to accelerate
- This destroys the attack of a signal
- This also dampens the output (at resonance) and that’s why you put drivers in a box to amplify the resonance
The effect on the transient with voltage-drive
Suppose a burst of three cycles at resonance as input
- It takes a full cycle to reach the intended amplitude
- After the three cycles you get an extra cycle of which the first half reaches the maximum amplitude
- The first cycle is destroyed
- The second and third cycle are as intended
- And you get an extra cycle of which the first half reaches maximum amplitude
Suppose a burst of half a cycle at resonance as input
- The first (intended) half cycle doesn’t reach the intended amplitude
- The second (not intended) half cycle does reach the intended amplitude
- And you get another half cycle of lower amplitude
With current-drive
- The output reaches faster it’s maximum output (second half)
- The first half gives more output than with voltage-drive
- The output is faster quiet (after a fraction of a cycle it dies out)
- It takes longer to come to the middle position, but who cares? (the non-
Analogy with a car
- Using the throttle gives a sensation
- Using the brakes gives a sensation
- Just letting it roll doesn’t give much excitement