Posted October 12, 200717 yr I'd just like to bring up a certain point to the every raging debate whether cone size plays a role in a sub's "quickness."At a certain frequency and excursion, any sub's cone will be traveling the same speed. No argument there.But what about the transitions from rest to that frequency and from one frequency to another? I'm looking at the Force = Mass * Acceleration equation here. If both a large sub and a small sub have the same motor structure, I believe it is safe to assume the force is constant. Therefore, an increase in mass has to lead to a decrease in acceleration. Are these differences in acceleration large enough for us to hear? Am I missing some other part of this? Please discuss.
October 12, 200717 yr Been posted plenty before, but might as well here:http://www.adireaudio.com/Files/WooferSpeed.pdf
October 12, 200717 yr Author Been posted plenty before, but might as well here:http://www.adireaudio.com/Files/WooferSpeed.pdfThat's a good write up. The graphs are hard to argue, but I do have one issue with it. He assumes a constant proportion between i and a. If mass changes, the proportionality constant will also change.
October 12, 200717 yr This is something I'll try to expand on in the morning, but if you have a lowpass filter in place with an f3 lower than the f3 created by the inductance of the coil, then the dominant factor is the enclosure, which is really just a highpass filter. Interesting additional note here: the mass of a speaker is also, in effect, a highpass filter. So yes, it is very relevant because frequency response and transient response are utterly and completely related.In short, Dan describes the effects that inductance has on a speaker quite well, but it is a tad misleading.
October 14, 200717 yr The enclosure effectively makes the mass of the driver a time dependent variable. The effective mass of the driver is proportional to the cone distance from rest (for a sealed alignment; it gets much more complex for a ported setup) and inversely proportional to the size of the enclosure. Now the next thing to consider is that the increased mass moving away from the rest position acts as a reduced mass going back toward center. Transient speed is the rate at which the cone can "turn the corner" and in a sealed enclosure the smaller the enclosure the more it assists the transition.If you want to get into straight Newtonian physics and argue about the dynamics of a sub based on mass, F=ma is not the only equation to worry about. Don't forget inertia. The lighter driver accelerates quicker with the same amount of force, but inertia must be overcome to reverse direction. Inertia is based on the square of velocity. If one driver has half the mass of another and they have the same motor (BL) the lighter driver will get moving 2x as fast per F=ma but have 2x the inertia to overcome to reverse direction. The 2x acceleration cancels out the extra inertia. Fixed mass becomes a non factor in woofer dynamics when it comes to transient response. Now you're left with the enclosure determining pretty much everything as DD was getting at.
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