I'll also look around for response graphs. The on paper specs put +/- 3db at 30-105hz, fwiw.
Cones being fast/slow is a myth and needs to be sorted IMO.The motor in any modern driver is more than capable of keeping control over the cone and accelerating it as fast as needed. Here are two drivers that use pretty much the same motor, one 18" and one 21": http://bcspeakers.com/products/lf-driver/21-0/4/21sw115?impedence=4http://bcspeakers.com/products/lf-driver/18-0/4/18sw115-4?impedence=4The difference we are talking about is more like this:One has a moving mass of 304g, and the other has a moving mass of 335g. That's about 10% difference.Subwoofers are like having a car being asked to accelerate to 30mph in about 30 seconds, and then smoothly decelerate. That car will not care if it has a couple of passengers that add 10% to the total weight. It's still well within the capability of the engine.Low frequencies do not require a fast-moving cone. If the cone is moving quickly, it's producing treble and your crossover is set incorrectly.High-frequency drivers need to be small and light. Here's an example.A 21" driver moving 10mm one-way at 50Hz has a peak velocity (as it passes through the zero position) of just over 3m/s. The acceleration is around 1000m/s/s, so the voicecoil is exerting just over 300N of force (about 30kg, 66lb). That will result in an SPL of a smidge over 121dB at 1m, groundplane. That's around 1KW power input.That same cone producing 121dB at 5kHz would be moving 0.01mm, with peak accelerations of 15000m/s/s, requiring 4500N of force (992lb). To produce that force, you'll need to put around 60KW in there and hope it survives.A 4.5" driver producing 121dB at 5kHz needs to move 0.07mm one-way, requiring a larger acceleration of 77,000m/s/s. The moving mass is about 3g, though, so you only need 231N of force to get it there. That particular driver would need around 5KW input power to manage that, which it won't survive. Dropping the moving mass further (thin titanium diaphragms) and bolting a horn on the front would improve efficiency and reduce the power requirements, though.Edit - couple of people have posted while I typed that.Free-air resonance is not more important than the size of the driver. Resonance (Fs), among a bunch of other parameters, will help determine the shape of the response of the driver in a given cabinet. The size and linear excursion, and thermal power handling of the driver will tell you how loud it can go.Chris
Chris that's not what I said, and by omitting the first three words of my sentence, you are taking my statement out of context. I said (and did not edit) "For sub frequencies..." meaning relative to, and did not say that it is just "more important".
Sorry John, looks like I misinterpretted you. Thanks for clearing that up.I find the amount of misinformation around with speakers in general quite frustrating, which is probably why I jumped on your post.Chris
One is Slew rate (how fast an amp reaches full power, and usually 100V/microsecond would be typical of higher end amps) The other is Damping factor, (the ability to stop the speaker cone, or the "breaks" and "torque" in your car analogy, before you put it in reverse and accelerate negatively, a typical example being 800 to 1 at 400Hz).
What I find funny is that one line of amps that has been considered to be "great" has one of the worse slew rates.The old Crown MA series had a "terrible" slew rate, as compared to others.Damping factor in amps is also highly over rated.The "system" has a MUCH larger effect than the amp itself.Years ago (late 90s) I did some testing (just listening-no measurements) and we had a decent variety of amps by different manufacturers.The amp that had the highest damping factor (by a good bit) had the "loosest" sound.The one that had the lowest damping factor stood right up with the highly regarded Crown MA2400. This amp was also the next to the cheapest one in the test.Historically, the amps with the best damping factor had the most "controlled" sound-so that was "assumed" to be, because of the damping factor.The speaker wire and connectors is much bigger factor.Often the "simple numbers" will result inaccurate assumptions.
Ivan the Crown MA 2400 had a slew rate of 75V/microsecond,
However, the higher damping factor made the bass frequencies sound better.
But as I said in my test, amps that have a much lower damping factor can sound as "tight" and amps with a much higher damping factor can sound looser.Damping factor is greatly over rated-at least in terms of amplifiers.It is basically a measurement of the output impedance of the amp relative to the load impedance.The cable makes a much larger difference in the overall system than the amp itself.
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