Woofer "Speed" Question/Explanation

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The problem is with how you defined the variables in your analogy. For a loudspeaker the force is BLi, for a car it is horsepower. Therefore BL is not analogous to horsepower, BLi is analogous to HP.

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all i can say is that the motor on the man hole cover would have to be substantially larger...higher end drivers have the requisite amount of motor force needed for their respective applications...and this is moot insofar as the alignment is concerned...drivers don't move around in a vacuum, while one should appreciate the driver, we must'nt forget that it is part of an overall system...it won't make bass without an enclosure...and then you put it in a less than perfect room ...

I'm not trying to get anyone on my side....I'm trying to have someone explain to me why I didn't get it I have no vested interest in things being either way...I just want to know for educational purposes.


So, my adaptation of the car analogy was a bad one I'm pretty hit or miss with my analogies... I'll try one more time though... whatever we define horsepower to be...we can all agree that MMS is equivalent to vehicle mass, right? If mass isn't an issue... then wouldn't all cars with the same engine and gear ratio, etc. accelerate the same? 1900 lbs or 4000lbs?


However, if the argument is being made that BL and MMS don't matter in terms of transient response...then any size motor driving any size cone should have the same transient response as long as Le is the same. No?


I should probably e-mail the author of the article...and I may...but there's no reason not to ask other interested parties for their input, opinion, etc. right?


I'm really not trying to prove this article wrong. I just don't understand it. I'm always looking for smarter people to educate me.

I'm trying to help.


I don't know how big of a gear head you are, so I'm going with a way "simplified" analogy here. Also the car analogy really doesn't work very well, so you have to group some things together for (i), but I think I can make it work.


BL= the motor strength of the car, max horsepower and torque only, throw away RPM.

M= the total weight of the vehicle

a= the 1/4 mile time. You will have to assume a perfect run every time.

i=would be anything that would affect power transfer to the ground, use gear ratio here In real life the engines power band (which is affected by a billion things) plays a critical role with gearing, so just assume that it's perfect for the gears selected. Also assume a perfect tire combo, and launch.


Race 1- mass is an issue when racing a stock 57 chevy with a trunk full of cement(high M), and a rail car (low M)with the same engine(BL) and gearing(i). Everyone sees that, no contest. The 57's extreme mass will slow it down.

Race 2- how about two 67 camero's only one has four people in it, and the gas topped off. Same BL, one has more M but not to much for the engine. This time its a lot closer, with the heavier car only a few tics behind.

Race 3- take two more which have the same BL and M and change the rear ends(i). One has 3.15(higher i) and the other has 4.10(lower i). This is an easy one again, the lower gear (the one with the higher number) pulls harder longer and pulls into the lead around the 1/8th and never lets up.

Race 4- now lets go back to Race 2 and give the good'ole boys a set of 5.10(lower i) and the solo the 3.15's(higher i). (remember to magically change the power band as well)This time solo makes it out of the hole faster but around mid track it's neck and neck, with the good'ole boys finishing a car length ahead of solo.


Good speakers generally fall into a Race 2 or 4 scenario. A good speaker with a heavy cone will have a large enough magnet to control it fairly well. If it doesn't it's a POS. A light cone with a crazy strong magnet will be induction limited. Still the more B in the BL the better just like a car, until your wallet cries anyway.


The best way to look at it is that if the BL and M are pretty close (i) will always be the deciding factor. If the mass is way off, then why are you considering it? It would be like your manhole cover and tweeter motor, dumb idea. It would have to be way off to even matter though. Looking at their example they added more than double the weight, and the change was very slight. Now when they changed the inductance there was a noticeable(on the graph) change.

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The start matters, no matter the distance. For every wave there is a race to push the driver one way, an another to push it back the other. A rise and fall, positive and negative. Once the wave crests the polarity changes and the cone is pulled the other way by the motor to complete the wave. It doesn't just push it out and let it snap back home, it controls it both ways. Another thing is that BL isn't constant with excursion, but that is another can of worms all together. Higher excursion comes with lower frequency waves, and higher SPLs. If inductance didn't matter at high excursion levels, all speakers would sound progressively different as the volume goes up.


This help?


EDIT: I'm assuming you understand the impulse graph. This is the non-techie version. Looking at the graph think of the horizontal 0 line as the cones home position. The graph shows how far it moved forward and backward on the vertical axis. The other shows time. You want the highest first peak in the shortest amount of time possible, and then it should stabilize after the second peak into a flat line ASAP. Notice the green one never quite got the tone completely out before heading back the other way. Lazy good for nothing.

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Beautiful. This makes a lot of sense to me! Thank you!!!

This whole issue is ridiculous because a bigger cone won't be required to move as "quick" as a smaller cone. A smaller cone can't move quicker than a bigger cone unless the smaller cone reproduces frequencies higher up within it's passband.


Quicker or slower, this is frequency (and SPL) related. Remember one thing. When we talk about woofer speed, we are really talking about bandwidth limited signals. A bandwidth limited signal is just that, bandwidth limited.


A cone only needs to move as fast as it has to to reproduce any given frequency within it's passband. A bigger cone doesn't need to move as quick because cone travel will necessarily be reduced because the cone has a larger surface area which means it will have a better impedence match to air.


And if anything, small cones need to move really fast. Not big cones. A small cone will be required to move quickly to reproduce a low tone because it will need to move further; to move more air. And the further it moves, the longer it takes to produce the frequency.


A bigger cone doesn't have to move as far and, in fact, can finish it's cycles in a shorter period of time (unless the smaller cone had the same linear excursion, in which case both drivers would reproduce any given frequency in the same given amount of time), which, technically speaking, means that the "fastest" cone is the cone moving the lowest, the loudest.


--Sincerely,

Obviously gonten recalls some of the posts by both myself and Dan Wiggins from long ago when we went round and round with this one here and elsewhere. He essentially covered the important issues.

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I can almost guarantee that the Le figures you were looking at were only applicable at some higher frequency and further investigation would show that the effective Le at lower frequencies was quite high on the driver that began to roll off at 60Hz. The now discontinued Avalanche drivers had such characteristics.

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Incorrect. Tweeters need very low mass for reasons of efficiency, not transient response. The (typically) required small cone/dome area for a tweeter makes it less efficient as a radiator so you need a good bit of force from the motor to achieve good efficiency. A stronger motor tends to have more inductance, which limits high frequency reproduction. A stronger motor also tends to have more wire, which has mass, which simultaneously counters your added motor strength. It really is a matter of balancing all of the factors, not any one specific parameter or value being "best."

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Not really.


To make gonten's statement correct, simply preceed it with:


For a given cone/radiator size... the magnitude of acceleration is SPL.


Anything that happens quickly, must include high frequency. Unfortunately that doesn't cover all of the factors that come into play with the different personal definitions listeners equate to subjective "speed."