Woofer "Speed" Question/Explanation

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which makes the case that inductance, as opposed to BL/mms is what determines the woofer's perceived speed. I had a question, and was wondering if anyone could clarify this for me.

They make the case that BLi = ma, and since BL and m are time invarient, they have no effect. To go with the car analogy they use, if BL is the horsepower of the engine and m is the weight of the car...(call i the reaction to the race start light) A car with a lot of horsepower and small mass is still going to accelerate faster (and get a faster 1/4 time) than a car with less horsepower and more mass. The start reaction will certainly affect it as well...but it seems like the force/mass factors are completely discounted, while I would expect them to have some effect. Using an extreme example...if you used a small magnet to power a manhole cover sized/weighted cone...you're telling me this would have the same transient response as a TC-2000 as long as the inductance in the coil is the same? I'm far from an expert, but something just seemed off about this to me. I could use some clarification from someone who knows more about it than I do

Now, taking the car example further...I would think that the shorter the distance you're racing, the more the "start" will matter. In the same way...I can see that when excursion is low...the inductance would seem to matter more, but once you start getting into higher excursions, it would seem that BL and mms would start to matter a lot more.

Help explain this to me, please!!! Much appreciated.
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I'm a firm adherent on the lower Le=faster view, however I have a couple of examples of low Le drivers that also have high Mms, and they both have poor transient response (even compared to drivers with higher Le, but lower Mms), one has so much Mms that it begins to roll off at 60hz...

So just like the rest of a drivers parameters you can't just look at a single one and make a judgement on performance.

If Mms had no effect on transient response then tweeters wouldn't need to have the very light cones/domes that they have.
Ok, good. So I'm not crazy Thanks!
Help explain this to me, please!!!

Send an email to the author of the article vs. trying to get people to take your side hehe
Quote:
 Originally Posted by IDW They make the case that BLi = ma, and since BL and m are time invarient, they have no effect. To go with the car analogy they use, if BL is the horsepower of the engine and m is the weight of the car...(call i the reaction to the race start light) A car with a lot of horsepower and small mass is still going to accelerate faster (and get a faster 1/4 time) than a car with less horsepower and more mass. The start reaction will certainly affect it as well...but it seems like the force/mass factors are completely discounted, while I would expect them to have some effect. Using an extreme example...if you used a small magnet to power a manhole cover sized/weighted cone...you're telling me this would have the same transient response as a TC-2000 as long as the inductance in the coil is the same? I'm far from an expert, but something just seemed off about this to me. I could use some clarification from someone who knows more about it than I do Now, taking the car example further...I would think that the shorter the distance you're racing, the more the "start" will matter. In the same way...I can see that when excursion is low...the inductance would seem to matter more, but once you start getting into higher excursions, it would seem that BL and mms would start to matter a lot more. Help explain this to me, please!!! Much appreciated.

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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Quote:
 Originally Posted by IDW So, I've read http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf which makes the case that inductance, as opposed to BL/mms is what determines the woofer's perceived speed. I had a question, and was wondering if anyone could clarify this for me. They make the case that BLi = ma, and since BL and m are time invarient, they have no effect. To go with the car analogy they use, if BL is the horsepower of the engine and m is the weight of the car...(call i the reaction to the race start light) A car with a lot of horsepower and small mass is still going to accelerate faster (and get a faster 1/4 time) than a car with less horsepower and more mass. The start reaction will certainly affect it as well...but it seems like the force/mass factors are completely discounted, while I would expect them to have some effect. Using an extreme example...if you used a small magnet to power a manhole cover sized/weighted cone...you're telling me this would have the same transient response as a TC-2000 as long as the inductance in the coil is the same? I'm far from an expert, but something just seemed off about this to me. I could use some clarification from someone who knows more about it than I do Now, taking the car example further...I would think that the shorter the distance you're racing, the more the "start" will matter. In the same way...I can see that when excursion is low...the inductance would seem to matter more, but once you start getting into higher excursions, it would seem that BL and mms would start to matter a lot more. Help explain this to me, please!!! Much appreciated.
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 ...
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BL=horsepower

M= mass

a= acceleration

i= final-drive gear ratio
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.
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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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 Now, taking the car example further...I would think that the shorter the distance you're racing, the more the "start" will matter. In the same way...I can see that when excursion is low...the inductance would seem to matter more, but once you start getting into higher excursions, it would seem that BL and mms would start to matter a lot more.
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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Cone mass will effect efficiency and Fs, not percieved speed. Even the magnet structure won't necessarily impact on "speed". Only on efficiency.

You must remember that SPL is acceleration. The more SPL generated, the more acceleration you have. Bigger cones can move more air at any given frequency compared to a smaller cone and this necessarily means that it won't be required to move as far as a smaller cone to generate any given amount of sound pressure.

Woofer speed is, as discussed in Dan's paper, a complete and utter misnomer.

--Sincerely,
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.

Even if a good speaker had a smallish magnet it doesn't necessarily mean that it will control poorly or be "slow". BL is important but it isn't the deciding factor.

--Sincerely,
Quote:
 Originally Posted by goneten Cone mass will effect efficiency and Fs, not percieved speed. Even the magnet structure won't necessarily impact on "speed". Only on efficiency. You must remember that SPL is acceleration. The more SPL generated, the more acceleration you have. Bigger cones can move more air at any given frequency compared to a smaller cone and this necessarily means that it won't be required to move as far as a smaller cone to generate any given amount of sound pressure. Woofer speed is, as discussed in Dan's paper, a complete and utter misnomer. --Sincerely,

Beautiful. This makes a lot of sense to me! Thank you!!!
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You are most welcome.

--Sincerely,
soho, thanks a lot for your responses too I appreciate the efforts.

Goneten's description of acceleration being SPL is what really turned the corner for me. I saw the graphs...but just wanted to understand why that was happening.

In your/our analogy with the car...you're saying that mass matters...but not as much as the other factors. That's still an answer I'd accept....but didn't seem to be the answer being given. The reason I think that is, is that we don't really care about the acceleration for this, like goneten described...we care about the ability to change acceleration. I don't know that there's a real way to make that analogy work with cars...though I'd be interested if you wanted to try!

Thanks to all of you for trying...and for goneten for succeeding! See, I really just wanted to understand
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,
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Acceleration is not SPL. SPL is produced by the amount of air moved. It is a measurement of pressure not time. It takes a larger stroke to produce more SPL, but this is not what the papers were about.

This was about actual acceleration, not perceived speed. This paper and goneten's cone size vs SPL idea, are two separate concepts on different things. One has nothing to do with the other. They can both happily live together, if you drop the SPL is acceleration thing.
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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 Originally Posted by Volenti I'm a firm adherent on the lower Le=faster view, however I have a couple of examples of low Le drivers that also have high Mms, and they both have poor transient response (even compared to drivers with higher Le, but lower Mms), one has so much Mms that it begins to roll off at 60hz...
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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 So just like the rest of a drivers parameters you can't just look at a single one and make a judgement on performance. If Mms had no effect on transient response then tweeters wouldn't need to have the very light cones/domes that they have.
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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Quote:
 Originally Posted by soho54 Acceleration is not SPL. SPL is produced by the amount of air moved. It is a measurement of pressure not time. It takes a larger stroke to produce more SPL, but this is not what the papers were about. This was about actual acceleration, not perceived speed. This paper and goneten's cone size vs SPL idea, are two separate concepts on different things. One has nothing to do with the other. They can both happily live together, if you drop the SPL is acceleration thing.
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."
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Nope. Acceleration is the rate of change of speed. An increase or decrease in acceleration corresponds to a change in sound pressure. If you double SPL, you will double acceleration. If you halve the SPL, you will likewise half the acceleration.

I am amazed that this is even being disputed.

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 This was about actual acceleration, not perceived speed.
Um, I was talking about actual acceleration.

--Sincerely,
Quote:
 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.
Do I ??? I don't recall. Nice to see you again Mark. It's been a very, very long time.

--Sincerely,
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