"B x l," also known as "Force Factor," is one of the canonical Thiele-Small Parameters.
As explained in the linked-to paper, Jim Tuomy and I believed that a new Parameter, complementary to and analogous to Force Factor, would be helpful. We call that new Parameter "Load Factor."
Then, when one expresses the relationship between Force Factor and Load Factor, we call that result the Agility Factor.
Load Factor and Agility Factor are “Quick and Dirty” methods to quantify what an experienced designer might in any case be able to intuit from scanning the data sheets on two different drivers.
No more; but certainly nothing less.
A comparison to the well-accepted parameter Force Factor (B x l) illuminates. Force Factor has no need of complexity. Force Factor has no need of calculus, the symbol Pi, or constants. It would be very difficult to have fewer “moving parts” than does Force Factor.
Force Factor relates a physical characteristic (voice-coil length) to an electromagnetic phenomenon (flux density) by the simple arithmetic operation of multiplication.
Load Factor is analogous and complementary to Force Factor. Load Factor is merely an expression of density rather than mass.
In much the same way as Force Factor is derived, Agility Factor relates a physical characteristic (cone density) to an electromagnetic phenomenon (Force Factor). Except, in this case, the simple arithmetic operation is division.
Looking at the Table of drivers under consideration, it is almost impossible to escape the conclusion that the woofer-mid with an Agility Factor of 71.96 is more Agile (or, more responsive; or, just plain better at starting and stopping) than the woofer-mid with an Agility Factor of 26.78.
We believe that the burden is on the naysayers to prove that the above conclusion is illusory.
https://positive-feedback.com/audio...proposed-additions-to-the-thiele-small-canon/
john
As explained in the linked-to paper, Jim Tuomy and I believed that a new Parameter, complementary to and analogous to Force Factor, would be helpful. We call that new Parameter "Load Factor."
Then, when one expresses the relationship between Force Factor and Load Factor, we call that result the Agility Factor.
Load Factor and Agility Factor are “Quick and Dirty” methods to quantify what an experienced designer might in any case be able to intuit from scanning the data sheets on two different drivers.
No more; but certainly nothing less.
A comparison to the well-accepted parameter Force Factor (B x l) illuminates. Force Factor has no need of complexity. Force Factor has no need of calculus, the symbol Pi, or constants. It would be very difficult to have fewer “moving parts” than does Force Factor.
Force Factor relates a physical characteristic (voice-coil length) to an electromagnetic phenomenon (flux density) by the simple arithmetic operation of multiplication.
Load Factor is analogous and complementary to Force Factor. Load Factor is merely an expression of density rather than mass.
In much the same way as Force Factor is derived, Agility Factor relates a physical characteristic (cone density) to an electromagnetic phenomenon (Force Factor). Except, in this case, the simple arithmetic operation is division.
Looking at the Table of drivers under consideration, it is almost impossible to escape the conclusion that the woofer-mid with an Agility Factor of 71.96 is more Agile (or, more responsive; or, just plain better at starting and stopping) than the woofer-mid with an Agility Factor of 26.78.
We believe that the burden is on the naysayers to prove that the above conclusion is illusory.
https://positive-feedback.com/audio...proposed-additions-to-the-thiele-small-canon/
john
From my background we call it 'stiction' 😉 Regardless, it's 'part n' parcel' of my favorite way to refer to it as Pace, Rhythm & Timing (PRaT) that I've historically used for choosing drivers, so works for me based on my 515B's ~242 AF/'heart attack fast'/'jump' factor. 🙂
Hi all,
I'm trying to mentally relate this to a project. What does this agility mean in more common terms? I mean stuff like does it make frequency response extend higher? or more sensitivity? or more minimum phase, no delay? How to connect this idea of agility factor to system design, in which point of a system design process one would consider agility factor?
edit.
Tried to calculate AF for 15" driver I have https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=151060150
It seems to have high Agility Factor in comparison to 4-6" drivers in behind opening post link, but of course its not interchangeable for smaller driver.
Perhaps its useful metric to compare between 4-6" drivers like in the article as they could be somewhat interchangeable for mid woofer? 15" mid makes whole another system.
I'm trying to mentally relate this to a project. What does this agility mean in more common terms? I mean stuff like does it make frequency response extend higher? or more sensitivity? or more minimum phase, no delay? How to connect this idea of agility factor to system design, in which point of a system design process one would consider agility factor?
edit.
Tried to calculate AF for 15" driver I have https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=151060150
It seems to have high Agility Factor in comparison to 4-6" drivers in behind opening post link, but of course its not interchangeable for smaller driver.
Perhaps its useful metric to compare between 4-6" drivers like in the article as they could be somewhat interchangeable for mid woofer? 15" mid makes whole another system.
Last edited:
I have another 15" driver as well, so can compare these with the parameter with ease though. Is agility factor still useful metric to compare woofers for 3 way system?
Trying to get understanding on what it is all about. Thanks!
Trying to get understanding on what it is all about. Thanks!
BL is not constant with excursion. T/S parameters under non-1 Watt drive conditions may change (and do sometimes dramatically).
Question for Johnmarianmarks: is there any conclusion to be drawn from the differences in AF?
In your paper you compare the Eton and the Purify. Now what is your final take-out of the calculated difference in AF?
In your paper you compare the Eton and the Purify. Now what is your final take-out of the calculated difference in AF?
Ah yes! Also effective Sd seems to vary some https://purifi-audio.com/2021/10/14/some-speaker-problems-that-needed-solving/ as well as Mms with it. Seems like it could be about as dramatic as Bl change at least with extreme excursion.
That + Vas has been my main 'markers', but in comparing my horn driver Altec's 0.2/566 L to the more popular/common BR driver 416's 0.36/445 L with a slightly higher ~249 AF with the only other major difference being it's 10 Hz higher Fs, so now wondering if I've been fooling myself for all these decades because in numerous comparisons I've always clearly preferred the 515B's transient attacks, etc..
Wow, Purifi article Sd variance visualized in a GIF with ideal driver on ideal 200x350mm baffle. 5" driver whose surround stiffens loosens on the cycle and makes Sd change from specsheet 80cm2 to 55cm2 to 105cm2.
Hmm, all this just shows that bigger drivers should be used for better sound. Less excursion is the main reason I see, and also related to the topic they seem to have greater Agility Factor, if its indicating "betternes". GM 515B woofer with ~240AF is 3 times better than best small driver in the article.
Hmm, all this just shows that bigger drivers should be used for better sound. Less excursion is the main reason I see, and also related to the topic they seem to have greater Agility Factor, if its indicating "betternes". GM 515B woofer with ~240AF is 3 times better than best small driver in the article.
I found the "Agility Factor" very questionable, to say the least.
On the contrary, it is very possible to escape that conclusion, because you didn't provide any evidence of that - no measurements, nor controled blind subjective tests!
You get it backward - the burden is on you, that is how science works.
You made a statement (it is not even a hypothesis!), so you have to prove it is valid!
We can't expect too much science and/or engineering from a website more interested in creative writing -
"Positive Feedback is a community composed of writers and creative persons from around the world."
"Positive Feedback is a community composed of writers and creative persons from around the world."
Well, modern science is based on falsification of hypotheses. But only hypotheses that are firmly built on the framework we call science. Not just some statement like: 'there is ether because there must be ether'.
Although I should not draw any conclusions yet: this looks like another attempt to reintroduce the "woofer speed" concept by rehash of existing parameters. That topic has been flogged to death, but some sinners never give up.
I.m.o. the acid test is feed two woofers with different AF's with a narrow bandwith limited signal, say 60 to 150 Hz with 4th order slopes and see if the output waveform contains any fundamental differences. One crucial condition of course is the bandwith limited signal must fall within the passband of the woofer, which might be no so easy to realize with smaller woofers.
I.m.o. the acid test is feed two woofers with different AF's with a narrow bandwith limited signal, say 60 to 150 Hz with 4th order slopes and see if the output waveform contains any fundamental differences. One crucial condition of course is the bandwith limited signal must fall within the passband of the woofer, which might be no so easy to realize with smaller woofers.
I am going to propose...
Bl/(Qts*VAS) = just another Q factor
I just want to become famous, duh.
Bl/(Qts*VAS) = just another Q factor
I just want to become famous, duh.
The big question of course is: 'why?' Why would anyone try to add something to the TSP? Most of us here comprehend the limited use of TSP and more general of simple (1st order!!) approximations of physical phenomena. More comprehensive models exist since some time (as a lot of us know too).
I just remembered a quote from a friend/technician: π = 3 😉
I just remembered a quote from a friend/technician: π = 3 😉