I do think it can be helpful.
But why, for instance, not calculate the mass breakpoint like we do for compression drivers:
Appendix II: Calculation of
High-frequency Break-point:
The mass break-point frequency, fHM> >s given by the
equation:
f H M = (BI)²
/7rR E
M M S
We can calculate the value of f H M for the JBL 2445 driver
by taking the pertinent quantities and entering them into
the above equation:
Bl =18Tesla
R = 8.5 ohms
M = .00346 kilograms
fHM = 18² / Pi . (8.5) (.00346) = 3507 Hz
I mean, it actually calculates the maximum speed the driver will be driven electromechanically.
But why, for instance, not calculate the mass breakpoint like we do for compression drivers:
Appendix II: Calculation of
High-frequency Break-point:
The mass break-point frequency, fHM> >s given by the
equation:
f H M = (BI)²
/7rR E
M M S
We can calculate the value of f H M for the JBL 2445 driver
by taking the pertinent quantities and entering them into
the above equation:
Bl =18Tesla
R = 8.5 ohms
M = .00346 kilograms
fHM = 18² / Pi . (8.5) (.00346) = 3507 Hz
I mean, it actually calculates the maximum speed the driver will be driven electromechanically.
A 12" driver and a 5" driver can be manufactured to have the same Thiele-Small parameters. Will they behave identically? I don't think so. There must be some other property to describe the difference. Cone stiffness, field linearity, whatever.
In reality it is virtually impossible to manufacture a 12" and 5" driver with the same Vas. But in case you would manage, ceteris paribus, then small signal LF behaviour would be identical. T/S only deals with small signal LF behavour, not mid or hi. In my book cone stiffness by and large has impact only in mid and hi performance.
LF and AF are "Quick and Dirty" rules of thumb designed for the scenario where there is a spreadsheet of 40 or 50 possible drivers for a particular implementation, and you want to winnow that down to a manageable number like 4 or 5.
And once you get your short list down to 4 or 5, you look at all the other parameters (such as Sensitivity, Xmax, and Fs, for starters) and decide which makes and models to buy samples of. And then you listen and measure, or measure and listen.
My take-away from that table is that "the price to be paid" for the Purifi's remarkable Xmax and Fs is that as a system, it will not be as agile in starting and stopping as is the Accuton (or the Eton)--but it is all a matter of balancing tradeoffs, and none of "us" have suggested that these are the only metrics you need.
A few general observations:
Jim Tuomy has patents in electroacoustics and DSP; he spent 15 years as a top scientist at Bose. He was awarded Bose's "President's Medal." John Atkinson was kind enough to read an earlier draft. I am not aware of anyone who has published as many measurements of complete loudspeaker systems as John Atkinson (raw drivers are a different matter, and that honor most likely goes to Vance Dickason of "It's a Cookbook!!!!" fame). For his loudspeaker-measurement work, John Atkinson was awarded the AES' highest honor, the Richard Heyser Medal. John Atkinson did not react to our paper with "Howls of Derisive Laughter, Bruce!"
BTW, the reason our paper was published in a high-end audio magazine, and not somewhere you might think it more likely to be published, is that other outlets apparently were leery of naming names of the various drivers in Table 1.
My "day job" is as a classical music record producer--loudspeaker design is a lifelong hobby that morphed into a paying moonlighting job. I don't have the time, money, or the equipment (poor poor pitiful me, Dear Lord, Don't buy me a Mercedes Benz, buy me a Klippel NFS--with due respect to Janice Joplin) to make measurements of all those drivers.
Jim and I wanted to get our ideas out to where they might do some good, and give people one more tool to help select drivers.
I know that AF has helped me in my own design work. The Eton Symphony II 5-inch woofer in the build pictured below was chosen in part on the basis of AF.
Our hope indeed was that someone, perhaps a manufacturer with an active research program, would pick up the ball and run with it.
Thanks again to Jim Tuomy for being a great friend and colleague, and to John Atkinson for being a great friend.
john marks
And once you get your short list down to 4 or 5, you look at all the other parameters (such as Sensitivity, Xmax, and Fs, for starters) and decide which makes and models to buy samples of. And then you listen and measure, or measure and listen.
My take-away from that table is that "the price to be paid" for the Purifi's remarkable Xmax and Fs is that as a system, it will not be as agile in starting and stopping as is the Accuton (or the Eton)--but it is all a matter of balancing tradeoffs, and none of "us" have suggested that these are the only metrics you need.
A few general observations:
Jim Tuomy has patents in electroacoustics and DSP; he spent 15 years as a top scientist at Bose. He was awarded Bose's "President's Medal." John Atkinson was kind enough to read an earlier draft. I am not aware of anyone who has published as many measurements of complete loudspeaker systems as John Atkinson (raw drivers are a different matter, and that honor most likely goes to Vance Dickason of "It's a Cookbook!!!!" fame). For his loudspeaker-measurement work, John Atkinson was awarded the AES' highest honor, the Richard Heyser Medal. John Atkinson did not react to our paper with "Howls of Derisive Laughter, Bruce!"
BTW, the reason our paper was published in a high-end audio magazine, and not somewhere you might think it more likely to be published, is that other outlets apparently were leery of naming names of the various drivers in Table 1.
My "day job" is as a classical music record producer--loudspeaker design is a lifelong hobby that morphed into a paying moonlighting job. I don't have the time, money, or the equipment (poor poor pitiful me, Dear Lord, Don't buy me a Mercedes Benz, buy me a Klippel NFS--with due respect to Janice Joplin) to make measurements of all those drivers.
Jim and I wanted to get our ideas out to where they might do some good, and give people one more tool to help select drivers.
I know that AF has helped me in my own design work. The Eton Symphony II 5-inch woofer in the build pictured below was chosen in part on the basis of AF.
Our hope indeed was that someone, perhaps a manufacturer with an active research program, would pick up the ball and run with it.
Thanks again to Jim Tuomy for being a great friend and colleague, and to John Atkinson for being a great friend.
john marks
Attachments
Thank you for your thoughtful reply. Please see my general comments below.
As far as maximum speed goes, when you mentioned that, I immediately thought of "piston speed" in an automobile engine. But then again, I once worked in a shop that built (very expensive) SCCA tube-frame racing cars.
all my best,
john
Words, words,words: measurements or it did not happen. Tell you once thing : Lars Risbo wipes the floor with your honored friends.
Woofer speed doesn't exist? As in: one woofer can not be made to be faster than the other?
Can you explain the "Woofer speed.... OMG" from a technical perspective?
Btw last project I did also had 12" woofers selected specifically to generate the least cabinet movement. I picked the 12FH520. Less cone weight means less force on the basket, hence less on the cabinet.
Of course I just picked 12" woofers and selected the least heavy cones, but LF could have made this selection easier across various woofer sizes.
Sd is part of the TS parameters, so it should just pop out and tell your talent it matter even if the rest is similar, right?
Seems a compromise. Using 2 woofers push-push actively eliminates most of the energy that could go into the cabinet to move it.
dave
No: one woofer cannot be made faster than another within identical bandwidth and SPL
Incredible that such misconceptions still pop up with some regularity.
I need more popcorn.
Jan
Nice. In fact, the woofers were part of an MEH and more at around 100°, so the compromise was made to minimize further by means of moving mass;-)
The formal title (or subtitle) of this section is:
SPICE, PCB CAD, speaker design and measurement software, calculators.
LF and AF are the products of calculations. Albeit pen and paper, or pocket-calculator calculations.
Do you think this topic is more apt for the "2-Way Loudspeaker" section?
I had to choose somewhere rational to post.
I made a good-faith determination as to where the subject matter would meet its most natural audience.
The number of hits and comments suggest to me that the topic has found its proper audience.
john
What, where did you say anything about bandwidth?
You said "woofer speed... OMG".
This was exactly my point, great to see you reconsidered your statement.
Weird how nobody noticed that.
The misconception is the blanket statement all woofers have the same bandwidth. If you explain where those woofers are I'll send you the popcorn.