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Old 19th December 2011, 03:11 PM   #1
Scott L is offline Scott L  United States
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Default punch vs BL factor or force factor ?

I am in the design stage of a mid-bass system
to cover from 50 Hz -500hz. I realize 500 hz is above the so called mid-bass zone, but I need to cover that high.
I can choose between a 15" driver, or I also have some 12's. For this sake of discussion, let's take the difference in SD, or effectice cone area, out of the equation for now. I noticed the 12" version has a moving mass of 62.1 grams with a BL of 16.94 thus giving an FA of 272 (considered excellent)
as oppossed to the 15":
It's moving mass is 127 grams with an even higher BL of 23.44, none the less, the FA only comes out to 184.
I read somewhere else on these forums where the force factor (FA) is the BL product divided by the moving mass(?)
The 15 " has a Fs of 28 and a Qts of .24 while the 12's fs = 44 and a Qts of .32
Which unit, do you think, would be better for Mid-Bass (sound quality wise) ?
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Old 19th December 2011, 10:11 PM   #2
bbggg is offline bbggg  United States
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Neither. Remember Newton's law of motion, whereby force equals mass times acceleration. Now picture your woofer accelerating forward as a result of the force applied upon it by the voice coil. The woofer has no foreknowledge as to what kind of signal it is reproducing. It can be a large 90 Hz sine, for example, or it can be a small 900 Hz sine. Midway up a slope, a woofer cannot know which is which. Maximum acceleration a woofer can sustain is reflected in its frequency response. As long as it is asked to reproduce signals within its flat passband, it can accelerate well enough. The quality of reproduction will then depend on other parameters such as distortion, eddy currents, baffle rigidity, internal reflections, etc etc. In practice a woofer's maximum acceleration reflects the maximum allowed rate of change in current flow, which in turn will be limited by the high pass filter feeding the woofer.
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Old 19th December 2011, 10:40 PM   #3
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What is "Sound Quality"?

just kidding.

Please list the multitude of variables needed to determine if a driver is right for the application?

Sincerely,
revb.
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Old 19th December 2011, 11:26 PM   #4
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You might want to read up on VC inductance (Le). I think that's part of what you are looking for.

Last edited by revboden; 19th December 2011 at 11:34 PM.
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Old 21st December 2011, 10:05 AM   #5
Scott L is offline Scott L  United States
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Default Thankyou kindly

[QUOTE=revboden;2827424]You might want to read up on VC inductance (Le). I think that
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Old 21st December 2011, 10:31 AM   #6
Scott L is offline Scott L  United States
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Quote:
Originally Posted by bbggg View Post
Neither. Remember Newton's law of motion, whereby force equals mass times acceleration. Now picture your woofer accelerating forward as a result of the force applied upon it by the voice coil. The woofer has no foreknowledge as to what kind of signal it is reproducing. It can be a large 90 Hz sine, for example, or it can be a small 900 Hz sine. Midway up a slope, a woofer cannot know which is which. Maximum acceleration a woofer can sustain is reflected in its frequency response. As long as it is asked to reproduce signals within its flat passband, it can accelerate well enough. The quality of reproduction will then depend on other parameters such as distortion, eddy currents, baffle rigidity, internal reflections, etc etc. In practice a woofer's maximum acceleration reflects the maximum allowed rate of change in current flow, which in turn will be limited by the high pass filter feeding the woofer.
If I have read this right, given the option of hi-passing or not hi-passing the mid bass, the better choice would be no- high pass (?) Then all the other variables you listed come in to play.----Also, I have a 3rd set of woofers to choose from for this application, and low and behold, they have the lowest
Le of the bunch.Thanks for helping me see this.
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Old 21st December 2011, 11:11 AM   #7
AndrewT is online now AndrewT  Scotland
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I would think that a dedicated mid/bass driver would require a limited bandpass signal from the amplifier to allow it to perform near it's best.

That would require the wideband audio signal arriving at the amplifier input to be filtered to attenuate the LF signals and similarly that the HF signals should also be filtered.
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Old 21st December 2011, 12:26 PM   #8
bbggg is offline bbggg  United States
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Quote:
Originally Posted by Scott L View Post
If I have read this right, given the option of hi-passing or not hi-passing the mid bass, the better choice would be no- high pass
I'm sorry, my bad, I wrote high pass when I should have written low pass. The answer is no, but some may disagree.
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Old 21st December 2011, 12:27 PM   #9
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by Scott L View Post
I am in the design stage of a mid-bass system
to cover from 50 Hz -500hz.
Is 50Hz a mid bass frequency?
There are plenty of PA bass drivers that will reproduce 50Hz but not many that will go lower without x-max limitations.
What is the maximum spl that is required?
Regards Xoc1
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Old 21st December 2011, 12:31 PM   #10
bbggg is offline bbggg  United States
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As for your original question, you'll be better off if you post the drivers you are considering and ask for advice directly. There are many people here who will give you a thoughtful opinion. Posting riddles is not really going to help you much, especially so since you seem to be unfamiliar with the basics.
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