by Fishy » Mon Mar 26, 2007 9:24 am
Back in the early 1960s, Anthony Hoffman (the H in KLH) developed a mathematical formula that became known as Hoffman's Iron Law. Thiele and Small later refined the law's mathematics. The Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). To reduce the cutoff frequency from 40Hz to 20Hz you need to increase the enclosure volume by eight times. In other words, to produce half the frequency at the same output level you need a very big box. You can get around this by accepting a much lower efficiency, but this requires both a very large amplifier and a driver that can handle a lot of power, move a lot of air (requiring a long excursion), and do both while generating very little distortion.
A so-called reflex design provides a way
from here:
http://ultimateavmag.com/subwoofers/60/
Basically what Hoffman's Iron Law says is when it comes to sealed subwoofer sytems when striving for three things
1) Efficiency
2) Low Enclosure Volume
3) Low Frequency Extension
pick two of the three.
You can't have all of em. Fortunately with car audio we have cabin gain on our side so we can give up a little of #3.
Oh btw. I was NOT impressed with the way my 10w3d2's did sealed. I'd be looking for something with more Xmax. Maybe a Fi Q12? or, if you're a JL fan like me, a 12w6v2? though you're gonna need an amp thats stable running 2 ohm mono for that one.
[i]Back in the early 1960s, Anthony Hoffman (the H in KLH) developed a mathematical formula that became known as Hoffman's Iron Law. Thiele and Small later refined the law's mathematics. The Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). To reduce the cutoff frequency from 40Hz to 20Hz you need to increase the enclosure volume by eight times. In other words, to produce half the frequency at the same output level you need a very big box. You can get around this by accepting a much lower efficiency, but this requires both a very large amplifier and a driver that can handle a lot of power, move a lot of air (requiring a long excursion), and do both while generating very little distortion.
A so-called reflex design provides a way
[/i]
from here:
[url]http://ultimateavmag.com/subwoofers/60/[/url]
Basically what Hoffman's Iron Law says is when it comes to sealed subwoofer sytems when striving for three things
1) Efficiency
2) Low Enclosure Volume
3) Low Frequency Extension
pick two of the three.
You can't have all of em. Fortunately with car audio we have cabin gain on our side so we can give up a little of #3.
Oh btw. I was NOT impressed with the way my 10w3d2's did sealed. I'd be looking for something with more Xmax. Maybe a Fi Q12? or, if you're a JL fan like me, a 12w6v2? though you're gonna need an amp thats stable running 2 ohm mono for that one.