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Old 23rd February 2007, 02:47 PM   #1
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Default Question on transmission lines

Hi, I am considering one of these for a JX92 but have a few questions:

I read somewhere that the frequency response of transmission lines is extended due to the line resonance reinforcing the wave at the driver - does this mean the driver excursion is increased at this resonant frequency? How else can this resonance increase the bass volume if the port does not contribute anything? Is the driver 'loaded' similar to in ported designs?
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Old 23rd February 2007, 02:53 PM   #2
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You might find this interesting. Martin is the God of Quarter Wave math. http://www.quarter-wave.com/Theory/TL_Anatomy.pdf
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Old 23rd February 2007, 03:18 PM   #3
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Thanks, I have already seen this but don't have the time to digest all the maths as I'm off skiing this weekend - yipee!
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Old 23rd February 2007, 03:35 PM   #4
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In that case, and in a nutshell:

No: QWRs at line tuning frequency will actually exhibit minimal driver excursion. The system impedence curve displays this. A resonant line has a double-humped impedence curve (just like a BR cabinet), each peak occuring to either side of tuning frequency. The enclosure produces most of the SPLs at tuning frequency, with excursion being minimised at that point. This isn't actually a system resonance itself, but a combination of system resonances.

Keep in mind though that a TL not the same as a QWR. TLs have a flat, or nearly flat impedence curve -that's the primary objective of their design: to eat the back-wave of the driver, and they are usually pretty heavily damped in order to achieve this. Not much use for FR drivers which generally need all the help they can get in the LF. Enjoy the skiing BTW.
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