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Impedance Correction Conjugate Network [message #22533] Thu, 10 March 2005 15:03 Go to next message
FredT is currently offline  FredT
Messages: 704
Registered: May 2009
Illuminati (1st Degree)
The FredArrays' bass sounded nice and tight with the solid state amp but a bit uncontrolled with the SET. So I checked my crossover software and it indicated a 30+ ohm impedance peak at the enclosure tuning frequency, which I thought might be contributing to this problem. The suggested network to correct this included a series filter consisting of an 8 ohm resistor, a 1000uF cap, and a 10mH inductor (yes those are large values, but the filter is tuned to 50hz). The difference is amazing - the bass is down about 1dB, but the transient response is remarkably improved, maybe too much. I'll swap the 8 ohm for a 16 and see how it sounds.

What's interesting here is that I started this project with a simple 2nd order woofer network and a 3rd order tweeter network. Then it required an RC network to compensate for the woofers' rising impedance and nail the target crossover frequency. Finally, I added the conjugate network to tame the wooly bass.

The tweeter was still a bit bright so I added the RCL Zoebel network which Bottlehead corp recommends for this tweeter in the Straight 8. Finally a one ohm resistor ahead of the tweeter crossover tamed the last trace of brightness.

What started as a simple network now has 15 parts (17 including bypass caps), but each time I remove one section the sound is degraded. Whoever said simpler is better wasn't designing with cheap drivers?


Re: Impedance Correction Conjugate Network [message #22534 is a reply to message #22533] Thu, 10 March 2005 21:27 Go to previous messageGo to next message
Wayne Parham is currently online  Wayne Parham
Messages: 18787
Registered: January 2001
Illuminati (33rd Degree)

I agree. I appreciate the "simpler is better" approach, and find good solutions that are physically simple to be elegant. But a loudspeaker is a complex load, so a network that is physically simple often creates a system that is reactively complex.

Sometimes a conjugate filter is needed to compensate for the built-in filter of the speaker, itself. In this case, what appears to be complex is actually counteracting something else equally complex, balancing the equation to form something pure.


It's Adjustable Too [message #22537 is a reply to message #22534] Fri, 11 March 2005 06:31 Go to previous message
FredT is currently offline  FredT
Messages: 704
Registered: May 2009
Illuminati (1st Degree)
It's interesting how I can vary the effect by changing resistor values. Without the network the bass transient response sounds undercontrolled to my ears. Using an 8 ohm resistor the bass becomes very tight but sounds a bit overcontrolled (the typical Best Buy or Circuit City shopper would complain that the speakers "don't have enough bass"). A 16 ohm resistor provides a nice balance, even on bass transient heavy material like Brian Bromberg's "Wood" acoustic bass disk.

I remember Jim Vandersteen was talking about his company's subwoofers, and he said the first model had a Q of 0.7, but some customers were complaining they "couldn't hear the bass". So he modified the subs by incorporating a continuously variable Q control, giving the customer a choice of tight bass, fart box bass, or anything in between.

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