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Old 19th March 2012, 12:59 AM   #1
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Default Can you bi-wire using two different taps

Can a speaker be biwired using two different impedence taps on a tube amp? I have never seen it done but assume there must be some problem with doing this. Anyone know anything about this? Thanks
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Old 19th March 2012, 07:10 AM   #2
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ummm, why would you?
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Old 19th March 2012, 09:42 AM   #3
DF96 is offline DF96  England
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Given a perfect speaker with perfect crossover which gives a perfectly flat response when driven by one pair of wires it is fairly easy to show to anyone who understands electronics that true biwiring with real cable (i.e. with a little resistance) will cause a dip in response at the crossover frequency. Some real speakers with imperfect crossovers might benefit from an added crossover dip; others will not. The usual arguments for biwiring are pure bunkum; the real isue is whether a little dip will help or not.

Feeding via two wires from two different voltage sources is not really biwiring. It could only improve a poor speaker design which was unbalanced when fed from a single source. Is your speaker really that bad?
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Old 19th March 2012, 10:25 AM   #4
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Supposedly, biwiring prevents back EMF from entering the tweeter. There is controversy over this. The reason I would like to try two different taps is the impedence curve of the speaker shows rising impedence in the tweeter range. Regards
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Old 19th March 2012, 10:41 AM   #5
DF96 is offline DF96  England
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The 'back EMF' argument only makes any sense at all when you have a very low amp output impedance (high DF) and high resistance speaker leads i.e. SS amp with thin cables. Only in those circumstances would biwiring reduce coupling between drivers. If you have higher output impedance then that will provide coupling, whatever cables you use. If you have low output impedance and low cable resistance then you have low coupling with single wiring, so biwiring changes nothing. So the issue only matters in circumstances which are rare.

Of course, high resistance cables is also the scenario which maximise the crossover dip caused by biwiring.

The speaker designer should have already taken rising impedance into account. If you want a treble boost then do what you suggest, but you are really implementing a fixed tone control rather than biwiring.
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Old 19th March 2012, 10:44 AM   #6
SY is offline SY  United States
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Quote:
Originally Posted by john dozier View Post
Can a speaker be biwired using two different impedence taps on a tube amp? I have never seen it done but assume there must be some problem with doing this. Anyone know anything about this? Thanks
That can be a useful trick. Let's say that you want to drive the woofer (and its crossover) with a larger voltage signal than the tweeter (and its crossover). You can hook the tweeter to a lower impedance tap than the woofer. In the last set of speakers I designed (an MTM array), I put the woofers in series, then drove their crossover from the 16 ohm tap. The tweeter and its crossover were driven from the 4 ohm tap to achieve a -6dB attenuation without using resistors in the crossover as attenuators. Worked like a charm.

This assumes that the differences in voltage levels are something you want for a particular design!
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Old 19th March 2012, 04:31 PM   #7
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Wouldn't doing that change the reflected impedance on the tube? I would think using multiple secondary taps on something like an EL-84 would drop the impedance the tube see out of the ideal range. Maybe i'm just confused on this.
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Old 19th March 2012, 04:34 PM   #8
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To start with, if you connect a speaker to a single tap, the loading becomes non-ideal anyway- most speakers have impedances which vary all over the place with frequency.

In the example I gave, I connected the woofers in series to get something closer to 16 ohms, then used a 4 ohm tweeter. So, non-ideal, but no more non-ideal than a conventional speaker connected conventionally.
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Old 19th March 2012, 04:53 PM   #9
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If the coupling inside the transformer between the windings involved in the taps, the wiring manner is indistinct, the speakers will be so good coupled as the winding in the transformer itself.
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Old 19th March 2012, 05:17 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by DF96 View Post
Given a perfect speaker with perfect crossover which gives a perfectly flat
response when driven by one pair of wires it is fairly easy to show to anyone
who understands electronics that true biwiring with real cable (i.e. with a little
resistance) will cause a dip in response at the crossover frequency.
Hi, This doesn't make any sense, bi-wiring makes no difference, rgds, sreten.
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