Active vrs passive

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Using a transformer is a bad idea. If the woofer, mid and tweet all are the same nominal impedance to start with then that will get all screwed up with a transformer on the woofer. The only way to compensate for that is to give the low end current another path around the woofer. Bad idea! There goes your SPL!

The whole POINT was to answer your question about altering the SPL of the woofer relative to the rest of the speaker. That's what it's SUPPOSED to do. The transformer does so without any change in efficiency or the alignment. Yes, it changes the impedance- so what? Let's say you have an 8 ohm nominal woofer that needs a 6dB reduction in sensitivity. Its impedance will vary from (say) 6 ohm below resonance to maybe 30 ohms at resonance to 10 ohms above resonance; these are not atypical numbers. 2:1 stepdown means 4:1 impedance transformation, so the speaker impedance ends up varying from 1.5 ohm below resonance to roughly 8 ohms at resonance to 2.5 ohms above resonance. A decent SS amp will have zero problem with that- its source impedance is low, well under 0.1 ohm. So.. the passive solution works. It's not convenient- a big bass transformer is heavy and bulky, and biamping will be cheaper- but it's absolutely doable if you want a passive solution.
 
I understand that many years ago B&W used a transformer to lower the sensitivity of the 10" bass unit in their 3 way DM6 (also known as "The Pregnant Penguin". If you ever see a photo of a gloss white version you'll see why.). The cross over was published somewhere here a year or two ago.

Edit; and just for completeness the thread is; DM6 Recap. Post #1 24 June 2011.
Jonathan
 
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Why would Linkwitz say this as a simple "Case closed" statement if it wasn't true? He is an an authority on active vs passive if there ever was one. Yet he claims that the reason is quite simple..

"Crossovers may be implemented either as passive RLC networks, as active filters with operational amplifier circuits or with DSP engines and software. The only excuse for passive crossovers is their low cost. Their behavior changes with the signal level dependent dynamics of the drivers. They block the power amplifier from taking maximum control over the voice coil motion. They are a waste of time, if accuracy of reproduction is the goal."
 
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With as many choices as there are out there for all kinds of drivers why would anyone (who knows what they are doing) choose a woofer with a higher SPL than the mids or tweets for a multi-way passive crossover system and then try to fix that problem with a transformer?

So now you have the DC resistance of both the secondary coil of the transformer and at least one coil in the passive crossover in series with the woofer.

That's very counter productive.

James.
 
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You don't have to have drivers with the same impedance in a passive speaker. IE- 4 ohm woofer, 8 ohm mid, and 6 ohm tweeter is perfectly doable.

Later,
Wolf

its not about drivers having different impedances
like you say, no problem at all
its the varying impedance of each driver
that is real big problem, and plays a major role with passive crossovers
active is not troubled with this
 
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