When to use active crossover?

Discussion in 'Home Theater Projects' started by Ryan Leemhuis, Feb 1, 2005.

  1. Ryan Leemhuis

    Ryan Leemhuis Second Unit

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    I am reading an artical that says that he always uses active crossovers with his speakers. However, I don't think I have ever seen a non-subwoofer speaker with an active crossover. Can anyone please help explain to me what the advantages are and when they are generally used?
     
  2. George Hall

    George Hall Agent

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    I posted this a bit ago in the speaker forum...
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    The performance advantages are due to the following reasons -

    1 No passive x-over. Because most high quality powered monitors are bi-amplified (or tri-amplified), no passive crossover is used. Passive crossovers suffer from insertion loss, meaning they can reduce system efficiency by 3 to 6dB. Because all the crossover components in a typical powered speaker are active, their is no insertion loss. Meaning more actual power goes to driving the speakers. This means that a 50-Watt amp driving a driver directly would have an equivalent output to a 100-watt amp driving a passive x-over / driver.

    2 Powered monitors typically has more refined response (both on and off axis). Because a bi-amplified powered monitor uses an active x-over, it is much easier to create the proper crossover and add EQ to get the response "just right".

    3 Amplifiers can be perfectly designed for the drivers being used. This typically greatly increases reliability and overall system performance.

    Again, there are many benefits to going powered. Having said that, there are some reasons they may not be as popular for consumer applications. This because of the following reasons -

    1 Each speaker needs power. This may not be a big deal for some, but especially for surround speakers, it can be problematic.

    2 Because there is such a lack of understanding about the benefits of powered monitors in the consumer market place and because many dealers have a vested interest in selling separate amplifiers, it has made it very challenging to communicate the advantages of powered speakers to consumers.

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    If you google on the subject, you will find many articles on active speakers. Secrets has a good article of the pros and cons of this approach.

    There are some that may refute these advantages, with the truth being in the sound of the speaker. If it sounds good to you, then that is all that counts with the design.
     
  3. Ryan Leemhuis

    Ryan Leemhuis Second Unit

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    not on topic but I hope to avoid making a new topic altogether for another question...if I use a Zobel network to make the impedence of the speaker more constant at higher frequencies...it says it drops the nominal impedence. Is this drop enough that it could be a problem for a $150 kenwood amp?

    Secondly, Most of vifa's tweeters are not shielded. Will this bring any problems when making home theater speakers? What is the approximate range of the magnetic field of the magnets of the D25?
     
  4. Drew Eckhardt

    Drew Eckhardt Stunt Coordinator

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    I use actively tri-amplified main speakers, with a cross-over on top of the amplifiers rather than built into a powered speaker.

    Since they opperate into purely resistive impedances text book cross-over designs have the intended frequency response. This doesn't change with output level as it does with passive cross-overs (voice coil resistance changes with temperature, inductance changes with motion).

    The drivers can be electronically time-aligned at their cross-over frequencies so the peak output is on-axis and the baffle shape can be whatever it needs to be for the best polar response.

    Low power 1% resistors and 2% capacitors are inexpensive. It doesn't cost much to get an effectively perfect match between channels wich provides better imaging.

    Active cross-overs let you use drivers with wildly different sensitivities (say 88dB/2.83V in the midrange and nearly 100dB/2.83V in the upper bass) to reach your output goals without wasting amplifier power on attenuation. While this may not work for test signals, it's fine for music where there's more low frequency content.

    The same applies where sensitivity changes across the frequency range. A conventional speaker may knock 5dB (waste 3/4 of the amplifier power) off at high frequencies to compensate for the drop at low frequencies due to baffle step.

    When a bass note causes clipping the higher frequency drivers don't get any garbage and the sound is less objectionable (perhaps un-noticeable).

    You need smaller amplifiers to get the same output. Playing equal loudness high and low tones you get the same output with 100W each as you'd have with 400W into a passive speaker.

    Market acceptance is the only place passive cross-overs win as you move away from inexpensive gear.
     
  5. Ryan Leemhuis

    Ryan Leemhuis Second Unit

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    Thanks for the explanation. If anyone can answer any of the off topic questions in my previous post please do.
     

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