Active Biamping DIY speakers

Discussion in 'Home Theater Projects' started by Seth_L, Oct 15, 2004.

  1. Seth_L

    Seth_L Screenwriter

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    I'm going to be building a pair of speakers with Adire Extremis 6" mid woofers and a tweeter based on Adire's plans (ETA unknown on the plans). I am thinking of actively biamping these.

    Is there a good not too expensive method for active bi-amping?

    I was looking at a Behringer Ultradrive Pro DCX2496 for the crossover functions, but then I need 4 channels of amplification and a volume control.

    Or, is it not worth biamping with all solid state components and I should just use a passive crossover and a 2 channel amp?
     
  2. Saurav

    Saurav Cinematographer

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    You could use John Pomann's kit, I would think. It's a good basic starting point, and you can make it fancier as you go along (better opamps, more complex circuits). The Linkwitz Lab website has schematics for a bunch of circuits that you may or may not need. For instance, if you need/decide to implement notch filters or BSC or whatever in your active XO.
     
  3. Seth_L

    Seth_L Screenwriter

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    I think I'd tend to favor the digital solution for the crossover over an analog one (more customizaable) even if it is more expensive.

    A psuedo cheap, but quality way to power 4 channels is what I'm missing.
     
  4. Seth_L

    Seth_L Screenwriter

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  5. Michael R Price

    Michael R Price Screenwriter

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    I developed an active crossover for the Kit281 and the result is rather good. I am almost done building my "final" prototype which includes the crossover itself plus a chip-amp for the tweeter so no additional amplifier is needed. This whole thing costs about $250 to build. It could be easily adapted to other drivers and you can customize every aspect of the response by changing components in sockets...
     
  6. Wayne A. Pflughaupt

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    ”Pseudo cheap?” Isn’t that an oxymorn? [​IMG]

    The nice thing about active bi-amping is that you don’t need a lot of power, since you’re not using power-robbing passive elements. And low-powered amps are pretty cheap.

    One “for instance,” Adcom used to make a 4-channel 60-watt amp, the GFA 2535, and a stereo 60-watt amp, the GFA-535. You’ll have no problem finding the former or a pair of the latter for well under $300 on eBay.

    Regards,
    Wayne A. Pflughaupt
     
  7. Mark gas

    Mark gas Second Unit

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    What about using one of those panny SA 30 Receiver with 6 channel inputs in party mode and using a cheap car audio xover form ebay run buy a ATX power supply?
     
  8. Scott Simonian

    Scott Simonian Screenwriter

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    All that paired for an extremis?

    Atch!

    [​IMG]
     
  9. Seth_L

    Seth_L Screenwriter

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    You wouldn't even need to use an ATX power supply. A car crossover doesn't use much power. A wall wart would work fine.

    A lot of people on Audio Circle and AVSforum are raving about the sound of the new mini all digital recievers. A Panasonic XR50 looks like a good way to get 4 channels of power with a volume knob. I wish they had a 6.1 input instead of a 5.1 input though. Then I could Tri-amp the speakers (I'm pretty sure I will use 2 Extremis 6's per speaker.
     
  10. Seth_L

    Seth_L Screenwriter

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    But, what do you use for a pre-amp to control all the channels volume at the same time?
     
  11. Mike Keith

    Mike Keith Second Unit

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    The front 2-channel outputs of any standard Preamp go to the Active crossover’s 2-channel Inputs, then the signal is split to the separate Woofer and Tweeter outputs, these go to the two separate Woofer and Tweeter amps. A configurable multi-channel amp like my Sony 5/4/3/2 amp with impedance matching and BTL bridgeable mode, its capable of running a 2-way bi-amped front channel pair with a single ch subwoofer. And dose it very nicely.

    Going cheep on a proper Active bi-amped setup is technically impossible; it’s Hofmann’s iron law. Paraphrased “If there are three values to determine an outcome, and you select two to control, the third will be selected for you (based on the summation of the two you picked).

    So expect to spend a good bit on a multi channel amp with good power and flexibility. 2 2-channel amps will cost the same (used), either way you will spend several hundred unless you get really lucky. Also a good quality Active crossover will allow you the proper flexibility and have an acceptable noise floor. The only problem with any cheep active crossover is Noise Floor, don’t skimp, and get a good kit like the Marchand, or buy the Behringer or best of all the DCX2496 (very expensive). In addition you will have twice as many cables, don’t skimp here either. A thousand dollars could get you the crossover and used amp’s and DIY cables, if you really shop.
     
  12. Seth_L

    Seth_L Screenwriter

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    I was thinking of putting the active crossover between the source (my PC) and my volume control / amp. That will greatly reduce the significance of the noise floor and allow me to avoid another unnecessary A/D conversion because I can feed the Behringer DCX2496 a SPDIF input signal.

    What would be the benefit of putting the active crossover between the pre-amp and the 4/5/6 channel amp if I only have 1 source?
     
  13. Seth_L

    Seth_L Screenwriter

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    How much does the GFA 2535 typically go for? I see two of them on Ebay that I'm watching.
     
  14. Mike Keith

    Mike Keith Second Unit

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    Master Volume control is the advantage, I've never heard anyone successfully placing a proper Active crossover between the source and Pre, and you will loose one of the best benefits of the crossover, separate gain control over each driver. I would definitely not recommend using a active crossover this way, do it like your supposed to, between the Preamp and amp, noise should be the same, but you will have total control over the drivers gain and dampening.
     
  15. Wayne A. Pflughaupt

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    Seth,
    As Mike noted, you have a big problem here, Seth.

    The reason is that the levels of the tweeter and woofer are usually set from the crossover or perhaps gain controls on the amplifiers (if it has them). With active bi-amped speakers, calibrating and adjusting the tweeter/woofer levels takes time and effort to get it right, so that tweeter’s level blends appropriately with the woofer. Once it’s done you want to “lock down” the settings and not mess with them anymore.

    The way you’re talking about doing this, needing the capability to adjust the volume for each amplifier channel after the crossover, is completely unworkable. Anytime you want to raise or lower the overall system volume, you’ll be re-adjusting the tweeter and woofer independently and you’ll be screwing up the proper balance between the two. Not only that, but you’ll be messing up the balance between the left and right speakers as a whole.

    Bottom line, Seth, you’re going to have to find a way to get your volume control in front of the crossover.

    Regards,
    Wayne A. Pflughaupt
     
  16. Seth_L

    Seth_L Screenwriter

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    You are right. If I were to use something like the Adcom I would need to put the the crossover in between the amp and the pre-pro.

    However, if I use the infamous digital JVC RX-F10 I can control the volume to the 4 amps at the same time while maintaining the balance between the different channels. This would allow the crossover to go in between the source and the amps (because the amp is really a reciever).
     
  17. Seth_L

    Seth_L Screenwriter

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    Two just sold tonight.

    One closed for $162.50 and the other for $187.50. The cheaper was listed as "I have not used but it lights up when turned on"
     
  18. AjayM

    AjayM Screenwriter

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    You guys realize that just because it's an active x-over doesn't mean you're going to get away from all of the complex sides of x-over design. You still need to account for cone breakup, impedence issues, etc ,etc.

    Basically if you don't have a way to measure and design for those types of issues then you aren't going to save yourself much, if anything that you couldn't do by making a "standard" x-over, or buying a pre-built 2-way passive unit from PE for $20-30 (other than the "usual" pluses to active designs).

    Andrew
     
  19. Michael R Price

    Michael R Price Screenwriter

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    I was hinting that I could help with that. [​IMG]
     
  20. Wayne A. Pflughaupt

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    How is that going to work, Seth?

    Regards,
    Wayne A. Pflughaupt
     

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