Passive crossovers: Making Lpads for MTMs

Discussion in 'Home Theater Projects' started by GaryLP, Nov 19, 2004.

  1. GaryLP

    GaryLP Agent

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    If I made a 2-way passive crossover for a 4 ohm tweeter (with a 92dB SPL) and a 4 ohm midrange (with a 89dB SPL), I would need to make a 3dB Lpad for the tweeter.

    But say I wanted to use (2) 8 ohm mids (with a 86dB SPL) in parallel instead…how much should I pad down the tweeter?
     
  2. ThomasW

    ThomasW Cinematographer

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  3. GaryLP

    GaryLP Agent

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    Thanks for the response Thomas, but it doesn't answer my question...I already know how to make an Lpad.

    What I'm asking is...If I made a 2-way passive crossover for a 4 ohm tweeter (with a 92dB SPL) and a pair 8 ohm mids in parallel (with a 86dB SPL)...how many dB's should I pad the tweeter down? 3dB? 6dB?
     
  4. ThomasW

    ThomasW Cinematographer

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    Given the variability of the acoustical characteristics of any given room; the usual proceedure is to measure the output level in the room, and adjust the tweeter level from those measurements.

    So most designers use a variable L-pad to adjust the level, then pull it out of the circuit, and measure the values for their fix unit.

    Unfortunately Phoenix Gold, the only supplier of variable 4 ohm L-pads, has stopped production.
     
  5. GaryLP

    GaryLP Agent

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    Hi Thomas, I just wanted to use the textbook answer as a starting point. I will be experimenting, but don't want to buy too many resistors.
     
  6. Michael R Price

    Michael R Price Screenwriter

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    Gary, if those are the exact sensitivity numbers for the drivers... since 4db is a typical amount for baffle step compensation, the mids will be have a sensitivity of (86+6)-4 = 88db at low frequencies so you will want to pad down the 92db tweeter by around 4db to match. Of course there is a lot of variability but that is what I would use as a starting point.
     
  7. GaryLP

    GaryLP Agent

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    Hi Michael,

    Thanks for the response.
     

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