DIY MTM speaker + NAD amp = 'hot' tweeter

Discussion in 'Home Theater Projects' started by Mark Wilson, Dec 19, 2003.

  1. Mark Wilson

    Mark Wilson Agent

    Joined:
    Dec 18, 2002
    Messages:
    30
    Likes Received:
    0
    I've been wondering about this forwawhile.

    My Adire Kit 281's have always sounded a bit bright to me. I was orginally suspecting my room, but after aiming them all over the place I couldn't really get the brightness to decrease or increase. I then suspected my NAD PE2200 amp. Tested it with a couple different sets of speakers (no other MTMs) so I don't believe it is that. (It does sound pretty bright, running through other speakers, but not nearly as bright as when running the adires)

    We all know how an MTM speaker works, but I'll say it again just so I'm understanding it correctly.

    You have a tweeter of a certain sensitivity. The midrange you want to use is lower then the tweeter, so rather then padding it down, you add a second midrange.

    You usually run them in parralel to get an extra 6 dB sensitiy from them. 3 dB from doubling the surface area, and 3 dB from doubling the wattage. (Which you get from halving the resistance, eg if your using an 8 ohm mid, adding the second in parralel will give you a 4 ohm load accross the mids)

    I think that's all correct. Now, what happens if you have an amp (such as most NAD's which have 'power drive')

    As far as I understand, with a power drive equipped NAD, it will supply the same wattage into an 8 ohm load as a 4 ohm load and vice versa. As compared to most amps which when you halve the impedance, you hopefully gain twice the wattage. With the NAD's powerdrive, you gain a lot of dynamic power going from an 8 ohm load to a 4 ohm load, but still the same average sustanined wattage.

    Now, does this mean that in an MTM with a 8 ohm tweeter, and your 4 ohm mids that your midranges are only going to benefit from double surface area, and not doubling the power? And because of that, your tweeter will be 3 dB 'hot' compared to your mids? (Or 3 dB louder then whatever the speaker designer wanted them to be at)
     
  2. Brian Tatnall

    Brian Tatnall Stunt Coordinator

    Joined:
    May 21, 2003
    Messages:
    149
    Likes Received:
    0
    Contact Adire. Did you get one of the earlier kits? I think I remember reading about some people complaining a little and Adire supplying a fix. My .02
     
  3. Mike Keith

    Mike Keith Second Unit

    Joined:
    Jan 24, 2002
    Messages:
    324
    Likes Received:
    0
    Pad the tweeter down with a resistor, say 4ohm 20W non inductive from radio shack.
     
  4. Mark Wilson

    Mark Wilson Agent

    Joined:
    Dec 18, 2002
    Messages:
    30
    Likes Received:
    0
    Brian, I'm not really too sure how old it is. I bought it through Creative Sound Solutions about a year ago. Took me quite awhile to get them all built up [​IMG]

    The x-overs did come fully assembled. All pre sauldered and everything, if that says anything.

    I will contact Adire though, thanks!
     
  5. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    Use an L-pad not a single resistor.

    If you want to remove the variable L-pad, set it to the tweeter output level you want, then cut it out of the circuit. Be careful not to change the setting. Then with a DMM measure the 2 resistor values and make a fixed L-pad with the appropriate resistor values.
     

Share This Page