Amps, SS filters, phase? Please help

Discussion in 'Home Theater Projects' started by Richard Little, Sep 13, 2003.

  1. Richard Little

    Richard Little Stunt Coordinator

    Joined:
    Jun 20, 2003
    Messages:
    105
    Likes Received:
    0
    You have to help me; my eyes are crossing up looking at all the different options. To start with I have 2 AV15's and a BFD. Initially I only want to make one ported box for one of the drivers and power it with at least 500 watts of real power but would like to use the same amp to power an additional identical sub in the future. I also need to have a subsonic filter and a phase adjustment would be nice. For the subsonic filter, either like to buy constant variable or make a DIY low-cut filter so it can be made to match the enclosure. What do I need to do? I hate the idea of spending $400 on one component just to get the SS filter (rane pe15) use and another $140 for something to convert from a home audio AVR out to a pro amp in. Can anybody suggest something that might help with all this? Do DIY low-cut filters put in series with the sub amp work ok? The Mackie 1400i has the SS filter but is a little short on the watts. What else is out there? The SVS black box is great but what if I need more than at 15, 20, or 25 Hz filter. What can I do?
     
  2. Dave Milne

    Dave Milne Supporting Actor

    Joined:
    Jul 2, 2001
    Messages:
    568
    Likes Received:
    0
    Richard,
    Are you comfortable building your own little electronics projects? Sallen-Key active filters are pretty easy to design and build. Variable frequency is a pain... but with fixed-frequency designs, you can put the frequency-setting resistors on DIP headers and plug in what you need. I believe there are some kits out there... probably something on Rod Elliott's site. Adding the phase adjustment is simple: just another op amp with a pot and a few passive components.

    And no, you can't do this passively (in series with the sub). The component values would be HUGE and expensive.

     
  3. Jack Gilvey

    Jack Gilvey Producer

    Joined:
    Mar 13, 1999
    Messages:
    4,948
    Likes Received:
    0
    As usual, the DIY option is best, as Dave mentions. I don't DIY these type of things, so I grabbed an SVS/Marchand box...a great, well-made unit. It's a good buy if you need both of the functions it provides. It has something like 18dB of clean gain, so it'll allow just about any AVR to mate with the higher levels of many pro amps. Also, the SS filter is 24dB/oct, much steeper than others I'm familiar with. Largely due to this, your filter frequency doesn't have to be right at your Fb. The 15Hz setting should be good for anything below 20Hz or so. Since it's so steep, it can start the rolloff a little deeper and still have adequate filtering.

    Also as Dave says, there are plate amps out there that will certainly do an AV15 justice. This one looks particularly nice:
    http://www.acoustic-visions.com/~aco...s/keiga_52100/
    Its infrasonic filter is something like -3dB @ 17 hz, second-order...I can e-mail you the .pdf on it if you'd like.

    Of course, the pro-amp route will allow more flexibility in the future for another sub.
     
  4. Richard Little

    Richard Little Stunt Coordinator

    Joined:
    Jun 20, 2003
    Messages:
    105
    Likes Received:
    0
     
  5. Jack Gilvey

    Jack Gilvey Producer

    Joined:
    Mar 13, 1999
    Messages:
    4,948
    Likes Received:
    0
  6. Dave Milne

    Dave Milne Supporting Actor

    Joined:
    Jul 2, 2001
    Messages:
    568
    Likes Received:
    0
    +15 V and -15V is not exactly the same as 0V and 30V. You need the bipolar supplies to avoid having to bias up the midpoint and capacitively couple the input and output.

    I believe Rod has some easy bipolar supply designs on his site. The current requirements for an active filter are quite modest... a dozen milliamps or so are all that is typically required.
     
  7. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    Color me curious, but unless one is playing vinyl why does anyone with these high excurson, high power handling drivers want or need any subsonic filtering?

    Since I gave up on vinyl (1984), I haven't use an SS filter on any sub I've owned.
     
  8. Dave Milne

    Dave Milne Supporting Actor

    Joined:
    Jul 2, 2001
    Messages:
    568
    Likes Received:
    0
     
  9. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    I have Shiva's, DPL-12"s, BluePrint 1503's and HE-15 based subs in the house. Never had any problems letting them run sans SS filters.
     
  10. Richard Little

    Richard Little Stunt Coordinator

    Joined:
    Jun 20, 2003
    Messages:
    105
    Likes Received:
    0
  11. Dave Milne

    Dave Milne Supporting Actor

    Joined:
    Jul 2, 2001
    Messages:
    568
    Likes Received:
    0
     

Share This Page