Check my measurements, please???

Discussion in 'Home Theater Projects' started by Jeff Elliott, Oct 16, 2004.

  1. Jeff Elliott

    Jeff Elliott Stunt Coordinator

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    Hi All - Just rebuilt sub and it doesn't sound nearly like it did in my old room. I know that the acoustics of a room can make or break things, but this room should be much better than it's predecessor.

    This is the old AV-15, not the mkII. Here are the parameters:

    Fs: 19.7 Hz
    Qms: 4.71
    Qes: .399
    Qts: .368
    Vas: 228 L
    Re: 2.97 ohm
    Z: 4 ohm
    BL: 15.5 Tm
    Cms: .25 mm/N
    Mms: 260 g
    Pe: 500W
    1W/1m: 88.5dB
    2.83V: 92.5dB
    Xmax: 23 mm
    Xsus: 30 mm
    Sd: 802 sq cm

    My enclosure is about 6.5 ft^2 net and I am seeking a tuning of about 17hz. WinISD said the port length should be 46.5" as I'm using S&D PVC which is 6.875" in ID. I'm using a rythmic 350w amp and I'm crossed over at about 60hz. Basically, it sound terrible and I suspect the port length is wrong.

    Anyone care to double check my design? Any suggestions? I've tried tons of other placements but the sub still sounds rotten.

    Thanks
    Jeff
     
  2. KyleGS

    KyleGS Second Unit

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    You'r calc is correct. However after at a certain length your port can act as a resonator. It may be ringing out.
    Most people try to keep the ports at under 20-25" in length max.
    This may be your problem.

    To correct it you would need to go with a smaller pipe (single 5" or 4"). The lengths would be resonable but you may hear chuffing with moderate power.

    So now the only way to fix this is use passive radiators. this allows you to "port" the box without 4ft of PVC.

    The only other possibility would be a defective driver. I've heard from the source that the original AV's had a few problems in a certain batch or two.

    If it were my driver I would test it free air (LOW power) and make sure everything is tight.

    Then seal it up @ 3 to 3.5cf and pour on the power. [​IMG] That's just me.


    Hope this helps...
     
  3. Jeff Elliott

    Jeff Elliott Stunt Coordinator

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    Thanks for your insight, Kyle!

    This also sounds like good advice. Should I be using test tones to check things out? What should I look / listen for? I hear ya on the LOW power suggestion!

    Thanks again Kyle and also to anyone else who can spare a second to help!

    J
     
  4. Jeff Elliott

    Jeff Elliott Stunt Coordinator

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    Anyone?

    Thanks!
    JE
     
  5. KyleGS

    KyleGS Second Unit

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    That slot port looks like a good solution. You may get chuffing at extreme levels. (probably not) Depends on how loud you like it. You may want to round-over the edges of the slot port to help a little.
    I would exhaust all measures before chunking that box. [​IMG]


    To test it out you could simply run a very bassy rap song, organ, dance etc. The best way would be just to download and burn some test tone wav files.


    You could look for the NCH tone generator on your fav search engine and burn you a few tones from 20-100hz in any increments.
     

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