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port noise and other concerns I may be missing

Discussion in 'Home Theater Projects' started by Geoff Rinella, Apr 14, 2005.

  1. Geoff Rinella

    Geoff Rinella Member

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    I am planning on building a ported box for a 15" quatro. I've been playing with WinISD, and it looks to me like a 5.5 cuft box ported at 20.12 Hz will work best. I am thinking about making a slotted port with an opening of 2"x10" and length of 21".

    WinISD predicts the air velocity peak of 73.8 ft/s at 16.5 Hz. Will this produce port noise?

    Do my box plans look good, or am I missing something else?

    Thank you.
     
  2. Mattak

    Mattak Well-Known Member

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    I would say yes, there's a possibility of noise. On the other hand, I don't think it's such a big issue as other people seem to think.
     
  3. Mike Keith

    Mike Keith Well-Known Member

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    Your right on the cusp, you'll probably be ok with real music content. Most work in terms of M/s which is easier to understand. The rule of thumb from my experience it to stay under 20M/s.
     
  4. Geoff Rinella

    Geoff Rinella Member

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    Thank you. That helps a lot. One other question I have is, when calculating the box volume, do you have to subtract the volume that the port takes up?
     
  5. Brian Bunge

    Brian Bunge Well-Known Member

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    Geoff,

    Yes, you do.
     
  6. Mattak

    Mattak Well-Known Member

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    ...and the bracing, and the driver displacement... [​IMG]
     
  7. Geoff Rinella

    Geoff Rinella Member

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    perfect, thank you. I am just about ready to start buidling. [​IMG] hopefully I won't run into any more questions.
     
  8. Jack Keck

    Jack Keck Well-Known Member

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    ....as well as the displacement of the amp, if you are installing it in the box.
     
  9. Dan Wesnor

    Dan Wesnor Well-Known Member

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    I wouldn't worry about port, noise, that's a HUGE port. Remember that airspeed increases as the sub plays louder. I don't know what output level WinISD is computing air speed at, but it's probably much louder than you'll actually listen at, maybe even louder than what the driver can produce before hitting Xmax.
     
  10. Dan Wesnor

    Dan Wesnor Well-Known Member

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    UniBox says that you won't get port noise until you hit 250W, at which point you'll be putting out 112dB. At this point, the chuffing noise is barely audible in a quite room - you won't hear it with a woofer putting out 112dB. Also the cone has exceeded Xmax, so the distortion will be much worse than the chuffing. The first port resonance is at 280Hz or so, and that also might be louder than the port noise (but still not noticeable).

    If you cut the width of the slot in half, you can still get 106dB before chuffing starts, and the first port resonance will be an octave higher, meaning you will be much less likely to hear it. 106dB is about the maximum level an LFE sub will put out when DD is played at reference volume.
     

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