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Port plugging

Discussion in 'Speakers' started by Joe Wilmore, Mar 10, 2005.

  1. Joe Wilmore

    Joe Wilmore Stunt Coordinator

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    Does anyone know where I can find the posts that talk about the difference in db's between blocking the top or bottom port on their SVS's?
     
  2. Eric Hargrove

    Eric Hargrove Stunt Coordinator

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    Hi Joe,

    I am not quite sure what you're asking but I'll give it a shot. There should be no discernable difference between ports. Any port you plug will drop the tuning of the subwoofer the same amount. What I have noticed in my room with my CS Ultras while running sinewave sweeps is one port plug for each Ultra is the best of both worlds for me. I gained an incredible 12db at 15Hz. The only downside is you sacrifice a little bit of output,typically 2db or so in my room which I consider a small price to pay for the added extension.
     
  3. Joe Wilmore

    Joe Wilmore Stunt Coordinator

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    Sorry for not being more clear. I was talking about people who have a PB2+, or a PB2 ultra. I remember a thread where someone talked about there being a difference in db's, depending on whether they plugged the top, middle or bottom port.
     
  4. Eric Hargrove

    Eric Hargrove Stunt Coordinator

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    Oh, OK! Still should not make any difference. If you have an SPL meter, you could experiment abit. It has never made a bit of difference for me. I'm sure if it made a difference, Ron would have put it in the manual.
     
  5. SVS-Ron

    SVS-Ron Screenwriter

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    Joe,

    There is NO difference in "dB's" at all, with regards to which port you plug. Zero.

    Now, there IS a difference in total headroom above the tuning point with each port you plug. A PB12-Plus/2 (formerly known as the PB2-Plus) is set to 25Hz with all ports open (figure flat extension to around 20Hz in most rooms), 20Hz with one port closed (you'll be linear to around 15-16hz then) and 16hz with two ports closed (call it 10-11Hz... corner loaded, mid-sized room).

    The bill to be paid?

    Figure about a 2dB drop in total headroom (the ability to handle a transient, or more dynamic range) above the new tuning configuration. Given how much headroom this sub starts with, most folks don't consider the 20Hz setup a compromise of any kind and like the combination of depth and power. So, while you drop a bit of "headroom" when you use one plug, and more with two plugs, you gain power down low.

    Physics, as they say, is a PITA.

    Keep in mind it's critical you match your port config with your subsonic filter settings.

    Drop us a line if you need more detailed help.

    Ron Stimpson
     
  6. Joe Wilmore

    Joe Wilmore Stunt Coordinator

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    Thanks Ron for the response. I was aware of that part, but I thought that at least one person had noticed a change in db's. For example, if they ran a scene from a movie in the 20hz tune, they might have hit 115 db's with the bottom port plugged, and 113 db's with the top port plugged.
     
  7. SVS-Ron

    SVS-Ron Screenwriter

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    Could be Joe, but holding the meter a few inches differently or being a second off on the bass peak in question could easily explain it.

    There's no design or acoustical reason one plug will affect things differently than another.

    The good news is you have one thing less to worry about on setup! ;^)

    Ron
     
  8. Joe Wilmore

    Joe Wilmore Stunt Coordinator

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    Ok, thanks for the quick response.
     

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