# confusion on subsonic filter adjustmets



## tonyvdb (Sep 5, 2007)

Ok, Ive been trying to figure out how to properly use the subsonic filter on my PB13 Ultra. I'm not sure if moving this to the SVS sub forum is where I want it to be as this should pertain to alot of different subwoofers not just SVS.

I was under the impression that the subsonic filter is used to stop frequencies below what it is set at from going to the sub and is a sort of protection against over excursion caused by those frequencies (below 10Hz).
Now with the SVS PB13 Ultra it is also important to use the "Bungs" (plugs) that come with it to plug the ports as you change that setting lower.
My question is can a person not leave the bungs out and just use the subsonic filter? What are the reasons and how should I go about this to properly do this.
My room is large 4500sq ft and am also using another sub to help with the lows.

confused:scratch:


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## bobgpsr (Apr 20, 2006)

tonyvdb said:


> My question is can a person not leave the bungs out and just use the subsonic filter? What are the reasons and how should I go about this to properly do this.


No you should not -- if you do, you risk the chance of damaging the driver. 

When you plug a port you lower the tuning freq. The driver's excursions are generally constrained at or above the tuning freq. After you plug a port you may then reduce the frequency of the protective high pass filter. Below the tuning freq the driver is not constrained (often called unloading) by the ported box design (port and box volume) and it needs the right setting of a high pass (low cut) filter to protect it.


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## tonyvdb (Sep 5, 2007)

Ok thanks, so that means that I should simply leave the ssf set to 20Hz (its highest setting) with no plugs?


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## drdoan (Aug 30, 2006)

yes, the manual explains that. You should match the sub filter with the number of plugs (or lack of plugs). That way, you are much less likely to bottom out the sub. I keep mine set to 20HZ (or is it 25, I can't remember, but it is as the manual says) with no plugs installed. Since I use Audyssey MultiEQ on my Denon to balance the speakers, I get an amazingly clean and balanced bass. Have fun. Dennis


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