# Subsonic Filter Setting



## sbelew (Feb 13, 2011)

I've been experimenting with test tones. My enclosure is/should be tunes to 32 Hz, my subsonic filter is set to around 30 Hz. Should I be able to hear test tones from 30 Hz down to 20 Hz?


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## mmakay (Oct 24, 2010)

Depends a lot on the filter. If it is 24bd/octave or higher, the sound will drop off pretty fast below 30hz.


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## minbari (Mar 3, 2011)

yes you will still hear them, but as mentioned they will fall off pretty quick. an SSF is not a magic switch that just cuts out all content below the setpoint (nor would you want it to)


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## req (Aug 4, 2007)

yes.

a filter, as the name implies FILTERS out sound. for example, a subsonic filter, will LIMIT the SUB SONIC (aka non-audible) sound. but it does not act like a brick wall, it will not stop all sound below that point instantly. there is a gradual drop off.

here is how this works... lets say you set your SSF at 20hz. there are different levels of filtration, a "first order" filter will cut frequencies at a slope of 6db per octave. an octave is either 1\2 a given frequency, or 2x the same frequency. so one octave below 20hz is 10hz. so at 10hz, any sound will be limited by 6db.

so you should be able ot hear 10hz, but significantly less loud than 20hz. and then at 5hz, it should be 12db less than 20hz. obviously there are other factors - but this is a general number of whereabouts the loudness will be.

so this is kind of what your sound amplitude would look like with a 25hz subsonic [email protected] 6db\octave and a low pass filter at about 70hz @ 6db\octave. (just there abouts on the graph, not exact numbers but im close)

does that make sense?


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## sbelew (Feb 13, 2011)

It is a 24 db subsonic filter, (just checked) So if I am understanding this, with SSF set at 30Hz, then at 15Hz, it will drop 24 db? So the volume of the 20 hz test tone would be significantly quieter? So then I am guessing at 20hz, it would drop 18db?

Im trying to learn how to set the SSF, I would like to buy a CC-1, but I would like to learn how to do it and exactly what it does instead of just hooking up a pc of equipment, and adjusting till it tell me it is correct.


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## minbari (Mar 3, 2011)

it will be in the ball park yes. with it set to 30hz it will be 24db down at 15 hz. 12db down at 22.5hz.

the moral to the story is, it will reduce, not eliminate sounds below the set point.


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## sbelew (Feb 13, 2011)

Ok, I think I got a handle on it now. Without having a db meter, it is nearly impossible to set the SSF this way with any accuracy. All I can do is to set it according to the markings on the amp and trust it to do its job. Might be time to order a CC-1

So thanks guys for the info.


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## minbari (Mar 3, 2011)

for all practical use. get it close and call it good. it you are hearing what you think is bottoming out due to low freq, then raise it very slightly.


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## req (Aug 4, 2007)

yea there is no reason to buy a piece of test equipment for a subsonic filter. look at the enclosure type. if it is sealed, you really should not need it. if it is ported, set it to around one octave below the tuning frequency.

its always a safe bet to set it around 15~25hz.


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## sqshoestring (Jun 19, 2007)

For ported I always set it to the box. I would play tones and sweeps to determine where it unloaded, you get more xmax at that point (at some medium volume enough to see xmax). As you sweep down on a slow sweep you see xmax nearly go away at tuning then get large under tuning. So try to find a tone just under tuning and turn the SS up in frequency until the xmax goes back down. Slow sweep again to ensure it is cutting xmax under tuning. You will want higher SS if you push the sub hard you can leave some xmax under tuning if you don't.

Sealed will tend to get more xmax the lower you go, so just a matter of controlling xmax for the output you want to reach. You would be pushing a sealed hard to need it, though it can save you amp power to use it.

I don't want one on my IB 15s, but then I am not overpowering them either.


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## Richv72 (May 11, 2012)

Interesting, never thought about it before because i guess I figured the ssf was a brick wall also.


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## minbari (Mar 3, 2011)

Richv72 said:


> Interesting, never thought about it before because i guess I figured the ssf was a brick wall also.


Nope, it is just a fancy name for a high pass filter on you're sub

Sent from my phone using digital farts


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## sqshoestring (Jun 19, 2007)

Just like a sub that is happy up high will need a lower lowpass, because it will play beyond it.


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