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How to set your Subsonic filter


BeatNdown8o8

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Hey guys Im sure everybody knows what a subsonic filter is but I know not everybody knows how to set it.Ive seen and heard alot of people ask where it should be set at...When I was looking around I found this read on decibel car.com..I thought maybe it could help somebody else out as it did for me!!!..I wasn't sure where to put this so Im sorry if this is in the wrong spot,But here it is an enjoy!!!!.....A subsonic filter is basically a High Pass Filter for very low frequencies, generally 45hz or lower. That is, whatever you set it at; only frequencies above that setting go through. Anything below that setting is attenuated (made quieter).

As only frequencies higher than your setting pass its a high pass filter.

A subsonic frequency is very low, so low the human ear can barely detect it, but your body can feel it. Because you cant hear it, and they're prone to damaging woofers, filtering subsonics is a desirable characteristic in subwoofer amplifiers.

A subsonic filter is used differently in sealed enclosures than in ported.

In a sealed box: The lower the frequency, the more excursion your subwoofer exhibits in order to play it loudly and accurately. A sealed box is tuned by enclosure volume, larger enclosures tune lower, smaller enclosures tune higher.

Subsonic frequencies potentially damage your subwoofer because they make it expend a lot of energy, travel right to the limits of its excursion and play below the enclosures tuning.

So for safety, we want to cut those frequencies out. For a sealed enclosure you adjust the subsonic filter to 25-35 Hz, to filter the extremely low bass frequencies your woofers unable to play.

In a ported box: You tune the port to a certain frequency, the enclosure is then capable of playing all frequencies above that tuning without an issue. The enclosure can also play below that frequency, but only half an octave, before the cone starts over-excurting and there's potential for damage.

So for safety, we set the subsonic to 1/2 an octave below our tuned frequency. Whats half an octave you say ? Lets do some maths ! One octave up is double the frequency, One octave down is half the frequency.

Lets say you are tuned to 45 Hz:

- 45 Hz / 2 = 22.5 Hz (one octave lower)

- 22.5 Hz /2 = 11.25 Hz (half an octave lower)

So we take 45 - 11.25 = 33.75 Hz (rounded up to 34 Hz)

In other words, you set your sub-sonic to 34 hz. So that way, if there's music below the ports frequency, it gets filtered out protecting your woofer.

Always remember the subsonic filter is NOT a cut-off. It has a roll off "slope" where whatever frequency its set to will be attenuated, and the attenuation effect increases as the frequencies get lower. Thus the power to the woofer decreases at filtered fequencies, which reduces the excursion and risk of damage.

As a final note for the audio geeks: Subsonic filters have steep slopes such as 3rd or 4th order(18 or 24dB/Oct) this is so u can set it nice and close to your 1/2 octave frequency, or 25-35 Hz sealed, without losing power in the neighboring frequencies.

{mos_fb_discuss:9}

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noooooo wayyyy. this has never been discussed on this forum ever. some good info for those who dont know i guess and who cant search.

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its about time someone does a write up on this. thanks op..

sticky it, still waiting on sticky.... now plz... o wait, doign a noob thing here and expecting a result right away. my bad.

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I think this is a large generalization as every install(box, subs, power level, design, vehicle, etc) is different. It's one of those "rule of thumb" type things. IMO most people would have enough trouble accurately setting their filters that trying to do something as exact as this would be a waste of their time

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I think this is a large generalization as every install(box, subs, power level, design, vehicle, etc) is different. It's one of those "rule of thumb" type things. IMO most people would have enough trouble accurately setting their filters that trying to do something as exact as this would be a waste of their time

Agree,...

I see it as over kill,......beyond overkill..

and then there is the ON or OFF filter that many amps have.....say, set at 28hz...(Non adjustable)

you really gonna design a box, off of your ssf?

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The best way I've found to set a SSF is to generate a sweep from 45 down to 10hz, about 60 seconds long, turn the subsonic up, then let that sweep rip full tilt and watch/listen to your subs. Turn it down as much as you can before the subs move "too much" when they get blow tuning.

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I think this is a large generalization as every install(box, subs, power level, design, vehicle, etc) is different. It's one of those "rule of thumb" type things. IMO most people would have enough trouble accurately setting their filters that trying to do something as exact as this would be a waste of their time

On the flip side, I think it's a good place to start. If you're just guessing as to what frequency to set it at. On top of that you're guessing where that frequency is on the knob as a lot of amps have very poor marking around the knob forcing you to guess where the frequency is where you want to set it at. Put these together and you could be way off either way. At least you knock some of the guess work out of it this way. It may not be exact, but at least it would be closer.On the flip side, I think it's a good place to start. If you're just guessing as to what frequency to set it at. On top of that you're guessing where that frequency is on the knob as a lot of amps have very poor marking around the knob forcing you to guess where the frequency is where you want to set it at. Put these together and you could be way off either way. At least you knock some of the guess work out of it this way. It may not be exact, but at least it would be closer.

You're not going to blow up your car playing below tuning. Just don't be reckless with it. SSF @ 25hz is fine.

You and I may be fine with not being reckless with it, but I don't care what you tell someone who you've just installed and setup their system, they'll go overboard. Why do you think most places set people's gains rather conservatively, etc? It may not eliminate the possibility of them killing their sub/amp/etc. but at least it makes it a little harder for them to do.

I don't run a subsonic on my level 5, but that's because I'm careful with it as well as it being rather forgiving, but when I had my 8" RF Punch HX2 in one of my summer cars on my Earthquake PHD2000, I really wish I had a subsonic on it. Not because I am reckless, but for example, I had the usb drive with all of my songs from my audio car and the last song in a folder finished and the next folder had my Tones in it. That folder started out with an 8hz tone. I wasn't at full tilt, but even so, the sub still bottomed out for about 2 seconds before I was able to switch to a different album.

Even though this is an extreme case, I've had to set the subsonic on a friend's hifonics brutus 15 (very short throw sub in a very undersized prefab box with a terribly sized port). In a trunk car with an inexperienced user and an amp that puts out 1.5 times what the sub can handle, that's a recipe for disaster. I just set the subsonic by ear, but if I would have known this at the time, I would have used it as a starting point and probably could have gotten a bit more low end output out of it vs. guessing and then setting it ultra conservatively because I didn't have time to run it through a gammit of songs.

Either way, my point is, while this guide may not help anyone, I think it's still good information for a lot of people. I would compare it to setting an amp's gain by ear vs setting it with a multimeter. Sure, neither of the methods are very accurate, and it's much easier to set the gain by ear, but at least with a multimeter you've got something to go on. And yeah, you should use an o-scope or DD-1 (I personally have a DD-1), but not everyone has one or access to one. In those cases I'd recommend using a multimeter AND by ear vs just by ear, at least you have something to go off of. In the case of subsonic filters, it's pretty parallel, to do it RIGHT, you should have a CC-1, but without having one, I'd say this is probably the next best method available.

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