# Vented Enclosures Require a Subsonic Filter



## ElNuke

I have seen variations of the statement in subject line so many times while reading mobile audio articles & help docs that I have just come to think of it as gospel. However, I am facing a situation where I was going to run a ported box for a new sub, but then I realized I will not have a subsonic filter in the setup. So now I am questioning dogma...

I would not mind terribly if I had to run a sealed box with this sub, and do it because my amp lacked the subsonic filter, but I am wondering just how much concrete the "Vented Box + Subsonic Filter = LUV 4EVER" assertion is set in...


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## Jroo

I know back in the day people would run those FMODs to get a subsonic filter if the deck or amp didnt have one. 
https://www.amazon.com/Harrison-Labs-Inline-Subsonic-Crossover/dp/B00S8XXYHC

Basically you find the correct one for you needs and run them inline on the RCA.


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## Bayboy

Subsonic filters are useful, but not a total requirement. It really depends on where the tuning frequency is vs how low the program material goes.

I've installed a few setups where the tuning frequency was around 39hz, but in one case the vehicle owner only listened to Blues, Jazz, and R&B at moderate levels compared to the subs maximum output/handling before excursion issues occurred below the tuning frequency. That system appeared to play lower than what the tuning frequency suggested. Had a few ported setups to where a lower frequency was more useful despite having a subsonic filter to clean up the bottom end and protect the woofer. Not so black and white with this topic. 

Sent from my SM-G955U using Tapatalk


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## ElNuke

Jroo said:


> I know back in the day people would run those FMODs to get a subsonic filter if the deck or amp didnt have one.
> https://www.amazon.com/Harrison-Labs-Inline-Subsonic-Crossover/dp/B00S8XXYHC
> 
> Basically you find the correct one for you needs and run them inline on the RCA.


Dang those are nifty, I've never seen them before, but they do resemble some hootuses we used to remove off the cable lines to get more channels. I suspect they work on the same concept at some level.

Thanks!



Bayboy said:


> Subsonic filters are useful, but not a total requirement. It really depends on where the tuning frequency is vs how low the program material goes.
> 
> I've installed a few setups where the tuning frequency was around 39hz, but in one case the vehicle owner only listened to Blues, Jazz, and R&B at moderate levels compared to the subs maximum output/handling before excursion issues occurred below the tuning frequency. That system appeared to play lower than what the tuning frequency suggested. Had a few ported setups to where a lower frequency was more useful despite having a subsonic filter to clean up the bottom end and protect the woofer. Not so black and white with this topic.
> 
> Sent from my SM-G955U using Tapatalk


The sub's documentation says to tune for 31.8 hz for the ported [email protected] cu ft. But now that I think about it, I'm not sure how much of my music gets down really low anyway. Crapolla on a cracker!! 

Now I'm starting to waffle...I already have a sealed box that this sub would fit into, why am I not utilizing it instead...i can always buy a ported box later if I can't make the sealed one work to my liking...

I swear, if I could just pick something and stick with it instead of redoing it, replacing it, or changing my mind before I buy it, I would be the happiest hillbilly this side of the Pecos!


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## Weigel21

As said before, there are conditions where one is a must and conditions where it matters not. The general rule of thumb has been to set an infrasonic filter 5Hz below the tuning frequency of the enclosure, though setting one no further than half an octave below the tuning frequency is more so the rule, I believe. With a tuning of 32Hz, that be 24Hz, not a lot of the average listeners music has much below that, so more than likely, minimal damage will occur. Many factors are involved though, even if one were to play music with 20Hz unless the intensity of the note played were strong enough for the amplifier to push the sub into hitting it's Xlim, which requires much less effort below tuning btw, then there's little worry.


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## mark3004

Below the tuning frequency, the cone excursion have exponential increase. Most vented enclosure are tuning in the range 25-35, so in my opinion subsonic in vented enclosure is a must.
I run vented enclosure with 20hz subsonic (5th order) and the difference in the cone control with or without it is clearly noticeable.


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## ckirocz28

ElNuke said:


> The sub's documentation says to tune for 31.8 hz for the ported [email protected] cu ft. But now that I think about it, I'm not sure how much of my music gets down really low anyway. Crapolla on a cracker!!
> 
> 
> 
> Now I'm starting to waffle...I already have a sealed box that this sub would fit into, why am I not utilizing it instead...i can always buy a ported box later if I can't make the sealed one work to my liking...
> 
> 
> 
> I swear, if I could just pick something and stick with it instead of redoing it, replacing it, or changing my mind before I buy it, I would be the happiest hillbilly this side of the Pecos!


I'd definitely go with a subsonic filter with that tuning frequency, even kickdrums can reach way down into the teens, possibly damaging depending on your power level. However, since you have a sealed box for your sub, just use that for now.


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## openglcg

some subs have more xmech than others. whether it sounds good or not is a crap shoot though. i remember my sundown ev3s could handle the full power from a matched rms amp at 20hz even though the box was tuned at 30+hz. the sound was not to my liking though. the sound quality was amazing down to like 24hz but after that it felt like the output was fighting backwave and you heard noise too much in relation to the music. my x15 is similar with 2" xmech one way and 30mm xmax it wont bottom out easily even with an over rms amp and well below port tuning. can make my whole car oscilate on its shocks but not bottom out.


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## ckirocz28

openglcg said:


> ...can make my whole car oscilate on its shocks but not bottom out.


That's fun, and sometimes nauseating!


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## ElNuke

ckirocz28 said:


> That's fun, and sometimes nauseating!


Just like magic mushrooms! :laugh:


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## JCsAudio

IDK, I was always under the impression that low tuned boxes don’t need a subsonic. I generally tune my boxes in the low 30’s (depends on sub) and never use a subsonic and never had a problem. There isn’t much program material below 30 Hz in my opinion and I’ve watched it on an RTA while playing music of all types. 

Now if you are tuning higher, we’ll then you might want to consider it. Best thing to do is model it in WinISD or Bassbox Pro to try and predice excursions with any given box, fb, frequency, and RMS power. If your subwoofer bottoms out, you will hear it


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## ckirocz28

V8toilet said:


> IDK, I was always under the impression that low tuned boxes don’t need a subsonic. I generally tune my boxes in the low 30’s (depends on sub) and never use a subsonic and never had a problem. There isn’t much program material below 30 Hz in my opinion and I’ve watched it on an RTA while playing music of all types.
> 
> 
> 
> Now if you are tuning higher, we’ll then you might want to consider it. Best thing to do is model it in WinISD or Bassbox Pro to try and predice excursions with any given box, fb, frequency, and RMS power. If your subwoofer bottoms out, you will hear it


You're partly correct, the need for an SSF is based on program content and power. A whole lot of power can over-excurt just about any ported sub, with the right music.


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## JCsAudio

ckirocz28 said:


> You're partly correct, the need for an SSF is based on program content and power. A whole lot of power can over-excurt just about any ported sub, with the right music.


Agreed, for me I like to use bigger amps for more headroom but set the gains to match the power requirements of the subwoofer being used. I can use a 1000 watt amplifier on a subwoofer rated for 500 watts and never have a problem. I also don’t abuse my equipment so that helps allot too.


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## Hillbilly SQ

I've run several ported boxes and never run a subsonic filter even when I had that option. Never a problem. Had a pair of Fi x10's (entry level Fi at the time) tuned to around 35hz and they ate up more than rated power on low bass heavy rap and begged for more. Keep in mind who's behind Fi so ymmv greatly. Most of my other ported boxes have been tuned upper 20's.


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## Bayboy

The only time i've had issues with excursion below port tuning was playing bass tracks like DJ Billy E, Bass 305, etc. Even then that wasn't on every track and the sub wasn't tuned particularly low either (mid to high 30's IIRC). Alll other music program genres presented no problem. Even though the bass sounded deep, it just didn't get as low you think. 

I will say this though... if you listen to Hip Hop even on occasion, particularly old school East Coast, it's hard to beat the performance of a ported sub with it. Just doesn't resonate the same with a sealed. 

Sent from my SM-G955U using Tapatalk


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## Hillbilly SQ

I'm more of a 90's west coast kinda guy. Coolio, Snoop, etc.


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## ckirocz28

V8toilet said:


> Agreed, for me I like to use bigger amps for more headroom but set the gains to match the power requirements of the subwoofer being used. I can use a 1000 watt amplifier on a subwoofer rated for 500 watts and never have a problem. I also don’t abuse my equipment so that helps allot too.


I do the same, never blown a decent sub, I have however melted the voice coil on 3 Kicker C12's with about 300 watts each (old school C12's).


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## ckirocz28

Bayboy said:


> The only time i've had issues with excursion below port tuning was playing bass tracks like DJ Billy E, Bass 305, etc. Even then that wasn't on every track and the sub wasn't tuned particularly low either (mid to high 30's IIRC). Alll other music program genres presented no problem. Even though the bass sounded deep, it just didn't get as low you think.
> 
> I will say this though... if you listen to Hip Hop even on occasion, particularly old school East Coast, it's hard to beat the performance of a ported sub with it. Just doesn't resonate the same with a sealed.
> 
> Sent from my SM-G955U using Tapatalk


You just need the tiniest bit of distortion to listen to that with sealed subs.


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## Weigel21

Bayboy said:


> The only time i've had issues with excursion below port tuning was playing bass tracks like DJ Billy E, Bass 305, etc. Even then that wasn't on every track and the sub wasn't tuned particularly low either (mid to high 30's IIRC). Alll other music program genres presented no problem. Even though the bass sounded deep, it just didn't get as low you think.
> 
> I will say this though... if you listen to Hip Hop even on occasion, particularly old school East Coast, it's hard to beat the performance of a ported sub with it. Just doesn't resonate the same with a sealed.
> 
> Sent from my SM-G955U using Tapatalk


I seldom listen rap and hip hop these days, but I'll agree, ported is the way to go with those genres. My Polk MM1540 in 2CU.Ft. sealed down firing enclosure powered by a JBL MS-A5001 does OK with it, but its not ideal.


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## Bayboy

ckirocz28 said:


> You just need the tiniest bit of distortion to listen to that with sealed subs.


Errrr... nope

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## Bayboy

Weigel21 said:


> I seldom listen rap and hip hop these days, but I'll agree, ported is the way to go with those genres. My Polk MM1540 in 2CU.Ft. sealed down firing enclosure powered by a JBL MS-A5001 does OK with it, but its not ideal.


With as many subs and configurations I've fiddled with throughout the years, certain genres just sound better with ported. Can't say I prefer one over the other as I like both sealed & ported, but it's very hard to replicate the more effortlessly pronounced notes of a correctly built ported sub when using a sealed. We're not just talking about the very bottom end either..

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## miniSQ

If possible you should always use a SSF with a ported box. By design the box will unload the woofer at a certain frequency, and you need to protect that driver from freq at and below the unloaded point or risk damaging it. It has nothing to do with SQ or missing music, and everything to do with protecting the driver from freq's the box is not designed to play.


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## WilliamS

Having a SSF wont hurt anything if setup right and save your gear. I have used them for years and usually dont hear them really affect the music unless its old big band or jazz. Those genres usually have big low end, most newer music wont ever dig into that zone. Id rather have one set at 25hz and not need to worry about something tearing a coil vs just the hope of not needing it.


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## Hillbilly SQ

Bayboy said:


> With as many subs and configurations I've fiddled with throughout the years, certain genres just sound better with ported. Can't say I prefer one over the other as I like both sealed & ported, but it's very hard to replicate the more effortlessly pronounced notes of a correctly built ported sub when using a sealed. We're not just talking about the very bottom end either..
> 
> Sent from my SM-G955U using Tapatalk


Yeah, the effortless sound is what I like. Can't stand it when something sounds like it has to force out the notes. Same reason I will let a larger cone play higher if it sounds more realistic in a given range than the smaller driver it's handing off to.


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