What is a SSF?

[RbAudio_Geek 10+ year member]

What is a SSF and how do i know if i have one? Is it on a amp,sub,, or what? Sry if i sould like a noob but this is somthing new that came up with the box i am building. Also what is the difference in a slot port? Form a reguler square port?

thank you

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[Johnny Drama 5,000+ posts]

Sub Sonic Filter, It cuts off the lower end bass so that you dont play your subs below their tuning specs in a ported box.

By the way, It would be on your amp...

 

[Johnny Drama 5,000+ posts]

Where is Nroman? I use to live in Benton, Ar

 

[RbAudio_Geek 10+ year member]

2hrs south south west out of little rock 1 hr our of Hot Springs 15mins from Gleenwood. lol i hope that narrows it down.

i want to tune my subs to 35 hertz b/c i listen mostly to rap. but if a song goes below 35 herts it wont play on the subs??? would the ssf be on the subs or amp or somthing i buy seperate?

 

[Polecat 5,000+ posts]

copied from another site:

SS filters are a good insurance policy when using ported subs. If low frequency (signals below PTF) are present in the audio content, the sub "unloads" (cone becomes unstable) and goes into cardiac arrest mode. Basically, we want to filter out as much audio signal power below PTF as possible to prevent woofer destruction.

For example:

We talk about SPL in dB or decibles. This is a unit of measure as to how much acoustic output an audio system can reproduce. We know that audio signals are electrical impulses from a source like a HU or amplifier. The amout of voltage it can put out, can be converted to dB's of sound pressure level. Hense SPL. The speaker (transducer) converts this electrical energy into sound waves. How much sound we hear out of that speaker is generally expressed as SPL in dB. (not voltage) Did I lose you yet?

Now, with ported sub applications, we know there is a lot of bass energy in todays' music. Some lows we can hear very well. Very low frequencies, (subsonics) are signals present, but we cannot hear them. We may feel them at a theater with movies like Volcano, Jurrasic Park and such... but we really cannot hear them. The subwoofers used in these applications are massive and designed to reproduce bass below human hearing. Best most of us can hear is ~25-30 Hz. Bolow that, it's mostly below our hearing ability... but we can feel it.

OK, back to business on filters. Say you have a sub and amp. The amp is say 300 RMS and the sub is moderately efficient. (89 dB of SPL at 1 watt, 1 meter away) The sub will reproduce bass well in sealed enclosures and net about 125 dB of SPL in bass range of 40-150 Hz. As the sub gets signals below ~ 40 Hz, the dB # will naturally rolloff at a predictable rate. (slope) The term used in audio is -X dB/octave. In the case of a sealed box design, that slope is -0dB at 40 Hz., -6dB loss of SPL at 20 Hz., -12dB at 10 Hz. (these are octaves.. 40,20 &10 Hz.)

In ported designs, the Port Tuning Frequency (PTF) determines how low the sub will play and still be distortion free. When porting, we get a nice passive peak in bass near the PTF. That peak is about +3dB more than a sealed enclosure will deliver with same sub and same power input. So now, you have +128 dB of output VS the +125 dB we mentioned earlier.

Near the PTF, the cone produces very little audio. The sound comes from the port. The cone does not move very much near PTF as the back pressure in the enclosure is being released into the port. That means the lack of cone movement, reduces cooling of the voice coils. This is where a lot of subs get fried. Not much movement and loads of power being dissapated in the form of heat. That's what fries a sub coil.

Below PTF, the cone motion returns, but there is so little backpressure in the box, it cannot control the cone movements. (unloading) Basically, this acts like there is no enclosure at all. (a "free air") sub is the result. With no control over the cone movement, the sub goes spastic and will often jump the gap or the coil bottoms out. Again, the result is a damaged sub.

When we use a SS filter, the filter will remove a goodly portion of sound energy that would normally pass to the woofer. The larger the slope of the filter, the better. Less watts of power (SPL) to the sub, below PTF is how we protect expensive woofers. The most efficient way to do this, is prior to amplification. That helps the amp as it does not waste large amounts of power, trying to amplify signals below PTF. In car audio, we don't get much music content below ~35-40 Hz. If PTF is say 40 Hz., we want to filter out as much signal content as possible, as we approach PTF. This is where good filtering is needed.

Let's say a sub is getting 300 watts of signal at 40 Hz. That's pretty loud stuff. Now, insert a 40 Hz SSF, 12dB/octave and the output watts will drop to (~20 watts) flowing to the sub at 20 Hz. That's safe for the sub to dissapate heat in that range. A 40 Hz SSF, 18dB/octave slope will lower the power to sub even more. Here, the sub is getting about 4.5 watts at 20 Hz. The basic line of designing a good filter, is to know that for each 3dB of sound we filter, it drops the watts input to the driver by 50%.

Here's a chart:

dB slope/octave........................................wattage to speaker

0dB reference...(no filtering).....................300 watts @ 40 Hz.

-3dB........................................................150 watts @ 20 Hz

-6dB.........................................................75 watts @ 20 Hz.

-9dB.........................................................37.5 watts @ 20 Hz.

-12dB.......................................................18.75 watts @ 20 Hz

-15dB....................................................... 9.38 watts @ 20 Hz.

-18dB....................................................... 4.7 watts @ 20 Hz.

See how that works? It's logrithmic, not linear.

Hope this helps some of you as you look at Ported enclosure designs

 

[RbAudio_Geek 10+ year member]

ok i will be running 2 S12L7's kickers they are getting 750rms (1500 peak) watts. So what kind of SSF will i need and where can i get one?

 

[JimJ 5,000+ posts]

Usually the amp will come with one built in - if it doesn't (like my old Avionixx 800.2 did and the JBL BP1200.1's do, for example), you could always buy an external one that goes inline with the RCA interconnects, like Harrison Labs FMOD's. TheZeb.com sells those.

 

[RbAudio_Geek 10+ year member]

I just pulled out my amp to see if it has one and it does now it has different settings on it like 50hz 75hz 100hz 225hz and 250hz it also has 0-180 degre phase. what is that and waht setteing will i need to set it to?

 

[RbAudio_Geek 10+ year member]

It says Subsonic Filter right under the different settings? What is that if its not a ssf?

 

[tRiGgEr 5,000+ posts]

That can't be a subsonic filter with the frequencys you listed.

Post up a pic of the amp's controls.

 

[RbAudio_Geek 10+ year member]

How did i post my pitcure?

 

[RbAudio_Geek 10+ year member]

I guess the pitcure didnt work

 

[RbAudio_Geek 10+ year member]

I got the piture in my images. I think you can look at it there. I would post it here but i dont know how to lol.

 

[RbAudio_Geek 10+ year member]

Anyone wanna help me?????

 

[RbAudio_Geek 10+ year member]

Come on you just cant leave me hangen...........