Questions regarding subsonic/infrasonic filters.

[whitesharingan 0]

1:Is there a difference between these two?

2: Does the filter have to match the boxes tuning?

Or is there an acceptable range?

I have the RF T-2500.1BD amp with a 28Hz infrasonic filter.

3: If I use a box that is tuned at 32Hz, will this be sufficient?

4: If not where can I find a good subsonic filter?

Thank you for any answers or suggestions.

[Impious 1,476]

1:Is there a difference between these two?

No. They are the same thing. And really it's just a fancy way of saying it's a highpass filter with a really low crossover frequency and generally a steep slope.

2: Does the filter have to match the boxes tuning?

No. And actually, since the SSF is simply a highpass crossover the crossover point is defined as the -3db point of the signal. So if you set it to your tuning frequency, you will actually be attenuating the output by -3db at the tuning frequency (and attentuating output above the tuning frequency also).

Or is there an acceptable range?

Yes, you need to set to a point where the filter reduces the signal enough to keep the driver from overexcurting below tuning.

There are a dozen "rules of thumb" that people go by. Probably the easiest thing to do is load your driver, enclosure and power into an enclosure simulation program and look at the excursion graph. Look at the point where the excursion for the driver exceeds Xmax. You would want to set the SSF somewhere around or slightly above that frequency. "Generally" you should be safe for about a half octave below tuning (half octave = frequency * .75)

I have the RF T-2500.1BD amp with a 28Hz infrasonic filter.

3: If I use a box that is tuned at 32Hz, will this be sufficient?

Yes, should be fine.

[NDMstang65 403]

Filter is too shallow at 12dB per octave..

We suggest putting an in line adjustable in and setting it 2-3Hz below tuning.

You can get one from harrison labs.

[Impious 1,476]

Filter is too shallow at 12dB per octave..

Really? That's odd for for an SSF.

I (incorrectly) assumed it would have been steeper. It would probably still be fine. But if you really want the added protection from the potential dumbass attack you can add an inline as Nick mentioned. Or you could model cone excursion in WinISD with an added 2nd order highpass filter to simulate your amps SSF.

[NDMstang65 403]

Yep that thing is junk at best for a filter...

I don't understand why Rockford won't spend the 3 dollars on a pot, 2 resistors and a capacitor to make it adjustable and 18dB/octave..

[XxedgarxX 2]

sorry to steal but i will need one if my kicker has a fixed 25hz and i want a ported box to 33hz to 35hz

[NDMstang65 403]

Definitely

[XxedgarxX 2]

thanks

[whitesharingan 0]

I don't understand why Rockford won't spend the 3 dollars on a pot, 2 resistors and a capacitor to make it adjustable and 18dB/octave..

I assume that you are referring to the F-mod SSF found Here with the 30Hz value.

Also are you saying that the SSF should have a 18dB/octave,

because the one here only has a 12dB/octave.

[NDMstang65 403]

An adjustable 12dB/octave one is fine...one that is not adjustable is not...because you can turn the 12dB/octave one up a little more and get by with it peachy.

I haven't had the time to start making filters yet..is on my to do list though.

[C4W18 0]

hrm....sucks...got the same setup as him..i was told it should be fine considering i'm tuned 4 Hz above the cuttoff. and yea, i do think its bullshit that i pay a little less than a grand for this amp and it has a switched infrasonic. herp derp.

Edited March 5, 2011 by C4W18

[whitesharingan 0]

I haven't had the time to start making filters yet..is on my to do list though.

When you do let me know and I'll be happy to pick one up.

[Robert 9]

Same here.

[95Honda 486]

You can easily just cascade the filter... Just add one of the F-mods to the input with roughly the same frequncy and you'll have a 4th order rolloff to match the box....

[NDMstang65 403]

Exachary

[C4W18 0]

same frequency of the cutoff for the infrasonic filter or the helmholtz resonance of the box?

i'm guessing you mean the filter.....the 12 db rolloffs combine? interesting if thats what you mean....didn't know that.

[Impious 1,476]

Yes, the slopes will combine. If you have exactly the same crossover frequency on both 2nd order filters the slope will be -24db/oct and the signal will be down -6db at the crossover frequency as opposed to -3db.

This is exactly what a Linkwitz-Riley crossover filter is. Two cascaded 2nd order filters.

If the xover frequencies are staggered, things are little different...but the filter slopes will still combine.

[C4W18 0]

thanks, very informative. Haven't learned about that before. This seems like an excellent solution for me.

[whitesharingan 0]

So in my case, will having the amps built in 28Hz 12dB/octave SSF

combined with a F-Mod SSF with a 30Hz value @ 12dB/octave,

attached in line, make everything perfect with a box tuned to 30Hz?

[C4W18 0]

i think he means if you have the f-mod at 28 the 12 db/octaves combine to make it 4th order (24 db slope). i guess i'll be doing the same thing for a temporary fix, that is until I get my hands on a DQXS.

[95Honda 486]

So in my case, will having the amps built in 28Hz 12dB/octave SSF

combined with a F-Mod SSF with a 30Hz value @ 12dB/octave,

attached in line, make everything perfect with a box tuned to 30Hz?

Should work just fine....