Just to clarify, you can go active with amps such as Sundown Amps or any other brands that have mutiple crossover settings on it? I know it isnt the best active setups or wont be in a SQ competition but you can do the basics with amps right? So others wont get confused that you gotta have headunit to at least try it.

For example in my system I run my front, rear and sub filters Through and let the amps do the work.

Correct. You can do a basic active setup with the crossovers in some amplifiers, such as the Sundown amps. IIRC this is the reason Jacob chose the frequency ranges he did for the crossovers in his amplifiers. It will not be the epitome of flexibility, but it will technically work.

But I never thought that the subsonic filter was another highpass filter. This is good to know. I thought the subsonic filter cut out low frequencies that would harm the sub.

I.E.

lp crossover at 80 hz

subsonic at 25 hz.

They can be used for that, and that is the reason most manufacturers include them in an amplifier. However they are simply a highpass crossover with a different "label", so if you choose to use them in another manor that is perfectly acceptable also

I just learned recently that lets say my box is ported and tuned to 32hz that the subsonic filter should be set below the tune of my box?

Correct. When you run a driver in a ported enclosure below tuning you run the risk of damaging the driver due to unloading. The SSF can and should be used to help protect the driver.

On a side note I was trying to figure out what I should set my SSF to on my amplifier for my subwoofer. I see in the link you posted it should be half an octave lower than port tuning, my port tuning is gonna be 30Hz. What is half an octave of 30Hz?

I was thinking it should be set at 22.55Hz but Im still learning. Since half an octave would be 1/4 the frequency, 30 x .25=7.5

So basically no matter which high pass filter (1 or 2) is set higher or lower than the other one it wont matter. The one that is the lowest is cutting off frequencies lower at steeper octave that decreases towards the highest high pass filter frequnecy setting).

Correct or still off?

Wording could use a little refinement, but I think you have the jist of things.

Correct, it doesn't matter which filter is set to the higher frequency and which to the lower frequency. As you approach 2nd crossover frequency, the rate of attenuation (or slope) will increase (or steepen). And I just want to clarify that you understand the slope of the crossovers themselves doesn't change. It is the effect of the multiple crossovers summing that increases the final rate of attenuation of the signal.

Also want to point out that the word highlighted in red above should be "rate of attenuation", or "slope". Octave describes the interval between frequencies. The term "decibels per octave" is used to describe the crossovers rate of attention, or slope, (in decibels) per the interval between frequencies (octave).

On a side note I was trying to figure out what I should set my SSF to on my amplifier for my subwoofer. I see in the link you posted it should be half an octave lower than port tuning, my port tuning is gonna be 30Hz. What is half an octave of 30Hz?

I was thinking it should be set at 22.55Hz but Im still learning. Since half an octave would be 1/4 the frequency, 30 x .25=7.5

You would be correct that 22.5hz is half an octave below 30hz.

Half an octave is one of many general recommendations. One thing you could do would be to load your sub and enclosure into an enclosure simulator and run an excursion plot. Look at the graph and see when the plotted excursion exceeds the capabilities of your subwoofer.

Ok thanks I know my word choice would of been off but yeah Im getting it now. So I understand that regardless of the frequency the slope range will stay the same (constant) and not change unless one of the filters' get changed. Clear as water now

Just so I got it as well... again box ported tuned to 32 hz so 1/4 octave below is 32 x .25 = 8, then 32-8 is 24 hz is what my subsonic filter should be set at. That is cool that I have a nice round number to work with. Makes it easier.

Good stuff guys.

Just so I got it as well... again box ported tuned to 32 hz so 1/4 octave below is 32 x .25 = 8, then 32-8 is 24 hz is what my subsonic filter should be set at. That is cool that I have a nice round number to work with. Makes it easier.

Good stuff guys.

Yeah I would say start at 24Hz or in the region and work you way up if you feel like your sub is reaching its mechanical limit.

I feel like the Lawnmower Man and Impious is Pierce Brosnan! "I think my knowledge has now surpassed your own, doctor." Yeah right.

That shed a lot of light dude. I cant believe Im absorbing this on a Saturday night!

Just so I got it as well... again box ported tuned to 32 hz so 1/4 octave below is 32 x .25 = 8, then 32-8 is 24 hz is what my subsonic filter should be set at. That is cool that I have a nice round number to work with. Makes it easier.

Good stuff guys.

Just an FYI; To find a half octave you can just multiply the frequency by .75

32 * .75 = 24

Just so I got it as well... again box ported tuned to 32 hz so 1/4 octave below is 32 x .25 = 8, then 32-8 is 24 hz is what my subsonic filter should be set at. That is cool that I have a nice round number to work with. Makes it easier.

Good stuff guys.

Just an FYI; To find a half octave you can just multiply the frequency by .75

32 * .75 = 24

And if you want a half octave up you can multiply by 1.5. Not that you need to here for absolutely anything.

Octave down = 1/2x, Octave up = 2x

This a very informative post! Thanks to all!

I still have more questions about things but Im out applying what I learned to midrange speakers and Im getting more depth out of them and suprised how low they can get for some PA speakers. If anybody has any questions or things to add please feel free to add.

Very technical thread !

1) I thought you had to set the sub sonic fillter just under the tuning frequency of the box.

My box is tuned at 32 Hz, and I tried to set the ssf at 30Hz. Is it really too high ?

2) BTW how can you be sure of the amps settings? It's difficult to see on all the amps I had : there are just a few numbers written for the amps settings.

Thanks a lot for all the informations we receive on this forum !

Very technical thread !

1) I thought you had to set the sub sonic fillter just under the tuning frequency of the box.

My box is tuned at 32 Hz, and I tried to set the ssf at 30Hz. Is it really too high ?

2) BTW how can you be sure of the amps settings? It's difficult to see on all the amps I had : there are just a few numbers written for the amps settings.

Thanks a lot for all the informations we receive on this forum !

1) You should set the subsonic such that your excursion is realistic for your sub. Rule of thumb's IMO are not the way to do it. A quick model in Win ISD will show you the excursion for your power and box size.

2) You can measure. Filter frequencies are -3dB points so you could play a 10v sine wave and measure on a voltmeter, keep reducing the frequency until you hit 7.07V and that will be your crossover frequency or 3dB down point. I'd recommend burning a CD with a whole range of sine tones around your frequency of interest and use them. Of course you could use a single one if you know specifically what frequency you want it to be at. For instance, if that were 30Hz burn a 30Hz sine tone on a CD. Play the CD through your system with the filters off and measure the voltage. Now multiply that voltage by .7079. Now turn on your filter and turn the knobs until your DMM reads whatever voltage you just calculated.

very informative thread, I tried rating it 5 stars, but I clicked on 2 stars by accident

Thank you M5.

I need to study some more !

I must try to set my amps like that, one day!

I love this forum !!!

Say I had two crossovers the kind that go in line with the speaker (+) wire. Both are exactly the same. If i use one, it's -12dB/oct

If i put them in series (amp---[x-over]---[x-over]----speaker) that translates into -24dB/oct?

Say I had two crossovers the kind that go in line with the speaker (+) wire. Both are exactly the same. If i use one, it's -12dB/oct

If i put them in series (amp---[x-over]---[x-over]----speaker) that translates into -24dB/oct?

Did you read through the entire thread, if so then it is answered for you. If not then please take the time to read through the entire thread thanks.

Say I had two crossovers the kind that go in line with the speaker (+) wire. Both are exactly the same. If i use one, it's -12dB/oct

If i put them in series (amp---[x-over]---[x-over]----speaker) that translates into -24dB/oct?

I've never seen two that are "exactly the same"