Going Active

[jcarter1885 995]

As for the process of going Active I understand that part, my definition of going active is letting your headunit, processor or amp's crossover capabilities control the speakers frequency range. Instead of using one speaker to play a wide range of frequencies you can split them up into a 2-way sytem (midbass/midrange and tweeters) or 3-way system (midbass, midrange and tweeters); where each speaker plays its own certain frequency range such as midbass, midrange and highs. That is my simple understanding of going active and not the best or most accurate definition.

Now onto the question at hand I use Eminence Alpha-6a for now on my Sundown SAX-125.2 (2 per channel) and they ran on high pass filter from 300/500Hz on up. I noticed that when I messed around with the Subsonic on the amp it changed the sound that the speakers put out. After talking to Jacob he said "Subsonic is always active - so it will increase the slope of the high pass within it's range. The subsonic is just another HPF filter -- it makes the cut-off steeper starting at where the knob is set." After he told me this I asked for the dumb downed version of it so a beginner like my self in going active would have a better understanding, then he said it cuts out more low frequency stuff. I kinda want to know the why and how it does this, do you use the 10-500Hz frequency range(that the Subsonic filter can be set at) as a guide or is that totally irrelevant

So anybody who will take some time in breaking this down further for a more broad scope so I can get a better feeling for active and what happens when you make adjustments by turning the subsonic filter knob? I actually want some experience people to help me and no guesses or what you think it is, so this topic wont become cluttered with opinions just facts.

[Impious 1,476]

I guess I'm a little confused on what it is you are actually asking. Jacob's description is spot on. But I'll give it a shot and we'll go from there.

A subsonic filter is nothing more than a highpass filter (crossover). Filters (crossovers) are cumulative; If you are using more than one filter, then the slope of each filter used will combine.

For example, lets say you have the highpass filter on your headunit set to 500hz, and it's slope is 24db/oct. You then also use your amp's 24db/oct subsonic filter and likewise set it to 500hz. We will assume both are butterworth filters, which means the crossover frequency is the point at which the signal has decreased by a level of -3db.

Now, in this particular scenario since we are using two crossovers of the same slope and alignment, both set to 500hz, the net result is that the signal will be down -6db at 500hz and the net slope will be -48db/oct. This is because, as noted earlier, the two crossovers combine. They both affect the signal.

Or we could cascade the filters. We could set the crossover on the headunit to 500hz and set the subsonic filter at 250hz. In this scenario, the signal would only be down -3db at 500hz and the slope at that point will continue at the original 24db/oct rolloff. Now, normally at 250hz (one octave lower than 500hz) the signal would be down -24db due to the 24db/oct slope of the headunit's crossover. However, as we approach 250hz the signal will begin to decrease in level quicker than 24db/oct because the 2nd, cascaded, filter (in this case, the subsonic filter) will also begin affecting the signal. The signal at 250hz will instead be down -27db (original 24db/oct slope + -3db from subsonic filter) and from there continue to decrease at 48db/oct due to the combined effects of both the headunit's 24db/oct filter and the 24db/oct subsonic filter. So the frequencies below 250hz will be attentuated much more quickly than above 250hz.

This can be done with any two filters (crossovers). You could use the lowpass crossover on your headunit and the lowpass crossover on your amplifier to obtain the same affect on the top end of your midrange, for example. Or the highpass in your headunit and highpass on your amplifier to steepen the highpass filter on your tweeters. Etc.

This is a simple, idealized example for explanation purposes. In reality there may be some other factors to take into consideration such as the Q of the filters and such.....but it should provide you an idea of what Jacob was talking about.

Clear as mud ?? Help, not help?

[jcarter1885 995]

Car audio wise it makes sense but to an average joe like me it is not muddy but murky water im in. I guess I just need to get a better understanding of crossover's, slopes and so on to get a better grasp of this thats all.

Yeah I know my question wasnt clear but you answered it correctly.

[Impious 1,476]

Crossovers unfortunately can be an extremely complicated subject. The above wouldn't even qualify as a snowflake on the tip of the crossover iceberg.

But for the basics, if you haven't read it yet, you can start here;

http://bcae1.com/xovrslop.htm

[jcarter1885 995]

So what about this example, if I set my highpass filter at 300Hz on my midrange and the Sub Sonic Filter at 500Hz will that cancel out the high pass filter or raise the octave slope?

[Impious 1,476]

Two of the same type of filters (highpass and highpass, for example) won't "cancel out". They will be cumulative, they will combine. How they combine will be affected by a multitude of factors, including but not limited to the slope of the filters and the crossover frequencies.

In your example, the signal would be affected by the subsonic filter until the signal begins approaching 300hz, at which point the net slope will be a combination of both the subsonic filter and the headunit's highpass filter. It will increase the attenuation of the signal, or in other words, it will cause the slope to steepen and increase the -Xdb/oct rolloff rate of the signal.

[jcarter1885 995]

I dont think I will ever understand the background info to this stuff but I do appreciate your help and info you provided.

[blue fury 3]

Wait, I was told this a long time ago:

"Slopes in a crossover don't add together for a final amount. If they're both 12db, it's a 12db slope. If one is 12 and one is 24, then you have a 24 db slope, rendering the 12db useless. "

This isn't true? I never really could understand how what I quoted to be true since my logic told me exactly what you posted above, Impious.

[Sir-Lancelot 216]

Passive FTW.

[jcarter1885 995]

I guess once I get an understanding of the technical side then I can go out and apply it to the real world, it seems simple but trying to apply it may be difficult. Its like I want to learn it on paper (or words form) then take it outside and test it system wise to see if there is a sound difference associated with it.

Question #1:

I understand how if you drop the sub sonic filter below the high pass filter it will attenuate the frequencies lower than the subsonic filter faster than the ones above it till it reaches the high pass filter point. So if the sub sonic filter and high pass filter are the same then it will attenuate the frequencies below both filters. So does it affect the frequencies above the filters?

Question #2:

Can you set the sub sonic filter above the high pass filter (I know manually you can just by turning the knob but is it common). For example if you set the high pass filter at 500Hz and sub sonic filter at 750Hz or higher, how would it affect the frequencies?

Thanks Guys

[bigrank916 72]

I guess once I get an understanding of the technical side then I can go out and apply it to the real world, it seems simple but trying to apply it may be difficult. Its like I want to learn it on paper (or words form) then take it outside and test it system wise to see if there is a sound difference associated with it.

Its soo hard for me to abundantly learn without some visual aides. I need to see it, to understand it.

Dont worry dude. It will come to you eventually. I thought I was going to shit myself on Impious' last post!

[jcarter1885 995]

I guess once I get an understanding of the technical side then I can go out and apply it to the real world, it seems simple but trying to apply it may be difficult. Its like I want to learn it on paper (or words form) then take it outside and test it system wise to see if there is a sound difference associated with it.

Its soo hard for me to abundantly learn without some visual aides. I need to see it, to understand it.

Dont worry dude. It will come to you eventually. I thought I was going to shit myself on Impious' last post!

Haha yeah I feel you and we are on the same tip, when I go out there and mess with the filters I can hear the difference but I kinda want to know why that difference is happening or how it is happening? Then I didnt know it was gonna be that technical but hey time is my friend so it will come to me with the help of these knowledgeable individuals on this forum.

[Impious 1,476]

Wait, I was told this a long time ago:

"Slopes in a crossover don't add together for a final amount. If they're both 12db, it's a 12db slope. If one is 12 and one is 24, then you have a 24 db slope, rendering the 12db useless. "

This isn't true? I never really could understand how what I quoted to be true since my logic told me exactly what you posted above, Impious.

Completely false. Don't know who told you that, but it's completely untrue.

[Impious 1,476]

Question #1:

I understand how if you drop the sub sonic filter below the high pass filter it will attenuate the frequencies lower than the subsonic filter faster than the ones above it till it reaches the high pass filter point. So if the sub sonic filter and high pass filter are the same then it will attenuate the frequencies below both filters. So does it affect the frequencies above the filters?

You mean, for example, if we set them to 500hz how would 1000hz be affected?

Go back to the BCAE1 link I posted earlier in the thread and look at the graph.

Question #2:

Can you set the sub sonic filter above the high pass filter (I know manually you can just by turning the knob but is it common). For example if you set the high pass filter at 500Hz and sub sonic filter at 750Hz or higher, how would it affect the frequencies?

I think it would help if we stopped calling the subsonic filter a subsonic filter, honestly. It helps for identification of which filter we are talking about, but I think it might be causing you to think of the subsonic filter as something it's not. Subsonic filter is just a fancy (an in many ways, wrong) term that we use to describe a highpass crossover that can be set to very low frequencies. It is no different than the highpass crossover on the amplifier, or in your headunit. They are the exact same thing, we just use different terms to identify them. We'll call the headunit's highpass crossover Filter 1 and the "subsonic" crossover Filter 2.

If we stick with our highly idealized situation and continue to assume they are both the same slope; Setting Filter 1 to 500hz and Filter 2 to 750hz is exactly the same as setting Filter 1 to 750hz and Filter 2 to 500hz. The results would be identical.

A better question is; Why would the result be different? They are both doing the exact same thing to the signal. It doesn't matter which comes first if they are both doing the same thing.

[jcarter1885 995]

Honestly Impious if those graphs were helping me I wouldnt be asking these questions but I can go with High pass filter 1 and high pass filter 2. My high pass filter 1 is my amps filter since I have the filter on the headunit as through so the amp controls it till I get a better headunit.

After reading posts #85My link Im getting a better understanding of the slope thing.

[Impious 1,476]

Hrmph. I guess maybe I presumed you knew something you didn't when I was writing out my previous responses.

Suppose maybe I should have began by asking if you understood the crossovers, slopes, etc

Maybe this post I made a few years ago will help some also?

http://www.caraudio....548&postcount=2

Let us know where you're still a little confused, we'll try to help

[blue fury 3]

Wait, I was told this a long time ago:

"Slopes in a crossover don't add together for a final amount. If they're both 12db, it's a 12db slope. If one is 12 and one is 24, then you have a 24 db slope, rendering the 12db useless. "

This isn't true? I never really could understand how what I quoted to be true since my logic told me exactly what you posted above, Impious.

Completely false. Don't know who told you that, but it's completely untrue.

Thanks for confirming it. I didn't do a direct quote becuase it's on a different forum. .

So in a nutshell for basic situations, the xover slope is summed together.

Edited December 13, 2009 by blue fury

[hove 15]

Honestly Impious if those graphs were helping me I wouldnt be asking these questions but I can go with High pass filter 1 and high pass filter 2. My high pass filter 1 is my amps filter since I have the filter on the headunit as through so the amp controls it till I get a better headunit.

After reading posts #85My link Im getting a better understanding of the slope thing.

just a quick question, sorry to but in but i dident think this was worth making a new thread lol

will my pioneer 6100BT work good for my active setup?

[///M5 2,833]

The 6100 doesn't have active filters for anything but a subwoofer, so no it won't do an active front stage. Assuming the link I found in Europe holds true for here as well.

[jcarter1885 995]

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.

[jcarter1885 995]

Hrmph. I guess maybe I presumed you knew something you didn't when I was writing out my previous responses.

Suppose maybe I should have began by asking if you understood the crossovers, slopes, etc

Maybe this post I made a few years ago will help some also?

http://www.caraudio....548&postcount=2

Let us know where you're still a little confused, we'll try to help

This page that you posted helps out drastically as I also went through old Sundown posts and read all the ones I posted and others did about using the amps crossover flexibility. I spent the whole day to get this background info and technical aspect done and Im slowly understanding this. After I finish reading this link again I may have some more questions for you, Thanks

[deathcloud 6]

Wow reading this thread I think increased my IQ a bit. Hahaha. Joking aside, I learned a hell of a lot. I usually just do the through on my headunit as well assuming that my amp will sound better due to it having 24 db slope. 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.

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?

With all these tweaks and such (going from 24db slope to 48db slope) I am excited to start really tuning/tweaking my settings now.

[jcarter1885 995]

Im glad people can learn from this, that is what it is here for since I know Im not the only one who wants or needs to know this.

[Impious 1,476]

Wait, I was told this a long time ago:

"Slopes in a crossover don't add together for a final amount. If they're both 12db, it's a 12db slope. If one is 12 and one is 24, then you have a 24 db slope, rendering the 12db useless. "

This isn't true? I never really could understand how what I quoted to be true since my logic told me exactly what you posted above, Impious.

Completely false. Don't know who told you that, but it's completely untrue.

Thanks for confirming it. I didn't do a direct quote becuase it's on a different forum. .

So in a nutshell for basic situations, the xover slope is summed together.

In a basic nutshell, correct.

This is the essence of a Linkwitz-Riley crossover

[jcarter1885 995]

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?