Leaderboard

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. 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.

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?

Have you done anything M5 or myself have previously suggested in this thread? If not, then there's no point in continuing to try to assist you. If yes, please report back with what you have done and the results.

I like the Alpine Type Xs Also, you mention only 80hz and below for BTLs. That means, everything else from ~100hz and up, is all about the components right? Even front speakers? What I mean with BTL canceling was that I want loud and good components so my mids and highs are clear and are not lost with the boom boom of the BTLs. Thats why I want good components too.

Amusingly you deleted your recommendations after reading my post.... ya i read almost all of it.....missed your post....... then after re-reading it decided you are more then likely right .... mite change the sound alittle, but not get super lounder... so no sense getting a pissing match going when you are right !

hey guys so this will be my first box build. I have 18in fibl dual 1ohm with a jbl gto 1200.1 watts 1114 watts rms at 2ohm. my max demsions are 37L by 20W by 15 Depth. Im using Re enclourse calculater. But i want to know whats a good port area size and port width and any other factors that i should be looking for liiek what it should be tuned at. I want it to sound loud, hit lows, and have good air flow. If you guys could help id appreciate it

Passive FTW.