LPF and Difference Between Mono and Dual output?

[omnipseudo 10+ year member]

Hey - 2 very newbie questions here

1. On my Boss ( ew yes ) amp, theres a copper button marked "LPF" Ive been informed that this is "Low Passover Filter" - When I press it, theres a noticable difference in sound from the subs. Id just like to know techincally whats going on when I do this?

2. I just installed the Sony CDX-F7005X into my Wrangler and on the back where the RCAs go, there was a set of RCA connectors w/ a "Mono Sub" tag on them. I tried to plug the RCAs from my amp into these, and it worked fine. But because I wasnt sure what this was doing, I went ahead and installed the RCAs into the "Rear Audio" spots on the back. Whats the difference here?

System info can be found in my sig //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

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[omnipseudo 10+ year member]

1) Without getting overly technical, a low pass filter operates by filtering out frequencies higher than the crossover frequency while allowing a frequencies lower than the crossover frequency to pass through. Contrary to popular belief, a low pass filter doesn't just "cut off" the frequencies above the crossover frequency, but rather attenuates them at a certain rate known as the slope.
Let's say you have a -12 dB/octave LPF set to 80 Hz and your amplifier produces 1000 watts @ 80 Hz and below. At 160 Hz (1 octave above 80 Hz), your amplifier would only produce 62.5 watts (-12 dB). At 320 Hz (2 octaves above 80 Hz), your amplifier would only produce 3.90625 watts (-24 dB). At 640 Hz (3 octaves above 80 Hz), your amplifier would only produce 0.24414 watts (-36 dB), etc.

2) The difference can be large, but I'm not familiar with that particular head unit. If you were to use the Mono Sub output, you'd probably be able to use a lot of functions on the head unit (Subwoofer output control, low-pass filter, etc.) that you wouldn't get using the rear output. Also, on some head units, the sub output is a higher voltage output than the front/rear outputs.

Awesome - Thanks for the detailed reply!

Ive tried playing around w/ the LPF and I just dont like it on with most of my music (bassy rap and r/b) but with the Alt Rock and more vocal songs I listen to, it seems to project the voice better.

Ill be connecting the subs to the mono RCAs tonight, I just wasnt sure if that was limiting the channels or whatnot. This new HU has a LowXover setting, along with my amp, should these readings match or correcspond with eachother?

 

[omnipseudo 10+ year member]

It seems to project the voice better ? That doesn't make sense to me ...

Yeah lol I retract that comment. After going and changing the RCA connections, I played w/ the LPF some more...I guess I said it projects voice better cuz my x-over is around 80...and so it "cut" the bassy rolls out, so i heard my speakers more than the subs. But after a little fiddling around, Ive realized what you were saying, Im just not quite sure as to how Id use this LPF to my advantage to make my stuff louder/more SQ like...

Oh, and the mono RCA inputs helped alot...with the sub-control on my HU, my subs are reaching new depths of bass! Cant wait to get my new amp! //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Question : On the HU theres a High xover, and it doesnt seem to do much to my sound, if anything. Is this cuz my speakers are hooked up to my HU and not an amp?

 

[jinx8402 10+ year member]

That high pass x-over on your headunit effects your front and rear speakers. Use it at the same point that you have for the subs. So if your subs at low passed at 80 hz, high pass your regular speakers at 80 hz. Except for the 4x6's, you might want to cross them just a little bit higher because they can't handle those lower frequencies. Even though you can't tell the difference, still use them as they will protect your speakers from playing the low bass which they can't handle

 

[omnipseudo 10+ year member]

That high pass x-over on your headunit effects your front and rear speakers. Use it at the same point that you have for the subs. So if your subs at low passed at 80 hz, high pass your regular speakers at 80 hz. Except for the 4x6's, you might want to cross them just a little bit higher because they can't handle those lower frequencies. Even though you can't tell the difference, still use them as they will protect your speakers from playing the low bass which they can't handle

Thanks - So with my current setup, all 4 of my speakers are on the HU. And the 2 subs on my amp. So if i set the highpass to 125, lowpass to 80 on the HU and keep my xover on the amp @ 80 i should be good?

sorry if im asking redundant questions, im just getting into this whole tuning thing

 

[tgwX 10+ year member]

thats a question of mine as well, if you set the headunits lowpass to lets say .... 80 then, what does the amp need to be set at?

 

[jinx8402 10+ year member]

You don't have to set both crossovers on your HU and amp. You can just set one or the other to where ever you want. If you want you can set both up, as some argue it steepens the slope, but there is no real need to do it. If you are going to use just one of them, use which ever has the steeper slope. If your HU has a slope of 6db and the amp has 12db, use the amp or vice versa.