Not understanding active on HU's

[dtavano 10+ year member]

OK, I'm quite a bit confused as to how you can go active with the head unit itself. For the subs what difference does it make, can't you just use the crossover on the amp? Or is it for on-the-fly crossover changing, which doesn't seem necessary at all?

I only have a 2 channel amp for my components, but do 4 channel amps have 2 sets of RCA inputs? Aren't there 2 sets of crossovers on a 4 channel amp? Or do most amps not have active crossovers on them? Both of mine do. The only thing that would help me is 2 sets of RCA so I can adjust the subwoofer and comps volume separately.

Only thing that makes logical sense to me is that 4 channel amps have 2 sets of RCA inputs. I don't know //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif

Click to read more...

 

[Beat_Dominator 5,000+ posts]

4ch amps have a pair of inputs... and most amps didn't have x-overs on them back in the day.

Active setups just offer more flexibility, something you need in a car as a car is the worst place to try to reproduce sound accurately.

 

[RAM_Designs 5,000+ posts]

I run my 8053 active //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif ...definitely worth the time/experimentation.

 

[99StangGt 10+ year member]

Most 4 channel amps dont have the bandpass crossover for the mids. The active headunit crossovers have bandpass(both hp and lp crossover for the mids)

 

[tRidiot 10+ year member]

Or is it for on-the-fly crossover changing, which doesn't seem necessary at all?

For some of us it is...

 

[matrxx dude 5,000+ posts]

he dont sound like he really cares about sq

 

[tRidiot 10+ year member]

he dont sound like he really cares about sq

The OP? Bah... SQ ain't everything. I think the "SQ" of most competition-type systems sounds pathetic, personally.

Oh well.

 

[dtavano 10+ year member]

he dont sound like he really cares about sq

Uh... right. I just didn't realize that amps didn't have the "extras" mine does. For example, to get a bandpass crossover I can just run a highpass from my sub preamp and than set the lowpass on my component amp: this would create a bandpass crossover. Oh well, I guess my amps just provide flexibility enough to work around it. Or perhaps 4 channel amps only have one crossover for all 4 channels? Than it would be necessary to have the HU controlling it.

 

[99StangGt 10+ year member]

Also crossover slopes, most decks will do 24db slopes. It is nice to be able to adjust from the front seat and have different presets for different music.

 

[mvw2 10+ year member]

I don't think dtavano was talking about a full active setup, just the low pass/high pass filter used between the full range speakes and subwoofer.

The LPF/HPF on the HU or amp both serve the same purpose. It really doesn't matter which one you use.

Generally the HU will have either 2 sets or 3 sets of RCAs

Front - Highs

Rear - Sub

or

Front - Highs

Rear - Highs

Sub - Sub

By highs I mean full range speakers in general, everything above the crossover point.

Using the HU one, it will throw everything above the crossover point to the full range speakers(Highs) and everything below the crossover point to the Sub output.

For example, if you pick 120Hz on the HU. Your HU has just 2 pairs of RCA outs, just Front and Rear. It will send everything above 120Hz out the Front RCAs as well as the Front speaker output wires. It will send everything below 120Hz to the Rear RCAs and Rear speaker output wires.

The amp does not split both frequencies as it only has one output. If you pick LPF on the sub amp and set it to 120Hz, it will output everything below 120Hz to the subwoofer. However, it does nothing with everything above 120Hz and has no control over your full range speakers as they are not hooked up to the amp.

Now if you had a 4 channel amp using Ch 1 and Ch 2 to power the full range speakers and Ch 3 and Ch 4 to power the subwoofer, you have two LPF/HPF crossovers built in, one for Ch 1 & 2 and one for Ch 3 & 4. You would set the Ch 1 & 2 filter to HPF and set to 120Hz. This sends everything above 120Hz to the full range speakers. Then you set the Ch 3 & 4 filter to LPF and 120Hz. This sends 120Hz and down out Ch 3 & 4 to the subwoofer.

One some higher end HUs and even some amps, the crossover slope is adjustable, but most amps and entry/mid level HUs are all the same.

For the most part, it doesn't matter what you use.

-Low pass filter(LPF) passes everything below the choosen crossover frequency to the speaker, passes everything below the frequency to the speaker.

-High pass filter(HPF) passes everything above the choosen crossover frequency to the speaker, passes everything above the frequency to the speaker.