Thoughts on Active Crossover

[All_Logix 10+ year member]

Hey guys, I am going to be getting a 2011 civic EX and I am going to run JBL GTi 6.5' comp in the front and just some GTO 6.5 in the back dash. I am going for SQL so I only want to run one 12 and I will have it all wired into one 5 channel amp.

Here is where I am looking for your thoughts. I was thinking about running the mid bass drivers into the left and right channels of the rear on the amp, and running the tweets to the left and right on the front channels and of course the sub onto the sub channel, this way I have an active crossover and control frquency pass directly to the tweets and mid-bass. That means I would just just run the back 6.5" off of deck power, since they are basically filler speakers anyway . Is this a good idea? The amp puts out 55 Watts RMS to each channel and the speakers have a ratting of 150 Watts RMS if you run the passive crossover network.

On a side note, if I ran the back speakers off of deck power, electrically speaking if I wired the ouputs from the deck for the rear and front positive lefts together and the neg lefts together and same for right and ran it directly into one speaker, it would just sum the current together at the connection node and therefor double my watts, however I am not sure if this would have some sort of effect on the signal, since singal is basically just can alternating current with amplification based on the amplitude of the wave, (watts) is that possible, anyone ever tried?

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[Phoenix Risen 10+ year member]

the only way i would run the mids in parallel is if they are exactly the same, if not youll never be able to get them tuned where both sound the best they can.

 

[helotaxi 5,000+ posts]

He's not talking about running the mids in parallel. He's talking about running the front stage active off the amp. The last part of the post is talking about summing the power from the HU. As far as that goes, don't. It isn't going to work the way you think and you don't want much power going to the rears at all anyway. Worst case it cooks the HU. Best case you lose any kind of fade capability.

What processor are you planning on using to run the front stage. If you don't have a pretty good one, don't waste your time. The GTi crossovers are probably quite good. Use them. Bridge the amp and run the front stage off the bridged pairs and the rears off the rear channels of the HU.

 

[keep_hope_alive Premium Member]

He's not talking about running the mids in parallel. He's talking about running the front stage active off the amp. The last part of the post is talking about summing the power from the HU. As far as that goes, don't. It isn't going to work the way you think and you don't want much power going to the rears at all anyway. Worst case it cooks the HU. Best case you lose any kind of fade capability.
What processor are you planning on using to run the front stage. If you don't have a pretty good one, don't waste your time. The GTi crossovers are probably quite good. Use them. Bridge the amp and run the front stage off the bridged pairs and the rears off the rear channels of the HU.

agreed on all counts.

you don't need rear tweeters if your goal is rear fill. powering speakers off a head unit requires careful level setting so you don't introduce audible distortion.

active crossovers won't give you a lot of advantage over the specifically designed passives that come with the speakers. if you had time alignment then you may have an argument for active. also, does your amp allow for slope adjustment as well as x10 frequency selection?

bridging the amp to the front components will give you the best performance.

 

[All_Logix 10+ year member]

Thanks to all of the replies, I don't have a good signal processor, so I will run just the passive network, I'll have to double check on the amp freq. adjustment. I was a little weary of running tweets directly into the amp because the HU I am looking at has a 5V preout and I can only adjust the gain down to 6V, I figured I would probably end up killing the tweets.

My only concern with bridging the channels to run the front and give more power into the left and right independently is that the THD raises when you bridge them. I'm not looking into competiton, just to have enjoyable sound with a good dynamic range... I know when I said SQL everyone assumed I was looking into major details but I just wanted to specify I don't want "bump in the trunk"...

 

[helotaxi 5,000+ posts]

If the amp is worth a ****, the distortion is still going to be inaudible. I wouldn't worry about that at all.

 

[All_Logix 10+ year member]

What do you guy think about actually powering the back speakers. I know it isn't common but has anyone gotten any good sound from having the rears plugged into an amp?

 

[keep_hope_alive Premium Member]

there is a lot to consider when amplifier channels are limited. given the options of:

1. fronts and rears powered from a 4 channel - 55W available

2. fronts only powered bridged - probably around 200W available

3. fronts powered bridged and rears off a head unit - 200W to the front and 12W to the rear

in previous systems i have had and installed all three above. #2 was my hands down favorite.

while THD is rated higher when bridged, you have 4x as much power available. so instead of operating at max output to get 50W (and max THD) you are operating with a lot more head room. the result is much less distortion in dynamic peaks (and the ability to reproduce dynamic peaks). you can't achieve SQL without a lot of power.

when running rears off the head unit, they are subject to the head unit distortion. so you need to make sure your gain structure takes that into consideration. you still have your fader to help with rear attenuation.

when bridging - use a DMM and test tones to get your gains equal - don't just judge by the dial position as that is quite inaccurate.

each person has different expectations. some aren't happy without rear speakers playing as loud as the front. it's mostly personal preference. i've ran and installed amplified full range front/rear systems for well over a decade. when i removed rear speakers i was happier because i had 4x as much power to give to my front components - which made them come alive. the only reason i power rears now is because i have an adequate active processor and enough amplifier channels to do what i want. my rears are time delayed, bandpassed, and level set for true "rear fill". you can't tell they are even on until i turn them off, then the car sounds like it's smaller. rears on or off my sound stage height/width/depth is unaffected. but i would rather not have rear speakers if i cannot properly filter and delay them.

 

[All_Logix 10+ year member]

Thanks man, only one question, wont I loose stereo if I do that, it would be pushing all the power from the front into the left and all from the rear into the right... Is there a way to set an amp that you know of so that it can run stereo like that, i know thats picky but I want it to have that ability and not be mono

 

[helotaxi 5,000+ posts]

You use a y-splitter to run the right input into the "front" channels of the amp and the left input into the "rear" channels. Still stereo.