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active crossover input/output voltage


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the_edsta 
Member - Posts: 7
Member spacespace
Joined: April 09, 2006
Location: United States
Posted: March 20, 2010 at 9:10 AM / IP Logged  

Hello All,

I have decided that, rather than bridging my 4-channel into a passive setup for my front components (rear fill will run off the headunit), I am going to wire each channel directly into the individual components by running an active setup.  I am going to use an older (2004ish?) profile active crossover that has 7volt (max) inputs and 10 volt (max) outputs.  My sony deck has 4-volt preamps and the crossover will be outputting to a 4-channel alpine amp.

The instructions say to turn the 'output' gain on the crossover all the way up and to use the multi-meter or 'wait until I hear clipping' method to set the overall gain by adjusting the INPUT voltage on the crossover.  This doesn't at all make sense to me as I'd obviously want to use all four volts of my input signal.  And this procedure doesn't even mention the gain on the amp... which just confuses me. 

How would you guys adjust the gain?  I'm thinking about just maxing the input and output gains on the crossover and then adjusting from the amp, especially given that the head unit and crossover both have 105+ S/N ratios and the alpine amp is lower (90db Signal/noise?).  And in my experience, setting amp gain as low as possible is always a good thing...

Don't post often... but you can rest assured that when I do, I am certainly in need of assistance!

Your input is much appreciated...

Building a new system for my 330i... Alpine amps, sony headunit, CDT midranges, focal tweeters, MB quart 12" (sealed), active crossover setup... ready in 3 weeks?
icearrow6 
Copper - Posts: 497
Copper spacespace
Joined: February 02, 2009
Location: California, United States
Posted: March 20, 2010 at 7:21 PM / IP Logged  
ok, so from what I understand is that you want to get rid on the front component "inline" crossover and run the 4 channels from the amp to each of the speakers.
If my understanding of your project is correct, Then I would suggest that you stop right there!
you see my friend that "inline" crossover that you want to get rid of, does more than just limit the lowest frequencies that reach the speakers. It usually also limits the highest frequencies that reach the "midrange" speaker.
Also, the overall frequency response of the component system is design to be operated with that crossover.
So, lets get to the real problem here.
I think that what you are trying to do is to get LOUDER by amplifying EACH speaker. am I right? Well my friend there are other ways of going about doing this.
For one i would just bridge channel 1+2 to run the LEFT channel.And bridge channels 3+4 to run the RIGHT channel. of course you set your RCAs wiring accordingly.
As for the crossover, it CAN still serve a purpose.
the_edsta 
Member - Posts: 7
Member spacespace
Joined: April 09, 2006
Location: United States
Posted: March 21, 2010 at 12:04 AM / IP Logged  

Hmm... no that didn't quite get it right.  SQ is the goal here.  If I wanted volume, I would bridge the amp to 150 watts to each side and run it right into the passive.  Instead, I am running each component directly, which will result in only 100 watts per side.  But an unbridged amp generally produces a higher S/N ratio and will sound cleaner.  And 'you see my friend', my active setup has bandpass capabilities so no worries about high frequencies there.   Additionally, using an active setup will allow me to raise the x-over point from 3500 to 5000, something that will be good for both my midranged (CDT, flat even above 5k) and my focal tweeters (can handle 3500, but will sound much cleaner at 5K).  And so... the problem isn't the setup, it is simply a question as stated: gain adjustment using both two knobs (input/output) on the active unit as well as amp gains.  Which ones are maxed (if any) and which are used for tweaking final gain levels? 

(I think both posts should prevent thoughtful folks from thinking me a noob... car audio experience isn't limited to this forum, after all!)

Building a new system for my 330i... Alpine amps, sony headunit, CDT midranges, focal tweeters, MB quart 12" (sealed), active crossover setup... ready in 3 weeks?
icearrow6 
Copper - Posts: 497
Copper spacespace
Joined: February 02, 2009
Location: California, United States
Posted: March 21, 2010 at 12:24 PM / IP Logged  
Nice, ok then.
To set your gains you'll need some test tones.
Check out the realmofexcursion website under the "downloads" section.
There are many tones there to download.
Now burn these to a CD in NORMAL cd burning. NOT mp3.
Now to set your gains start by determining the maximum output from each of the components on your system. I would set all the gains about 25% so u get sound.
First start with the sony. play your chosen test tone and turn the volume up intill you hear distortion. (if its a sine wave tone, you'll hear the sound actually change in tone.)Then back off till the tone is normal again.
once you have determine what volume number on your sony, THAT is your new maximum for the unit.
Next, move on now with the INPUT of the crossover. Same steps here. play tone till distorts, then back off.
next, with the input of the amplifier.
On a quick note, you may want to give your speakers a minute or two between "tests". Also, since we're not setting the gain on the BASS amp you may want to bypass it during the test.
Which test tone to use is dependent on your desired frequency crossover point and slope.
the_edsta 
Member - Posts: 7
Member spacespace
Joined: April 09, 2006
Location: United States
Posted: March 21, 2010 at 12:42 PM / IP Logged  

Thanks man.  I do know how to set amp gain, though; this is a specific active crossover question.

Anyone w. experience w. active crossovers on here?  I'm sure there are!

W. an active setup, there will be three gain knobs: input & output voltage on the xover and gain on the amp.  The manual states to adjust according to the input on the xover, and I think that is absurd as I want to use all 4 volts from the original source signal.  My question is whether there advantages/disadvantages to maxing both input/output voltage knobs on the x-over and adjusting only by the amp.  In short: how should these three gains be set and which should be used for final adjustments?

Building a new system for my 330i... Alpine amps, sony headunit, CDT midranges, focal tweeters, MB quart 12" (sealed), active crossover setup... ready in 3 weeks?
the_edsta 
Member - Posts: 7
Member spacespace
Joined: April 09, 2006
Location: United States
Posted: March 21, 2010 at 10:29 PM / IP Logged  

So (for the benefit of anyone that may stumble across this), it seems that, logically enough, since an active crossover cannot amplify a signal in any way, the only use of the gain knobs is to attenuate signal.  Hence setting any voltage knobs on an active crossover at max output is advised, only then following the usual gain-setting procedure using the amp's sensitivity (gain) knob.  There was some pretty decent info about crossovers, gain levels, and high S/N ratios at this site:

http://www.termpro.com/articles/levelset.html 

Building a new system for my 330i... Alpine amps, sony headunit, CDT midranges, focal tweeters, MB quart 12" (sealed), active crossover setup... ready in 3 weeks?

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