Dumb audio questions: amplifiers and aux ins

vettejock99 · 12-12-2006, 02:40 AM

Greetings all,

I have been trying to piece together everything I need to know to get this done right, but the info I find is either incomplete or conflicting. Here's the deal: after installing a carpc in my 300c and having fair success, I decided to put one in my HOV car, a 2004 Prius. I am getting some hum, although unlike with the 300c it doesn't change pitch when the engine RPMs change, though it does get louder when I brake (which may be unique to the Prius) however. Here are some key points and questions:

1) I am using an amplifier in both cases, mainly because neither car came with an aux in. Now that they are available, if I get something like a PAC AUX-BOX that connects to the CD changer port on the back of the factory radio, and I plug in my car PC to the aux in, will I get sound out of all my speakers or just the fronts? If all, I presume it is the car stereo cloning the signal to the rears?

2) If I stay with the amplifier, and I mount it somewhere mid-vehicle (such as under the passenger seat), is grounding to the rear of the vehicle (about 7 ft of cable) with an 8 or 10 gauge wire sufficient for a 350W amp or does it have to be much shorter? If it must be shorter, how do most shops ground amps that aren't in the very back or very front near main ground points?

This should get me started - thanks!

spoonraker · 12-12-2006, 04:03 AM

1) Yes you should get sound out of all speakers if you use the AUX input on your head unit or cd changer. No it doesn't "clone" the signal to the rear speakers. It depends on how you have it hooked up really, but it decodes the audio signal from the PC just like it would if it were playing a CD.

2) With ground cables, shorter is always better. You don't have to use an existing bolt to ground to, you can make your own if it's necessary to keep the length down, however the only way to see if you're picking up noise is to test it. Yes, 8 gauge wire is plenty thick for a 350W amplifier.

scott_fx · 12-12-2006, 10:24 AM

how doesn't it clone the signal? if you're putting in analog stereo it's not going to decode 4 seperate chans.

spoonraker · 12-12-2006, 11:54 AM

It will clone the signal if you wire it that way. If you use digital output, which is available on most creative cards it won't. I think there is probably a way of making a single input that reads from all 3 channels, or at least the two you're talking about, but I don't know.

I guess scott is right, in almost all cases it will just clone the signal, but that is only because it's decoding only has a single channel.

vettejock99 · 12-12-2006, 12:59 PM

That's what I thought. So basically I can use the amp and use optical and get true 5.1 when the source presents it, or have it do phantom 5.1 or else use the aux in and get the front L/R cloned to the rears, which is how most non-premium stereos operate these days, I believe.

Even if all this is true, for future reference riddle me this: If I did have a "premium" system that says that it does Dolby Surround Sound, and I plugged in an aux in unit in the same fashion, wouldn't it essentially be taking the analog stereo signal and creating a phantom 5.1 as well? Is that how they work? Physical connection issues aside, I know our Volvo XC90 says it has Dolby Pro Logic II or something.

Anyway, good info, thanks. It seems that in light of the difficulties I've faced getting amplifiers and carpcs to work together (the PC stuff is easy for me, it is understanding all of the input level, grounding, cable types, etc. that is tough for someone who never worked in an install shop), I am leaning towards going the "easy" aux in route....

zryder · 12-13-2006, 09:04 AM

I see a lot of people getting confused between Dolby Pro Logic, Dolby Surround, and Dolby 5.1 Dolby Pro Logic is the way it decides to send audio to the rear speakers, depending on what it has coming in the mains. Dolby Surround is a "sound format", that is truly only 2 channel, but is designed to be split and sent to the rears, similar to PL. Dolby 5.1 is the only "true" surround sound out of the group, because the format is actually carrying 6 individual channels of sound. 5 speakers and 1 subwoofer. because the subwoofer isnt full range, thats why they call it .1

vettejock99 · 12-13-2006, 10:13 AM

Quote: Originally Posted by zryder

I see a lot of people getting confused between Dolby Pro Logic, Dolby Surround, and Dolby 5.1 Dolby Pro Logic is the way it decides to send audio to the rear speakers, depending on what it has coming in the mains. Dolby Surround is a "sound format", that is truly only 2 channel, but is designed to be split and sent to the rears, similar to PL. Dolby 5.1 is the only "true" surround sound out of the group, because the format is actually carrying 6 individual channels of sound. 5 speakers and 1 subwoofer. because the subwoofer isnt full range, thats why they call it .1

Ah, I suspected as much. Thanks for clarifying that for me!