and no rear speakers. Someone recommended a 80Hz and up for the door 8", I would let it go down to at least 60 Hz and crossover your two subs at 80Hz, you'll have some overlap but everything will sound like it's coming up from the front like it should.

 

Meh... I know a little bit, but I don't claim to be an expert by any means.

Sure, given the scenario above and assuming that there is noise present that is being induced into the system. Let's break it down a bit.

Electrical noise can come from a lot of different sources. The ignition system, alternator, bad grounds, stuff like that. If that noise were to be induced into the stereo system, then odds are it could be measured... so it stands to reason that the higher your signal level is between your HU and your amplifier (or other electronic components in the vehicle) then the lower the overall signal to noise ratio is going to be. That's just simple logic.

But as you clearly pointed out, to take advantage of something like the Matrix, you would need to be able to mount it close to the HU to help reduce the possibility of noise being introduced at that point. You would also need something on the 'receiving end' of the signal that could take advantage of the Matrix's output.

In Thrash's case, he went from a line driver that could output 8 volts, to the Matrix that can output 13 volts. The Audio Control DQXS can only handle a 7.5 volt input signal... so "upgrading" to the Matrix because it can output 13 volts is unnecessary, simply because he can't drive the DQXS at that level. It's like saying that you upgraded your old engine that could rev to 8k RPM to one that can handle 13k RPM... but your transmission can only handle 7.5K RPM. Is it really an upgrade if you can't use it?

Now that's not to say that the Matrix wasn't an upgrade at all... if his old line driver didn't have balanced outputs, then that will also help with noise reduction, simply because the DQXS and his Arc Audio amps can accept balanced inputs. If they didn't, then it really wouldn't matter in that regard because the equipment wouldn't be able to use the feature.

It would be like upgrading to a crossover that had digital optical inputs, but you were driving it with analog signals... if you have it and you don't use it, what is the real "upgrade?"

Actually, that's backwards. The amplifier will be working with less gain, because it now has a higher input voltage. But your thinking is correct in that regard.

The gain circuit is a flexible design feature that allows us to take a given amplifier and utilize it into various different systems. Some, like the Arc Audio amps or the Xtant that I have, are designed with maximum flexibility. Balanced/unbalanced inputs, low/high voltage inputs, widely adjustable gain, etc...

Simple gain circuit design: take a given input and allow the amp to drive to full output. If you have a 1 volt input, then the gain circuit will need to compensate and increase ALL signals on the line (music and noise) to allow the amplifier to drive it's output to max. Drive it with 2 volts, and your effective noise level just dropped in half. Drive it with four volts... well, you can do the math. If you try and drive an amp that can take a 4-5 volt input signal to 13 volts, then all you are going to do is overdrive the input and cause it to clip... and that means distortion.

That was the point that that I was trying to make earlier. Just because "this one goes to eleven" doesn't mean that it's better... it all depends on the equipment being used and how it's setup.

I think that S/N is important in every system, regardless of what equipment you run. But the OP wasn't asking about noise, he was talking about using the JBL MS-8 to 'level out' the signals from the HU. I might be mistaken about his intent, but that made me think that he assumed that Bose had somehow 'tweaked' the signal coming from the HU such that it compensated for the speakers and cabin effects before it reached the amplifier. Some manufacturers did this, boosting the bass or crossing over signals at one point or another. That's why the Clean Sweep was such a good idea at the time; it looked at the outputs and then essentially 'reversed' those changes to give you a clean signal to be amplified/crossed over/EQ'd using your nice, new, aftermarket equipment.

That simply isn't necessary with the GM systems in the C6. The signal leaving the HU is 'unraped' in that respect. When the four HU outputs reach the amp (FL/FR/RL/RR) that's where it's mixed around to send signal to the L/C/R, rears and subs. If the OP is replacing all of that, then simply tapping into the four low-level outputs will give him a clean signal to use. It really is that simple.

Now, if he was bumping up against some noise that was being induced between the HU and the amps, then that's when he could upgrade to a line driver to boost the signal to the amp... but as you said, that would need to take place as close to the HU as possible to help eliminate the noise... but I didn't see that as the issue at the time, hence my posts in this thread.

Does that make sense, or am I...

 

I'm sorry, but just because the HU runs on 14 VDC and the iPod runs on 5 VDC, it doesn't mean that their respective outputs run at that level.

I looked at the iPod classic specifications, and it says that it's analog output is 30 mW per channel. Assuming that the 32 ohm headphones are designed to allow the iPod to drive them to full signal, that tells me that the headphone jack on the iPod runs at approximately one volt at full output. (Perhaps the output at the bottom connector is higher? I honestly don't know, as I never measured it.) So if you tried to take that one volt input and drive an amp to output when the amp design is supposed to see a 5 volt input, and assuming that you have noise being induced into your system, then it's no wonder why there were issues. Any noise would be boosted at a ratio of 5:1 in the amps gain circuit, decreasing your S/N ratio overall.

One of the reasons that the Alpine HU I have was so well received was because it was the first to grab the information from the iPod digitally, and the DAC's in the HU were much better (higher quality) than the ones in the iPod, which increased the overall S/N ratio and allowed the system to sound so clean. (Assuming that you used decent audio compression, anyway.)

I have no doubt about the capabilities of the Matrix. Audio Control makes some fine equipment. I just don't think that because it worked in your case that it's a 'universal solution' for all things audio in that regard... and certainly not in the case of the OP's original post.

 

I can't comment on whether or not you're crazy, but it all made sense to me!

I missed that Thrash replaced a line driver with the AudioControl unit. Your comments make much more sense within that context. I had interpreted your "every-day type system" comment to be more of a general statement against the need for either a line driver of some kind, or head units which have boosted outputs (like Kenwoods Excelon line).

I did mean 40% less gain... Actually, I think I meant to type "40% higher voltage", but was thinking about the resulting lower gain. Sometimes I even confuse myself!

And to keep to the OPs thread - I had started to comment that I think the OP may have meant matching the high level output to the low level inputs with the MS-8 when he mentioned leveling out, but realized I wasn't sure what he meant... And everyone had commented on the output of the OEM head unit already. So my actual comments were all a bit off topic around the line driver aspect specifically. But I think the MS-8 may offer a lot of benefit in flexibility, and the automated setup of the system (for example time delay).

Good info - thanks for the input!

 

Nice guess! That was exactly my intent. I heard from some sources that Navi head unit introduces a lot of tweaking of the signal and I was planning to use the sound processor to fix that.

Thank you guys for the fruitful discussion and recommendations.