4v pre-outs vs 2v, digital time correction, Bass engine Pro. Plus Alpine says it's the "top of the line". Not that any of these features would keep me from buying a different model if it had one feature I liked better. Or if it was $20 cheaper.

 

Oh I'm a bit gutted , I had the 178 bt in my hands. To a novice , how important are the differences in pre outs ?

 

So the 178 BT is the unit to go for? The difference in price between the 178 and 185 is only £20. I can't decide between the two!

 

Is this a European model? I can't seem to find this in the USA

 

Higher voltage pre-outs do nothing except reduce the effect of noise picked up by the RCA cables between the HU and external amp. They don't actually reduce the noise itself, but they do allow you to turn down the input control on the amp, which reduces all sound levels by an equal amount, including the noise.

Let's say your amp is designed to provide full power output with a 1.0 volt input signal. If you connected a HU with 1v pre-outs you would turn the input level control on the amp all the way up so the amp sees the full output of the HU and can produce it's rated power. Any noise picked up by the RCA cables, let's say .01v, is sent to the amp full strength, because the input level is at max.

Now let's say your HU has 2v pre-outs. In theory you should set the input level on the amp half-way, so the amp never sees more than 1v. By reducing the input level you not only reduce the audio signal by half but you reduce the .01v of noise to .005v. The amp still sees 1v of audio so you get the full output power, but the noise is reduced by half.

Now let's use 4v pre-outs. The input level is set to 1/4, and the amp still sees a 1v signal so it can produce full output power. But now the noise from the RCA cables is down to .0025v, 1/4 of what it originally was. You can see how higher-voltage pre-outs can reduce cable noise, but only if you actually have cable noise. If you don't have any noise induced into your RCA cables then higher voltage pre-outs buys you nothing.

In your particular situation you want to compare 2v pre-outs with 4v. 4v will reduce the noise voltage by half, which is 1/4 the power at the speakers, or 6dB. That might sound like a lot but it's probably not as noticeable as you think. To get a good example of what a 6dB change sounds like, go into your car, turn on the stereo, and set the volume where ever you want. If you have a sub you should turn it off, because we only want the left and right speakers operating for this test. Now turn the left-right balance all the way right. You just reduced the sound output by 6dB. Not that significant is it?

Want to be really surprised? Do this - set the balance full right and turn up the stereo so it's pretty loud. Let it play a while and get used to how loud it is. Let's pretend this is as loud as your system can get with it's current amplifier. Now swing the balance back to the middle so the left and right speakers are playing. This is what it would sound like if you had 4 times the output power.

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Great info !!!! Should I get the 178 back ? If you says yes I probably would !!!