Need help wiith testing frequency response from head unit RCA's

[Salami]

I thought I had a link save somewhere but I can't find it. I have a laptop, REW, True RTA, and XLR-USB mobile pre interface. What am I missing to check and see how flat the response if from a DDX5901HD?




I found the thread but the images are missing. Can some one help out on how I make the connections? http://www.diymobileaudio.com/forum/...headunits.html

[erinh]

you've pretty much got it.

the big thing is this: use a voltage divider to attenuate the voltage going in to the mobilePRE (MP) to keep from frying it. If you test the headunit at a very low volume it will likely be putting out less than 0.50vRMS, but once you start turning up the volume the voltage will get to the point that it can damage the MP.

You can use a 1/4" TRS-to-RCA cable or use an XLR to RCA cable.
In lieu of a voltage divider from resistors, you can buy an in-line RCA attenuator like this one:
http://www.parts-express.com/harriso...-pair--266-244

If you go the XLR to RCA route, you can buy an XLR attenuator (they typically come in higher attenuation values). To determine the amount of attenuation you need for the XLR you can use this site:
http://www.sengpielaudio.com/calcula...lification.htm

Punch in the input voltage (the voltage your headunit will put in to the MP and the attenuation (-xdB)) and you'll get the attenuated voltage. For example, if you use 5v input and -40dB XLR attenuation, you get 0.05v output. More than enough to keep from frying your MP.

[Salami]

Thanks Eric.

I have couple more questions. How do I wire up the XLR connecter to the RCA plug? I all ready have both ends but am unsure what terminal goes to what.


My mobile pre is a Shure X2u which has 30 dB of gain adjustment. Assuming it took speaker level inputs fine I should be correct using a 5V RCA input, correct?

[Hic]

https://www.youtube.com/watch?v=mks6C-qCGhE - might help