If you’ve been in to our store, you have likely seen the tags that we post on every head unit stating “We Tested it!” If you’ve ever wondered what that means, here is your explanation.
When we get a new head unit in and install it on the board, the first thing that we do is test the output voltage of the pre-amp outputs. We do this with a special test disc and an oscilloscope. One of the many things that an oscilloscope can do is to graphically show when clipping is occurring on know good signal. Clipping is bad and the number one cause of blown speakers. After properly connecting the oscilloscope, we slowly increase the volume on the deck until we see distortion on the Oscope. We then back down the volume until the distortion is gone and read the AC voltage at that point. Both the voltage and the volume setting are recorded for future use.
These measurements are extremely important when building and tuning a system. Lets take a look at the max AC voltage first. In any system, the signal starts at the deck (yes, I know it could start at an iPod or DVD player, etc. but for the sake of this article, it starts at the deck!) Obviously, the stronger and cleaner the signal is at the start, the better the overall sound quality will be as it moves down the path. Once the signal leaves the deck, it heads right into the amplifier via the RCA cable.
An amplifier’s jobs is to amplify. That’s it. It need to take a signal coming in and make it louder with as little impact on the sound as possible. Lets say that we are looking to get to 20 volts AC on the output of an amplifier. Head unit A is putting out 2 undistorted volts and head until B is putting out 5 undistorted volts. Simple math says that, for head unit A, the amp will need to multiply the signal by 10 to get it to 20 volts. On head until B, the amp will only need to multiply the signal by 4. For head unit B, the amp will not have to work as hard, the output will be cleaner and the noise floor will be lower. The gain control on the amp hooked to head unit B will be able to be kept much lower. End result: Better, cleaner sound! Have you ever listened to a “high end” system at a low volume and heard a hiss? Very likely this was caused by a high gain setting or a poorly tuned system.
What about the maximum undistorted volume setting on the head unit? This is extremely important when we tune the system. In order to achieve maximum volume on a system while still making it sound great, we need to know where the signal distorts at the beginning. Without knowing where the head unit begins to distort, how would we be able to properly tune the system? We couldn’t. We would simply be guessing!
This is one of the things that sets Mobile Edge apart from many other shops. We don’t guess. We have all the proper tools to tune your system and we know how to use them. Great products and quality installations are important, but improper tuning can kill the best systems! Stop in and we will show you what we’re talking about!
This is great information. But how do we measure the output voltage from a head unit or from the output of an electronic crossover (such as an Audiocontrol)? I’ve made several attempts using my multimeter and always keep coming up with a reading of zero. I’ve tried every setting on my multimeter starting with the ACV setting and can never seem to get a reading. I’ve tried to measure it with individual songs, sine waves, and pink noise. Any idea what im doing wrong here? Thanks
You need a high quality test CD with various sine wave tracks… 80 hz, 1000 hz, etc…. You should also have an oscilloscope… Set your deck to max undistorted output…. measure across the RCA outputs of the device in question and turn up its gain until the Oscope shows clipping… Back it off slightly until clipping is gone and read the AC voltage. That is a very basic explanation, but gets you into the ballpark… reading voltage is meaningless unless you know you have a clean waveform… A DVM alone is not very helpful… You need a scope.
Thank you Mitch. Can you recommend a cheap oscilloscope that’s good enough for the job? What about the little DSO nano pocket sized oscilloscope? Thanks for the help?
We use the TPI440… I understand that there are some other less expensive options available. The TPI440 is a great choice for what we described in this post.
Hi, I would like to know the undistorted voltage (volume) for the car stereo Pioneer DEH-X 9550 SD please. Is possible for you guys to give me an answer to this please. Thanks in advance !