I thought it best to give people a quick run down on setting amplifier gains for your car audio system. I have been installing and configuring car audio for years so i thought i’d share with you all how to do this, with the help of a portable Oscope available from Little Bird. This guide does not go into details of test tones, db gain/slop or any EQ technicalities, nor does it show how to configure your Oscilloscope (please read you owners manual).
Tools you will need:
- Suitable portable Oscilloscope with X10 probe
- A car
- A car with an amplifier installed (this guide does not cover amplifier installation)
- A working receiver (head unit, dvd player, radio etc.)
- A CD containing test tones (as a safe bet, use tones with -3db)
For this tutorial, we are going to assume that you will be testing a 4CH amplifier which will drive a set of speakers. It doesn’t matter if those speakers are component/coaxial or any combination thereof. Ensure that your engine is turned ON for this test, to identify if there’s any alternator whine in the system but also to ensure you don’t kill your battery as you will be stressing your equipment - even though you won’t hear it!
Step 1: The head unit.
You firstly need to ascertain the clipping point of the head unit (source) before you set the gain on your amplifier. Ensure that you turn off any EQ/Fade/Balance/Time alignment settings. Disconnect the inputs to your amplifier from the source unit.
Step 2: Double check you have disconnected the source inputs from your amplifier!
Step 3: Insert your test CD, and play a test tone on repeat. As a general rule, the following tones are applicable to different speaker types: 50hz for subwoofers -3db, 1000hz -3db for mids and 3500hz -3db for tweeters. If you have a component setup, use 1000hz.
Step 4: Configure your Oscilloscope to the correct values. Measure the sine wave from your source unit against the + and - outputs of each speaker channel that goes to the amplifier. These outputs could be RCA cables or speaker wire. Turn up the volume on your source unit until you begin to see the sine waves begin to flatten out. Turn the volume down until those flat spots are gone and you’re left with a nice peak on your sine wave. These flat spots on the sine wave are called clipping, and must be eliminated so not to cause damage to your expensive car audio equipment (note some source units will allow full volume without clipping). Now, remember the number on the volume dial you recorded before the signal clipped - this is your new maximum volume and you cannot go louder than this without certain damage to your equipment or speakers (often both).
Step 5: Reinsert the amplifier inputs from the source unit, and disconnect the outputs to your speakers or subwoofers (failing to do this may result in blown speakers). Turn the volume up to the maximum value recorded in step 4 on your source unit, and play an appropriate test tone as you did in step 4 as well. Connect the Oscilloscope, this time with the X10 multiplier, to the first outputs of your amplifier (CH1). Watch the sine wave, and gently turn up the gain on the channel being measured until again, you see the sine wave begin to clip (square off). Back off the amplifier gain until you see a nice pointy peak without any squared off signal. Repeat this process for all remaining channels.
Step 6: Reconnect your speakers to the amplifier and enjoy your music! As long as you don’t go over the volume number recorded in step 4, you will not damage your speakers and allow them to get the maximum power from your system.
Step 7: Reconfigure your EQ settings, with an emphasis on reducing levels rather than increasing them so as to not damage components in your system, as this may further introduce a clipped signal.
This is a great alternative to expensive measuring tools, and always ensures that your speakers/amplifiers and other devices are operating within safe ranges. Setting gains any other way risks damage either to your equipment or your hearing.