As discussed in my post “Amplifiers: A Beginner’s Guide,” I discussed the benefits of installing an aftermarket amplifier in your vehicle. The main reason? To boost the overall output of your system so that you can get LOUD! The question is, how do you get loud without causing damage to your speakers? The answer is setting your gains properly. In this post, I will discuss what the gain is and some different ways to adjust it to help prevent speaker damage while giving you the best possible audio.
So what is the gain adjustment? The gain adjustment is used to match the head unit’s output voltage to the amplifier so that the signal remains “clean” and is not distorting or clipping. If you are listening to music and you turn the gain adjustment up, you will notice that the volume of the music will also increase. But, this does not mean the gain knob is a volume adjustment. By randomly turning the gain up, you are introducing distortion into the output signal of the amplifier. Not only does this make your music sound like trash, but you can also potentially damage your speakers or subwoofers.
Think of it this way, if you have two head units that have a maximum volume of, let’s say, 35. One of those head unit’s preamp output voltage measures 0.5V and the other measures around 5V. If they are connected, one at a time, to the same amplifier and the volume turned up to around 50%, you can hear the loudness difference between the 0.5V output and the 5V output. The head unit with the 5V output would be significantly louder than the head unit with the 5.0V Now, if you played both at 100% volume, the 0.5V output head unit’s audio signal would be fairly loud, while the 5V output head unit would have, more than likely, damaged the speakers or even the amplifier itself. This is where setting the gain adjustment is critical to match the head unit voltage to the amplifier.
Setting The Gain
There are several methods to set the gain on an amplifier. Some are not really recommended but can get you fairly close to an optimal setting. In this section, we will cover two proper ways to set the gain on your amplifier so that you will achieve the best possible sound quality, get loud, and nearly eliminate the potential of damaging any components. We will be discussing the steps needed to set the gain on a subwoofer amplifier. A multi-channel amplifier will be similar, but you will use a 1KHz test tone instead of the 40 Hz tone.
NOTE: Before setting your amplifier gains, please make sure that you find the clipping point of your head unit. This can be accomplished in a similar fashion of setting the gain of the amplifier. I will not be covering how to do this in this post. In my explanations, I am assuming this action has been performed beforehand. An unofficial “rule of thumb” for finding the clipping point of a head unit is to calculate around 80% of the head unit’s maximum volume. For example, A head unit with a maximum volume level of 40, theoretically, should be set no higher than 32 to avoid clipping the audio signal. This can vary and should be confirmed before setting the amplifier gain.
Using An Oscilloscope
In basic terms, an oscilloscope is a device where you can actually see the audio signal of an amplifier clip or distort on its display. To use the oscilloscope, you will want to make sure you have all the speakers disconnected from your head unit and your amplifier. This is to prevent damage from the high volume the 40 Hz test tone will be played at. To begin the gain setting procedure, begin playing the 40 Hz tone and turn the volume up to the maximum value recorded when you found the clipping point of your head unit. Connect the oscilloscope, with the X10 multiplier, to the outputs of your amplifier. Watch the sine wave on the screen. Slowly turn up the gain until you see the sine wave begin to square off at the peak. This means the signal is clipping. Now, back off the amplifier gain until you see a nice smooth peak without any squaring off of the sine wave, or signal. Now you have what is known as a “clean” signal.
SMD DD-1 / DD-1+
The SMD DD-1 or DD-1+ performs a similar task as the oscilloscope, but without the graphical interface. The DD-1 utilizes LED lights to indicate that a signal is being seen by the device and when the signal from the amplifier is clipping. To use the DD-1, you will want to make sure you have all the speakers disconnected from your head unit and your amplifier, just as discussed when using the oscilloscope. This is to prevent damage from the high volume the 40 Hz test tone will be played at. To begin the gain setting procedure, begin playing the 40 Hz tone and turn the volume up to the maximum value recorded when you found the clipping point of your head unit. Connect the red DD-1 lead to the positive (+) speaker terminal and the black lead to the amplifier’s ground (-) cable, Watch the 40Hz indicator LED. Once it has lit up, slowly turn up the gain until you see the red clipping LED illuminate. This means the signal is clipping. Now, very slowly back off the amplifier gain until you see the clipping indicator light go out. You have now properly set your amplifier gain with the DD-1.
NOTE: Remember, do not exceed the maximum volume setting you ascertained from the head unit. Even with your gains set properly, exceeding the maximum volume of your head unit that you calculated will cause the signal to clip and may cause damage to your speakers or amplifiers.
Bass Knobs and Bass Boost
If your amplifier included a “bass knob” please use caution when using it. It is actually a way to remotely tweak the gain of your amplifier. If you are going to utilize the knob, I recommend setting it to its mid-level setting, then set the gains on your amplifier. Once the gain is set, you can utilize the remote to reduce the gain to lessen the amount of bass, but never go past the mid-setting as it will begin to introduce distortion and may cause damage. If you want to go “FULL TILT,” set the knob to its max and then set the amplifier’s gain, but again, I don’t recommend this.
If your amplifier has a “bass boost” setting, and you want to be brave, you can try adjusting it. My view on bass boost settings is LEAVE THEM ALONE! Do not use it. You are only asking for trouble. Using the bass boost settings only adds unwanted distortion to your setup. It’s better left alone.
I hope this post has given you some insight as to what the gain adjustment is and how to set them properly. This post was intended to give the novice car audio enthusiast the basic knowledge to set up their amplifier in a way other than by ear or just turn the gain knob as if it is volume control.