Tuning the subwoofers
Subwoofers are a key component of the car’s speaker setup, as they provide the thumping bass sound. The process of identifying the perfect bass sound from the subwoofers in your car can be a bit time consuming, but the audio experience that well-tuned subwoofers offer is well worth the wait and effort.
Please note that here we will be discussing the process of tuning the subwoofers and amplifiers, step-by-step. So, if you're instead looking to buy new subwoofers, please consult our Subwoofer Buying Guide. You can always come back to this article later when it is time to set up your car's speaker system.
Stage One: Removing distortion from the speaker system
Distortion is the crackling, sometimes hissing, noise that prevents the natural flow of music. It is one of the main reasons that reduce the lifespan of speakers and subwoofers. The gain produced by the amplifier powering the speaker system causes this distortion. In order to remove the distortion, begin by setting the amplifier's gain at low and play music. With the music playing turn up the volume till you hear distortion. Now lower the volume till the distortion fades. Mark the volume. You have now identified the maximum volume at which the car stereo receiver can play distortion free music.
A similar process needs to be followed for the amp gain. With the receiver volume set at the distortion free level, increase the amplifier's gain till the distortion is audible again. Now slowly reduce the gain till the distortion dissolves in the background. You have now successfully set the amplifier's gain. You can now reduce the receiver volume to a level that is comfortable for you. In case you car speaker system doesn't have an external amplifier, the process of identifying the maximum volume for the receiver still needs to be carried out and set at the distortion free level.
Stage Two: Opening the low-pass filter and flattening the bass tone
In the second stage, begin by reducing the subwoofer's amplifier gain to the lowest point, then switch on the low-pass filter and set it at the highest point. Remember to turn off the bass boost, if present. Also, set the remote level control at the mid position, as later this will allow you to boost the bass or cut it off for each song.
Now the stereo receiver's bass tone control needs to be adjusted to the flat setting. Note that in some stereos this is marked by zero or the middle setting. Certain stereos also have a subwoofer level control, which also needs to be adjusted to the middle setting or the no gain setting, as might be the case.
Remember that if the receiver has a crossover, bass boost or low-pass filter those are all turned off. The reason for doing this is that if the crossover, bass boost and low-pass filter on both the amplifier and the receiver are used simultaneously it generates phase distortion at the frequency level of both filters and crossovers, which in turn has a negative impact on the quality of sound.
Stage Three: Adjusting subwoofer amplifier gain and low-pass filter
Set the receiver volume at the one-quarter level and start playing music. Slowly begin increasing the subwoofer's amplifier gain, and continue this till the sound produced by the subwoofer becomes louder than the sound being produced by the speakers. However, make sure that there's no distortion. Now try to concentrate on the subwoofer's sound and turn down the amplifier's low-pass filter. This needs to be continued till the subwoofer stops reproducing high and mid frequency notes.
The job of the low-pass filter is to control the tone and eliminate notes that you prefer the subwoofer to not play. So, it essentially can filter out the sound of string instruments like guitar, the cymbals, and even the vocals, and leave only the bass or low-frequency drum sounds.
Stage Four: How to use bass boost and the role of subsonic filter
At this stage slowly turn up the bass boost and pay attention to the sound of the drum. Even a little increase of the bass boost sharpens the edge of the drum kick. So be careful because this is one of the reasons for introduction of distortion in the speaker system. However, applied intelligently the bass boost can really take the audio experience to the next level. In case of distortion, start reducing the subwoofer's amplifier gain till the distortion fades.
A subsonic filter comes in handy in case of ported subwoofers. Using the filter on the amplifier helps keep the loud low frequency notes under control. Now adjust all the filters in place to create the bass sound you prefer. Once you’re happy with the bass level remember to turn down the subwoofer amplifier gain completely down.
Stage Five: Subwoofer level matched to the receiver volume
This is the final stage. Firstly, turn the stereo receiver's volume all the way up to its maximum, but distortion-less level. Now begin increasing the subwoofer's amplifier gain and stop when the bass sound is in balance with the music playing. Test the remote level control by turning it up and down and listen how it affects the music.
A quick tip: If you feel that though the bass is loud it doesn't have punch you expect, try reversing the subwoofer's speaker leads. What this does is it reverses the movement of the subwoofer's cone. Try it both way and check which sounds better.
In case after all the adjusting and testing it is still not possible to get the right bass sound from the subwoofer that can match the other speakers and yet not produce any distortion, it means that you will have to purchase a subwoofer and amplifier combination that has higher power-handling capacity. Don't make the common mistake of reducing the gain on the amplifier in an attempt to match the subwoofer's lack of volume. This is likely to have an adverse effect of the speakers. This is the reason why it is advisable to seek some professional help at the beginning, even if just to consult, so that you can avoid such a situation.