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How to Tune and Adjust Amplifier Gains and Bass Boost

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by: Kyle Duffy

You might want to force this into your head because tuning your equipment is one of the most important things you can do. Car amplifiers have lots of knobs and buttons that, when adjusted the right way, will make your subwoofers or speakers perform at their best. Improper tuning can create distortion, which can sound like buzzing, crackling, hissing, whomping, and various other noises that intrude on the instruments of your music. This is a ballpark method for setting up an amplifier, always refer to the owner’s manual first for more detailed and specific instructions. Most of us do not have an oscilloscope to properly tune a system, but the method outlined below will work well enough. Now let’s get down to tuning!

Kicker IX500.4 4-Channel Class D Amplifier- Kicker IX500.4


Step 1: Setting Volume and Gain Control

With your sound system off, disconnect the RCA cables that run to your amplifiers. Next, turn your system back on and turn the volume on your radio up to max, make sure no music is playing in the system. Disconnecting the RCAs makes sure nothing is playing through the amplifiers which would risk blowing your amplifier, speakers, subwoofers and eardrums. If your speakers run off of your radio and you have a subwoofer amplifier that your trying to set, disconnect all your speakers for safety, then reconnect them after you find the 75% volume level highlighted below. You can leave the speakers connected only if you are 100% sure no music is playing through your system. Most radios have a numerical association, for example the max volume could be denoted as “60” on the dial. The numbers for each radio differ; some might be at 10 max while others could be at 30 or even 100 max. Now that you have the max volume number, multiply it by .75, this will get you 75% of your max volume. For example, if our max volume is 60, then 0.75 x 60 = 45. Now that we have that figured out, turn your volume to zero and plug in your RCA cables or speakers if your running off the headunit. Now, turn the volume down to the 75% point (45 in this case) and turn the gain on your amplifier to zero. Set all bass boost and crossover filters to off, and make sure your headunits built-in EQ is set to “Flat”.

We recommend you use a 1-kHz sine wave tone from a test disc for this next step. If you cannot get a test disk purchase a store bought CD with your favorite music and use it instead. With your sound system off, plug in your speakers if you disconnected them and RCA cables and then turn your system back on. Now start playing the tone, slowly turn the gain up on the amplifier until you hear distortion, also known as clipping. Back off the gain about 1/8th a turn or until it becomes clear again. Remember to mark the gain level and the volume level should you need to reset them at a later date. This is the maximum volume your system will play before it might start clipping the signal. If you have multiple amplifiers, use this method for each amplifier separately. So, hook up only one amplifier at a time, unhook it and move on to the next one.

AutoSound 2000 CD-104 Amplifier Level Setting CD- AutoSound 2000 CD-104


Step 2: Tuning Frequencies

Time to adjust the built-in crossovers on the amplifiers in your system. Most subwoofer amplifiers have a Low-Pass Filter which prevents higher frequencies from reaching your subs. Subwoofers are designed to reproduce low frequency bass tones, so a low-pass filter is very important. A great starting point is around 80 to 100Hz on the low-pass crossover. Disconnect all other amplifiers and play your favorite music type from a CD at 75% volume. While listening to what the subwoofer is playing, slowly adjust the low pass filter from high to low until the mid-frequencies and high-frequencies disappear. You need to filter out cymbals, vocals, guitars, strings, and any other instruments that are not bass or low drum type. If you experience any popping or muddy sounding music from the subwoofer, turn the filter down lower.

For your speaker amplifier, you will have a Low-Pass and a High-Pass filter set on a switch so you can choose which to use. The High-Pass filter lets all frequencies above the setting to go through to your speakers while preventing the lower bass notes from getting through. Disconnect all other amplifiers and start playing your favorite music from a store bought CD. Your subwoofer will handle the lower notes, so a great place to start on the high-pass filter is where you set your low-pass filter on your subwoofer amplifier if you are using one. If not, a good starting place is between 60 and 80Hz. Listen to your speakers as you adjust the high-pass filter slowly. Get rid of any bass or low drum kicks that might cause distortion in your speakers.

Step 3: Bass Boost

If your subwoofer has a death wish, this is often the way to grant that wish. Bass boost can be very effective but it is rarely ever set correctly. The objective of the bass boost, should you want to use it, is to get more kick out of your subwoofer. For most, the bass boost is best left untouched, but you’re not most are you? Ok, so set your gain to zero, and toggle your bass boost button, switch, or turn dial. Play your favorite music and slowly turn the gain up until you get distortion. Back off the gain setting until the woofer is clear again, then start adjusting the low-pass filter. You will need to mess with the low pass and gain until you feel your woofer sounds just right. Bottom line; if you’re going to turn the bass boost up, make sure to turn the gain down. Bass Boost is not a toy and must be used responsibly.

Step 4: Mix it All Together

Kicker IX500.4 Speaker Polarity Checker- PAC TLPTG2


Phew, final step! Let’s connect all amplifiers in the system, turn the radio down to zero and start playing that CD. Slowly turn the radio up until you hear distortion or you reach that 75% limit, do not ever go past that limit. If everything was done correctly, all speakers and subwoofers should be distortion free until that point. If the bass is overpowering the speakers at the 75% volume point, lower the gain on your subwoofer amplifier until it blends well with your speakers. Do not adjust the full-range speaker amplifier to match the subwoofer(s). If your bass is not sufficient enough for your needs, you will need to upgrade to a bigger subwoofer and a more powerful amplifier.

If you can’t seem to get your system to sound just right, we highly recommend you take it to a professional. It is possible your components could be damaged, connected improperly, or simply not efficient or of enough quality to produce the sound you need. Simple things such as replacing power, ground, and speaker wire with higher quality cable could help improve the sound of your system. It is also possible that the polarity on your speakers could be switched, resulting in awkward sound reproduction. A polarity checker can fix that issue quickly. If you listen to a wide range of music, try readjusting your gain controls using different CDs with different music types to get the most even sound. Tuning is all about hearing the difference.

 

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Written By: Kyle Duffy