How to Set the Gain & HZ on an Amp

by Blaze Johnson

External car audio amplifiers have the potential to vastly improve the performance of a vehicle's speakers. Certain after-market component and direct-fit factory replacement speakers may require the use of an external amplifier, due to the power requirements of the speakers used in the sound system. Subwoofers also need an external amplifier, as low-frequency bass reproduction typically uses more power than what factory or after-market stereo head units provide. Properly adjusting the amplifier's gain and crossover controls ensures optimal speaker functionality and longevity.

Turn off the sound system.

Examine the controls on the amplifier and locate the "Gain" setting. Adjust the "Gain" to the lowest setting.

Select the appropriate crossover setting for the amplifier with regard to the type of speakers used for the system. Switch the crossover to the "LPF" setting when powering one or several subwoofers. Set the switch to "HPF" when dealing with full-range, component or coaxial speakers. The "LPF" setting blocks high-frequency sound waves from reaching the speaker, while the "HPF" setting restricts low-frequency bass signal.

Determine the appropriate frequency range of the speaker, measured in Hz and kHz, by examining the speaker documentation. Typically, speaker manufacturers include a helpful frequency response chart, specific to the product and designed to give a visual representation of the speaker's sound reproduction capabilities.

Adjust the "Hz" cutoff on the amplifier to the appropriate frequency, within the recommended range of the speaker manufacturer.

Start the vehicle's engine and turn on the stereo head unit. If the head unit powers the full-range, component or coaxial speakers in the sound system, check the documentation supplied with the head unit to verify if the product features HPF/LPH crossover settings. Program the HPF settings on the head unit to the same LPH setting on the subwoofer amplifier. Matching the HPF settings for the head unit to the LPF setting on the subwoofer amplifier facilitates proper frequency transition between both speaker types.

Play a high-quality music test track that features a dynamic mix of high-frequency sounds and low-frequency bass. Adjust the volume to the highest setting, before the point of audible speaker distortion.

Adjust the amplifier's "Gain" setting in a progressive manner while playing the test track. When the speakers connected to the amplifier begin to distort, slightly reduce the "Gain" setting. Properly setting the gain on the amplifier enables peak performance while reducing the likelihood of speaker or amplifier damage at high volume.

Listen to a variety of music to test the system's sound reproduction capabilities. Make small adjustments to the head unit's bass, balance, treble and other available sound fields as necessary, to suit your personal listening preferences.

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About the Author

In the spring of 2008, Blaze Johnson decided to share his expertise through writing. He studied business administration at a local community college and runs his own driveway mechanic service, specializing in computer-controlled vehicles and custom car audio installs. Johnson also serves as the de facto computer repair person for his family, friends and coworkers.