Setting Amplifier Gains When Retaining a Factory Harley Radio

Harley Speakers and Amplifiers

 This article is specifically for all 2014 and later factory Harley radios when adding aftermarket amplifiers but is largely still valid for aftermarket radios as well. The key difference is that many aftermarket radios distort at full volume and therefore you need to find the radios maximum undistorted volume level and treat that as the radios max volume point. Factory Harley Radios do not have this problem.

Before Setting the Amplifier Gains You Must

  • Put the bike on an automatic battery charger with an amperage capacity of at least 30 amps.
  • Set proper high pass crossover point on all speaker channels
  • Phase check all speakers after setting crossovers. Phase checking is the process of aligning the entire speaker systems acoustic polarity by ear.
  • Make all equalizer adjustments with the gains set very low and the radio set to max volume

If you do not complete the list above before setting your amplifier gains, you will run a high risk of damaging your speakers and the system will not sound right. All equalization settings need to be done with the radio at max volume and the gains low enough that the speakers are only playing at a medium level. This is because the radios response is not flat below full volume (and that's a good thing but an entirely different article all together). Battery tenders are not an option. Your battery charger will need to be capable of replicating the charge cycle of your bike as if it were running. 

Common Crossover Points for Reference

  • Fairing speakers high pass 150hz with a slope of 24db
  • Lower fairing speakers high pass 150hz with a slope of 24db
  • 6x9 lid speakers high pass 80 to 100hz with a slope of 24db
  • Bag Woofers High pass 50hz with a slope of 24db and no lowpass

Center and Bypass

  • Center the tone controls and fader on the radio
  • Turn off the speed controlled volume feature

Flash Your Radio

Flash your radio before you start. The one exception to this rule is if you are using a Live Tune Enabled system with the Helix MFour DSP amplifier or the Velocity 8 DSP. It is still advised that you flash your radio when using the MFour or Velocity DSP amplifier to simplify the tuning process, but the Velocity and Helix DSPs are capable of being properly tuned without a flash. Flashing the radio simplifies the tuning process in all cases. Always use a TechnoResearch brand flash tool and always select the Rockford Fosgate tuning profile regardless of what speakers and amplifiers you are using.

Get Some Music Ready on a USB Drive

Don’t use your phone. You can use your phone for listening to music after the tune is complete but smartphones have too many variables that can interfere with your tuning process. Eliminate the headache by not using your phone for music while tuning. You can purchase quality and legal popular music tracks for about a dollar each at https://us.7digital.com/ . 

Recommended Tracks for System Performance Evaluation

  1. Somewhere, Somebody (Digitally Remastered), by Jennifer Warnes
    This track is my go to track for dialing in vocals. The track is also well balanced tonaly. The high frequencies, mid frequencies, and low frequencies are all represented. This makes the track very useful for evaluating if your system is too heavy or too light in any of these general ranges.
  2. Billie Jean, by Michael Jackson
    This track is especially useful for evaluating bass frequency response, aggressive bass atack, speaker phase, and a system's high volume limitations. The track has a consistent bass line that goes up and down in frequency. This allows you to hear if any part of the bass range is off. The aggressive attack of the bass line makes this track very useful for detecting when speakers are out of phase. The recording level and tonal balance of this track are very good reference points as well. I like to use this track to test and set a speaker's maximum output.
  3. Boogie Shred, by Mike Dawes
    This is a spectacular example of a great recording of live instruments. No vocals though. It is definitely my favorite track to use when showing off a killer system.

Select a Quality Modern Recording

Select a recording with a consistent volume level, focused sounding vocals, and a range of low and high frequency energy. Also pay attention to the recording level as compared to other recordings. Some recordings are recorded at a higher level than others. Some recordings are made to sound loud but are actually just recorded with distortion in them to make them sound screaming loud (avoid these recordings!). Find recordings that are recorded at a fairly high level without any distortion. Your selection should be based on the technical merits of the recording and not on your flavor of music. There is a lot of good music to choose from.

Setting Your Gains

Do not exceed volume levels that are safe for your ears. If your speaker system is capable of exceeding safe sound pressure levels, you should purchase musicians ear plugs and use them while tuning your bike. Musicians' earplugs are inexpensive (less than $30 on Amazon) and they allow you to accurately hear your system at a safe level for your ears.

Mute All Speaker Channels With the DSP if You Have One

Unmute just one pair of speakers and bring your radios volume to max volume level. Turn the gain for the selected channels up until the speakers meet but do not exceed their mechanical limitations. You need to use your ears and discretion in order to determine the speaker's limitations. If the speakers sound like they are under mechanical distress then turn the gain back down some.
Next turn the radio half way down and mute these channels with your DSP if you have one. If you do not have a DSP, use your radio’s fade feature or unplug the RCAs to mute these channels.

Repeat this process with each pair of channels one pair at a time.
Once you have found the max safe gain settings for each pair of channels, unmute all channels and fine tune your gians so that the speakers have a good volume balance amongst each other as a group.
Remember that when fine tuning the gains, you want to only reduce any channels that are playing too loud as compared to the other speakers. Do not increase any channel gain in order to bring any pair of speakers up to the level of a louder pair. You have already set all gains to maximum speaker potential. Turning the gain up any more will only lead to over driving the speaker and causing damage.

How to avoid overdriving your speakers

Only two things will cause a speaker to become blown.

  • Exceeding the speaker's mechanical limitations can tear the speaker apart.
  • Exceeding the speaker’s thermal limitations by overdriving it over time.

Exceeding thermal limitations is the most common way to blow a speaker. Amplifier energy is turned into heat at the voice coil within the speaker's motor. You can monitor this heat by feeling the speaker magnet. A speaker that is getting hot will not last long. Speakers with neodymium magnets run warmer to the touch than ones with large iron magnets. This is normal because the Neo magnet does not have the surface area to dissipate heat. It is not the temperature of the magnet that matters though, it is the temperature of the voice coil inside the speaker that matters. The wire of the voice coil can only get so hot before melting down. You can also smell the voice coil getting hot due to the resins that hold the wire windings in place breaking down.

If at any point you have reason to believe that you are nearing the thermal limitation of your speakers, give them time to cool off. If you get them hot enough they can fall apart internally even after you have reduced the volume.

Time is a major factor

Speakers have two power ratings stated by the manufacturer. RMS and Max. RMS is the maximum amount of power the speaker can handle for long periods of time and Max is the amount of power the speaker can handle in very short bursts. It is easy to blow a speaker by maintaining an average power level that is slightly higher than RMS over a period of time. Just because you are under the max power rating does not mean that you can not blow your speakers.

Signal Distortion Kills

Signal distortion happens when one of the electronic items in your system exceeds its limitations. This is called signal clipping and can happen in the radio, the DSP, or the amplifier. Any time there is distortion in one of these items the amplifier can and will produce large spikes of power. These spikes in power can easily far exceed the power rating of the amplifier and cause damage to the speakers. Speakers are never safe from being overdriven when the signal is clipped. Even when the amplifier is rated for far less power than the speakers. Amplifiers are commonly overdriven by guys attempting to squeeze more out of the amplifier than it is capable of. Use your ears to detect and avoid signal distortion as well as speaker limitations.