Gravity GBR300.4DM Motorcycle Amp Review | The Amplifier that Makes the Difference

You want to get the most out of your motorcycle. This has left you looking for a great motorcycle amplifier. How do you know which one is the best? This article can help! Our team has reviewed a lot of the top motorcycle amps on the market. This is our comprehensive Gravity GBR300.4DM Motorcycle Amp review. 

How does the Gravity amp compare to our current favorite bike amplifier – the Rockford Fosgate PBR300X4 Punch 300 Watt 4 Channel Boosted Rail Amplifier? Read further and you will know whether it makes the cut or not! 

Gravity GBR300.4DM Motorcycle Amp

The Gravity amplifier is a solid amp. There are a lot of great features on this one, but there are also some pretty hefty drawbacks. While we do like it quite a bit, it isn’t quite as good as the Rockford Fosgate. Here is pretty much everything you need to know about this amp.

Gravity Build Quality

Gravity amps are pretty well built. They’re not as solid or durable as the Kevlar made Rockford models, but they can take a decent amount of dist and water and still keep running. 


When it comes to installation, every bike is different. You will nee to know the specifications if your bike to find the best place to install this amp.

In general, keep the weather in mind. This has waterproofing, but that only does so much. Keep it away from as much moisture as possible. The same can be said of dust. 

You also want to check the mounting bracket against the girth of your handlebars. If you can’t mount it, then you can’t fit it.

Make sure your wires aren’t crossed. You want to connect the correct wires to the anode and cathode of your power source. If you swap sides, the amp won’t work.

Bad soldering can also mess your amp up and prevent it from working. Make sure there aren’t any cold shorts when you connect things. 

This amp is relatively easy to install in most bikes. The connections have named locations for you so that you can put them in exactly the right places. 


The configuration is largely dependent upon user preferences. You can use the LPF and full cross over to get your exact balance when it comes to perfect sound. 

Gravity Performance

This amp performs pretty well. The power cable could be a little longer, so you will have to extend it. While it doesn’t run as hot as other brands, it does get warm; so keep in mind that it won’t be as cool as the Rockford to use. 

Sound Quality

The sound quality is surprisingly good for a little amp. The 600-watt peak power is nice because it allows for a more clear sound and a better bump to the bass. It’s not quite as powerful or capable as the Rockford, but it does a really good job nevertheless. 

It performs pretty well at higher volumes, too. While we didn’t like the performance quality when the volume reached above 80%, it did just fine in the 55-75% range. 

Technical Specifications

The Gravity amp is a full range digital amplifier with 4 channels and bridgeable technology. It is an IPX65 full waterproof amplifier, so you can even run this if you like to bike in the rain.

It includes 2 ohm and 4 ohm stable 600 W RMS with 150 watt x 4 at a 2-ohm load and 300 watt x 2 at a 4-ohm bridged.

It is micro compact to take up very little space, at only 1.5 x 4.25 x 9.5 inches and is LPF with full or HPF X-Over for adjusting your system to get your perfect sound. 

It also comes with a full 1-year replacement warranty. The crossover range is 40 to 400 Hz. The gain range is 0.2 to 5 volts. The frequency range is 20Hz to 20KHz. It weighs 3 pounds. 

An Extreme Solidity

The bass has a decent solidity. While the Rockford has an extreme solidity thanks to the extra subwoofer in its 800-watt bass range, this 600-watt peak amp does a pretty good job sharpening, aligning, and defining your bass. 

Good for Large-Signal Purposes

This amp is a pretty decent large-signal amp. Large-signal amps are designed to amplify larger input voltages and switch heavy load currents. They are designed for audio and driving loudspeakers.

While this isn’t going to be a massive large-signal amp, as it is compact, it does a reasonable job amplifying the gain for a clear sound to your system. 

Complex and Current Demanding Loads

This system can handle 2 and 4-ohm loads. The gain range is going to be up to 5 volts, so it can handle a decent current load. IT can cross over at up to 400 Hz. 

Competitor Amps

Now that you’ve seen everything the Gravity has to offer, here are a couple of its closest competitors.

The Rockford Fosgate PBR300X4 Punch 300 Watt 4 Channel Boosted Rail Amplifier is still our hands-down favorite bike amplifier of all time. We love it even more then the Gravity!

This amp can handle continuous power to 400 watts with an 800 watts peak. 

It’s compact, so it fits both the front and rear, weighs very little, and includes a 1-year warranty!

The amp has Kevlar reinforced material to provide the necessary air for a thunderous subwoofer boom. 

The other close competitor is the Kenwood 1177524 Compact Automotive/Marine Amplifier. We really like this one, too, but it ranks third after the Rockford and the Gravity. This one utilizes 45 watts x 4 at 4 ohms for a 400-watt power peak. This gives it less power by far then the Rockford or Gravity amps. 


The Gravity amp is easy to install and runs some decent power. It peaks at 600 amps, has fantastic crossover and frequency ranges, and uses a harness overmold for the input and output power.

We still prefer the Rockford model amp for our bikes, but this is a decent second place amp.