Polk MM651UM Marine Speaker Review

  • nominal power: 100 watts
  • peak power: 200 watts
  • impedance: 4 ohms
  • sensitivity: 92 dB/W/m
  • frequency response range: 40 – 25,000 Hz
  • unit weight: not specified
  • unit dimensions: 6.5 x 2.88 inches (diameter x depth)
  • warranty: 1 year (applies to purchase from Amazon.com)
  • user manual: click here
  • wireless: no
  • battery life: n/a
  • signal range: n/a

Polk’s MM651UM speaker set is their premier performance marine speaker system. Similar to the slightly lesser but still very powerful MM651 model, the MM651UM’s build quality is on a higher level than most marine speaker products. The suffix UM stands for Ultra Marine, denoting that it’s intended use is in marine environments.

Polk Audio is a long time user of Klippel measurement and testing equipment. Klippel is the manufacturer of some of the most precise loudspeaker analysis tools in the world, and the name is very highly regarded amongst audio fanatics.

The MM651UM is a coaxial system with a 6 ½ inch mid-bass driver with a cone made from composite material and a 1 inch treated silk dome tweeter. The tweeter is fitted on the grille to better isolate the mid-woofer voice coil and magnetic circuit from the environment. It’s a notch slightly above the MM651, which we reviewed very favorably for the set’s great power and near professional level sensitivity rating. So, if you want your system to get really loud, the MM651UM is right up your alley

Power: 10/10 – Once again Polk Audio shows that it means business when talking decibels. This system and it’s cousin MM651 are the only two marine speaker sets that have a triple digit continuous power rating. The Key difference between the MM651UM and MM651 is that the MM651UM has an impedance of 4 ohms. This means that you can power them from Head Unit without the use of amplifiers, which you really can’t do with the MM651. We do recommend though to invest anyway in a decent amplifier because without one you risk to feed a lot of distortion to the speaker which might damage it over the long run. But still you can consider investing in the speakers now, and later upgrade the whole system with dedicated amplifiers. At 92dB/W/m you will have enough output directly from the head unit.

Aesthetics & Style: 4.5/5 – This speaker set uses the same wheel and cog futuristic design as the MM651, which we really like. Both set’s are available in a black or matte grey finish.

Portability & Convenience: 4/5 – The MM651UM’s get some slight favoritism for not requiring an amplifier, which makes initial set up a more flexible and simple for those who choose to forgo that. The crossover network for the MM651UM marine speakers is located in the back of the speaker, behind the magnet in a sealed enclosure as well. This makes the whole system easier to install than its brother MM651 model which has a separate box for the filters. It’s great that it keeps the same depth of 2.88 inches. Unfortunately the manufacturer doesn’t specify if the magnets are shielded, so take care when dealing with any separate magnetic equipment nearby like a compass.

Durability: 4.5/5 – The build quality is even more geared for marine environments. Special glues are used that wont fail in the face of elemental exposure, and the MM651UM model also passed all the UV and saltwater tests per ASTM B117-03 and D4329-99 standards set by the American Society for Testing and Materials. The only potential downside is that the glass composite cone has a high percentage of its surface exposed so care must be taken not to pierce it.

Warranty: 3/5 – Polk Audio offers 1 year warranty for their marine speaker systems. It’s a bit on the short side compared to other products and brands, but at least you’ll have coverage from a potentially defective unit.

Price: 9/10 – It’s a bit more expensive than the MM651, but it’s a great deal for the amount power, durability, and flexibility that you get. Not to mention, if you choose the MM651’s instead, you’ll have to invest in an amplifier system.

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Bottom Line: 8.8/10

This speaker set uses great materials, passes rigorous durability and performance tests, and boasts excellent specs, all for a very decent price considering what you get. If you’re planning on investing in a high quality long term marine sound system, then right now these are in our opinion the best choice on the market.