Polypropylene Cone - Neuron Series is equipped with Polypropylene Cone and is the preferred choice to withstand moisture and create a consistent playback Day or Night. Polypropylene has great characteristics that make it the ideal choice for vehicles. PEI Tweeter - Neuron Speakers are equipped with Integrated crossovers for the tweeters, a near perfect blend with the speakers cone. PEI tweeters have been chosen to keep them light weight and withstanding high temperatures creating exceptional playback. Heavy Gauged Stamped Steel Basket - Neuron performance speakers use a heavy gauged stamped steel basket coated in flat black to minimize vibrations. Vibrations on the speaker basket create distortion and making the basket thicker in gauge dramatically reduces the chances of occurring.