Pioneer TS-A1676R 320W 6-1/2" 3-Way TSA Series Coaxial Car Speakers
PEI is an acronym for "Polyetherimide" which is an amorphous, amber transparent, high-performance thermoplastic.
Efficiency (1w/1m) is not an accurate indicator of a subwoofer's output capability and should not be used as a comparison to other speakers or subwoofers to determine which one is "louder".
Shallow mount speakers will typically have a mounting depth of 2" or less, while shallow mount subwoofers will typically have a mounting depth of 3" or less.
Please refer to the product image and description for further details about the speaker.