Review on Enhanced Noise Filter B25N: BOSS Audio Systems Ground Loop Isolator for Optimal Car Audio Performance by Mark Green

This product does an excellent job of reducing noise due to its transformer isolation properties. However, it fails due to its frequency response, which is typical for this type of product. If you search online for "car audio isolator frequency response" you will find about 10dB drop at 100Hz which is terrible if you like bass. The answer lies in using a professional grade audio isolator, sometimes referred to in the audio industry as a straight box. I've used Art Pro Audio DTI gear, which has a flat frequency response down to 20Hz with extremely low distortion. Feel free to browse the Q&A sections with "Frequency Response". One person in this Q&A posted a flat frequency response from 20Hz to 20kHz but then showed that the bass rolloff characteristics were significant and therefore NOT flat. What you will generally notice with this type of product is the lack of frequency response or distortion specifications as manufacturers know their products fail in this area. I hope this helps people who really enjoy their music. David. PS anticipates around $70-$80 for a Pro unit.