HMF Universal Quiet Core and Spark Arrester The HMF Quiet Core is an insert made of TIG welded steel and installs on most HMF exhausts in seconds. It's designed for sound sensitive riding areas and decreases the sound level approximately 3-6dB. HMF requires that you run the Spark Arrestor with the Quiet Core for further sound reduction and a tighter fit. Will NOT work for other exhaust manufacturers or in HMF Series: Competition, Street, Mini or Quiet Race Series.