The Insight and Focus CDs must be listened to through stereo headphones or earphones in order for the technology to have an effect, but any stereo headphones or earphones with a frequency range of 20Hz–18,000Hz or better will work just fine. If you do not already own headphones or earphones, most inexpensive headphones or earphones (under $20/pair) can reproduce a range of 20Hz–20,000Hz or better, so you will not need to purchase expensive equipment in order for the audio technology to be effective. Inexpensive headphones and earphones capable of handling a broad frequency range are available in large retail stores such as Best Buy or Wal-Mart and through many online retailers such as Amazon.com.

Shown below is a small sample of the headphone brands and models used and recommended by our staff.

Koss KTXPRO1 Titanium Great frequency response range and good sound quality for under $20.		Koss KSC24 Behind-the-neck Headphones Sport/Active headphone style and good sound quality for under $15.
Sennheiser HD 202 Great sound quality and good reproduction in the low frequency ranges for $25-$30		Sennheiser HD 212 A step up from the HD 202 headphones, the HD 212 model handles a slightly broader frequency range. Priced at $40-$50.
Sony MDR7506 Professional Headphones Great frequency response range and terrific sound for around $95.		Bose Triport Headphones Pricey at $130-$140 but they're comfortable, lightweight, and provide fantastic sound.