Introduction
The ISOtunes Sport DEFY Slim Basic provides superior electronic hearing protection in a compact design. This device is engineered to protect your hearing from harmful noises while allowing you to maintain situational awareness through its Tactical Sound Control technology. This manual provides essential information for the proper setup, operation, and maintenance of your DEFY Slim Basic earmuffs.

Image: ISOtunes Sport DEFY Slim Basic electronic earmuffs, matte black.
Product Overview
The ISOtunes Sport DEFY Slim Basic is designed for various applications requiring hearing protection and situational awareness. Key features include:
- Tactical Sound Control: Amplifies ambient sounds up to 8 times their natural volume while instantly suppressing harmful gunshot noises within 2 milliseconds.
- 20 dB Noise Reduction Rating (NRR): Effectively reduces noise levels to protect against sounds typically ranging from 150-170 decibels, such as gunshots.
- Ultra-Slim Design: Weighing approximately 310 grams, these earmuffs offer comfort and a low-profile fit for extended wear and ease of use with other gear.
- Long-Lasting Battery: Provides up to 300 hours of operation using two AAA batteries.
- IPX4 Durability: Resistant to water splashes, sweat, and dust, suitable for various environmental conditions.
- Note: This product does not feature Bluetooth connectivity or an integrated microphone for phone calls.

Image: The DEFY Slim Basic earmuffs are suitable for range use, law enforcement, training, and hunting.
Box Contents
Upon opening the package, verify that all the following items are included:
- ISOtunes Sport DEFY Slim Earmuff
- 2 AAA Batteries
- Auxiliary Cable (3.5mm)

Image: The package includes the DEFY Slim earmuffs, two AAA batteries, and an auxiliary cable.
Setup
1. Battery Installation
- Locate the battery compartment on one of the earmuff cups.
- Open the compartment cover.
- Insert the two AAA batteries, ensuring correct polarity (+/-).
- Securely close the battery compartment cover.
2. Fitting the Earmuffs
- Gently pull the earcups apart and place the headband over your head.
- Adjust the position of each earcup by extending or retracting the headband arms until the earcups fully cover your ears and create a comfortable, secure seal.
- Ensure no hair or clothing interferes with the seal around your ears, as this can compromise noise reduction effectiveness.

Image: Proper fitting ensures optimal hearing protection and comfort.
Operating Instructions
Power On/Off and Volume Control
- Locate the power/volume knob on one of the earcups.
- Rotate the knob clockwise to power on the device and increase the volume of ambient sounds.
- Rotate the knob counter-clockwise to decrease the volume and power off the device.
Tactical Sound Control (TSC)
The DEFY Slim Basic features Tactical Sound Control technology, which automatically manages ambient sound levels:
- Ambient Sound Amplification: When the environment is quiet or moderately noisy, the earmuffs will amplify sounds like speech and environmental cues, enhancing your situational awareness.
- Harmful Noise Suppression: Upon detecting sudden loud noises, such as gunshots, the TSC system will instantly suppress these sounds to a safe level, protecting your hearing. This reaction occurs within 2 milliseconds.

Image: Tactical Sound Control provides rapid noise suppression and sound amplification.
Using the Auxiliary Input
The included 3.5mm auxiliary cable can be used to connect external audio devices (e.g., radios, MP3 players) to the earmuffs for listening purposes. Insert one end of the cable into the auxiliary port on the earmuff and the other end into your audio device.
Maintenance
Cleaning Instructions
- The earmuffs are designed for Hand Wash Only. Do not machine wash or submerge in water.
- Use a damp cloth with mild soap to gently wipe down the exterior surfaces of the earcups and headband.
- Avoid getting moisture into the electronic components or battery compartment.
- Allow the earmuffs to air dry completely before storage or next use.
Storage
Store the earmuffs in a clean, dry place away from extreme temperatures and direct sunlight. Remove batteries if storing for extended periods to prevent leakage.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No power/No sound | Dead or incorrectly inserted batteries. | Replace batteries with fresh AAA batteries, ensuring correct polarity. |
| Poor sound amplification or noise reduction | Improper fit; earcups not sealing correctly. | Adjust earmuffs to ensure a tight seal around the ears. Remove any obstructions like hair or glasses arms. |
| Distorted or intermittent audio from auxiliary input | Loose auxiliary cable connection; faulty cable or audio source. | Ensure the auxiliary cable is fully inserted. Test with a different cable or audio source if possible. |
Specifications
- Model Number: IT-40
- Noise Reduction Rating (NRR): 20 dB
- Tactical Sound Control: Amplifies up to 8x, 2ms reaction time
- Battery Type: 2 x AAA batteries
- Battery Life: Up to 300 hours
- Weight: Approximately 310 grams
- Durability Rating: IPX4 (water, sweat, and dust resistant)
- Connectivity: 3.5mm Auxiliary Input (no Bluetooth)
Warranty and Support
ISOtunes stands behind its products with the following:
- One-Year Warranty: Covers manufacturing defects.
- 30-Day Money-Back Guarantee: Allows for returns within 30 days of purchase.
For customer service inquiries, please contact the ISOtunes support team. Visit the official ISOtunes website for the most current contact information and support resources.





