Impedance is the resistance to the flow of electrical current.  The maximum power transfer from your radio through your headphones to the sound volume in your ears occurs when the impedance of your radio matches the impedance of you headphones.  When impedance is mismatched, neither the radio nor the headphones will deliver their optimum output.

The GCR IMS – Model 1916 uses a Bogen T725 Transformer in combination with two all Brass Rotary Switches to match the impedance of radios with the impedance of headphones.  Brass Binding Posts are used as the contact points between the Radios and the Headphones.  The bottom panel of the IMS Model 1916 can be removed for full access to internal wiring.  The IMS Model 1916 has a Tropical Walnut Frame, Rubber Feet, and measures 6″W x 5″D x 4″H.