GFB Whistling Trumpet (suits all valves)The 5702 can be used in place of the standard trumpet on all GFB valves, and will make the whistling sound more readily than the 5701 (high boost and RPM is required to get the whistle from a 5701), and at a slightly higher pitch.? Like the 5701 however, it is necessary to run the valve so that all (or most) of the air vents through the trumpet ? Respons valves will typically not generate the velocity required to whistle when set to 50 50 venting.