a method of adjusting a frequency response in a ladder - type electric filter having a pair of parallel resonators and a pair of strip - shaped series resonators arranged in a predetermined manner to form a fundamental filter circuit in which at least one of corner portions of each of the strip - shaped series resonators is beveled without changing its length l to regulate its resonance frequency so that the device can be stored within a case without displacing it from its proper position and held in contact with a contact at its node of vibration .