I've been in the process of designing an experiment that requires precise control over the frequency and amplitude of sound waves and must encompass ultrasonic frequencies, ideally up to 70 kHz. I'm aware that is well outside the range of human hearing and closer to the frequencies used in ultrasonic cleaners. Many bird callers and electronic pest control devices advertise the ability to produce ultrasonic frequencies but it is unclear how much range these speaker possess and if they can be modified for other applications. I have also seen ultrasonic piezoelectric speakers that advertise frequencies up to 70kHz but I am uncertain, again, how limited their range is. Ebay is full of signal generators that can produce sine waves of almost any frequency but I believe these still require a transducer to convert the signal and are probably replaceable by various computer programs.
So this is my question: can anyone with a background in sound engineering or alike recommend a minimally expensive, maximally accurate system to produce pure tones of a precise frequency and amplitude (as well as ultrasound more generally) and a speaker to transmit them?