Highest frequency Superman has ever heard.

[alschroeder]

I suspect the radio waves thing is actually a function of his super-EYESIGHT, rather than his hearing (unless he's hearing some radio receiver that is converting it back to sound.).  Remember, in "Whatever happened to the Man of Tomorrow" he asked Toyman and Prankster, "Do you know what radio waves look like? Because I DO!"
    He probably said "heard"  to keep from making a big explanation.  
    As far as his hearing is concerns---limits....hmmm.
    There seems to be two "components" of his super-hearing. One is amplification of normal sounds (perhaps his own energy working to amplify the tiny sounds he hears....) and the other is being able to extend the range of his hearing along the spectrum of sounds.  He could certainly hear Jimmy's watch, for instance, but I'm not sure he can hear  all ultra and infra sounds---I think I've heard Superman mention that he keeps that particular part of the ultrasonic spectrum "open". Superman doesn't seem to hear everything around him, at all times---he has to "open up" his hearing to do that. Which is probably well for his sanity....
    Nevertheless, from Louisiana, he heard a woman in Washington DC clear her throat. (DC Comics Presents, Alan Moore-written story with Swamp Thing.) That's---pretty good.
---Al

[llozymandias]

Superman's super-hearing seems to enable his ears to operate as radio receivers.  Just as his super-voice powers seem to enable his vocal cords to double as a radio transmitter.

[Captain Kal]

Thanks for the reminder, LLozymandias.  I forgot he could generate radio signals with his super-voice.  That's one way he's able to summon Krypto when the pet is in space.

Remember what I said on another thread about his super-ventriloquism being possibly related to his super-mind?  Real ventriloquism is just an illusion, but super-ventriloquism truly is the ability to remotely throw his voice.  Along with his ability to generate radio signals with his voice and communicate on an 'ultra-wavelength' in space with Vartox, that tells us his super-voice is capable of not only generating more than just ordinary sound waves, but that he could probably remotely throw those EM and ultra-wavelength signals anywhere he wants to.

Our cells and even our unliving matter responds weakly to EM signals.  It would make sense that his super-hearing is so amped up that it can detect and translate that slight EM effect on his ears into sound waves (in the same fashion as sound frequency electrical stimulation of tissues and bone are interpreted by the brain as sound -- ref. a Popular Science issue from decades back).

Related patents granted using principle of electrical stimulation to create perception of sound:

Nervous System Excitation Device, US Patent #3,393,279, Gillis Patrick Flanagan, July 16, 1968. A method of transmitting audio information via a radio frequency signal modulated with the audio info through electrodes placed on the subject's skin, causing the sensation of hearing the audio information in the brain.

Hearing System, US Patent #4,877,027, Wayne Brunkan, October 31, 1989. A method for directly inducing sound into the head of a person, using microwaves in the range of 100 MHz to 10,000 MHz, modulated with a waveform of frequency- modulated bursts.

[RedSunOfKrypton]

Nervous System Excitation Device, US Patent #3,393,279, Gillis Patrick Flanagan, July 16, 1968. A method of transmitting audio information via a radio frequency signal modulated with the audio info through electrodes placed on the subject's skin, causing the sensation of hearing the audio information in the brain.

I thought you didn't put much stock in Flanagan.  

Oh and some recent news on the effects of RF on cells, though it's completely unrelated to hearing: http://www.wpbfnews.com/news/5377374/detail.html

[Captain Kal]

I don't trust Flanagan, at least as far as his debunked pyramid power support is concerned.  But if the US patent office granted him a patent for this gizmo and it jibes with a whole lot of other credible inventions I've seen elsewhere using the same principle, I believe him on this.  Remember that I said I wouldn't take anything from him without corroborating evidence from outside sources.

Note that I quoted both an old Popular Science article I read and another related patent.  Those certainly qualify as outside supporting evidence.

I'm not taking Flanagan on his word alone.  Those two other sources plus the patent office make this one pretty solid.

OTOH, no US patent has ever seen the light of day re: pyramid power.  I know Czechoslovakia issued a pyramid power patent but -- not to sound too snide -- the Eastern Bloc has been notorious for grandiose claims for their science that cannot be replicated nor substantiated by other countries' scientists.  The US patent office has a demonstrably higher standard and credibility, though even they sometimes patent clunkers.

[Psybertrack]

I think superman's sight and hearing and vocal powers were intended to be the science fiction version of their magic counterparts.  So explaining them in real world physics/mathematics is sometimes tricky or nearly impossible. Still you all have come up with some brilliant explanations which fit the facts. Well done!
As Wonder Woman is the Mythic Heroine, & as Captain Marvel is the Magical Hero, and Plastic Man is the Comedic Hero, & as Batman is the Mystery Hero, so Superman is the Science hero. Superman is the Man of Tomorrow. The Man of the Future. The reason things like superhearing and telescopic vision seem to perceive beyond the speed of sound even at real time or light speed levels is because they are based on being a sci -fi version of Clairaudience and Clairvoyance.  Supeman can hear a high frequency sound from Jimmy's watch. He can hear dog whistles.
And much more. Pretty much I think his eye and ear powers will prove virtually limitless as time goes on.

re radio waves...some versions of Supes have this power, other times he is simply hearing a radio that is turned on somewhere. His power to emit and receive radio waves has been depicted in several comics, but is ignored in others.  He uses a JLA communication/alert  device sometimes doesn't he?

[Captain Kal]

You're right re: the JLA communicator.

It must be noted that Hal/GL also sported said JLA signal device despite his omnipotent power ring which could perform the same function.

I suppose a few reasons could explain the above.  If Superman or Green Lantern were in an emergency situation themselves that meant they needed outside help, it's very possible that their relevant communication powers might be compromised or neutralized altogether.  An independent signal device not dependent on their respective powers would be a wise precaution.

While most of us are capable of mental mathematics, most of us go the lazy route by using a pocket calculator instead.  Maybe Superman sometimes feels the need to take the load off his own powers and let the JLA gadget handle talking to his buddies instead.

An element of not wanting to show the others up may be another aspect: For the dignity and self-respect of the others, Superman may just choose to use the device instead of his own powers.

[RedSunOfKrypton]

I don't trust Flanagan, at least as far as his debunked pyramid power support is concerned.  But if the US patent office granted him a patent for this gizmo and it jibes with a whole lot of other credible inventions I've seen elsewhere using the same principle, I believe him on this.  Remember that I said I wouldn't take anything from him without corroborating evidence from outside sources.

Note that I quoted both an old Popular Science article I read and another related patent.  Those certainly qualify as outside supporting evidence.

I'm not taking Flanagan on his word alone.  Those two other sources plus the patent office make this one pretty solid.

OTOH, no US patent has ever seen the light of day re: pyramid power.  I know Czechoslovakia issued a pyramid power patent but -- not to sound too snide -- the Eastern Bloc has been notorious for grandiose claims for their science that cannot be replicated nor substantiated by other countries' scientists.  The US patent office has a demonstrably higher standard and credibility, though even they sometimes patent clunkers.

I was just teasing.

Re: The US patent office, they've been letting in a lot of clunkers lately. I swear they should stick with the "must have a working prototype" rule.