Designing a sound that localises well I am trying to create or find a sound that localises well.

I read that emergency vehicles are changing their sirens; people found it difficult to localise the sound of the old siren (a sinusoidal sweep), and apparently this led to a lot of accidents. Apparently a single frequency is difficult to localise.

I've experimented using harmonic tones — I found that my brain can resolve higher frequencies, say > 600Hz, much better than lower frequencies,  say &lt; 150Hz.

Unfortunately this is no good to me — I'm building a musical trainer game, and it's important that I communicate a direction without suggesting a pitch, so I need something else, maybe something like the sound of glass breaking or a clap -- anything that doesn't suggest a pitch.

I've experimented with static bursts, and found they don't localise nearly as well as the tones.

Could anyone suggest a good sample sound source?

I wonder whether something like a twig snapping would trigger some sort of primal reflex :)
You want something that has lots of features in the spectral domain and in the time domain. However you have to be careful what other content or meaning you would like to convey or not. Spectra conveys pitch and/or coloration and timbre. Time transients convey rhythms and/or patterns.

For example you could do band limited noise burst with different center frequencies and patterns. That would allow yo to vary localization, spectrum and rhythm without directly conveying pitch. You could also use different percussion samples with different rhythms.