For a very relaxing white-noise generator that will seem to send noise in all directions, you can build the stereo version shown in Fig. 3 simply by doubling up the original version, and sending the outputs to a pair of stereo headphones, speakers, or the line inputs on your audio amplifier. Because there are two independent noise generators running, the sound will seem to come from all directions, which works amazingly well for audio-deprivation experiments where the subject is wearing headphones or is placed directly between the two speakers.

If you do plan to build the stereo version, try to keep all parts the same make and value, so that the sound is even on both channels. Because some transistors may behave slightly differently in this circuit, they should both be exactly the same. To simplify the stereo circuit a bit further, you could replace the LM386 with a stereo amplifier IC to reduce the parts count a bit. If you plan on feeding the output directly to a line input on an amplifier, then you actually can eliminate the entire amplifier section and simply feed the output from the center tap of VR2 directly to your amplifier’s input.

If you are planning to use headphones, turn down the volume control (VR2) at first, because the output of the audio amp can be very loud. If you find the output to be much too loud, remove capacitor C2, and that will change the gain on the LM386 from 200 to only 20, making the output much quieter. 

Now you can move the circuit from the breadboard to a more suitable performance (perf) board. The perf-board version of the white-noise generator shown in Fig. 4 is extremely small, so it can be installed into just about any cabinet.

On a single 9-V battery, the white-noise generator will run all day, although you also could use a 9- or 12-V direct-current (dc) adapter for batteryless operation if needed. The 4-inch-diameter speaker shown in Fig. 4 may be fine for a small room, but for a larger room or a more bassy sound, you probably would want to use a larger speaker or one already mounted inside a cabinet. A 10-in speaker in a cabinet will make the white noise much richer and more like wind rather than a hissing radio.

The cabinet-mounted system shown in Fig. 6 is great for filling a room with rich, bassy white noise that sounds more natural than what comes from a smaller speaker. Because of the full range the quality speaker allows, all the tones are represented rather than just the higher, “hissy” frequencies.

Fig. 7 shows what white noise looks like on an oscilloscope or computer input. Because white noise is comprised of every possible frequency at ;the same time, there is no discernible pattern or tone that can be detected, which is why your mind finds it so relaxing to listen to. 

White-noise generators are often used in digital machines that need to create some kind of chaos for a random output. Digital encryption and lottery machines are prime examples of using white noise as a source for random information, because digital circuits cannot generate truly random sequences that never repeat.

The white-noise generator you've built here is great for use as a sleeping aid or when you want to work in a noisy environment without being distracted by background noise. Some ideas for design might be the addition of a voltage sweep circuit to simulate ocean waves, or perhaps the addition of some type of audio equalizer or filter to shape the white noise into pink or brown noise.