I googled and found out through some forum that:
DC has a constant amplitude which overheats and destroys the voice coil of the speaker.
Could someone clarify if this answer is complete and accurate?
Electronic – Why are DC signals bad for loud speakers
dcspeakers
Related Solutions
Added:
For components try searching for "speaker" and sort by size.
In Digikey's catalog "speaker" will get you this and after you reject the expensive tiny specialist units you get eg.
Drawing low on dimensions.
A few here
Allegedly 13mm x 2mm.
http://www.puiaudio.com/pdf/AS01308MR-R.pdf
Or these - prices and datasheet.
From 13 mm dia
http://www.mallory-sonalert.com/Articles/TechAppGuides/Miniature%20Speaker%20Models.pdf
http://search.digikey.com/us/en/products/PSR-11N08S-JQ/458-1119-ND/2071435
Earpiece.
Magnetic earpiece (some)(mot common)
Piezeoelectric earpiece (some)
Many but not all of these will be relevant, with links - via Magnetic earpiece
The buzzing is AM detected signal.
The reason of audio amplifiers being hit by GSM signal is that contemporary audio semiconductor parts are actually very functional up to high GHz range. For GSM-800-900MHz range any 80mm copper trace works like 1/4 wave antenna, or stripline resonator. The signal is AM detected on any non-linearity (transistors or diode structures in chips) on multiple points of amplifier simultaneously, also including power regulator chips and so on.
It is translated into audio range as tiny but very sharp and periodic dips or pops of averaged conductivity of non-linear parts (AM detection), which are DC powered.
Think of low speed oscilloscope trace showing straight line with beads of UHF flashes. Simple sharp spikes of consumed DC current will become audible with amplifier.
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Best Answer
The voice coil on a speaker is effectively a big inductor. It happens to also generate sound, but the loops of wire in a magnetic field make it act like an inductor.
Inductors change impedance with respect to frequency. This is because any change in current through the system must build up the magnetic field in the coils. The faster you oscillate the current, the more pronounced the effect. This causes inductors to have a high impedance at higher frequencies, and a low impedance at low frequencies.
So what happens at DC? Well the impedance of an ideal inductor at DC is 0. That means no resistance at all! Of course, this isn't an ideal inductor. There is a bunch of wire, and that wire will provide some resistance. However, it is trivial to see that the resistance of the coil at DC will be far less than it will be at a higher frequency.
Now most amplifiers are voltage sources. They output a specified voltage, and are designed to provide enough current to maintain that voltage across the impedance of the speaker. Thus, if you have a very low resistance, you will have a very high current, much higher than might otherwise form. This current means your coil has to dissipate a lot of heat!