My article on "Loudspeaker Failure Modes" in the TWO: 1999 issue of Speaker Builder, pages 34-43 discusses topics related to loudspeaker breakdowns, including:
The most common cause of breakdown is thermal overstress. Even if input power is limited to prevent catastrophic failure, voice coil temperature can still rise enough to cause a major shift in DC resistance. This results in changes in the loudspeaker's performance in the circuit including speaker, power amplifier, and crossover. The article includes calculations for measuring and predicting temperature rise in copper voice coils.
Click here to open an MS Excel spreadsheet containing the calculations of Figures 1, 3, 4, and 5 from the article. If your browser is configured right, it should automatically launch Excel and open the sheet. It may also open a blank spreadsheet in front of mine, which you will need to close. You should then be able to select "File/Save As..." to create a copy on your local hard disk.
In the references I mention an online magnet wire data book from Alcatel Inc. However, they have reorganized their web site a number of times, and I can't find the data book any more. Click this link for a local archived copy. I've also posted a page of wire table info on this site.
In the article, I mentioned two companies that used to manufacture Beat Frequency Oscillators for audio work, General Radio (now handled by IET Labs), and Brüel & Kjær. Their products were very well made, and are still available on the used market.