It's been a while since I wrote TPlaySound. Did you notice its class declaration?
Tplaysound = class(TAboutPlaySound)
TAboutPlaySound is a class declared in unit aboutplaysound.
TAboutPlaySound = class(TComponent)
The purpose of this is to be able to display an About dialog in the Object Inspector at designtime.
You can see this at runtime if you want:
1. Drop the component on a form (playsound1)
2. Drop a button1 on the form
3. On Button1Click call
playsound1.About.ShowDialog;
Compile and run.
If a dialog shows when you click the button, it was created in the TAboutPlaySound.Create constructor code.
There's no need for the About property at runtime of course, and splitting the component into designtime and runtime versions is something I never got round to doing.
TPlaySound is a component sorely in need of refurbishment. I only wrote it as a kludge to play wave files in the Linux version of a game. I noticed a functional error when reviewing the code just now which I should get round to fixing.