Voice--getting your characters to speak

Looking at the title of this post, you may think this is about style or dialogue, but instead this is about a problem I'm having in my own writing. I am about to have a scene where a main character is about to confront a supporting character about an insult given by the supporting character that resulted in an incident that was potentially fatal for more than one person. That's just a vague description, I know, but the plot behind the confrontation is not what my problem is. I have a problem with the supporting character's (let's call him L) voice.

With L being a character that doesn't show up all the time, I've lost exactly how his voice sounds. I can describe it, but the way that the words come out of his mouth, the way his lips work them has escaped me. The main character (let's call her R) has been in quite a few scenes since the last time we heard from L (being a main character, of course) and while I could superficially describe R's voice, I have a decent grip on how words come out of her own accent and slang without too much trouble.

This is a problem that I know a lot of writers struggle with. I've named more than one famous author that didn't even attempt to differentiate his characters' speech patterns. So here are a few ideas to deal with the problem of a character without a voice, or a lost voice for a character.

• Tell a mundane story in their voice. Write out a paragraph of something that happened to you, or even something that happened to the character in a neutral voice. Then rewrite it in the voice of your character. Use phrases, words, and slang that your character would. Include accent markings with apostrophes.
• Listen to TV. Normally, TV would be the bane of any productive writing regimen, but TV gives you a place to listen to a variety of speech patterns all in your living room. The key here is to listen. Turn on the stereo put leave the picture off. Turn the TV on and type the words you hear. Eventually, you may get an idea of how you wish a character to speak.
• Base a character's speech patterns on someone you know. It's always tricky to base a character on someone you know, but in this case it may be harder for them to recognize themselves in the final product and thus reduce their anger. Or it may do this exact opposite. Either way, this is the easiest way to develop a character's voice, since you could always call the friend and ask them to tell you about their day to get the subtleties of they way they speak.
• Reread old dialogue featuring the character. This is best for when you've lost the way a character speaks. To compound this technique, read it aloud, in their voice. You may want to do this alone to avoid ridicule. :)