Why most voices sit higher than they need to
Your speaking pitch isn't fixed at one note. You have a range, and where you settle in it depends on tension, breathing, volume and mood. Nerves push it up, so do speaking fast and talking over noise. Many people end up speaking well above the relaxed low end of their range all day. That low end is what you're training towards: not a forced growl below your range, but the bottom of the part that's comfortable.
1. Find your relaxed low note
Say “mm-hmm” the way you would to agree with someone, lazily, without thinking about it. The “hmm” usually lands near your relaxed speaking pitch. Now sigh “ahh” from a comfortable note down to the lowest note that still feels easy and clear. Don't go into a crackle. Use the meter to see both numbers.