I coach both singers and public speakers, and I have been asked whether a voice can be deepened so many times I've definitely lost count. Men think women find low voices more attractive, women think they'll be taken more seriously with lower voices--and they're not wrong. Margaret Thatcher was famously advised to lower her voice in order to be elected, and took lessons with Lawrence Olivier to lower her pitch and "develop a calm authoritative tone." Research has repeatedly shown that men and women with low voices are viewed with more leadership capacity, and even as physically stronger than their high-voiced counterparts. Women remember more easily and prefer men with low voices. Women even prefer their female leaders to have masculine voices. And I guess that tells us why this questions keeps being asked.
So, what's the answer? If you want to, can you lower your voice? The short answer is, yes, you can. But the real question you might ask yourself is, should you? I've written about vocal dysphoria before and I always encourage my students accept and be comfortable with their natural voices. Many problems can result from artificially manipulating your voice to sound lower, ranging in seriousness from simple vocal fatigue to actual vocal injury. The truth is, the size and make-up of your larynx determines your most natural speaking range. Think violin v. cello. One is bigger and therefore deeper. The violin will never sound like a cello.
Are you disappointed? Don't be. Because while I wouldn't encourage you to actually lower the pitch of your natural speaking voice, there are things that you can do to influence the perception of your listeners. There are many factors besides frequency/pitch that influence what we perceive as a "deep" sound, and these can be healthily altered.
Let's start out with what NOT to do. If I were to ask you talk to me like Sean Connery, James Earl Jones, or Santa, here's what you'd probably do:
1. You'd create a "yawn" space in your throat or pull your tongue back (or both).
2. You'd drop your chin, maybe even smashing your neck a little.
3. You might push your lips forward. In the case of a Sean Connery imitation you'd probably lock your jaw into sort of a slack open-ish position.
Here's what you're doing: You're depressing your larynx and widening (the yawn or slack jaw) and/or extending (the puckered lips) your resonance chambers. This will result in a lowering of your pitch and a more "full" sound. Not all of these techniques are bad per se, but taken to extremes they all lead to vocal fatigue--a.k.a. hoarseness and voice loss. The lowered larynx is especially problematic. You're placing a huge amount of strain on some pretty small muscles--the geniohyoids, sternohyoids, and sternothyroids. It simply isn't sustainable. In the words of Richard Miller "The history of the low-positioned larynx is a long and depressing one." (National Schools of Singing, pp. 221)
Get it? Depressing? Isn't he punny? :)
So now you know that the way you instinctively mimic your deep-voiced idol is wrong because it will wear out your voice. Besides this, weirdly manipulating the shape of your resonance chambers (i.e., mouth and throat) most often results in a somewhat garbled and "cloudy" sound. It's much harder to understand someone who is speaking with a lowered larynx and puckered lips.
Another consequence of speaking lower than is natural to your relaxed larynx is that this results in vocal fry. You know, that weird gravelly Kardashian I-don't-really-care-about-what-I'm-saying-and-I'm-not-interested-in-anything vocal quality? That's vocal fry. And many vocal professionals have described it as an epidemic. If you're auditioning or interviewing for anything that has to do with speaking or singing, I guarantee you that they'll notice you frying-out at the end of your sentences. And while I've generally seen articles dedicated to the impact vocal fry has had on women, in my experience vocal fry affects men as well. Purposely lowering the pitch of your voice will lead to vocal fry.
All right then, what should you do? The first step is to identify the factors besides pitch that make up a deep sound. The first is vocal color. A dark or bright color exists apart form the pitch itself. High pitches can sound dark and low pitches can sound bright, depending on how they are produced. Vocal color is largely influences by your vocal placement. I talk about it a bit in this blog post, but basically you don't want to sound like Santa or the Wicked Witch. A nasal sound is generally considered bright and irritating. By playing around with your placement on a pitch that is in your comfortable not-too-low range you'll find that you can significantly alter your vocal color and create a deeper, richer tone. Think Golden Mean on this one. Go for something in the middle, and avoid the urge to overly "darken" your sound.
Second, you want to avoid a breathy sound. Not only can it be difficult to understand, it's vocally inefficient and can be fatiguing. Neither do you want a strident, tense sound to your voice. Relax and aim for a clear, consistent sound. This will come across as confident but not aggressive. This trait is all about balancing your airflow with your muscular manipulation. One thing that might help you explore breath effeciency and balance is this.
And last but not least is vocal line. I'll explain what I mean by this because it encompasses a couple of things. The first thing I mean when I say vocal line is the flow from one word to another. English is kind of a choppy language when compared to others. I've studied and spoken French for years now. When I began to really master the French "accent" I realized that this referred to not only my pronunciation, but the flow from one word to the next. When I started to pay attention to my airflow while I was speaking, ensuring that it was more of a continuous stream and much less puffy and choppy, my accent improved considerably. I also developed a more melodious "line" to my speech. I have noticed that English speakers will mellow, attractive but not breathy voices speak with more continuous air flow than those who do not. You still want to be understood, so ultimately it's not a good idea to smoosh your words together too much, but it doesn't hurt to play around creating a little more connectivity in you vocal ine.
The other thing I mean when I talk about vocal line are your infections. "Up-talk" is an example of an annoying vocal inflection habit, and it's become more and more common. If a lot of what you say ends up sounding like a question, you're probably up-talking. It tends to come across as youthful and uncertain and could be undermining your interviews, presentations and auditions a lot more than the pitch of your voice. I often find that people who are going for "sincere" can up-talk as well. But sometimes it can sound more like you've just memorized what you're saying because the inflection isn't normal. This combined with breathy whisper-talking is one of my pet peeves. I have hard time hearing the words behind the tone if this is the way you're speaking. Aim for smooth confident statements. This can be achieved through deliberate inflection and smooth consistent airflow.
To sum up, if you want to develop a deeper more attractive voice, don't focus on the pitch. Instead, work on you vocal placement, breath consistency and inflection. It's not easy to change the way you talk--you've been doing it your way for years--but it is very possible. So play around. Develop an attention to vocal qualities other than pitch and you'll be well on your way to a more confident successful sound.