Maximum Flow Declination Rate (MFDR) is not something often discussed by singers (or even voice teachers) but it is an important part of having a powerful voice.

In this episode, John explains what MFDR is and how best to develop safe and healthy vocal power.


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Episode Transcript

Episode 96 – The Key to Vocal Power

Hey there, this is John Henny. Welcome back to another edition of The Intelligent Vocalist. I do so appreciate you spending your precious listening time with me. Alright, a little bit of housekeeping today. A week from today, the day that this is scheduled to come out, I will be at the OHNI Vocal Masterclass in Hollywood. I will put a link in the show notes, if you’re interested in attending. It’s going to be an amazing event for voice teachers and for singers and voiceover artists. So go to for episode 96. I’ll have a link there in the show notes. Also, my Contemporary Voice Teacher Academy is open. I’d previously only been opening it a few times a year, but I’ve kinda got it streamlined and now I’m going to, for the time being, leave it open year-round, unless it becomes a little unwieldy. But if you would like to get in, just go to or if you’re on my website, you can always just hit the Teacher Training tab up there in the menu. It’ll take you to the page to give you all the info. And that’s everything.

Alright. Let’s jump in. What is this key to vocal power? Well, it’s this little known concept of MFDR. And I am sure just about all of you except the serious vocal geeks are going, what the heck is MFDR? Well, it stands for Maximum Flow Declination Rate, which is even more confusing, but it’s just a sciencey way of saying the maximum flow, or the flow of air, declination, how quickly it declines — the rate of decline in the flow of air. So even put more simply, how quickly your vocal cords close. Now, why do we care about how quickly our vocal cords close? Well, let’s talk a bit about how power is created in the voice. So it’s a system of compression. I’m sending air to my vocal folds and the vocal folds are resisting the air. The more resistance, the greater the energy. So if I just create a little bit of resistance, I’m going to get a breathy voice. If I create a lot of resistance, I’m going to get more power, but it’s going to kind of be this pressed, strained to sound. So I want this nice flowing sound, these nice balanced sound waves, balanced yet powerful sound waves emanating from my vocal folds. And then I can further filter them through my vocal track, which is going to create different vowel sounds. So we want these vocal folds to close quickly, and the reason being is when the vocal folds open and then close slowly, there’s not as much energy built underneath the folds. There’s not as much compression.

We want to increase the amount of time the cords are staying closed as opposed to open, and this is also called the closed quotient. And if the cords are staying closed a little longer than they’re open in this cycle of opening, closing, opening, closing very quickly. If the closed phase, if the closed quotient, the fancy science term that we use, is a little longer, we’re going to get a little more power. Also, when these cords close more quickly, they tend to square up better. They tend to come together better, which is going to give you a better sound. If you buzz your lips, you notice you have to put a certain amount of pressure on the lips in order to get them to buzz. Otherwise they don’t really work. If you add tension to the lips, like you’re– imagine a trumpet player playing a high note, if you’ve ever played trumpet, you have to add even more tension, muscular tension to bring those folds together to get them to square up — I’m sorry, not folds. Your lips — so that the squaring up, the coming together, and getting enough surface contact for that robust sound is really important.

When the cords close quickly, you’re going to get more of that contact. So if we put it on a graph, we have like a little hill. If we’re charting the cords opening and we draw up as they open, it looks like a little hill going up. And then if they close slowly, then it’s like a little hill going down. Alright, but if we get this MFDR, this Maximum Flow Declaration Rate, the cords open up, it’s like a hill, but then suddenly the top of the hill is open just a fraction longer and then there’s just sudden drop-off. Boom! It’s like a cliff, and that’s the cords closing quickly. So that’s what we want to have happen in order to get these nice, robust balanced sound waves. It’s kind of a funny concept that just because the cords are closing more quickly, we’re going to get a better sound and more power, but that’s exactly what’s happening.

Now, this is where it gets a little tricky and this is where we as singers fall into the trap of muscle and force and effort, because in order to get that maximum flow declination rate for the cords to close very quickly, we have a few options. We can start to use more muscle and squeeze them together. Then we’re going to have to blow more air because we’re muscling up, so the cords aren’t going to come apart easily. So we have to shove more air at the folds. But that excess muscle will slam the folds shut and you will get more power. But it’s not going to slam them shut in a necessarily healthy way. And the cords can come together with too much force, and when the cord starts coming together with too much force over and over and over. Imagine clapping your hands very loudly for five minutes.

I mean you, if you could do it, your hands would be absolutely stinging. But your vocal folds are opening and closing hundreds of times a second. And when they’re coming together with that much force, it doesn’t take long before they start to swell, before you start to have issues. And then as you know, you continue to do that, you can start to develop things such as nodules, which are calluses on the cords and cysts on the cords. It’s just terrible stuff. So muscle is not necessarily our best option. It really isn’t unless it’s done very, very carefully. And there is a certain amount of muscle involved, but not this gross shoving together and slamming the cords. So what’s our other option? Well, our other option is to utilize something called inertive reactance, which now is another crazy idea, all these science terms. But this one basically means that the air above the vocal cords have an inertance. In other words, they’re a little lazy. They don’t feel like moving. So when this pressure’s building up above the vocal folds, or I’m sorry, when the pressure is building underneath the vocal folds and then the cords pop open, if the air above doesn’t want to move right away, then what happens is the air rushes in between the vocal folds, this energized air from below that you’ve compressed, but there’s a little resistance from the air above it. It’s been sitting still and it weighs something. It doesn’t want to move right away. So this air between the folds is trapped and meanwhile more air is coming to join it. So the vocal folds are pushed apart even more and then finally when the air above gets the memo and decides to move, then the air rushes up, the energized air and then the cords, because there’s an elastic recoil and this pressure’s been building up with the vocal cords being pushed open, they – boom! – come together very quickly.

So we get this maximum flow declination rate. But the great thing is we’ve done it with acoustics. We’ve done it with the sound waves themselves, with the air itself and not with muscle. So how do we get this sluggishness in the air above? How do we increase that so that we can increase the resulting MFDR, the resulting power? Well, the best way to do it is through vowels. And if you’ve been listening to my podcast a lot, you know I love me some vowels. So if we get the vowel balanced properly and we align our resonators, our throat resonator and our mouth resonator with the sound wave in an optimal way, here’s what’s going to happen. There is an energy boost, and when we get this energy boost and energy boost of acoustic energy, we shape our resonators in such a way that certain parts of the sound wave become enhanced, excited. There’s more energy and the energy flows out your mouth toward the listener, but the energy also reflects back down towards the vocal folds and what this does, this energy coming back– Imagine you are swimming in the ocean and you are deciding to swim to shore. There are waves coming to shore that are going to push you along. However, there’s also the force of the waves coming back in towards the ocean, and those are going to fight against you. And that energy coming back is going to make that air above the vocal cords– it’s going to make it even harder for them to move initially. There’s going to be even more delay, which is then going to create more pressure between the vocal folds if they’re open, and those energized air molecules come in while now there’s even more inertive reactance. There’s even more resistance from the air above the folds, so the cords are pushed open even a little bit more.

There’s a little more delay so that when the air finally does move, bang! You get that really strong MFDR. Now, I know this is a ton of science coming at you. So let’s see if we can recap this in a really simple way. You’re compressing air underneath your vocal folds. That air is becoming squished together. Energy is building. At a certain point, the pressure builds to where the vocal cords open. So open they do, and the energized air now goes to rush out. But if you’ve set everything up right, and if you have a really good vowel, those sound waves reflect back down to the vocal folds. The energy’s coming back towards you, and when that energy is reflecting back now the sound can’t rush through the vocal cords as quickly. There is a resistance, so the vocal folds are pushed open even more, more energy’s built because there’s this elastic recoil.

It’s like pulling a rubber band further and further or a slingshot. You’re building more energy within the folds. And so they are going to – boom – they’re going to close very quickly, but they’re not going to slam. They’re not going to slam the way they do with muscle. There’s this little cushioning effect of the air as it goes through. It’s so subtle. It’s such a tiny thing, but it makes all the difference in the world. And you are able then to get this quick closure, which then increases the closed phase, increases how long the cords are staying open and the pressure building underneath. And it also brings the cords together in a more optimal way, and all of this combines to give you a sound wave that is vibrant yet balanced. Because when you do it through muscle, the sound wave itself, the fancy word is source harmonics, but the raw material coming from your vocal folds, that’s then going to be filtered through your throat and mouth resonator.

That raw material is not so optimal. It’s actually going to sound steely. It’s not balanced. It’s going to sound steely, squeezy, shouty, strained. Not that you can’t do that as a vocal artist, and if that’s what you choose to do and if that’s the sound you want to do, then go right ahead. But just understand what it is that you are doing and understand that it is stressful on the voice, so you don’t want to be doing it all the time. You certainly don’t want to be doing it by accident. You certainly don’t want to make that the only way you can get more power. So by balancing your resonators, your vocal tract, by getting that balance, by forming an optimal vowel, the energy reflects back.

The reflective energy keeps the cords open more because there’s that sluggishness in the air. It’s like an LA traffic jam. And then the cords come together really nice and cleanly. You get that better MFDR, maximum flow declination rate. I feel so smart even just saying that. And you end up with power. And when I work with students, when we’re able to get into this spot and we tune the vowel in such a way that that inertive reactance is occurring and you’re getting that sluggish air and you’re getting that really good MFDR, they often look at me and just say, “Oh my gosh, that’s so easy.” It becomes so easy. You don’t feel stressed. You know, people will say, “Oh, I want to sing without tension.” Well, there’s no such thing. There has to be some amount of tension in order to create sound, but it’s not excess tension. It’s a balanced tension. And you, the singer, it feels almost effortless. It really does, because rather than you using muscle in order to get the MFDR, you are utilizing acoustics and sound to get it, and it’s a completely different experience. It really is.

That’s why I encourage singers to really understand vowels and learn to tune vowels and learn to balance the resonance. That’s your secret to power. It’s not shoving more air. Although if you’re not using enough air, you do want good airflow, but there’s no magic. You don’t need to develop these muscles to shove more air, and it’s certainly not using more muscle at the vocal fold. It’s adjusting your vowels, it’s tuning your vowels. So get out there and become a vowel nut. Learn vowels. Learn how they work, find them in your voice, learn to tune them, learn to adjust them. Now, one more thing. When you’re working your voice, a great way to increase inertive reactance and to increase MFDR is to vocalize through a straw, and I’ve talked about it couple of podcasts back.

I’ve also done one on SOVT exercises, Semi Occluded Vocal Tract Exercises, but this utilization of a straw, what it’s going to do is because now everything’s going through this narrow space and it’s elongated your vocal tract, you’re going to get more energy reflected back to the vocal folds, or let’s just say you’re going to get energy reflected back without you having to tune your vowel. So it’s a great way to warm up. And also because it’s essentially made your resonating tube longer because you now have the straw, there are acoustic things that are going to happen that make the transition easier. The transitions are going to happen a little sooner when the cords are under less tension. It’s just going to be easier for you to go through. So I really, really encourage you to utilize the straw.

Again, I use this oovo straw, I will put the link at the website, or this episode, Also, if you use my last name as the coupon, H-E-N-N-Y, they’ll give you a little bit of money off. I think it’s 10%. Anyway, I highly recommend this straw, but if not, get yourself some straws that you carry around and keep with you at all times. Just a great way to warm up the voice. Great way to increase inertive reactance and increase MFDR and to start feeling vocal power without you having to use muscle.

Hey, I so want to thank you for listening. Again, go to my website for more about me. You can find out information on studying with me and sign up for my email list. And I always send out special offers and certain things to my email list, and you’ll always get notices when there’s a new podcast. And until next time, to better singing. Thank you so much. Bye-bye.