JOHN DANKOSKY: This is Science Friday. I’m John Dankosky in for Ira Flatow. One of the marks of the holiday season is folks coming together to raise their voices in song. But once again this year, some caution is still required, especially when it comes to airborne particles. We all know that masks can make voices a bit less distinct, though, so what is a vocalist to do?

Thomas Moore is the Archibald Granville Bush professor of natural science and a professor of physics at Rollins College in Winter Park, Florida. He recently gave a presentation at the Acoustical Society Meeting about masks and singing. Dr. Moore, welcome to Science Friday. Thanks so much for joining us. I appreciate it.

THOMAS MOORE: Great to be here, John. Thanks.

JOHN DANKOSKY: So we know that a person’s voice sounds a bit different coming through a mask. But maybe you can explain, first of all, why?

THOMAS MOORE: Well, there’s actually two reasons why this happens. The first one is when you put a mask up close to your mouth, then the material can interfere just with your lip movement, so the diction doesn’t sound quite right. But the second and the more important problem is that you sound like you because of your oral cavity that is your throat, your head cavity, your sinuses, and things like that.

But when the sound comes out of your mouth, it meets the air, and some of it gets reflected, just like with a musical instrument. If you put something in front of your mouth, that changes what the sound sees, if you don’t mind me anthropomorphizing the sound. And so you sound different. This is the same reason that cheerleaders use megaphones. You want to change the resistance to the sound going from your mouth into the air. Well, this happens inadvertently with masks, and it changes the way you sound.

JOHN DANKOSKY: And so you started looking at different types of masks on singers. What did you find when you started to explore this? Well, the first thing we found is that if you don’t take into account whether the mask is making your voice softer or louder, if you just look at what it sounds like, up through about 1,000 Hertz, which is where most people talk and sing, everything works fine. You don’t get much change in the mask. But if you get above that level, then there are vast differences in the masks.

THOMAS MOORE: And you might think that, well, if we don’t sing or talk above 1,000 Hertz or so, then it doesn’t really matter. But it does because that’s what makes you sound like you. It also gives you the sharpness, the T’s, the S’s, things like that. So when you put on a mask, it sounds muddy. And it sounds muddy because you’ve lost all those overtones or those higher harmonics. You haven’t lost them. They’re just down much, much lower than they should be.

JOHN DANKOSKY: So we do actually have a couple of sound files that you recorded so that people can hear this difference. And let’s go through them. First of all, here is the singer that you recorded. And she’s singing with no mask on whatsoever.

CAITLIN MOHR: (SINGING) When the sky is a bright canary yellow, I forget every cloud I’ve ever seen. So they call me a cockeyed optimist, immature and incurably green.

JOHN DANKOSKY: All the show tunes fans will be out today. I really like the way she sounds. It’s clear. And obviously, she’s not wearing anything on her face. So let’s go to the next one here. On this one, she’s wearing what kind of mask? Just like a cloth mask, the kind that you get at the store?

THOMAS MOORE: Yeah, it’s a two-layer cloth mask, the kind that I wear every day. But this is a homemade, two-layer cloth mask. Lots of people wear them.

JOHN DANKOSKY: OK, let’s listen.

CAITLIN MOHR: (SINGING) When the sky is a bright canary yellow, I forget every cloud I’ve ever seen. So they call me a cockeyed optimist, immature and incurably green.

JOHN DANKOSKY: Wow, so you can really hear the difference. I mean, the first thing that I hear is it does sound very, very muffled. And you can’t hear all the consonants. Her words aren’t coming out very clearly.

THOMAS MOORE: That’s exactly right. And that’s what happens when you knock off those higher frequencies. It’s sort of like listening to your stereo through the bass only. You miss all those high frequencies. You don’t sound like you. By the way, I would like to say that the soprano is Caitlin Mohr, who’s a professor here at Rollins College, and she sounds more like the first than the second.

JOHN DANKOSKY: And she sounds really good, even through the mask. And I should also say that these were corrected to the same loudness because the loudness is also something that is adjusted, right? I mean, when you have to sing through a mask, it is quieter than if you’re singing without a mask.

THOMAS MOORE: That’s true. And that’s actually one reason why we decided to use a professional singer rather than, say, a speaker, like some other people have tested masks with, because a professional singer can actually adjust a little bit to make herself sound like what she wants to sound like. And so that took out a lot of the variability that you’d find just due to the fact that the mask makes you not quite as loud.

JOHN DANKOSKY: So the third example we have here is her singing with what’s called a singer’s mask. And I guess, so the people have a visual of what this looks like, explain what a singer’s mask is and how it’s different than the one that we might be wearing to the grocery store.

THOMAS MOORE: Now a singer’s mask actually has a frame that separates the cloth from the face. And so the mask actually is not touching the lips, first of all. And second of all, there’s an area of several inches between where the mask starts and where the lips end. And so you’ve got this cavity in there that allows the air that when you’re speaking, it allows your voice to hit the air more like it would in a room. It sort of looks like a duck bell. It looks a little funny, but it sounds a whole lot better.

JOHN DANKOSKY: Let’s listen to that one.

CAITLIN MOHR: (SINGING) When the sky a bright canary yellow, I forget every cloud I’ve ever seen. So they call me a cockeyed optimist, immature and incurably green.

JOHN DANKOSKY: So what do you hear there that’s different from the other mask?

THOMAS MOORE: Well, from my standpoint, the first thing you notice is, it sounds more like a soprano, but you can hear that crispness in the consonants, as you said, that you aren’t going to hear when you’ve got the other mask on. If I didn’t know who was singing, I could clearly identify who it is. Is it different? Slightly.

If you get up to the very high frequencies, we notice a slight difference in the amount of power in those higher frequencies, but nothing even close to what we get with just a cloth mask. With just a cloth mask, you get up around the 10 kilohertz region, which is fairly high, but it’s important for the consonants to come out well. You’ll see a drop off of 50 to 100, whereas with the singer’s mask, you’ll see a drop off of maybe 1 and 1/2.

JOHN DANKOSKY: Part of your research isn’t just how things sound, but where the air is actually going. So maybe you can talk about that, the visualizations that you’ve made of where the air is going when you’re wearing a mask and singing.

THOMAS MOORE: Yeah, this is actually what we started looking at. We have a technique known as transmissional electronic speckle pattern interferometry that can see– actually visualize the breath as it comes out of the mouth. And that’s due to the temperature change between your breath and the ambient air. And so what we looked at was what does the breath look like when you sing without a mask? Because we were concerned about, obviously, transmission of COVID amongst choirs.

And it looks about what you’d expect. The air goes out. It goes out about three or four feet. It kind of starts to stop. But then you can easily see it rising because it’s hotter than the air. When we put a mask on, any mask that we tested, because they don’t make a good seal to the face, what happens is, is most of the exhaled aerosol goes out the sides and the top. The mask will stop what we call ballistic particles, the kind of big spittle particles.

But a lot of the stuff comes out the sides, the top, and the bottom. And at first, we thought, wow, that’s a serious problem. We need to look at sealing these masks to the face. But in reality, unless you’re in a medical situation, it’s not a bad thing. What happens is, is the air comes out the top or bottom or side of the mask. Because it is warmer than the ambient air, it immediately rises, and it gets above head level.

Furthermore, because it’s close to the body, your body is hot, and there’s already rising air due to your body, which we can see in using this technique. And so realistically, any of these masks will significantly help reduce the spread of COVID-19, but for a reason really maybe a little different than what we originally thought. It gets the aerosols up above the head. It’s mixed in the ambient air. It’s diluted. And so there’s a much less probable transmission of the virus.

JOHN DANKOSKY: So, yeah, if you’re singing in a choir in a big high ceilinged church, you can probably imagine that most of that breath is just going right up to the sky.

THOMAS MOORE: It actually is, and it’s a good thing. Unfortunately, most rehearsal and performance spaces are just like my house, where they bring the air into the room from above, and it exits somewhere lower. So in the long run, we probably ought to look at whether we can reverse that because in the next pandemic or this one, if it ever ends, we need to keep the arts. And to keep the arts, we’ve got to have performance. And so a simple solution, if you could call it simple, is just to bring the air into the room from the bottom and exit from the top.

Obviously, there are thermal considerations here. There aren’t many air conditioning and heating people who would think that’s a good idea. But those problems can be addressed. And I really think that if we just started thinking about bringing the air from the bottom and taking it out through the top, that yes, you could sing in a choir again.

JOHN DANKOSKY: Now you’ve also studied musicians playing wind instruments, too. I saw a video on your site of a flutist playing with an air shield and without. And in that example, the tone hardly changes at all, at least to my ear, but there’s a big difference in how far the breath travels.

THOMAS MOORE: Yeah, what you’re talking about is just a sheet of acetate that goes in front of the mouth so it hooks into the head joint. And it has, as far as we can tell, no acoustic effect. Because it’s beyond the point where the air interacts with the flute, we can’t hear the difference. However, what happens is, is because the flutist is breathing out, she’s breathing right toward either the violins if it’s an orchestra or the conductor if it’s a band.

But by putting the sheet of acetate over the head joint, the breath hits this piece of acetate, and it goes straight up and down. Without it, it will go actually further than singing, but once you do this, the aerosol goes up or down. And just like with singing, it’s entrained into the upward flow to the heat from the body. It’s hot anyway, so it goes up. And we actually see it get way out of the head.

JOHN DANKOSKY: That’s so interesting. And getting back to the masks quickly, in the singers that you worked with, did any of them say, yeah, this is pretty comfortable, or this is really annoying to wear these singer’s masks? Because I think the comfort of a musician is probably just as important as anything else if they want to perform at their best.

THOMAS MOORE: Oh, I agree. They prefer the singer’s mask to all the others, but I think that if you just ask them, I think that is due to the fact that they can hear themselves better, and they sound better. They look funny, there’s no question about it. Obviously, they would rather sing without a mask. But given the choice, we’ve tested a tenor and a soprano, and of course, they want to sing without a mask. But if you’ve got to have a mask to sing, you want a singer’s mask.

JOHN DANKOSKY: So if we’re getting together for some sort of a holiday singalong, going out Christmas caroling or something, do you have any tips for people about masking and not masking if you decide to go out and sing around this year?

THOMAS MOORE: Yeah, truthfully, if you’re outside, you probably don’t have to worry about too much. You don’t want to be close to someone where the big particles or little spittle particles can get to them. But outside, the ambient air is moving so much that it takes that aerosol and just whisks it away. I would prefer to stand upwind from somebody who’s got COVID, rather than downwind. But if you’re going to wear a mask, wear something that gives you some room between the lips and the mask itself, and you’ll sound great.

JOHN DANKOSKY: Thomas Moore is the Archibald Granville Bush professor of natural science and a professor of physics at Rollins College in Winter Park, Florida. Thanks so much for talking with us.

THOMAS MOORE: It was a pleasure, John.

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