Post-Conference Ashkahn is still out of the recording studio, but fortunately Jake is keeping Graham company in there.

Graham and Jake break down the differences between decibels and STC ratings, two very important to understand when figuring out soundproofing. There’s a lot to digest in this episode, but fortunately the guys keep it easy to understand by providing a broad level overview of the different concepts.

Further reading on STC Ratings

Further reading on decibels

Understanding a full STC Rating

Listen to Just the Audio

Transcription of this episode… (in case you prefer reading)

Graham: All right. Welcome everybody. I am Graham.

Jake: I’m Jake.

Graham: Once again, no Ashkahn for right now. Instead, we are gonna keep tearing through construction questions that you send in. Today’s construction question is “I’ve heard STC and decibels mentioned when I bring up soundproofing. Which should I pay attention to? Which is more important?”

Well, I would say they’re both important. They kind of measure different things, and especially STC is not really, well, I guess neither of them really are as simple as you’d wish they were, but STC gets a little complicated.

So, kind of basically the difference here is decibels are the noise, that’s the volume of sound that’s reaching you, and STC is the, it stands for sound transmission class, and that’s how much noise is being stopped between the areas.

Jake: How much noise is being attenuated in between two spaces, yeah.

Graham: Yeah, exactly. So, they’re kind of two sides of the same coin. How loud is something is decibels, and then how much sound are you blocking is STC. So, in the context of a float center, you might hear decibels mentioned for, “oh, you’re right near a noisy street. Those cars are producing some mad decibels.”

Jake: Right.

Graham: To use street slang.

Jake: Mad decibels. Or there might be construction down the road, industrial noise, that definitely adds a fair amount of noise.

Graham: “Whoa, those are some blasting decibels out there”, people might say to you.

Whereas with STC, it’s like, oh, “we got to attenuate those mad decibels”.

Jake: Those are some quiet walls.

Graham: Yeah, “slap in some STC with some kicking, or slap in some STC”, that doesn’t make any sense. “Slap in some walls with some kicking’ STC” is what I was trying to lay down there. You picking up what I’m putting down?

Jake: I’m picking up what you’re putting down. Smelling what you’re stepping in. Smelling what you’re stepping in.

Graham: So, that’s the basics for it. There’s of course some more details to go into for each of them.

Jake: Yeah, absolutely. This is a deep, deep rabbit hole.

First off, the scales, both of them logarithmic, so when you’re jumping up, it’s quite a large jump in between the two. It’s one to the tenth, and to another tenth, and to another tenth from there. So, noise can get very loud very quickly, and blocking out sound can get very well done, very, very high ranges.

Graham: Yup. Yeah, just in case it’s been awhile since you took a math class, logarithmic just means it’s going up by multiplicative factor rather than just an additive factor. So, it’s not just if you have 10 decibels and then 20 decibels, you might think oh, that’s twice as loud. But in fact, it’s 10 times as loud.

Jake: Right, right, right.

Graham: Then yeah, same goes from there. From then 20 to 30 is again 10 times as loud, or 10 times as noisy on the decibel scale. It gets a little confusing for how we hear things. There’s this whole thing between sound being emitted, sound going through the air, our ear perceptions of sound-

Jake: Yeah, vibrations.

Graham: Which different parts of anatomy-

Jake: The pressure.

Graham: They vibrate different ways, so we’re just gonna give you the mile high view on this stuff. Both because this is a short form podcast and also we’re not experts. We deal with this stuff-

Jake: We’re not acoustical engineers.

Graham: On a, yeah, or acousticians.

Jake: Or acousticians. Do not make the mistake of confusing them.

Graham: We had an acoustical engineer get angry with us when we called an acoustician once.

Jake: Yeah, yeah.

Graham: He straightened his tie and told us in no uncertain terms that he was an acoustical engineer.

Jake: Yeah, yeah.

Graham: Not an acoustician.

Jake: All right. Well, some things about these two different scales here. STC, it’s important to note that those ratings are at kind of a specific frequency. So, frequency is that cycles per second that makes sound different, you know what I mean? Low frequency versus high frequency.

When you see an STC rating, it’s usually a rating of the middle range, the things that happen most in our daily life, and that product is going to perform differently at different frequencies. It performs particularly poorly at low level frequencies.

Graham: Mostly, yeah. It’s very common. Wall assemblies, other construction that we do, it’s just freaking hard to block out low sound. So, when you see the summary single STC number, I guess, yeah, just to elaborate a little bit on what Jake was saying, a full STC chart is actually what gets done for official STC ratings.

Jake: It’s a whole curve yeah.

Graham: Yeah, there’s a giant curve that shows exactly how much sound is being blocked over all these different frequencies.

Then from marketing purposes, the people who manufacturer these materials take that and summarize it into one number.

Jake: One pretty number that looks real nice.

Graham: Yup. Just like we were saying, that number tends to be skewed more towards the mid range, which means all of those loud vibrational noises from buses and from motorcycles and bass from speakers kind of gets left out of that single number summary. Unfortunately, that’s also the stuff that gets into float tanks the easiest.

Jake: Yeah. They are very pervasive. It kind of makes sense, right? It’s much easier to resonate a material 100 times per second than it is 1000 times per second. So, sound just being energy that’s going through the air and also through building materials, it’s gonna resonate at a certain frequency. If that happens, the sound gets through.

So, what do we do to kind of battle some of this? We employ a couple different types of soundproofing. We don’t just do one single wall. We’re gonna incorporate an air gap in between those walls, and then we’re going to use very heavy, very dense walls that it’s going to be very difficult for those materials to resonate.

Graham: An interesting note, too, the distance of the air gap between your walls actually affects the frequencies that are allowed to go through there. You can kind of think blowing over the top of a bottle.

Jake: Yeah, absolutely.

Graham: Which is the more space there is in between there, the lower that note gets, right? Once you’ve drank most of the Coke bottle all the way down, all of a sudden you have a really low noise.

Jake: You know how musical Ashkahn is? You should hear him with a bottle, three bottles. He can do amazing things with three different bottles.

Graham: Yeah, but he also really likes drinking beverages, so eventually they all just end up the same tone.

Anyway, so that’s what’s going on with the air gap there. You can actually kind of custom tailor your air gap to resonate for different frequencies. Or even adjust the width of the air gap going in your walls with skewed-

Jake: Yeah, you could even splay it by a few degrees, yeah.

Graham: -angles so that you’re not doubling down on a single frequency. Anyway, this is a little advanced tips. Feel free to jot that down in your notebook.

Jake: Yeah, jot it down, splay your walls a few degrees-

Graham: yeah.

Jake: So that you don’t have perfectly parallel walls.

Graham: Splaying, what does splaying mean? Sorry. So, we go off on crazy jargon rants sometimes during the construction ones.

Jake: It’s all interesting. It’s all tied together. These are tough categories. Often I’ll get asked how wide should this gap be in between these walls. One inch is kind of that minimum that we see when people are building out spaces. We see people building up to a couple inches. Some people are like, well, “what if I just do 16 inches?” I’m like, you could do that. You’re wasting a lot of square footage in your space, and I don’t know where you hit diminishing returns, right? You might be able to achieve perfectly good soundproofing at three, four, or five inch gap.

Graham: Yeah, even different kind of sound studios and experts for them disagree about exactly how wide that gap should be. Within reason. Obviously if you had walls that were a mile apart, that would be way better for soundproofing, right? But within that range of a couple inches to a foot or two, yeah, there’s some disagreement exactly where-

Jake: Yeah, definitely.

Graham: Yeah, yeah, where you hit diminishing returns.

Jake: I think a lot of it comes down to budget as well, too, right? You only have so much space within a float center.

Graham: You can’t have the mile thick walls, yeah.

Okay. So, back to decibels and STC. I guess just to kind of put it in some kind of understandable range for people, the sort of decibel scale goes from, you can actually have negative decibels, which is kind of crazy. Zero is just-

Jake: What a concept.

Graham: The human calibrated-

Jake: Threshold.

Graham: Range of decibels, yeah.

Jake: Yeah.

Graham: So, zero is where human hearing doesn’t pick anything up anymore. So you can go to, yeah, negative decibels and it just means, it was already below our realm of hearing, but now scientifically it’s even lower in volume than that.

Around-

Jake: Very heady.

Graham: Around 30 decibels is where it starts to kind of be a lot of your average, everyday noises going on. At around 50, 60 decibels you’re getting into loud noises. At around 70 decibels, that’s actually where you start getting into the realm of loud construction, really loud music coming through. If you’re exposed to that continuously for a day, you can start to cause hearing damage.

That kind of just scales up from there to around 85, 90 you start getting into the realm of, well, now if you’re really close to heavy construction, you’re there for even an hour without protection, you could get hearing damage.

140 is kind of the top range of what you even see summarized because 140 for humans is where it’s just immediate hearing damage. If you hit 140 decibels, bam. It’s like you’re right next to a jet engine and you might go deaf kind of thing.

Jake: You start bleeding out of your ears.

Graham: Yeah, and your dynamite that went off, if it, yeah, starts getting louder than that. So, that’s kind of the range of decibels.

Jake: Yeah.

Graham: Anything to add to that? I was gonna-

Jake: Not to decibels, yeah.

Graham: Summarize STC as well.

Jake: As long as we jump into STC, yeah, that’s where my brain runs to, maybe because we see things in STC ratings. You’ll see some marketing on packaging talking about it blocks out this many decibels or whatever, but the majority of what you see on packaging is STC ratings.

Graham: Yeah, and that’s again, it’s how soundproof something is, so you tend to focus more on what your wall can do, rather that what it’s trying to block. So, when you’re getting materials, things like that, that’s why you see STC represented more in that scenario than decibels.

But again, if you’re actually bringing in an acoustical engineer to run sound tests in your space and see how loud it is inside without any soundproofing, that’s where he might start bringing up decibels.

So, STC, this kind of goes in a range, too, from zero up to, we’ll just say around 70, 80.

Jake: Yeah, high 70s, yeah.

Graham: Functionally for what you’re hitting. 30 to 40 STC rating, that’s like when you’re in an apartment they’re like, wow, that place has thin walls. That’s what they’re talking about is-

Jake: Oh, they’re watching Judge Judy.

Graham: Range. Yeah, exactly. You can totally tell through the walls that Judge Judy is on next door.

Then if you-

Jake: Is that still relevant?

Graham: From 40 to 50 is, once again, twice as soundproof within a certain range of frequencies. Not to belabor that point.

That’s where you get to the point where you can kind of hear music. If someone just has a really boisterous voice, and you have an STC 50 wall between your lobby and that first float room, and someone’s talking really loudly-

Jake: And a really low voice as well.

Graham: Yeah, male, boisterous voice, you can probably totally hear them in room one. Little faintly.

Then you start getting up to 55, 60 STC. That’s where really what you hear is the bass coming through and loud music. You can’t even really hear loud conversation, which is great.

Jake: This is kind of our goal, too. We’re trying to get into these 60s. It’s not likely in the real world, and you can. You can just spend a lot of money. There’s a large jump between that 40, 50 STC rating, what you’re gonna spend on soundproofing trying to get up into those 60s and those 70s, right?

Graham: Yeah. Just keep in mind, too, if we’re talking about going from 40 to 50, we’re talking about not raising it up by 25%. We’re talking about 100% increase in soundproofing. So, now if you’re going from 40 to 60, that’s four times as soundproof. So although these numbers kind of sound like smaller increases, the effect is quite big because of that logarithmic scale.

Jake: Yeah, that’s a logarithmic scale there. Similar to pH.

Graham: Yeah. So, a lot of sound studios aim for that 60-65 kind of range is what they’re going for, and it’s unfortunate that that’s really hard to get to because we kind of, in an ideal world, a float center would be even higher in STC rating because a sound studio needs to be quiet when there’s loud instruments in there making noise, and a float tank studio needs to be quiet when it’s absolutely silent, which is almost sort of a whole other level of demand.

So, but that’s the goal. Again, somewhere between 50 and 65, if you can hit it, is great. Obviously above 60 is really nice, but now we’re talking about needing, the difference between hitting 50 and hitting 60 or 65 is a huge investment in money. You’re talking about really upping that quality of materials to get to sound recording studio level.

Jake: Yeah, several layers of, yeah, soundproofing drywall and stuff, yeah.

Graham: So, this is also interesting. I guess going back to the question, which is more important, decibels or STC rating?

Jake: You’re gonna see more STC ratings in your day to day operation, I guess.

Graham: Yeah, I guess if you’re gonna research one and get really familiar with it and what it is.

Jake: But if you want to get a little esoteric about it, if I didn’t have the decibels blasting at me, the STC wouldn’t matter, right?

Graham: Yeah.

Jake: So, they’re the problem, those decibels out there.

Graham: They also are related. It would be really nice if there was a direct relation and you can just say, oh, an STC rating is how many decibels get blocked from one area to another.

Jake: That would be nice.

Graham: But again, STC happens on this curve of frequencies. It doesn’t quite work like that. There’s no straight equation.

That said, layman’s, just easy summary projections, the STC is roughly the amount of decibels that you’re blocking.

Jake: Very rough.

Graham: Yeah. So, just for your raw understanding and rough calculations, if you had 80 decibels in one room and then you went and measured the decibel level in an adjacent room and it was down at 50, you’d call that 30 STC is what that wall assembly would be. Again, in rough calculations. If you actually wanted to measure it, it would probably be higher, lower, yeah.

Jake: A little disclaimer on that, the acoustical engineer will be straightening her tie and she might be looking down on that statement, but yeah.

Graham: Yeah, yeah, exactly. But rough, again, rough idea. That’s kind of the relation, at least. It gives you an idea of how to think about them.

Jake: Nice.

Graham: Yeah, I guess some last words on it, which is again, be careful about those frequencies. A single STC rating is a summary, not a qualification of quality.

Jake: Realize that you have multiple ways to hit that STC rating.

Graham: Yup.

Jake: Different systems are gonna get you there.

Graham: Also keep in mind your soundproofing is only as good as the weakest part of your soundproofing.

Jake: Oh, absolutely. Yeah.

Graham: So, if you invest in these really nice soundproof high quality walls, and then you install just a flimsy hollow core door, you just spent a lot of money on not a whole lot, right? The walls are not actually, all the sound is gonna skirt around the walls and just go in through your door area.

Jake: Also keep in mind when those companies send their materials off to be tested, they’re testing them in just pristine environments. Laboratory environments. They’ve built it perfectly. They’re not gonna send off a material that is flawed to be tested. So, it’s really hard-

Graham: And they’re paying-

Jake: Oh, yeah.

Graham: A lot of money for these tests.

Jake: Yeah.

Graham: So, you can be sure, and they really want to hit that highest number possible so they can brag about it.

Jake: Absolutely.

Graham: So, yeah. Their assemblies when they get them tested are-

Jake: I guess what we’re saying is that it will never be-

Graham: Perfect, yeah.

Jake: As good as they created it in the laboratory.

Graham: No, no, no. Yeah, if you buy STC 60 kind of grade materials, or you’re putting together an assembly that’s supposed to be STC 60, just knocked that down a little bit for the fact that the environment is a hard thing to deal with.

Yeah, I think that’s about it. Just relatively, if we’re talking about changes in STC, you’re comparing, you’re like, “oh, should I get something that’s STC 47 or something that’s STC 50?”

Jake: Oh, yeah. Yeah.

Graham: How big is that difference? So, usually a one STC change is imperceptible.

Jake: Nothing.

Graham: You can’t really tell a difference.

Jake: You can’t tell that. Same with decibels. You can’t tell the difference at one decibel.

Graham: Yeah. In fact, in sound studios, we typically kind of round to three decibels just because one is a little beyond the range of human hearing.

Jake: Yeah.

Graham: So, you’ll see those kind of pop up a lot.

So, one, imperceptible. About three change in STC is perceptible-

Jake: Barely noticeable.

Graham: But it’s not a huge difference.

Jake: Yeah.

Graham: A five is really where you, a five difference you start to notice it and you can actually tell, oh, this is a bit more soundproof. That’s where it might be worthwhile. So, now if you’re talking about the difference between 50 to 55, 45 to 50 for STC, that might be worth investing in. Then again, if you get up to a 10 STC difference, that’s going to be twice as soundproof or twice as un-soundproof, or whatever the antonym is right there.

Jake: Noisy, huh?

Graham: Twice as noisy, there we go. Un-soundproof was close, though, I think.

Yeah.

Jake: All right.

Graham: There you go. There’s a little STC decibel summary.

Jake: Yeah, thanks for coming down the rabbit hole with us. We appreciate it.

Graham: It goes so much deeper. Yup. All right. If you have questions of your own, go to floattanksolutions.com/podcast.

We will go and read them, and read them out loud to everyone else in the world and share answers to them.

Jake: Our answers.

Graham: Which is the premise of this very podcast. All right. Have a great one, everyone.

Jake: Yeah, thank you so much.

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