Look, acoustics can be complicated if you want it to be.
It can be an ocean of jargon: reflections, absorption, dispersion, directionality, membrane resonators, RT60, DSP correction, standing waves, room nodes..
It goes on and on.
It can feel so overwhelming that you give up before you even get started.
At least, it doesn’t if you run a typical hospitality business.
Let’s jump right in.
This is all about practical problems of noise in a restaurant, pub or cafe.
It’s not about building the ultimate room for your hi-fi, where you can hear a sneaky fart in the fifth row during the bassoon solo. That takes a lot more maths and physics, and often more money as well.
We're focusing just on how to give customers a better experience so they want to come back. I’ll do my best to keep the nerd stuff as basic as possible.
And just in case it’s still a bit much, I’m going to summarise it a few key points to remember along the way.
If you’re in a hurry, please feel welcome to skip to the summary of those points at the end.
Otherwise, let’s start by looking at the goals.
Key points:
It’s about having more customers spend more money with you more often.
When they’re comfortable and enjoy themselves, they’re more likely to stay and order more. They’re more likely to come back.
But when a room reflects so much noise back on your customers that it’s hard to chat, that can be a reason to go somewhere else.
Your noisiest times are usually when you are busy, so even if it can be quiet during the week, the noisy times are what more of your guests experience.
Older people have a harder time with it, and they’re a much bigger part of the consumer economy these days. They’re a larger part of the population now, and carry far less of the mortgage debt.
Often they just avoid certain places when it might be loud. That’s a limit on how profitable those times can be.
As a bonus, a space with less noise and echo also helps you and your staff.
Research suggests that noisy workplaces make workers less attentive and productive, more tired and stressed. When you look at what you spend on wages, it makes sense to set your everyone up to do their best.
Key points:
Sound is a vibration that ripples through the air. An object making sound is vibrating the air it touches.
These vibrations travel through the air like how a lake ripples when you throw a pebble. The air particles bump into each other, transferring the vibrating energy, creating areas of higher and lower pressure.
When it reaches our ears, our eardrums vibrate in the same way. Then our ears sends signals that our brains construct as sound. We hear this differently depending on the speed of the vibration.
Fast vibrations make a high-pitched sound, like the sound of birds chirping. Slow vibrations make a low-pitched sound, like the boom of a big drum.
You might have heard folks talk about the “frequency” of a sound. That’s just about how frequently the air vibrates. This is measured in Hertz, which is the number of vibrations per second.
So if someone says “100 Hertz”, then the air is vibrating 100 times per second. Humans can hear sounds as low as 20 Hertz and, if you’re young, as high as 20,000 Hertz.
Different frequencies of sound move around a restaurant in a different way. We’ll talk more about that soon.
Some of these sound frequencies are also particularly important for understanding human speech.
Key points:
Hey, ever use a phone? I mean the old-fashioned way, for talking.
Phone calls don’t sound exactly like you’re face-to-face, but they're definitely good enough for two people to talk to each other.
That’s because a telephone transmits sounds between 300 to 3,400 hertz. Our ears are particularly sensitive to this range. It’s where that all the vowels and consonants can be heard, that make the words and meaning understood.
For convenience, let’s refer to these sounds between 300 and 3,400 hertz as the “conversation frequencies”.
When there’s a lot of other noise in these conversation frequencies, it becomes hard to have a comfortable conversation. So what you want is a room where sound in this frequency range doesn’t echo too loud.
Now let’s talk about how that happens.
Key points:
All frequencies of sound travel at the same speed, approximately 330 metres per second. It varies a little bit with the weather, but not by much.
Having trouble picturing 330 metres? Think of the pitch at the MCG. 330 metres is about double that in length. Or about 85 Holden Barinas parked bumper-to-bumper in a straight line.
So if your walls are 5 metres apart, that sound bounces off them dozens of times in a fraction of a second. The sound loses energy as it travels, so each reflection is a bit quieter than the last.
Still, when you have a lot of these reflections, the noise adds up. In an untreated room full of hard, flat surfaces, about 70% of the noise in the room is echo from the walls.
That means the walls are more than twice as loud as the people.
Key points:
A room with lots of echo is still quiet with nobody in it. But that’s no way to pay the bills.
A couple of customers, still not too loud. But you’d probably prefer to be busier. As it fills up, the echo starts to smear into a rumble of voices.
Now if we had access to some Robocop stuff, we could configure different groups of people to speak in completely different frequency ranges. That way they're not talking over each other.
With regular humans, everyone competes to be heard in the same conversation frequencies. Men have slightly deeper voices than women, but that’s not enough to really matter.
So how do real human beings respond to this? They raise their voices to be heard. This is a tipping point, where every conversation is making everyone else’s conversation louder as well. Which only makes the echo louder too. It doesn’t have to get all that much busier to find that everyone is yelling.
Now you can’t hear your music anymore, so you turn it up. That creates more echo too.
Key points:
Most interiors these days have hard walls, floors, ceilings and furnishings, with lots of bricks, concrete and ceramic tiles. These reflect a lot of sound.
What’s going on with that?
Well, remember sound is a vibration in the air. What do you think happens when these vibrations hit something very rigid and dense, like brick or concrete or tile?
Well, have you ever tried bending these materials? They really don’t like changing their shape. Not even a very tiny bit. If they move at all, the whole object moves together or it just breaks.
So when a vibration in the air hits a brick or tile, it’s so unwilling to move that the vibration is just pushed back. It’s a bit like throwing a tennis ball at a hard surface. It just bounces back.
(That’s actually not a perfect metaphor, because it happens a little differently for different frequencies of sound. We’ll get to that shortly.)
For now, it’s enough to understand that as much as 99% of the sound in those conversation frequencies just bounces back. The sound just keeps bouncing around the room for as long as it takes the colliding air molecules to absorb the energy.
Key points:
If you thought “let’s put some stuff up to absorb the sound”, you’re on the right track.
But what does that actually mean? How can objects absorb sound?
Well, we talked about what happens when those vibrations in the air hit a rigid surface like brick or tile. What if it hits something like fabric or foam, that’s a bit more free to move?
When a vibration in the air hits a material like this, it vibrates too. That vibration is usually too fast and too small to see, but it’s there. This creates friction, which turns some of that sound energy into heat.
(The amount of heat this creates is so unbelievably small that it doesn’t really matter, which is why you can’t heat your home in winter by talking.)
Some materials are better at absorbing sound energy than others. The most suitable materials will be soft but will carry a bit of weight as well. Specialised acoustic foams and and insulation materials are designed just for this purpose.
There’s a bit more to it than just hanging a tapestry on the wall and calling it a day.
You need to make sure that it will actually soak up the full range of those conversation frequencies from 300 to 3,400 hertz.
Key points:
Have you ever lined up outside a loud nightclub or concert venue? You can hear the music, but not as clearly as if you were inside. It’s just a thump and rumble of the kick drum and the bass.
What you’re hearing is that those really low frequencies coming out the subwoofer, when they’re loud enough, can pass through walls.
That’s actually one of the reasons why treating a recording studio or cinema room can cost tens of thousands of dollars. Because those subwoofer frequencies are so hard to control.
In most hospitality environments we don’t need to worry as much about these subwoofer frequencies, which are well below the 300 to 3,400 Hertz range that matters for conversation.
But what’s going on here?
Well, let’s start with how they’re similar:
The difference is that the higher frequency sounds are vibrating more times per second. so each individual vibration is smaller. There are also many more of them. So higher frequency sounds will be intercepted many more times by much less material.
With lower frequencies, it’s the other way around. They don’t vibrate as fast, so there are fewer vibrations that are each much bigger.
So how much bigger are we talking?
Well, when you halve the frequency, each vibration becomes twice as large. At 1600 Hertz, each individual vibration is about 20cm. So at 800 Hertz, it’s 40cm, and at 400 Hertz, it’s 80cm.
You can follow this all the way down to 25 hertz, where each vibration is a whopping 14 metres.
14 metres is, like, 27 unicyclists in a row.
If you hate thinking in numbers, just remember this: at low frequencies, sound vibrations are big.
Which is how you hear that pounding bass drum from outside the building.
See, a small vibration just bounces off a hard wall because it's a rigid object that resists any change in shape. But when that vibration is much larger than the wall, the wall doesn’t have to change its shape because it can vibrate as a single object.
When the vibrations are large enough, they interact a much less with much smaller objects.
That’s why our ears are less sensitive to really low frequencies. They’re so much larger than our eardrums barely interact with them. Once the vibrations are large enough, we don’t hear them at all.
Key points:
Okay, so that’s pretty much everything. All that’s left is to put it all together.
What matters for conversations is soaking up the echo between 300 and 3,400 Hertz. And it’s those lower frequencies that require more material.
Where a lot of DIY efforts fail is by relying on soft furnishings, or those thin foam panels from Temu. That will only absorb those higher frequencies. It doesn’t remove the echo, it just makes it sound more boomy and less harsh.
That still helps a little. You might even persuade yourself that it’s working. But punters will still need to raise their voices to be heard.
A thickness of about 10 to 25% the size of the biggest vibration is a good ballpark figure. Using a denser, more absorbent material is important if the thickness is toward the lower end of this scale
A vibration at 300 Hertz is roughly 115 centimetres. 25% of that is about 28 centimetres. But it’s not always practical to hang something the size and weight of a mattress on your wall.
Aiming for 10% means a thickness of 11.5cm. This is more practical and looks nicer in most spaces. At this thickness though, you need be using a high quality material that’s both soft and fairly dense.
Another way to manage the weight of the panel is to have an air gap between the material and the wall. So long as this air gap isn’t larger than the actual material, it effectively adds to the thickness of the panel.
It really depends how much noise you’re dealing with. Somewhere between 10% and 30% of the surface area of the walls is good to aim for.
You don’t need to calculate it down to the last centimetre. We’re not trying to build a laboratory environment.
So long as you’re putting a decent thickness of a good material on the walls, it will help control the echo.
The best place for acoustic treatment is where the most sound will be reflected. That usually means being near to where people gather to talk. That’s especially true near corners and alcoves.
Again, you don’t want to sweat this part too hard. Your customers are going to have to look at them, so it’s worth thinking about where they would look nice too.
Key points:
Okay, so here's the deal:
Oh, and while we're here...
If you’re in the Melbourne metropolitan area and you’re having trouble with a noisy venue, please have a think about Echo Eater.
Our panels are built to cover all the conversation frequencies from 300 to 3,400 Hertz.
They can be built in a range of sizes. We can change how they look too, to suit whatever kind of establishment you have.
If you’re interested, or just have a query, please send me a message using the contact form. It would be lovely to hear from you.
A space for friends to enjoy a good chat
Customers who can hear each other are more likely to return
All panels are customised to match your venue's style
Quieter workplaces make staff happier and more productive