This page of the site is based on everything I’ve learned this year, primarily from the Acoustics classes,  and is my thoughts on the acoustics of Restaurants and Coffee Shops.  I’m focussing on these places as, like many people of my age range, I find they can be uncomfortable places to be in.  This section of the site isn’t a scientific example. Instead it’s an explanation of the causes and possible remedies for treating noisy restaurants/coffee shops.  Exact, or scientific, calculations and measurements can only be taken for specific rooms/spaces.  As I’m as affected by uncomfortable experiences as anyone else, this is the area of Sound Engineering which most interests me and in which, if possible, I would like to work.

 

Restaurants/Cafes

So what goes on with sound in a restaurant or coffee shop?  Why does it become a real hardship to have a conversation with the people at your table?  Why does this happen?   If you’re in an empty restaurant/café just clap your hands once, loudly. Then do it again above your head.  What did you hear?  Chances are you heard a fast echo of your clap.

To explain why this happens, we need to review some of the basic acoustic science of soundwaves.  Remember that soundwaves are like a ping-pong ball thrown into a box.  The ball will ricochet around and bounce of every wall (surface) until it runs out of energy.  Well that’s pretty much what happens to the soundwaves of conversations in our restaurant and cafes.   All the sounds of conversations and kitchen noises are reflected by the surfaces in the restaurant/café.   And as the restaurant/coffee shop becomes busy – so there’s more conversations and more noise to reflect and bounce around the room. Intelligibility of speech becomes a problem, particularly if you’ve not got perfect hearing to begin with.

The ideal sound level for normal conversation is between 55dB and 65dB. If you factor in the normal restaurant noise, your restaurant moves to about 70dB. At this point, you have to raise your voice to be heard. At 75dB, conversation is difficult and at 85dB, damaging.  It only takes several tables of people talking loudly to push the ambient noise levels up to uncomfortable levels.   (Note 85dB is the exposure level defined in the H&SW Act at which an employer must take action to protect their staff).

As the current fashion is for restaurants and coffee shops to have minimalist interior design, eschewing an industrial theme, so the room is filled with hard surfaces.  Wooden floors, brick walls, open and exposed heating/ventilation systems, bare tables, uncushioned chairs – and so it goes on.  Each one of these surfaces is reflective to soundwaves.   Consider the difference between todays restaurants/coffee shops and those of 15 years ago when plush soft furnishings were in vogue.   Yet the restaurant/coffee shop owner can’t but be aware that the acoustic ambience of their venue is poor.  Obviously, hard surfaces are easier to keep clean, thus improving food hygiene, and keeping costs down.

What can be done about it?

It’s not every part of the restaurant/coffee shop which will be so loud. The reflected soundwaves can interfere with the incident (original) wave, producing the constructive and destructive interference —it can increase its amplitude or, with phase cancellation, decrease the amplitude of the original soundwave. In a typical listening environment, we are hearing sounds that have reflected off numerous objects and surfaces, with the reflections themselves interfering with other reflections.

 Just as colour is determined by which frequencies of light are reflected or not, the “colour”, or acoustic characteristics, of a restaurant/coffee shop environment is determined by the angles and materials sounds may reflect off. Different materials reflect some frequencies more efficiently than others, due to their roughness or absorbency characteristics.   And we’ve seen that the design of the restaurant/coffee shop uses many hard, thus acoustically reflective, surfaces.

The distance both the incident sound and the reflected sounds must travel is another key element in the characteristics of the acoustic environment, since the incident sound typically reflects off many surfaces at differing distances from the listener, thereby striking the ears at differing times.  As you sit opposite someone at a table your direct speech goes straight to them, but it also reflects off the bare table, off glasses and wine bottle on the table, off the floor, off the ceiling and off a wall behind them. All of which contributes to the intelligibility difficulties. 

Architectural acoustics—a field that integrates architecture, building construction, and the physics of sound—is part building engineering (mitigating noise and vibrations) and part design. In the latter, more glamorous role, acousticians can deploy a wide range of materials and construction techniques to sculpt pleasant-sounding spaces that service a building’s function, be it a restaurant or a coffee shop.  Unfortunately, acoustics is often an afterthought, something used to correct errors after construction if noise proves annoying. By then, it’s too late because every aspect of a space’s design impacts the way it sounds: how the HVAC system is routed, the kind of wall insulation, the thickness of windows, and even how the electrical powerpoints are sealed. It takes a lot of effort to work through all the acoustic options which are inseparable from the architecture and construction of the space itself. A restaurant or coffee shop that’s loud because the ceilings are too high or because there’s nothing separating kitchen or bar noise from areas for table seating has space-planning problems. They can’t be fixed by hanging some fiberglass absorber panels to dampen the noise.

 

Traditional Acoustic Solutions

Traditionally, there are two options which can be used to treat a space. Absorption and Diffusion.  Most of the time in nearly all restaurants the main issues are intelligibility, volume, and reverberation/reflection. In everyday terms that means a loud, cave-like sound where it’s difficult to understand what anyone says. Which makes us all talk louder, thus raising the ambient noise levels, and so it gets worse.

Traditionally this is solved by using a specific mix of diffusion and absorption tailored to the acoustic signature of the room. Absorption is widely used as it’s inexpensive, easily obtainable, simple to install, and can be covered with aesthetically pleasing textiles. The trick is to use enough of it to make a space pleasant and then add some diffusion in specific areas with acoustic anomalies that fall outside the realm of reverberation issues. If you simply covered every surface of a room with 5cm and 10cm thick absorption and a few diffusers, it could actually make the issue worse by deadening the high frequency content of the room too much and accentuating all the low frequency, making it sound dark and muddy.  If you use too little, it often feels like nothing has been done.

Absorption panels

It should be noted that all absorption is not equal. Absorption works like a cross between a sponge and a speed bump for soundwaves; it must be porous enough to allow air molecules and sound energy to permeate it yet have enough density to create a blockage of the same air and energy from getting out. This means a narrow window of density.  Characteristics of fibreglass/rockwool used in absorption panels are widely available on the internet.  Alternative materials such as cork tiles can also be used to reduce reflections. The frequencies we are trying to treat lie in a fairly narrow band of between 1kHz and 6Khz. This is approximately where human hearing takes its cues for intelligibility of sound, and it’s also the frequency band which hard surfaces tend to reflect most efficiently.

It’s important to note that material thickness affects absorbed frequencies. There is a direct relationship between the wavelength of sound (frequency) being absorbed and the depth of material. Shallow materials affect only high frequencies and deeper materials affect lower frequencies.  Also, mounting the absorber approx. 5cm off the wall improves its absorption characteristics greatly. 

Diffusion panels

are almost the opposite of absorption panels. They’re intended to reflect soundwaves but to change the angles of reflection such that the soundwaves are broken up.  So they’re a control method in which sound energy is changed from a high concentration to a low concentration in a space.  Diffusion panels or ‘diffussors’ are typically made of wood,and look like the Manhattan skyline.  (The image at the top of this page is of a skyline diffuser panel) They are typically used in conjunction with  absorption and other traditional acoustic materials for best overall effect.  They are designed to take packets of sound energy and spread or scatter them more evenly.  As with many traditional acoustic panels, they are often more decorative than effective and when they are effective, they are only useful in limited frequencies or portions of the human range of hearing.  But there is a place for using them .       

Hearing Aids in a noisy Restaurant/Café

If you have to wear a hearing aid and are in a noisy restaurant/café it must be a nightmare.  Hearing Aids don’t work in exactly the same way that the human ear and hearing does.  Although modern  Hearing Aids can be controlled by Apps on phones they really are only being tuned to amplify certain parts of the audible spectrum.  They’re not working as human hearing does and using directional cues to filter out unwanted sounds (conversations).  They take a frequency range and bam! Amplify it.  If that frequency range contains all the reflected sounds then all the reflections get amplified too.   The only way to improve the environment for people with hearing aids is to treat the spaces to reduce the overall noise levels.  

Hearing aid wearers can improve their lot in a restaurant by not sitting with their backs directly against a wall, possibly sit at the end of the table which is away from the wall, nor sit close to an open kitchen area.  This is simply positioning themselves to be as far from large reflective surfaces as possible.  By doing this they will be receiving more direct sounds than reflected sounds.  As sound diminishes in the inverse square law they are giving themselves the best position for an acceptable experience.  But this is never going to be as effective or comfortable as being in a properly acoustically treated space.