There are many things that go into designing a new restaurant. From the initial design phase, that could change multiple times before being decided on, to the seating layout, the kitchen layout and utilities, the bathrooms, the menu, the flow, maximising space to allow for more bums on seats, the HVAC, the lighting, the point of sale system, the stock, the staff, the office, the training, the opening, the marketing, and so on and so on…

But what about the sound?

Audio is usually the last thought in the design phase, one that is almost always left until the end, and is almost always underestimated. Psychology plays a massive part in putting together a restaurant – everything from the colours, the type of seating, menu layouts, lighting, the position of the bathrooms, the decor; all play a part in adding to the ultimate experience of the patrons.

Many studies have been done on how music affects the human psyche, especially in hospitality environments such as restaurants, casinos and stadiums. All you need to do is type a search for these studies into Google and read through the many results.

Although there are many contradicting studies, the common trend throughout is the fact that music (or sound) does in fact play a massive part in affecting our behaviour. Whether the aim is for a fast food joint to get us in and out as quickly as possible or for a fine dining establishment to make us so comfortable and content, so we stay, eat and drink to our hearts content, the type of music or lack of defines how we will behave.

So why is it that we are the last ones to be called in? In my opinion, there is a huge misunderstanding of the differences between domestic and commercial sound systems. Domestic sound systems are designed to be used in the home, played for only a few hours a week with minimal handling. Commercial sound systems on the other hand are designed to be used in the busiest of environments, played for hours and hours on end and probably being handled by multiple people throughout the day and night.

Low cost domestic loudspeakers are designed to cover small areas, at lower sensitivities to commercial loudspeakers. Why is this important? Well because it is the difference of the loudspeaker actually covering the intended area or not.
So, how do we take all of the above information, and use it to design better restaurant audio systems?

Understanding the type of restaurant you are designing the system for is an important factor. The same distributed audio system that works in a fine dining establishment may not work quite as well in your local steakhouse pub.
Asking as many questions as possible will give you an idea as to what your client is expecting of the sound system, as well as give you the opportunity to educate them.

As previously mentioned multiple factors need to be considered before deciding on the correct loudspeaker for your restaurant audio system design. There are numerous physical attributes that will affect our decision. These are listed on the opposite page.

Understanding reverberations and reflections play a major role in loudspeaker choice and placement. As with everything you do over and over again, this will become easier with experience. Knowing what loudspeakers are available and what the individual specifications are assists you in making the correct decision.

Reverberation:

In an enclosed space, when a sound source stops emitting energy, it takes some time for the sound to become inaudible. This prolongation of the sound in the room caused by continued multiple reflections is called reverberation.

Reverberation time plays a crucial role in the quality of music and the ability to understand speech in a given space. When room surfaces are highly reflective, sound continues to reflect or reverberate. The effect of this condition is described as a live space with a long reverberation time. A high reverberation time will cause a build-up of the noise level in a space. The effects of reverberation time on a given space are crucial to musical conditions and understanding speech. It is difficult to choose an optimum reverberation time in a multi-functional space, as different uses require different reverberation times. A reverberation time that is optimum for a music programme could be disastrous to the intelligibility of the spoken word. Conversely, a reverberation time that is excellent for speech can cause music to sound dry and flat.

Reflections:

Reflected sound strikes a surface or several surfaces before reaching the receiver. These reflections can have unwanted or even disastrous consequences. Although reverberation is due to continued multiple reflections, controlling the reverberation time in a space does not ensure the space will be free from problems from reflection.
Reflective corners or peaked ceilings can create a “megaphone’ effect potentially causing annoying reflections and loud spaces. Reflective parallel surfaces lend themselves to a unique acoustical problem called standing waves, creating a “fluttering’ of sound between the two surfaces.

Reflections can be attributed to the shape of the space as well as the material on the surfaces. Domes and concave surfaces cause reflections to be focused rather than dispersed which can cause annoying sound reflections. Absorptive surface treatments can help to eliminate both reverberation and reflection problems.

(Source: Acoustics 101 on www.acoustics.com)

Matching the amplifiers

Once you have chosen the loudspeakers you are going to use in each area, you will need to power them with amplifiers. There are two types of systems – low and high impedance systems. This plays an important factor in choosing the correct amplification.

What is the difference between the two?

High-impedance systems are also known as constant-voltage systems, meaning at maximum output, the voltage stays the same. It allows for long-distance runs without signal loss. This voltage stays constant and is not affected based on the number of speakers.

It’s imperative to fully understand these differences; I have seen too many blown amplifiers because of improper loading. This results in wasted time and money and can often lead to a frustrated customer. Because these systems use a constant voltage and step-down transformers, they can be used for longer-distance runs. This would be particularly well-suited for paging and background music-type systems for hospitals, hotels and large retail and restaurant spaces.

In a low-impedance system most amplifiers are only rated to handle a load down to 4Ω. Some provide ratings as low as 2Ω; however, reliability in some lesser expensive amps can be extremely compromised at a 2Ω load rating. If you had an application that required eight speakers, and each speaker was rated at 8Ω, you would effectively require four stereo amplifiers – using two speakers on each amplifier channel, wired in parallel. This would therefore present each amplifier channel with a 4Ω load.

It has always been my practice to design systems running at 4Ω. I have used 2Ω on occasion; however, this was when I specified large touring amplifiers that were proved to handle these loads reliably.

Understanding ohms and impedance

In order to understand the rules for speaker connection, we need a bit of electrical theory.

You probably had this as a lesson in high school at some point, but were more interested in other things at the time. To relate it to something you are more familiar with, let’s consider the ordinary garden hose. Print this off and go outside, hook up the hose (no nozzle) and turn on the water. Pretty soon water should start flowing out the end of the hose. This flow of water through the hose is similar to an electric current, which is usually described as the flow of electrons through the wire and is measured in Amperes.

Now put your thumb over the end of the hose and try to stop the flow of water. Feel the pressure? This pressure is similar to voltage, which is the force of electricity that pushes the electrons through the wire. Notice that if you succeed in plugging the water flow, (no current) the pressure is still there. This is like an amplifier with no speakers attached, or an AC outlet with nothing plugged in. Voltage is present, but there is no current flow.

Finally, move your thumb a bit to allow some water to spray. By varying the position of your thumb, you can control how much water comes out of the hose. Your thumb is restricting the flow of water. In an electrical circuit, things that restrict or control the flow of current are said to impede current flow and are described as having impedance.

In a hose we use a nozzle to restrict the flow. In an electrical circuit the device that uses electrical energy and has impedance is called the LOAD.

It should be apparent by now that there is a relationship between pressure (voltage), flow (current) and restriction (impedance). Since voltage or pressure is what moves the current, increasing the voltage pressure should increase the current, assuming the impedance doesn’t change. Decreasing the voltage should decrease the current.
On the other hand increasing the impedance by restricting the flow of current will cause the current to decrease, like turning the nozzle toward “off’.

Lowering the impedance is like opening the nozzle to allow more flow. This relationship was analysed by a fellow by the name of George Simon Ohm a long time ago, and he identified a simple formula that is extremely important in electricity and electronics which bears his name: Ohm’s Law.

Ohm’s Law states: In an electrical circuit, current flow is directly proportional to voltage and inversely proportional to impedance.
Mathematically, this becomes: Current (in amperes) equals voltage (in volts) divided by impedance (in ohms).

So now that we understand the differences between high and low impedance systems and what impedance and ohms are, we can now match the amplifiers to the chosen loudspeaker system.

I like using high impedance systems when using multiple speakers in a zone where only background music is required. For anything more than background music I will always go with a low impedance option. However, I have often mixed both solutions into a single zone, like when the distributed system is used for standard dining times, and a low impedance system used for the DJ who may come on certain nights to start the party. In this case I may use the 100volt line system as a fill to the low impedance system.

Once we know what loudspeaker and amplification system we are using, we can look at zoning. This will dictate what kind of mixer will be used.

There are multiple options available in the market today when it comes to choosing a preamplifier for a restaurant application. Typically restaurants today have four zones – main dining, patio or smoking section, bar and the bathrooms. The questions that need to be asked are whether the owner would like different sources to be played in the different zones, and whether they would like to control this from within the individual zones or from a central point?

Other options would be whether any local inputs are required in any particular zone, such as a band or DJ input in the bar.

An extremely important factor is where the equipment is going to be installed. Space within a restaurant environment is very limited and equipment is installed mainly into the office or at a waiter station. One thing that I always insist on is that a fully furnished 19′ rack is used to install the equipment into. I do this for a number of reasons, but mainly because the only other option is to stack the equipment up on a shelf somewhere, leaving it accessible to, well everything. A rack will supply the perfect environment to guarantee the longevity of the equipment used, if it is installed correctly of course.

Another important factor is the power supply to the audio equipment. It is always best to request a dedicated power circuit to the equipment so that you are guaranteed that you are not sharing the same power with the fridges, ovens or even the HVAC system. I cannot tell you how often this is overlooked and the equipment is “just plugged in’ to the first available point. Buzzes and overloads take away from everything you have worked so hard for – and can completely discredit the sound system installation.

Of course in a perfect world it would be so easy to get everything we ask for, and the installations will be perfect time and time again. However, we do not live in that perfect world we so often talk about and (in the real world) we have to learn to compromise and use what we have instead of what we want. Focus on the correct equipment for the job, the correct loudspeakers with the right coverage matched to the right amplifiers – and you can’t go wrong.

By Justin Mamulis

ProSystems magazine – 3rd Quarter 2012