Written by Behzad Haki, B.Sc. and Eric de Santis, P.Eng.

You are sitting in a restaurant surrounded by some of your best friends. The food is great and the drinks are cold. The restaurant is gradually getting busier. Between the chatter and the background music, you begin to raise your voice to be heard by those at your table.  You are not alone in this. Almost everyone else is doing the same. The background chatter gets louder and louder as everyone in the room also raises their voice to be heard. This is the Lombard Effect: the tendency for humans to raise their voice in the presence of noise.

The background chatter gets louder and louder as everyone in the room also raises their voice to be heard. This is the Lombard Effect: the tendency for humans to raise their voice in the presence of noise.

While it is hard to know the extent to which a noisy eating environment can adversely affect a business, noise can be a major concern for certain customers and owners. In some restaurants, a loud environment is preferred so that the customers will be discouraged from spending too much time in the space. However, there are other restaurants in which a relaxing ambient environment is preferred. Nevertheless, in an eating space under normal conditions, most of the time, the customers want to be able to verbally engage in conversation with their companions. As a result, regardless of the type of a restaurant, the acoustic characteristics of the space should be such that customers do not need to over exert themselves when speaking.

As a result, regardless of the type of a restaurant, the acoustic characteristics of the space should be such that customers do not need to over exert themselves when speaking.

In an eating space, building services, background music, and most importantly, human-related activities such as talking, make the greatest contribution to the ambient noise level. The amount by which a source contributes to the ambient noise level is controlled by two factors: reverberation time (RT), and loudness of the source.

Reverberation time is a measure of the time it takes for sound to decay by a fixed amount (60 dB). If reverberation time is high, it takes a relatively long time for an unwanted sound to dissipate from a space. As a result, in spaces with high RTs, high levels of ambient noise can be expected if there are enough noisy activities taking place in the room. Moreover, louder noise sources create more ‘unwanted’ sounds that also result in high levels of ambient noise.

It is the ratio of a desired sound (the conversation to be conveyed) to all unwanted sounds that specifies how easily a conversation is audible. If the level of unwanted sounds is high, then to have a relatively acceptable audible conversation, one must speak louder. However, in a shared environment like a restaurant, speaking louder introduces more unwanted sounds for people who are not part of that conversation.

The above two way relationship, essentially puts a limit on the number of patrons who can occupy an eating space such that the ambient noise level will not exceed tolerable levels. However, if the ambient level is too high, reducing the number of occupants in order to achieve a better quality of verbal communication would be an unacceptable option for most restaurant owners. A better option would be to decrease the ambient level by decreasing the room’s RT (i.e. make the room less reverberant so that the room can get rid of unwanted sounds faster than before). This can be achieved by the addition of sound absorptive materials to available interior surfaces (i.e. walls, ceiling, floors, seats etc.).

However, some practical concepts, such as Acoustical Capacity, exist for the purpose of acoustic design and evaluation.

Now, the question is how much reverberation is allowable in a space with a certain number of patrons. Unfortunately, unlike many other types of interior spaces (e.g. lecture halls, theatres, classrooms), there is not much literature available on the desirable acoustical performance standards of eating spaces. However, some practical concepts, such as Acoustical Capacity, exist for the purpose of acoustic design and evaluation.

Acoustical Capacity of a space is defined as “the maximum number of people allowed in a room for ’Sufficient’ quality of verbal communication” [1]. Acoustical Capacity is dependent on the volume of an eating space and the reverberation time (RT):

There are basically two ways to interpret the above equation. To reach a desired number of occupants in an eating space without compromising speech audibility, either the reverberation time must be decreased (as already explained) or the volume must be increased (which is usually not a practical solution).

 Figure 1: 3D model of a restaurant with no acoustical treatment

 To illustrate the benefit of an Acoustic Capacity upgrade, consider the example of the restaurant shown in Figure 1. The restaurant eating space consists of a wood ceiling, a polished concrete floor, and steel stud gypsum-board cavity walls. The restaurant has a floor area of 1776sqft (165m²) and a ceiling height of 13ft (4m). We built an acoustic model of the restaurant using AFMG’s Enhanced Acoustic Simulator for Engineers (EASE). With standard hard reflective walls, floor and ceiling, the room has a model predicted RT of 1.2s (when occupied) and an Acoustical Capacity of 25 people.

Figure 2: 3D model of a restaurant with acoustical treatments on walls  and ceiling

 As shown in Figure 2, sound absorptive treatment was added to the ceiling and walls in the model. As a consequence, the RT was reduced from 1.2s to 0.5s. The Acoustic Capacity of the room was increased from 25 to 66 people.

The acoustic model was also used to auralize the untreated and treated space. You can listen to the demo files below to appreciate the difference. Headphones are strongly recommended!

Clip 1: Speech and background chatter in the untreated restaurant

Clip 2: Speech and background chatter in the treated restaurant

In short, with a few careful acoustic improvements, a restaurant can be more hospitable for customers (even without encouraging them to stay longer times than usual). Moreover, in some cases, the owner can be able to increase the room capacity without compromising the comfort of the customers. If you are an owner and you want to find out more about our services, contact us by phone at 604.492.2992, or by filling out our online form.

Sources:

[1] Rindel, Jens Holger (2012). Acoustical capacity as a means of noise control in eating establishments. Joint Baltic –Nordic Acoustics Meeting. link: http://www.odeon.dk/pdf/C116-BNAM_2012_Rindel_29.pdf

 

Written by Mark Gaudet, P.Eng.

I’ve heard it said that Vancouver is a no fun city. As a relatively new immigrant from London UK, who is used to pubs closing around 11pm, I find this attitude a little hard to understand. However, one thing I have noticed since working here in the field of acoustic consultancy is how noise regulation in this city is less onerous than it is in London. Vancouver appears to be a city with lower levels of noise regulation.

In London, much the same as in the Lower Mainland, pubs and clubs are controlled by liquor licensing laws enforced by local government.

In London, much the same as in the Lower Mainland, pubs and clubs are controlled by liquor licensing laws enforced by local government. If a licensed premises features amplified music, such as that played by dee-jays, or resulting from live music, then the local authority (municipality) will typically have in place a noise control policy for entertainment venue development. Typically, a noise control policy, such as the Supplementary Planning Document adopted with the Local Development Framework for the Royal Borough of Kensington & Chelsea, will prevent any increase in the night-time level of background noise measured in any third octave frequency band measured at a dwelling. This condition applies to situations not only where the licensed premises does not share the same building as the noise sensitive location, but also where there is a structural connection between the two. In the latter case, the aforementioned noise policy also applies during the day-time.

The current trend in pubs and clubs is for dance music with a very high level of bass. The type of clause referred to above aims at ensuring that the low frequency music components associated with heavy bass are 10dB below the background noise level, and are therefore for all intents and purposes inaudible. This is an extremely difficult condition to meet. In practice, where residential dwellings are located either above or adjacent to premises featuring loud music, it would mean that the entertainment venue would need to be built as a box-in-box construction, such as that typically seen in broadcast or recording studios.

There are also clauses within Canadian Municipal Bylaws, such as in the Ottawa Noise Bylaw, that seek to preserve the peace and comfort of any person in a residence or place of business as a consequence of any person operating sound reproduction or amplification devices.

In Vancouver, the City Noise Control Bylaw 6555 contains a number of clauses that apply to pubs and clubs.

In Vancouver, the City Noise Control Bylaw 6555 contains a number of clauses that apply to pubs and clubs. The most onerous of these is that the level of noise originating from the entertainment venue received in a bedroom or living room of a dwelling sharing a common partition with the commercial premises is no higher than 55 dBC. This level of noise is broadly similar to the level of traffic noise audible in a downtown dwelling close to a relatively busy street. This condition provides some protection to the occupants of residential suite, but does not result in inaudibility, or anything close. The bass beat will still be clearly audible.  However, as it stands the venue is obliged to do no more than to comply with the 55 dBC noise limit.

Over the past five years or so, the City Licensing Department has required an acoustic assessment for the operation of extended hour’s liquor establishments, new premises and pubs re-focussing as music venues. This assessment must address the relevant clauses of the noise bylaw, and to qualify for the extended hours license, it has to demonstrate that noise transmission from the premises to an adjacent dwelling does not exceed 55 dBC. For most of the venues applying for this extension in hours, meeting 55 dBC requires the installation of an heavy dropped ceiling in the venue to help control noise transmission to suites above. It may also require that the maximum output of the sound system is limited by using a form of noise limiter – either an electronic or software based compression system.

In Vancouver, a significant proportion of licensed establishments are housed in buildings which were originally cheap hotels with boarding rooms above. The pubs now invariably play music at levels of between 105 and 110 dBC. What were boarding rooms now tend to be SRO’s (Single Room Occupancies) or low-cost hotel rooms inhabited by people with little disposable income. If no extended hours application is made, then it is not incumbent on the licensed premises to demonstrate that it is compliant with the Noise Control Bylaw. As a consequence, many of the SRO’s or hotel rooms are subject to high noise levels until 1am or 2am. Nevertheless, if complaints are received in relation to noise emissions from a pub or club, the City will require the premises to seek advice from an acoustic consultant for the purpose of complying with the bylaw.

So, Vancouver is a city where there is only partial noise protection for residents who share a building with a licensed premises as only those with extended hours need demonstrate compliance. The quantitative bylaw limit is in effect less restrictive than qualitative clauses contained within noise bylaws in other Canadian municipalities and the quantitative noise criteria contained in planning legislation in the UK.