Page 26 - Summer2019

Acoustic Comfort in Restaurants
ll ml llmm-.
“refreshed” the space with a new coat of paint, so the ceiling
tiles are often old and painted. Unless the tiles were spray
WM M painted with nonbridging paint, the paint seals up the sur-
. ‘”" ‘W face of the tiles and essentially reflects sound back into the
room, making the tiles that would previously absorb sound
E E/J0: , r dlid up actually reflect it.
’ Muioilnm “MW
“WW w Technical Analysis of Intelligibility
.:,°;:‘§f"w # G mt“ M! in Restaurants
U,,.,,,,,,, "19 “” The speech transmission index (STI) is “an objective mea-
; & sure used to predict the intelligibility of speech transmitted
3 fl D Eugen a 3527 from talker to listener” (British Standards Institution 2011,
BS EN 60268-16) or how well speech is heard and under-
03:";-B stood from one person to another. The STI was calculated
in 13 untreated restaurants that suffered from poor acoustic
Figure 3. Average alzsarptian caeficients assaciated with variaus environments (Siebein and Siebein, 2017). The STI values
amaunts af alzsarlzing materials in restaurants. C, ceiling; W. wall; for the untreated restaurants ranged from 0.49 to 0.75 when
color blacks, average alzsarptian caeficient cf the actual surface (iii); unoccupied. To give context, according to BS EN 60268-16,
vertical bars, ranges af measured or values. Averages far it are 0.12. an STI of 0.50 is considered the target value for voice alarm
0.20, 0.27. 0.38, and 0.44, respectively. systems (a life safety system designed to provide spoken
emergency alerts in a building but may also include back-
ground music or other nonemergency signals); a STI of 0.58
in conjunction with up to 30% of the wall surfaces, will result is considered a “high-quality public address (PA) system”;
in an i of 0.38. And treating 80% or more of the ceiling sur- an STI of 0.70 is considered “high speech intelligibility”; and
face and over 30% of the walls will result in an (1 of 0.44. In an STI of 0.76 or greater is considered “excellent intelligi-
most restaurants, it is diflicult to treat more surfaces than this bility but is rarely achievable in most environments.” This
due to the number and locations of windows, lighting fixtures, may be why in these 13 restaurants, one could clearly hear
mechanical ducts, etc. Accordingly, the i of a restaurant typi- conversations from other diners at other tables when the
cally tops out around 0.44. restaurant was minimally occupied.
The higher the average absorption coetficient, the more sound The STI for patrons sitting at the same table should be
will be absorbed by the room surfaces. So, if a restaurant maintained as high as possible in all situations to optimize
is to offer a quiet, subdued environment, where people can the ease of communication among those diners. Assum-
talk quietly, it is important to use larger amounts of sound- ing no other patrons are in the area and the background
absorbing material on the awilable ceiling and wall areas. If a noise is quiet, the STI value here will be higher, meaning
venue is to have a more “energetic” feel, less sound-absorbing that speech will be more likely to be understood. It is desir-
material should be used but that material should be used in able to maintain high STI values for this situation under all
strategically placed areas that have the potential to get louder conditions. The STI from locations across the room should
than others. be minimized under all conditions to limit the buildup of
noise that would reduce the STI across the table. Generally,
Using no absorbing material in a restaurant, however, often the more sound absorption present in the room, the higher
results in acoustic environments that are uncomfortable and the STI value.
become excessively loud, even in places that want a more
“energetic feel.” This is typically why noise is considered one of However, the background noise level also has a significant
the chief complaints of patrons of restaurants. Many restau- relationship to the STI. In a dining or social space, average
rants have no acoustic material; they have hard floors, with background noise levels of 77 dB(A) (Scott, 2018) are often
painted gypsum board walls and ceilings. Some restaurants found. The “background noise” is the voices of all the other
have acoustic ceiling tiles, but older establishments mayhave diners speaking at their tables reflecting across the room
24 | AA:auIIiI:l‘I'b:Iay| Summer 2oi9