Water sound and acoustics

Water sound and acoustics

Water sound design, music playback and noise control

A fountain may be heard before it is seen. The sound of falling water can announce the presence of a water space along a sidewalk, provide a place to rest, or be part of an urban spectacle accompanied by music.

The same sound, if it is not coordinated with the location and operation method, can make it difficult to have a conversation, reach the neighboring residential units or disrupt the surrounding activities. Therefore, sound quality should be checked from the beginning of the design, along with architecture, hydraulics and lighting.

The purpose of this chapter is to provide a method for designing the listening experience of water fountain; An experience that is both favorable for the audience and compatible with the surrounding environment.

19–1. Defining the project's audio goal

For each fountain, it should be determined what role the sound plays. In an urban garden, the natural sound of water may be the most important part of the experience; In the theater, music plays a major role; And in the office area, limiting the sound of water should be a priority.

The audio objective can be expressed in an evaluable sentence:

"The sound of water should be recognizable in the seating area, not disturb the normal conversation and be compatible with the nearby uses at night."

This goal should later be translated into measurement criteria, evaluation points, and operating conditions.

Crystal Fountains also places the auditory experience alongside movement, light, perception of space and seasonal changes in introducing fountain design factors. This view shows that the sound is part of the overall design of the fountain. Crystal Fountains design approach ^[108]

19–2. Identifying sound sources

The sound that is heard in the place is the result of the combination of several sources:

These sources should be evaluated separately as much as possible. For example, the unpleasant sound next to the fountain may be from the engine room fan or the vibration of a valve; Increasing the volume of water or music does not fix the root cause.

In the musical fountain, the relationship between sources is more important. GSO introduces this type of fountain based on the coordination of water movement, light and music; In the sound design of such a project, the music must be evaluated in the presence of the actual sound of water. Introduction of GSO urban fountains ^[109]

19–3. Sound impression before design

Background noise measurement should be done before deciding on the type of water fall or the capacity of the sound system. A short withdrawal during quiet hours is not representative of all site conditions.

Checkpoints typically include seating areas, spectator areas, project boundaries, and surrounding sensitive uses. The harvesting time should also be related to the expected hours of activity of the water fountain.

Record the following information in the withdrawal report:

• position and height of the microphone;

• date, time and duration of measurement;

• wind and weather conditions;

• Activity of the main sources of sound;

• distance from facades and reflective surfaces;

• Measurement index and device specifications.

Along with the measurement, an aural note is also useful: is the sound continuous, pulsating, bass-dominant, or intermittent from a specific source?

Figure note from the source manuscript

Figure 1-19: Schematic site plan with location of fountain, main path, seating area, sensitive buildings and acoustic sampling points. Suggested subtitle: "Audio evaluation should cover the scope of the audience and the environment around the project at the same time."

19–4. The main indicators of sound measurement

The decibel number does not provide complete information without introducing the index, time and place of measurement.

Equivalent balance is not the arithmetic mean of decibel numbers. Also, an overall value may not accurately represent the difference between the smooth sound of water and a sound with an annoying component. Ambient Sound Measurement Guide, Brüel & Kjær ^[110]

The electrical power of the speaker or pump is also not the same as the sound pressure level at the listener's place.

For formal acceptance and delivery, the measurement device and method must be compatible with the purpose of the assessment. The IEC 61672-1 standard covers the performance specifications of sound level meters; This standard does not by itself determine the permissible sound limit of the project. Introduction to IEC 61672-1 ^[111]

19–5. Natural sound design of water

The sound of water in Dubai is not alone. The height of the fall, the shape of the flow, the way air enters, the material of the impact surface and the condition of the receiving basin also affect it.

To adjust the listening experience, several variables can be checked:

Drop Height: Changing the height changes the impact conditions and the resulting sound; Its relationship with decibel is not the same for all fountains.

Flow shape: continuous sheet, filament flow and dispersed droplets create different sound textures.

Receiving level: The impact with water, stone or architectural pieces should be compared in the real sample.

Number and dispersion of impact sites: A concentrated drop with several small drops along the path has a different spatial experience.

Flow rate and operating mode: Reducing the flow rate may change the sound, but it can also affect the continuity of the water curtain or the quality of the visual effect.

For sensitive details, it is more reliable to build a prototype with geometry and flow conditions close to the original design than to judge based on an internet audio file. The recorded sound depends on the microphone, distance and recording settings.

19–6. masking traffic noise; Capacities and limitations

The sound of water can reduce the audience's attention to traffic in some situations or improve their evaluation of the environment. This effect depends on the type of water sound, background sound, distances and user preference.

A research on the collaborative design of the sound of a fountain in a city park showed that the optimal choice was the result of a balance between the pleasantness of the sound of the water and the reduction of traffic noise; The scenarios were reviewed in the real context of the place and with the participation of the listeners. Research published in Applied Acoustics ^[112]

However, adding the sound of water does not usually mean removing the acoustic energy of the traffic. The environment may be judged to be more pleasant, while the overall sound level is increased.

Therefore, expressions such as "definite reduction of noise pollution" or "elimination of street noise" should not be used for the fountain without study. The measurable goal can be to improve the listening experience in a certain range.

19–7. Sound propagation and distance effect

For an almost point source, in the far field and free propagation conditions, the sound pressure level change can be calculated primarily from the following equation:

$L_{p,2}=L_{p,1}-20{\log }_{10}(\frac{r_2}{r_1})$

In this regard, $r_1$ and $r_2$ are the distance from the source. Under these ideal conditions, doubling the distance provides a reduction of approximately 6 dB. Audio Broadcast Guide, Brüel & Kjær ^[113]

Educational example

Suppose the contribution of a sound source at a distance of 5 meters is equal to 72 dB. Assuming that the observation direction and the mentioned conditions are fixed, at a distance of 20 meters:

$L_{p,2}=72-20{\log }_{10}(20/5)$

$L_{p,2}\approx 60\mathrm{dB}$

This number is the initial prediction of the source. It does not take into account the reflection of views, speaker orientation, ground, wind, obstacles and background noise.

Also, a long waterfall or extensive series of fountains is not considered a point source at all distances. This relationship should not be generalized to the whole fountain without checking the geometry.

Figure note from the source manuscript

Figure 2–19: Training plot of hypothetical source and points 5, 10, and 20 meters with approximate values of 72, 66, and 60 dB. Suggested subtitle: "Distance induced decay in a simple free diffusion model; The values ​​are not sound limits or definitive predictions of the site."

19–8. A collection of different sounds

dB levels are not combined with normal summation. For independent and non-coherent sources:

$L_{total}=10{\log }_{10}({\sum }_{i=1}^{n}10^{L_i/10})$

All values must relate to the same point, weighting, and comparable time conditions. The method of summing sound levels

Suppose that at one point, the contribution of the fountain is 60 dB(A) and the background noise is 55 dB(A):

$L_{total}=10{\log }_{10}(10^{60/10}+10^{55/10})\approx 61.2\mathrm{dB(A)}$

The result is not 115 dB. Two independent sources with an equal level of 60 dB also create a total of about 63 dB.

This method alone is not sufficient to accurately predict the interference of multiple speakers that broadcast a common signal; In that case, the difference in arrival time and phase is also important.

19–9. Cover design of music playback system

In a show, the goal of the sound system should be to cover the audience. Choosing based solely on the wattage of the amplifier or the number of speakers will not determine the outcome.

The design should start by determining the listening area: sitting, standing viewing, passing and places where music is not necessary.

Then the coverage angle, height and installation direction, frequency response, maximum usable output and environmental conditions of the speaker are checked. Audio design tools can be used to compare placement options and predict coverage. Bose Professional audio system design tools ^[114]

At some sites, a few speakers closer to the audience allow better control; But increasing the number of speakers without adjustment can cause inappropriate overlap and difference in arrival time.

The speaker should not be placed behind an obstacle that would obstruct its radiation path just to hide it. Also, the installation location must be accessible for inspection, adjustment and repair.

19–10. Sound delay and coordination with the show

Sound needs time to reach the audience from the speaker. Additionally, digital processing, networking, and broadcast equipment may also cause delays.

To estimate release time:

$t=\frac{d}{c}$

If the speed of sound in hypothetical air conditions is 343 meters per second, it takes about 29 milliseconds to travel 10 meters.

This calculation can be the starting point of the adjustment. For example, if an auxiliary speaker is closer to the evaluation location, its output may need to be delayed to more closely match the sound of the main speaker. The Q-SYS manual also explains the possibility of calculating delay based on distance and temperature. Q-SYS delay adjustment guide ^[115]

The coordination of the show, in addition to the sound emission, depends on the response time of the pump, the valve and the formation of the water effect. Sending commands at the same time does not necessarily mean seeing and hearing the result at the same time.

The adjustment should be done in the main range of the audience; A single amount of delay does not completely synchronize all points in a large field.

19–11. Fountain in enclosed and semi-enclosed spaces

In an atrium, enclosed courtyard, or covered walkway, sound reflections from hard surfaces can dominate the experience. A fountain that sounds good outdoors may sound louder or muffled indoors.

In these spaces, the relationship between the fountain and the ceiling, walls, glass and adjacent spaces should be checked. If music or speech is also played, it becomes important to evaluate the clarity and the duration of the sound.

The solution can be a combination of correcting the type of drop, reducing the source noise, changing the placement of the speaker and predicting sound absorption. Absorbent materials should be suitable for humidity, cleaning and construction requirements of the same place.

Louder music in a highly reflective environment does not necessarily produce more clarity.

19–12. Sound control of pump, pipe and engine room

Mechanical noise should be checked at the source. Improper selection of the pump, unfavorable suction conditions, vibration of connections or transmission of vibration to the structure can reduce the listening quality of the space.

KSB explains that the vibration of the body and pipes contributes to the system's sound generation, and cavitation can amplify the sound. This company introduces the correct selection of the pump and its proper operation as the main noise control measures. Pumps and systems sound guide, KSB ^[116]

Design measures, as appropriate, can include work point checks, design of supports, vibration isolation and transmission control through pipes. Seismic selection should also be engineered; Adding a piece of rubber everywhere is not a universal solution.

The acoustic cover of the engine room should be compatible with the ventilation and access for repairs. Also, the newly appeared abnormal sound should be investigated for technical reasons before covering or insulating.

Figure note from the source manuscript

Figure 3-19: Schematic section of the engine room, pipe route and adjacent structure; The possible paths of airborne sound transmission and structural vibration are displayed with two colors. Suggested caption: "Control of facility noise requires consideration of the transmission path next to the generating source."

19–13. Disturbance control in the surrounding environment

In addition to the land boundary, the neighborhood survey should consider the actual sound receiving locations such as windows of residential units or overlooking terraces.

The acceptable amount depends on the use, time, evaluation index and local regulations. Determining a general number is not suitable for all urban fountains.

To reduce the effect on the surroundings, you can check these options:

• Directing the speaker to the audience;

• Reducing unnecessary broadcasts outside the viewing area;

• Adjusting the spectrum and controlling the energy of low frequencies;

• Modifying the positioning of noisy sources;

• limiting the time and duration of the show;

• Defining a calmer mode for critical hours.

If an electronic noise limiter is used, its adjustment should be related to the measurement at the specified points. The number displayed on the sound processor is not directly equivalent to the dB level in the adjacent property.

19–14. Operation modes and delivery test

It is suggested to define the sound status of the water fountain in the operation plan:

This table is a suggested template. Abnama music system can take on the role of emergency notification system only if it is designed and approved for the relevant application.

Handover testing is best done in stages: background sound, water fountain without music, audio groups, and then the full show. Turning on all the equipment from scratch makes it difficult to diagnose the cause of the problem.

In delivery, listening coverage, timing coordination, effect on sensitive points and performance of limiting settings should be checked. Sound satisfaction at the control panel is not representative of all listening locations.

Figure note from the source manuscript

Figure 4–19: Actual photo of on-site sound measurement, showing device location relative to fountain and audience; No dummy number on the display. Suggested caption: "Sound delivery is based on measuring and listening at specific points." Enter the test specifications in the box with the image.

19–15. Documents for delivery and maintenance of audio quality

The final documents should allow for the restoration of approved settings. This collection includes speaker plans, equipment specifications, connection paths, processing and delay settings, display files, and audio test reports.

In periodic maintenance, the change in the sound of the water should also be checked. A drop in the water level, clogging of the nozzle or a change in the location of the collision can cause a sound different from the original situation. In the audio system, moving the angle of the speaker, the failure of a part or changing the settings may change the coverage and effect on the surroundings.

Recording a reference state at the time of delivery, including working water conditions, acoustic settings and measurement results, makes it easy to detect these changes.

In Chapter 20, the basics of hydraulics and fountain calculations are reviewed; From flow and pressure to pump head, path loss and turning an architectural plan into a system with calculable performance.

Water engineering and facilities