DASM conducted noise survey measurements and consulted on sound insulation and sound absorption solutions for the Sotetsu International Hotel Project - HCMC

In early March 2022, DASM - Institute for Development and Application of Acoustic Materials received an invitation to conduct noise surveys and consult on sound insulation and sound absorption solutions for several rooms at the Sotetsu Hotel Project in Ho Chi Minh City, with a total area of nearly 800 m², featuring 120 rooms, 19 above-ground floors, and 2 basement floors, in accordance with international quality standards.

To meet international 4-star hotel quality standards, as requested by the investor SOTETSU Group, one of Japan's major corporations specializing in hotel investment and management, the main contractor Vinata International trusted and selected DASM - Institute for Development and Application of Acoustic Materials as the direct unit to survey noise and consult on sound insulation and sound absorption solutions for this important project.

Although newly established in 2021, DASM - Institute for Development and Application of Acoustic Materials has always been the best choice for inspecting building quality regarding sound insulation and sound absorption capabilities. With the most modern measuring equipment in the world along with a team of experts and engineers thoroughly trained in acoustics, we are confident in providing customers with professional solutions and services in sound and architectural acoustics. Furthermore, we also consult on construction and quality-assured, high-efficiency sound insulation materials and sound absorption materials for sound insulation and sound absorption implementation.

1. Noise Measurement Standards

Parameter Test	Standard
Airborne sound transmission between rooms in a building	ISO 16283 ISO 140 ASTM E-336 ISO 354 ISO 717
Calculation of Noise Criterion (NC)	ISO 3382

Parameter Test	Standard
Heavy impact floor	JIS A 1418

According to ISO 16283 and ISO 140 standards, the report includes average sound pressure level measurements L1 and L2 across frequency bands for each measurement. Based on these parameters, the sound insulation performance of partitions, walls, or any location is evaluated. The NC coefficient is determined through the background noise level at each evaluated location. The TL coefficient must be based on the absorption area since the room space has been equipped with certain furnishings that allow an increase in the room's sound insulation capability.

2. Measurement Rooms

Three rooms will be measured for sound to determine the NC and TL coefficients, including Rm. 404, Rm. 406, and Rm. 407 (see floor plan drawing).

Survey reality

Parameters	Rm 407	Rm 406	Rm 404
Calculated volume [m3]	49.81	41.56	41.76
Large glass surface area [m2]	9.126	11.61	9.018
Drywall area [m2]	10.9	N / A	8.91
Main door area [m2]	3.86	3.86	3.86
Large glass door dimensions [m2]	1.55 x 2.42	1.55 x 2.42	1.55 x 2.42
Bathroom door dimensions [m2]	1.94 x 2.4	0.8 x 2.4	0.8 x 2.4
Main door dimensions [m2]	0.9 x 2.2	0.9 x 2.2	0.9 x 2.2

 3. NC Coefficient

Ambient noise generated from empty spaces or around the building – such as air conditioning systems, traffic noise, etc. – not only causes discomfort, stress, and fatigue for occupants but also reduces productivity and concentration, thereby affecting safety to a certain extent. In severe cases, it even affects communication capability.

NC (Noise Criterion) or NC curves are a way to describe measured noise levels across a frequency spectrum from 63.5Hz to 8kHz. They are useful in determining noise levels caused by mechanical systems such as motors in noise-sensitive environments like hotels and hospitals.

The criterion determines that the upper limits of each octave band spectrum must not be exceeded.

Classification	Application	Suggested NC Level
Residential	Private house or apartment	25-35
	Suburban residence	25-30
	Bedroom	20-30
	Living room	25-35
Hotel	Individual room or suite	25-35
	Meeting room or banquet room	25-35
	Service and support area	45-50
	Auditorium, corridor, lobby	40-45
Area public	Courtroom	30-40
	Library	35-40
	Church, Mosque, Temple	30-35
Factory	Production area	40-65
	Administrator / Accountant	40-46
Office	Meeting / conference room	25-35
	Private room	30-35
	General office area	40-45
	Business machine / Computer	40-45
	Break room / Lounge	40-45
Hospital and Clinic	Radiology department	35-40
	Operating theater	25-30
	Ward	35-40
	Laboratories	35-40
	Consultation room / Clinic	35-40
	Corridor / Public area	40-45
Commercial area	Theater	30-35
	Restaurants	45-50
	Recording studio / Audio broadcasting / TV studio	15-20
	Performance / Concert / Recital hall	15-20
	Sports stadium	45-55
	Spa / Facial treatment / Massage center	25-35
	Retail store	40-45
	Gymnasium / Workout room	40-45
School	Auditorium	35-40
	Classroom	35-40

4. TL coefficient

TLD: Transmission Loss Difference: The difference in sound energy level lost through a sound insulation wall.

Each sound insulation wall with different materials and structures will have different levels of energy loss. Depending on the intended use, we can design different partition models. Transmission loss tends to increase at high and low frequencies, and sound insulation can be improved by appropriate additional measures.

After an incident sound strikes a barrier (wall, partition), three mechanisms occur simultaneously: Reflection, absorption, and transmission. A part of the incoming sound is reflected back to the source, a part is absorbed by the obstacle, and the remaining sound is transmitted to the space on the opposite side of the obstacle. Transmission loss is the term used to describe the performance of a barrier as sound insulation between two spaces, with transmission loss increasing correspondingly with the increase in performance of the sound barrier. It is given by:

Where W_I is the incident sound power (watts) on the wall and W_T is the sound power transmitted to the space on the opposite side of the barrier.

5. Measurement method and process

a. Method

In general, we use a sound level meter to measure sound intensity in indoor spaces, next to the sound source. This sound source will generate a spherical wave pole larger than the background noise level to determine the sound insulation capacity of the wall (TLd coefficient). The sound level meter will be used to simultaneously determine the NC and TLd coefficients.

b. Measurement process

Determination of NC coefficient

Equipment: 1 Nor140 Sound Level Meter.

Results: Different noise levels measured by indoor noise.

Procedure:

• Use a Sound Level Meter (SLM) to measure different noise levels at 6 different points for each room.
• The average value of sound intensity in the room will be determined. Based on this average coefficient to determine the NC factor.

Determination of TL coefficient

Equipment: 1 Nor140 Sound Level Meter and 1 OMNI 4” Sound Speaker.

Results: TL result curve over frequency band

Procedure:

• Step 1: Measure the background noise of the receiving room and source room, setting the sound intensity of the source to be greater than the background noise of the room by approximately 20 dB.

• Step 2: Determine the dimensions of the receiving room, source room, and the dimension of the wall for which we want to determine the TLd coefficient. (Sw)
• Step 3: Measure the sound level in the source room at least 6 different points (pay attention to the measuring distance and the distance to the wall) when the OMNI 4” is turned on. (L1)
• Step 4: Measure the sound level in the receiving room at least 6 different points (pay attention to the measuring distance and the distance to the wall) when the OMNI 4” is powered on. (L2)
• Step 5: Measure the reverberation time in the receiving room at at least 6 different points (pay attention to the measuring distance and distance to the wall). (T)
• Step 6: Measurement of the background noise level of the receiving room. (Lb)

 6. Measurement positions

Each room will have 6 measurement positions determined at the most acoustically disadvantageous points, where there are unstable fluctuations in sound intensity. A non-uniform environment will affect the determination of the average sound intensity in each room. This is the reason why sound measurements are determined at these positions.

Each measurement position must ensure the requirement of being at least 1m away from the walls and 1m from the floor to ensure accuracy in the sound intensity measurement.

Position 1

This is the position closest to the glass door frame. Due to the structural change consisting of only a single layer of glass, the sound insulation performance will also be unstable and may become weaker.

Positions 2 & 3

These two positions are affected by the internal structural shape of the room where the right angles are located.

Position 4

This is the position next to the entrance door, affected by many factors such as gaps, joints with the wall, and the bottom of the door. These are all acoustically disadvantageous positions where sound easily leaks through.

Position 5

At the intersection between two different shapes of the room, there will be a change in the sound intensity level.

Position 6

This is the center position of the hotel room where the sound intensity level has the highest stability.

 Measurement position outside the scaffolding

This is a special position when measuring the sound insulation of the dividing wall between the inside and outside of the room. In this case, the sound source will be placed on the scaffolding and activate a sufficiently large sound source, much higher than the background noise level. When there is a difference in sound intensity, we can determine the sound insulation of the wall or partition.

7. MEASUREMENT EQUIPMENT

Two instruments are used to empirically determine the two coefficients NC and TL: 1- Sound level meter Norsonic 140 and 2- Sound Source OMNI 4’’.

While the sound source performs the task of generating a noise level higher than the background noise for the purpose of determining the TL coefficient, the sound level meter allows the determination of sound intensity at each measurement position across the 1/1 octave or 1/3 octave frequency bands.

8. RESULTS

The results for NC and TL will be exported separately. Each result is a measurement result confirmation sheet accompanied by this calculation description report.

The results were analyzed after in-situ measurements. The NC value meets the requirement at the NC 24 level. With drywall or glass doors, the requirement of 50dB at high frequencies is met, but at low frequencies, it does not reach the desired level.

Especially at the main door position, it does not meet the requirement due to the structure and improper sound insulation method.