What exactly is meant by sound insulation against impacts from floor slabs?

Many people write to inquire.

How do you obtain evidence of noise from upstairs?

How should we choose this?

A house with "no noise from upstairs"

Before we proceed, we need a technical term:

Sound insulation of impact sound from floor slabs

(The impact sound is similar to the sound made when an object collides with the floor.)

Next, we will start from the national laws and regulations.

Let's gradually understand this term.

(There are many points to note below, please take notes.)

Code for Sound Insulation Design of Civil Buildings

Impact noise:

Impact noise refers to noise generated when a vibrating body of a sound source directly contacts a building structure or when there is an impact between solids, and the vibration energy is directly transferred to the building structure.

According to the on-site sound insulation survey and testing data conducted by the National Building Engineering Quality Supervision and Inspection Center in recent years, residents' complaints about the impact sound insulation of floor slabs with a weighted standardized impact sound pressure level (L'nt,w) of around 80dB are far less serious than their complaints about the airborne sound insulation of partition walls with a weighted standardized sound pressure level difference of 40dB to 45dB.

This standard does not currently specify the impact sound insulation performance of the floor slabs in residential kitchens and bathrooms. This is because, firstly, the floors in kitchens and bathrooms need to be waterproofed, and the floor slabs are usually thick and the area is not large, so the impact sound problem is not prominent; secondly, kitchens and bathrooms have high waterproof requirements for floor materials (the floors are generally made of rigid waterproof materials such as cement and tiles), and it is impractical to require these floors to be made entirely of floating floor slabs or covered with elastic materials.

Impact sound insulation standards:

Definition: When there is an impact noise of 100dB upstairs, the noise that can be heard downstairs should be below 75dB.

Note: When there are genuine difficulties, the single-value evaluation of impact sound insulation for residential floor slabs may be less than or equal to 85 dB, but possible improvements should be made in the floor slab structure. (That is to say, the actual impact sound insulation standard for floor slabs in my country is ≤85 dB.)

Note: The international standard for floor impact sound insulation is 65dB.

How to measure and calculate impact sound

General rules:

Unless otherwise agreed upon beforehand, on-site measurements of impact sound insulation of floor slabs should be performed using 1/3 octave bands. Single-value evaluation quantities converted from octave band measurements cannot be directly compared with results converted from 1/3 octave band measurements.

The generation of a sound field:

The impact sound should be generated by the impactor.

The impactors should be randomly distributed and placed at least four different locations on the floor slab being tested. The distance between the impactor locations and the floor slab boundary should be no less than 0.5m. For anisotropic floor slab structures with beams or ribs, more locations may be required. The line connecting the impactors should form a 45° angle with the direction of the beams or ribs.

The impact sound level at the start of the impact may exhibit characteristics that change over time. In this case, the measurement should begin after the noise level has stabilized. If the stabilization condition is not reached 5 minutes after the start of the impact, a time period that meets the measurement requirements should be selected for measurement, and the measurement time period should be noted.

When measuring floors with soft surfaces, there are additional placement standards for standard impactors.

Impact sound pressure level measurement:

1. General Rules

Impact sound pressure level can be obtained by measuring a single microphone at different locations in a room, or by a fixed array of microphones or a continuously moving or rotating microphone. The sound pressure level measured at each microphone location should be averaged across all impact locations.

2. Microphone position

Below is the minimum spacing.

-The distance between the two microphone positions is 0.7;

-The distance between any microphone and the room boundary or diffuser is 0.5m;

-The distance between any microphone and the test floor slab to be impacted is 1.0m.

Note: If possible, a larger spacing should be used.

Fixed microphone position:

There should be at least four microphone positions, evenly distributed within the allowable range of the room space to be tested.

Moving microphone position:

When using a portable microphone, the scanning radius should be at least 0.7m, and the moving plane should be tilted to cover most of the measurable space. The angle between the moving plane and each surface of the room (walls, floors, ceiling) should be no less than 10°, and the scanning time should be no less than 15s.

3. Measurement

① Fix the microphone position:

At least six measurements should be taken using a fixed microphone position, with at least four microphone positions and at least four impactor positions used for one-to-one measurements.

② Move the microphone position:

Use a moving microphone to take at least four measurements, that is, one measurement at each impactor location.

When using six or eight impactor positions, measurements can be taken using one or two moving microphone positions.

4. Average time of the average value

At each microphone position, the averaging time for each frequency band with a center frequency below 400Hz should be at least 6 seconds. For frequency bands with higher center frequencies, the averaging time can be slightly shorter, but not less than 4 seconds. When using a moving microphone, the averaging time should cover all scanned positions and be no less than 30 seconds. To avoid surface changes caused by prolonged impact, the moving microphone should preferably perform real-time measurements in each filtered frequency band.

Test Report:

The test report should include the following:

Requirements for standard impactors:

The impactor should have five hammers arranged in a straight line. The distance between the center lines of two adjacent hammers should be (100±3) mm. The distance between the center of the impactor's support leg and the center line of the adjacent hammer should not be less than 100 mm, and the support leg should be equipped with vibration damping pads. The impact force of each hammer striking the floor slab should be the impact force of a 500g effective mass falling freely from a height of 40mm, with a permissible deviation limit of ±5%. Because the frictional force controlled by the hammers must be considered, not only the hammer mass and the falling height must be guaranteed, but also the hammer impact velocity must be guaranteed to be within the following range: if the mass of each hammer is (500±12)g, then its impact velocity should be (0.866±0.022)m/s. If the hammer mass tolerance can be reduced to within (500±6)g, then the permissible deviation of the impact velocity can be relaxed to ±0.033m/s.

The hammer should fall perpendicular to the surface of the test floor, with an error within ±0.5°.

The impact hammer head with an impact surface should be a cylinder with a diameter of (30±0.2) mm, and the impact surface of the hammer head should be made of hard steel and be a spherical surface with a radius of curvature of (500±100) mm. Whether this requirement is met can be verified by the following method:

1) Measure the impact surface using a measuring instrument moved along at least two parallel lines tangent to and orthogonal to the center point of the impact surface. If the measurement results are within the tolerance range given in Figure A.1, the curvature of the impact surface meets the specified requirements.

2) The curvature of the hammerhead can be measured using a ball gauge with three contacts on a 20mm diameter ring.

The impactor should be self-driven, the average time between two impacts should be (100±5) ms, and the time between two consecutive impacts should be (100±20 ms).

The time between the hammer striking and lifting should not exceed 80ms.

When using a standard impactor to measure the impact sound of a soft or uneven floor slab, ensure that the hammer can fall at least 4 mm below the plane of the impactor's support foot.

All standard and compliance checks on standard impactors should be performed on a flat, hard surface.