The set-up is visible in the attached figures: six metal bars of about 35 kg each, are placed about the center of a wooden beam couple, resting at the ends on blocks of expanded polyethylene almost at the center of the box panels.
The analysis of signals from the microphones placed in the HAU room, the NEB SAS and the NEB Hall will follow.
Some aluminum bars were placed in contrast between the concrete wall and the center of the accessible side panels, to study the effect on the acoustic and seismic noise of the system (e.g. see the attached figures).
The activity ended at about 18:10 LT.
Remarks on the structural damping and the inner acoustic isolation (#53144) of NEB AHU engine-fan box:
- the soundproofing has produced a reduction of the acoustic noise level in the AHU room for frequencies below ~30 Hz and of the seismic vibration of the AHU box above ~100 Hz;
- the effect of both stiffening actions is to reduce the seismic and acoustic noise of AHU room and SAS in narrow frequency ranges.
Below, we report some comments comparing all actions. The color code of the plots is the following:
purple--> No actions on the AHU fan-engine box
golden--> installation of soundproofing panels
green--> stiffening by means of metal bars of about 35 kg
blue--> stiffening by means of aluminum bars
- Microphones
- The soundproofing produces a visible reduction of the acoustic noise in the AHU room (e.g., about a factor 2 at 10Hz and 20Hz). The stiffening actions do not produce further reductions.
- In the SAS area, the stiffening-aluminum bars generate a reduction in the frequency band 6-10 Hz but a worsening in 10-14Hz.
- No noise reduction in the microphone of the experimental hall.
- Seismic sensors
- The resonance of the AHU box at ~9.76Hz is shifted by the actions: ~9.34Hz (soundproofing), ~7.68Hz (stiffening-metal bars), ~7.88Hz (stiffening-aluminum bars). The metal bars and aluminum bars create a slight reduction of box vibration noise at (8-11)Hz and (22-30)Hz.
- Both stiffening actions produce a seismic noise reduction of the AHU room floor in the frequency band ~(5-15)Hz.
- No noise reduction in the seismic sensor (ENV_NEB_SEIS*) of the experimental hall.
- Supply duct:
- the soundproofing produces a slight reduction of the noise in AHU and SAS ducts.
- Return duct:
- the soundproofing produces the same reduction (about a factor 2) of vibration noise on AHU return duct (west side) up to ~14Hz;
- the stiffening-aluminum bars cause a vibration noise reduction in (8-11)Hz of SAS return ducts (west and east side).
- Microphones
- the stiffening-aluminum bars cause a reduction of the acoustic noise floor in the AHU room in freq band (42-52)Hz and in the SAS area in freq band (34-40)Hz.
- Seismic sensors
- The vibration of the AHU box is slightly reduced in ~(46-50)Hz with aluminum bars.
- Return and Supply ducts:
- vibration noise reduction by means of aluminum bars in ~(48-56)Hz for SAS return duct (west side) and in ~(46-54)Hz for AHU supply duct.
- Microphones
- In the AHU room, the stiffening with aluminium bars and the suondproofing lead to an acoustic noise reduction in the freq band (60-70)Hz and in (78-90)Hz, respectively.
- Seismic sensors
- The aluminium bars installation produces a seismic noise reduction of AHU room floor in the frequency band ~(60-68)Hz.
- The attenuation of freq peak at ~84.43Hz visible in ENV_NEB_SEIS_*, it is not due to stiffening actions.
- Seismic sensors
- The panel installation leads to a reduction (about a factor 3) of AHU box vibrations in (100-125)Hz. This action produce a noise redctions of AHU room floor in freq range (110-130)Hz, as well.
- Return ducts
- vibration noise of AHU supply duct is reduced by means of metal bars in ~(120-140)Hz.
- Seismic sensors
- All actions performed on AHU box produce the same redutcion of vibration noise in (150-200) Hz. This effect is visible on the AHU room floor, as well.
- Return ducts
- vibration noise of AHU supply duct reduced by means of metal bars in the freq band ~(170-190)Hz.
