Comparative analysis of noise characteristics inside of tanks

This is an introduction to noise characteristics of Soviet/Russian armoured fighting vehicles. 

Vibrations, moving parts, and suspension all contribute to the internal noise level of a vehicle. These factors create oscillations that propagate through other modules increasing noise levels. To measure noise characteristics inside tanks, the driver's position and the turret crew's positions are measured separately. Units of measurement used for this are dB, dBA, octaves and Herz along with 2 different spectrums of sound; Level of sound pressure (LSP) "УЗД (Уровень звукового давления)" and level of sound (LS) "УЗ (Уровень звука)". 

Unspecified variants of T-64, T-72 and T-80 and a T-80UD were chosen. The charts below show the dB/dBA levels for the different crew positions relative to the speed at which the tanks are moving. Tests were carried out on a concrete track. Lines 1-4 indicate LSP values for T-64/T-72/T-80 and T-80UD, while lines 5-8 indicate LS values for the same tanks. 

Chart 1 - Driver's position noise characteristics. (X-axis is used for dB/dBA values)
Lines 1-4 LSP values; Lines 5-8 US values for T-64/T-72/T-80 and T-80UD

Chart 2 - Turret noise characteristics. (X-axis is used for dB/dBA values)
Lines 1-4 LSP values; Lines 5-8 US values for T-64/T-72/T-80 and T-80UD

Table 1: Level of sound pressure and level of sound inside of driver's position

Operation mode		LSP (Level of sound pressure), dB				LS (Level of sound), dBA
		T-64	T-72	T-80	T-80UD	T-64	T-72	T-80	T-80UD
Stationary		112	114	103	*	104	102	90	*
V = 5km/h		112	111	114	110	97	101	92	100
V = 30km/h		131	127	124	124	118	119	108	107
V = 60km/h		135	132	130	130	120	123	113	113

Table 2: Level of sound pressure and level of sound inside of turret basket

Operation mode		LSP (Level of sound pressure), dB				LS (Level of sound), dBA
		T-64	T-72	T-80	T-80UD	T-64	T-72	T-80	T-80UD
Stationary		103	110	108	*	97	104	90	*
V = 5km/h		113	108	109	107	93	99	90	97
V = 30km/h		127	123	122	123	112	111	106	102
V = 60km/h		131	128	129	128	114	116	108	108

As the speed of the tank changes, the LSP and LS patterns change smoothly, with individual emissions fluctuating due to resonance phenomena. The rate of increase varies from 1.2 to 0.8 dB (5-25 km/h) and from 0.8 to 0.25 dB (25km/h-40km/h). At speeds of 40 km/h and above, both LSP and LS remain almost constant. LSP curves change less smoothly than LS curves. This is explained by the presence of resonances in their relative spectrums in the frequency range of 31.5 Hz to 250 Hz. These resonances are smoothed out with A-Correction (typical resonances occur at speeds of 20 km/h for the T-72 and at 25 km/h for other tanks). In this case, they are proportional to the pitch size of the track). The tables above show data on LSP and LS inside the driver's position and turret basket typically used for assessing the acoustic condition of tanks that are stationary operating at maximum RPMs or moving at various speeds (5km/h, 30km/h and 60km/h) on a concrete track. 

It can be observed that the LSP and LS values for the driver's position are significantly higher than in the turret, considering that the driver is located further away from the engine transmission compartment. In the range of medium to high speeds (20km/h to 60km/h), the types of tanks considered can be arranged in the following order as the most significant acoustic characteristic increases - the sound level (dBA):

• Turret basket - T-80 P (102-108), T-80 (104-112), T-64 (111-114), T-72 (112-116)
• Driver's position - T-80 P (105-113), T-80 (105-116), T-64 (117-120), T-72 (118-123)

AFVs are checked for compliance with noise limit values during movement and stationary operation. In the latter case, the contribution to the noise generation from operating modules is counted towards the final acoustic values and compared to the values provided in technical and operation manuals. 

The following modes of operation are used to test AFVs for acoustic properties: 

1. Closed hatches, stationary position with the engine operating at medium RPMs.
2. Closed hatches, stationary position with the engine operating at maximum RPMs.
3. Closed hatches, stationary position with the engine operating at maximum RPMs along with all internal modules turned on.
4. Closed hatches, all modules operating based on the recommended mode of operation, engine turned off. 
5. Closed hatches, all modules operating based on the recommended mode of operation, engine operating at maximum RPMs.

Noise characteristics for crew positions inside 4 different tanks based on different operating modes (Table 1). The full chart is found in the reference section.

References: 

• Google Drive Excel Table 1
• Г. С. Жартовский, Д. В. Куртц, О. А. Усов. Защита оборудования и экипажа военных гусеничных машин от механоакустических и климатических воздействий: Монография. СПб.: Издательство "Лань", 2016.