Determining Sound Energy Level though Sound Pressure Levels

10653 words (43 pages) Essay

18th May 2020 Sciences Reference this

Disclaimer: This work has been submitted by a university student. This is not an example of the work produced by our Essay Writing Service. You can view samples of our professional work here.

Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of UKEssays.com.

Introduction_

The_purpose_of_this_lab_is_to_determine_the_sound_power_level_or_sound_energy_level_by_measuring_sound_pressure_levels_(SPL)_emanating_from_a_noise_source_(electric_drill,_in_this_experiment)_placed_on_a_hard_surface_in_an_environment_which_is_a_semi-reverberant_field._Methods_and_procedures_as_outlined_in_ISO_3744:2010_are_followed_during_the_laboratory_experiment._By_using_direct_method_and_comparison_method_correction_for_the_reverberation_effects_are_made.__The_ISO_3744:2010_methods_are_applicable_to_all_noise_types_(non-steady,_steady,_bursts_of_isolated_sound_energy,_fluctuating_etc.)_and_all_sizes_of_noise_source_(machines,_installations,_stationary_or_slowly_moving_plant_etc.)_provided_all_conditions_for_measurements_are_met_[1]._

Apparatus:

Apparatus_used_in_this_lab_experiment_are_listed_below:

  1. Electric_Drill
  2. B&K_Type_2250_Sound_Level_Meter_(SLM)
  3. B&K_Type_4231_Sound_Level_Calibrator
  4. B&K_Type_4204_Reference_Sound_Source
  5. Ear_buds_for_hearing_protection
  6. Ruler

Description_of_the_measuring_arrangement_and_Procedure

  1. All_the_required_equipment’s_were_gathered_
  2. The_electric_drill_and_the_B&K_Type_4204_reference_sound_source_were_plugged_into_power_outlets
  3. The_B&K_Type_2250_SLM_was_calibrated_using_B&K_Type_4231_Sound_Level_Calibrator_to_94_dB_with_a_frequency_of_1000_Hz_which_is_equivalent_to_a_pressure_of_1_Pa,_negating_the_use_of_different_filters_for_the_purpose_of_achieving_different_weighting_systems._
  4. The_calibration_was_achieved_by_first_turning_ON_the_SLM_and_selecting_calibration_from_menu_with_a_stylus._
  5. The_B&K_Type_4231_Sound_Level_Calibrator_was_then_turned_ON_and_slid_onto_the_B&K_Type_2250_SLM._
  6. The_process_of_calibration_was_then_initiated_by_choosing_start_calibration_on_the_screen_of_the_SLM
  7. It_was_assured_during_the_calibration_process_that_background_noise_interference_was_minimized_for_the_sake_of_achieving_accurate_calibration._The_calibration_accuracy_was_kept_within_±_0.2_dB.

Direct_Method

  1. With_the_B&K_Type_4204_Reference_Sound_Source_and_the_electric_drill_at_the_centre,_as_required_by_the_international_standard_(ISO_3744:2010),_the_measuring_locations_were_marked_as_in_Figure_1_(hemispherical_measurement_configuration)_corresponding_to_the_coordinates_in_Table_1.__
  2. Before_turning_ON_the_electric_drill_the_SLM_was_set_to_make_10_measurements_with_A-weighting_adjustments_and_at_specific_frequencies_of_125,_250,500,1000,2000,4000_and_8000_Hz.
  3. After_setting_the_SLM_the_electric_drill_was_turned_ON
  4. For_recording_measurements_with_the_microphone,_the_SLM_was_directed_straight_at_the_sound_source_in_order_to_record_the_most_accurate_measurements_at_each_of_the_10_locations_in_the_hemisphere.
  5. 10_measurements_of_the_A-weighted_sound_pressure_levels_at_specific_frequencies_of_125,_250,500,1000,2000,4000_and_8000_Hz_were_made_and_then_the_electric_drill_was_turned_OFF_and_moved_away_from_the_hemispherical_measurement_configuration_setup_area._The_recorded_measurements_are_tabulated_as_in_Table_2.

Comparison_Method

  1. With_only_B&K_4204_reference_sound_source_placed_at_the_centre_of_the_hemispherical_measurement_configuration_setup_as_in_Figure_1,_B&K_4204_reference_sound_source_was_turned_ON
  2. At_the_location_and_coordinates_as_in_Figure_1_and_Table_1_the_SLM,_set_to_measure_A-weighted_sound_pressure_levels_at_specific_frequencies_of_125,250,500,1000,2000,4000_and_8000_Hz,_was_used_to_make_10_measurements._
  3. To_make_measurements_the_microphone_of_SLM_was_directed_at_the_sound_source_from_each_of_the_10_location_in_order_to_get_accurate_readings.
  4. After_recording_the_10_measurements_the_B&K_4204_reference_sound_source_was_turned_OFF_and_the_readings_were_tabulated_as_in_Table_3
  5. All_the_equipment’s_were_turned_OFF_and_stowed_away

Figure_1:_Hemispherical_measurement_configuration

Table_1:_Coordinates_of_the_measurement_locations

Position_Number

X(m)

Y(m)

Z(m)

1

-0.99

0

0.15

2

0.5

-0.86

0.15

3

0.5

0.86

0.15

4

-0.45

0.77

0.45

5

-0.45

-0.77

0.45

6

0.89

0

0.45

7

0.33

0.57

0.75

8

-0.66

0

0.75

9

0.33

-0.57

0.75

10

0

0

1

Measured_Data_in_Tabulated_Form:

Table_2:_Measured_sound_pressure_levels_at_specific_frequencies,_when_only_the_electric_drill_is_ON

Drill_L_A_eq_(dB(A))_

Location

125_Hz

250_Hz

500_Hz

1000_Hz

2000_Hz

4000_Hz

8000_Hz

1

23

41.1

53.1

56

59.2

56.5

58.2

2

19.7

47.3

54.4

56.8

59.5

55.6

52.8

3

18.1

39.3

52.9

58.6

62.3

59

59

4

18.8

39.9

52.6

58.5

62.2

60.1

59.2

5

20.3

46.6

54

55.7

59.8

60

58.6

6

21.7

41.5

53.3

56.6

60.8

60.1

57.7

7

17.6

41.4

52.6

57.2

61.4

60.7

57.3

8

16.8

36.7

54

56.8

59.6

60.9

57.7

9

19.9

46.1

51.6

56.2

60

58.6

55.2

10

16.4

36

51.8

57

60.4

59.6

57.6

Table_3:_Measured_sound_pressure_levels_at_specific_frequencies,_when_only_B&K_4204_reference_sound_source_is_ON

Refernce_sound_source_L_A_eq_(dB(A))_

Location

125_Hz

250_Hz

500_Hz

1000_Hz

2000_Hz

4000_Hz

8000_Hz

1

61

68.3

74.8

78.8

77.3

77.7

71.4

2

60.5

68.5

74.3

78.2

78.6

78

71.6

3

60.5

68.9

75.2

79.7

77.8

78.1

71.3

4

61.3

67.3

72.8

78.9

81.6

77.5

71.7

5

60

66.8

72

79

80.7

77.8

71.5

6

60.8

66.8

72.8

79.2

81.6

77.6

71.5

7

58.1

65.7

71.6

79.7

80.2

76.4

69.9

8

57

64.3

71.1

79

79.2

75.7

69.3

9

57.9

64.6

71.5

79.7

79.8

76.1

69.6

10

55

65.4

74.5

81.9

80.1

74.7

66.9

Table_4:_T20_and_T30_measurements_of_reverberation_times_in_seconds

Reverberation_Times

_

_

125_Hz

250_Hz

500_Hz

1000_Hz

2000_Hz

4000_Hz

8000_Hz

Measurement_1

T20

0.82

0.58

0.56

0.55

0.49

0.4

0.35

T30

1.82

0.83

0.59

0.54

0.49

0.41

0.35

Measurement_2

T20

0.93

0.57

0.62

0.54

0.48

0.42

0.3

T30

1.75

0.74

0.58

0.54

0.46

0.42

0.33

Measurement_3

T20

1.39

0.69

0.51

0.49

0.5

0.42

0.29

T30

1.96

0.66

0.56

0.51

0.5

0.42

0.32

Calculations

In_order_to_obtain_the_sound_power_level_certain_descriptors,_need_to_be_found._Those_are_found_using_Equations_1-8_as_below:_

The_Average_Sound_Pressure_Level_( Lp(S)̅

)_is_calculated_using_Equation_1

Lp(S)̅=10log10(i=1101N100.1Lpi(S)

________(dB)   Equation_1

Where,_

Lp(S)̅

_is_the_magnitude_of_average_sound_pressure_level_from_the_source,_in_the_hemispherical_measurement_surface__

Lpi(S)_is_the_measured_sound_pressure_level_at_the_ith_location_of_measurement_

Sample_Calculation_

To_demonstrate_the_application_of_Equation_1_a_sample_calculation_for_125_Hz_frequency_for_the_10_measurement_locations_from_Table_2_(when_only_the_electric_drill_is_ON)_is_shown_below:

Lp(S)̅=10log10(110102.3+101.97+101.81+101.88+102.03+102.17+101.76+101.68+101.99+101.64)

      Lp(S)̅

=_19.71_dB_(A)   

Doing_the_same_thing_as_above_for_all_frequencies_the_average_sound_pressure_level_for_all_the_measured_frequencies_are_tabulated_in_Table_5

Table_5:_Average_sound_pressure_level_with_only_the_electric_drill_ON_for_each_frequency

_________________________________Frequency_(Hz)

__________________________________ Lp(S)̅

____dB_(A) 

__________________________________________125

_________________________19.7086730829

__________________________________________250

__________________________43.17862669

__________________________________________500

__________________________53.11879872

_________________________________________1000

__________________________57.0408499

_________________________________________2000

__________________________60.65466761

_________________________________________4000

__________________________59.39134157

_________________________________________8000

__________________________57.65155109

Similarly,_

To_obtain_the_average_sound_pressure_level_when_only_the_reference_sound_source_is_ON_using_Equation_2_is_tabulated_in_Table_6,_a_sample_calculation_for_which_is_shown_below:

Lp(S)̅=10log10(110106.1+106.05+106.05+106.13+106+106.08+105.81+105.7+105.79+105.5)

______________________________________________________________________________Lp(S)̅

=_59.61_dB_(A) 

Table_6:_Average_sound_pressure_level_with_only_reference_sound_source_ON_for_each_frequency

_________________________________Frequency_(Hz)

__________________________________ Lp(S)̅

____dB_(A) 

__________________________________________125

_________________________59.60654059

__________________________________________250

__________________________66.92881852

__________________________________________500

__________________________73.30073148

_________________________________________1000

__________________________79.52526939

_________________________________________2000

__________________________79.90648805

_________________________________________4000

__________________________77.08960105

_________________________________________8000

_________________________70.68524825

As_the_sound_pressure_level_measurements_above_were_measured_in_a_semi-reverberant_setup_therefor_the_effects_due_to_reverberation_need_to_be_taken_into_account_by_calculating_the_corrected_sound_pressure_level.

The_corrected_sound_pressure_level_is_calculated_using_Equation_2

Lp̅=Lp(S)̅K1K2

 _(dB)   ______Equation_2 

Where,_ Lp̅

_is_mean_corrected_sound_pressure_level

_____________ K1

_is_the_correction_factor_for_background_noise_

  K2

is_the_environmental_correction_factor _

It_should_be_noted_here_that_since_the_difference_in_the_noise_level_produced_by_the_electric_drill_and_the_noise_level_due_to_background_factors_is_greater_than_the_magnitude_of_15_dB_for_each_octave_band_centre_frequency_therefore_the_correction_factor_for_background_noise,_ K1

,_can_be_ignored_during_calculations.___

The_environmental_correction_factor,_ K2

_can_be_calculated_using_Direct_method_and_Comparison_method._The_Direct_method_calculation_for_environmental_correction_factor_is_done_using_Equation_3

 

 

Direct_Method_Calculation

     K2=10log10(1+4SA

)_ (dB)  Equation_3

Where,_S_is_area_of_imaginary_hemisphere_and_is_=_6.28_m2

_____________A_is_equivalent_sound_absorption,_area_of_the_room_

Absorption_area_of_the_room_(A)

      A=0.16_VT60

Where,_V_is_volume_of_room

Since_dimension_of_the_room_is_3.6_x_9.2_x_6.3,_therefore_volume_of_the_room_=_208.656_m3_

And,_T60_is_reverberation_time_in_room_in_seconds._T60_is_calculated_by_using_averaged_T20_and_T30_values_measured_in_the_lab_and_using_Equation_4_and_a_sample_calculation_for_which_has_been_shown_below:

_____________________T60=4*T30T20+T20

  Equation_4

Table_7:_Sample_calculation_of_T60_value_for_125_Hz_from_3_measured_values

125_Hz

Measurement_1

T20

0.82_____________________seconds

T30

1.82___________________seconds

T60

4.82___________________seconds

Measurement_2

T20

0.93___________________seconds

T30

1.75___________________seconds

T60

4.21___________________seconds

Measurement_3

T20

1.39___________________seconds

T30

1.96___________________seconds

T60

3.67___________________seconds

Average_T60_value_for_125_Hz_from_3_measure_values

4.233333333____seconds

Now,_values_for_K2_can_be_found_using_Equation_3_and_4._Those_have_been_calculated_and_tabulated_in_Table_8_

Table_8:_Calculation_of_K2_values_using_T60_and_absorption_area_of_the_room_(A,_m2)

____________Frequency_(Hz)

__T60_(seconds)_Reverberation_Time

______________Area_(m2)_

___________K2_

_____________________________125

_________________4.23333333

_____________7.88621103

___6.217272777

_____________________________250

_________________1.13333333

_____________29.4573177

___2.67818989

_____________________________500

__________________0.61666667

_____________54.1377727

___1.655414793

____________________________1000

__________________0.54

_61.824

___1.480825163

____________________________2000

__________________0.46333333

_____________72.053871

___1.298921859

____________________________4000

__________________0.42666667

_____________78.2459994

___1.20915566

____________________________8000

__________________0.3933333

_____________84.8770241__

____1.1297915

Now,_with_K2_known,_the_average_sound_pressure_level_can_be_calculated_using_Equation_2_a_sample_calculation,_for_125_Hz,_is_shown_below._The_average_sound_pressure_level_for_each_of_the_octave_band_frequencies_is_calculated_similarly_and_is_tabulated_in_Table_8.

Lp̅=Lp(S)̅K1K2

Lp̅=19.70867308296.217272777______dB_(A)

Lp̅=13.49______dB_(A)

Table_9:_Average_corrected_sound_pressure_level_in_dB(A)_for_each_frequency_

__________Frequency_(Hz)

______________K2

____________ Lp(S)̅

____dB_(A)

_________ Lp̅

____dB_(A)

_____________________________125

___6.217272777

_________________________19.7086730829

13.49140031

_____________________________250

___2.67818989

__________________________43.17862669

40.5004368

_____________________________500

___1.655414793

__________________________53.11879872

51.46338393

____________________________1000

___1.480825163

__________________________57.0408499

55.56002474

____________________________2000

___1.298921859

__________________________60.65466761

59.35574575

____________________________4000

___1.20915566

__________________________59.39134157

58.18218591

____________________________8000

____1.1297915

__________________________57.65155109

56.52175959

The_Sound_Power_Level_can_now_be_calculated_using_Equation_4

Sound_Power_Level

     Lw=Lp̅+10log10SS0

   (dB)  Equation_5

Where,_ Lw

_is_sound_power_level

 S_is_surface_area_of_imaginary_hemisphere_(radius_equal_to_1_m)_which_is_enclosing_the_sound_source_&_

 is_equal_to_=_6.28_m2

 S0_=_1_m2_

Table_10:_Sound_Power_level_values_for_each_frequency_using_direct_method

__________Frequency_(Hz)

_______ Lp̅

____dB(A)

_____Lw

_dB(A)_–_Direct_Method

_____________________________125

13.49140031

21.47099675

_____________________________250

40.5004368

48.48003324

_____________________________500

51.46338393

59.44298037

____________________________1000

55.56002474

63.53962118

____________________________2000

59.35574575

67.33534219

____________________________4000

58.18218591

66.16178235

____________________________8000

56.52175959

64.50135603

Comparison_Method_Calculation:

K2_from_comparison_method_is_found_from_Equation_6_for_which_first_the_uncorrected_sound_power_level_ LwRefRoom_

and__ LwRefAnechoic

need_to_be_found._

     K2=_LwRefRoom_LwRefAnechoic

   Equation_6

Where,_ LwRefRoom

_=_sound_pressure_level_of_reference_sound_source_measured_in_the_measurement_room_

  LwRefAnechoic

_=_sound_pressure_level_of_reference_sound_source_measured_in_anechoic_room

The_ Lw(uncorrected)

/ LwRefRoom

_is_found_using_Equation_7_and_is_calculated_and_tabulated_in_Table_11

____________________________________Lw(uncorrected)=Lp̅+10log10SS0

 (dB)_    Equation_7

Table_11:_Uncorrected_sound_power_level_for_each_frequency_calculated_using_Equation_7

_______Frequency_(Hz)

__________________________ Lp(S)̅

____dB_(A) 

Lw(uncorrected)

_dB_(A) /_ LwRefRoom

_____________________________125

_________________________59.60654059

67.58613703

_____________________________250

__________________________66.92881852

74.90841496

_____________________________500

__________________________73.30073148

81.28032792

____________________________1000

__________________________79.52526939

87.50486583

____________________________2000

__________________________79.90648805

87.88608449

____________________________4000

__________________________77.08960105

85.06919749

____________________________8000

_________________________70.68524825

78.66484469

The_ LwRefAnechoic

/_Lw_(A-weighted)_is_obtained_by_A_weighting_the_sound_pressure_level_of_reference_sound_source_provided_in_the_data_sheet_

Table_12:_A-weighted_sound_power_level_for_each_frequency__

Frequency_(Hz)

Lw_(dB)

Correction_Factor_(dB)

Lw_(A-weighted)_dB_(A) / LwRefAnechoic

_____________________________125

80.5

-16.1

64.4

_____________________________250

82.4

-8.6

73.8

_____________________________500

82.6

-3.2

79.4

____________________________1000

87.1

0

87.1

____________________________2000

86.9

1.2

88.1

____________________________4000

84.1

1

85.1

____________________________8000

80.7

-1.1

79.6

Now_using_Equation_6_K2_can_be_found_using_comparison_method_and_is_tabulated_in_Table_13.

Table_13:_Environmental_correction_factor_calculated_using_Equation_6_

Frequency_(Hz)

Lw(uncorrected)

_dB_(A) /_ LwRefRoom

Lw_(A-weighted)_dB_(A) / LwRefAnechoic

K2

_____________________________125

67.58613703

64.4

3.18613703

_____________________________250

74.90841496

73.8

1.10841496

_____________________________500

81.28032792

79.4

1.88032792

____________________________1000

87.50486583

87.1

0.40486583

____________________________2000

87.88608449

88.1

-0.21391551

____________________________4000

85.06919749

85.1

-0.03080251

____________________________8000

78.66484469

79.6

-0.93515531

Now_using_the_average_sound_pressure_level_and_the_environmental_correction_factor_(K2)_obtained_from_comparison_method_for_all_octave_band_frequency_when_only_the_electric_drill_is_ON_can_be_found_using_Equation_8_and_is_tabulated_in_Table_14.

Lp̅=_Lp(S)̅

-__K2      Equation_8

Table_14:_Average_sound_pressure_level_using_comparison_method_calculated_using_Equation_8

Frequency_(Hz)

__________________________________ Lp(S)̅

____dB_(A)_(Electric_Drill) 

K2

Lp̅

____dB(A)

_____________________________125

_________________________19.7086730829

3.18613703

16.52253605

_____________________________250

__________________________43.17862669

1.10841496

42.07021173

_____________________________500

__________________________53.11879872

1.88032792

51.2384708

____________________________1000

__________________________57.0408499

0.40486583

56.63598407

____________________________2000

__________________________60.65466761

-0.21391551

60.86858312

____________________________4000

__________________________59.39134157

-0.03080251

59.42214408

____________________________8000

__________________________57.65155109

-0.93515531

58.5867044

Now,_the_sound_power_level_can_be_calculated_using_Equation_4_and_are_tabulated_in_Table_14

Table_15:_Sound_power_level_obtained_using_comparison_method

Frequency_(Hz)

Lp̅

____dB(A)

Lw

_dB(A)_–_Comparison_Method

7.979596437

_____________________________125

16.52253605

24.50213249

_____________________________250

42.07021173

50.04980817

_____________________________500

51.2384708

59.21806724

____________________________1000

56.63598407

64.61558051

____________________________2000

60.86858312

68.84817956

____________________________4000

59.42214408

67.40174052

____________________________8000

58.5867044

66.56630084

 

Comparison_between_direct_method_and_comparison_method_

Table_16_tabulates_and_Figure_1_illustrates_the_comparison_between_direct_and_comparison_method_which_are_given_on_the_A-weighted_sound_power_levels_for_each_octave_band.

Table_16:_Comparison_of_direct_and_comparison_method

Frequency_(Hz)

_____Lw

_dB(A)_–_Direct_Method

Lw

_dB(A)_–_Comparison_Method

Difference_

_____________________________125

21.47099675

24.50213249

3.03113574

_____________________________250

48.48003324

50.04980817

1.56977493

_____________________________500

59.44298037

59.21806724

0.22491313

____________________________1000

63.53962118

64.61558051

1.07595933

____________________________2000

67.33534219

68.84817956

1.51283737

____________________________4000

66.16178235

67.40174052

1.23995817

____________________________8000

64.50135603

66.56630084

2.06494481

Figure_1:_Sound_Power_level_(Lw,_dB_A)_comparison_of_direct_and_comparison_methods

Cite This Work

To export a reference to this article please select a referencing stye below:

Reference Copied to Clipboard.
Reference Copied to Clipboard.
Reference Copied to Clipboard.
Reference Copied to Clipboard.
Reference Copied to Clipboard.
Reference Copied to Clipboard.
Reference Copied to Clipboard.

Related Services

View all

DMCA / Removal Request

If you are the original writer of this essay and no longer wish to have your work published on UKEssays.com then please: