KB994: Decible measurements on SDH164D

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               Decibel measurements on SDH164D Digitrax Sound

 

 

Sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The commonly used "zero" reference sound pressure in air is 20 µPa RMS, which is usually considered the threshold of human hearing (at 1 kHz).

 

Examples of some Loudness rating in both Pa and dB          

Hearing damage (over long-term exposure, need not be continuous)                      0.356 Pa                   85 dB

Handheld electric mixer                                                                                                                                  65 dB

TV (set at home level) at 1 m                                                                                     2×10−2 Pa                  60 dB

Normal conversation at 1 m                                                                       2×10−3 – 2×10−2 Pa                  40 – 60 dB 

Very calm room                                                                                     2×10−4 – 6.32×10−4 Pa                 20 – 30 dB

Light leaf rustling, calm breathing                                                                          6.32×10−5 Pa                  10 dB

"Zero" reference sound pressure in air                                                                        2×10−5 Pa                   0dB     

 

Pa

2x10-5

2x10-4

2x10-3

6x10-2

8x10-2

0.010

0.013

0.016

0.018

0.025

0.032

0.041

0.051

0.062

0.078

0.102

dB

0

20

40

50

52

54

56

58

60

62

64

66

68

70

72

74

 

         60 dB@4’ is generally where we like our TV sound.  

       66 dB@4’ is twice the loudness (Could be we add a second speaker.)

                                                                                                                                                                               

A SOUND LEVEL METER can measure Pa as rms and display the reading in dB.

 

         Electronics Express Sound Level Meter                                      Part No. FO1SL650   

      Range: Lo 35 dB to 90 dB              Range: 32 to 8000 Hz   Has a Low Battery indicator (50 Hrs life)

      meter.jpg

It is easier just to put this SOUND LEVEL METER at a fixed distance of 4 Feet.   All the readings of a dB Volume  change can be done by changing the CV58 Master volume controlof the SDH164D.  The dBA @ 4’ is easy to measured from 40 to 85 dB.   This type of Volume measurement can be reported by anyone.

     

            Note 1:  Put the switch to:  A-frequency-weighting   

                

After you get a sound reading , then you can measure a Voltage at the Speaker.  With the measured dc resistance of the speaker, you can get a “rough” estimate of the power at a volume setting.  (A 10 Ohm resistor has a Browm, Black, Black band. A dc Ohm meter must read very close to 10.  On a 8 Ohm rated speaker, the dc  resistance of the speaker coil must be below 8 Ohm. (The speaker marking is an impedance value, generally measure at 1 KHz.) 

            Note 2:  A Diesel horn, Steam whistle or Run sound can be measrued, if it has a CONSTANT sound level.  When you press F2 on the throttle, the display on the SOUND LEVEL METER will quickly come up with a reading that is still jumping around on the last digit.  I round up or down and only report the first two digits.   

                                                                                                                                                                               

 The Mid. to Peak filter (shown below) is a diode charging a 470uf Capacitor with a 33 ohm current limiting resistor that pulse charges the Capacitor with positive peaks, and a 22K resistor load across the Capacitor, that discharges the Capacitor (67% in 1 sec. after the power is removed.)

M.toP = Vdc meter reading + 0.6 volts dc, for the diode loss                                                         

tester.jpg  

The Mid to Peak Filter

 

Example 1

A 200 ohm 1 Watt resistor on 12 Vdc draws 60 ma or 0.72W.   The MtoP = 11.4 Vdc +0.6= 12.0 Vdc Peak

  (12.0 x 12.0 / 200 Ohms = 0.72 Watts)

 

Example 2

The 200 ohm 1 Watt resistor on DCC track.   The MtoP= 14.9 Vdc + 0.6= 15.5 Vdc Peak

  (15.5 x 15.5 / 200 Ohms = 1.20 Watts and this is over the ratting, and got very hot quickly.)

 

Example 3

A 200 ohm 1 Watt resistor on 12 Vac (60 Hz) draws 60 ma or 0.72 Watts

The MtoP= 16.2 Vdc + 0.6= 16.8 Vdc Peak    Then MtoP  x 0.71 = Volts rms

16.8 x 0.71 =  12 Vrms     Then 12 x 12 / 200 = 0.72 Watts

 

Example 4   With one speaker

Sound file Tone880 is an 880 Hz sine wave in a SDH164D Digitrax Sound

          The MtoP= about 4.6 Vdc with a 32 Ohm resistor in place of a speaker.

          4.6 x 0.71 = 3.55 Vrms   Then 3.55 x 3.55 / 32 ohms = 0.35 Watts

 

 Example 5   With two speakers in parallel 

           4.6 x 0.71 = 3.55 Vrms   Then 3.55 x 3.55 / 16 ohms = 0.7 Watts

 

                                                                                                                                                                     

            Sound file:  Tone880Hz.wav is an 880 Hz sine wave and is used as a Bell with CV141 = 64 Max.

            first.jpg

            Sound file: 1983_horn.wav is a sustain wave in the Gerenic_38a download.  Horn CV142= 64 Max.

            middle.jpg

            Max. Horn and Max. 880Hz together.  (Window for time was reduced from 120 ms to 60 ms)

            last.jpg

 

  Bob Frey PE Wisconsin, Retired                                                                  Revised:  7 Aug 2012

  Website: http://bobfrey.auclair.com/               U.P. & Western R.R.                                                                       

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