Advancing the Technology and Practice of Noise Control Engineering

Examining Measured Sound Power Variances in Telecommunications Equipment NC14_125

Eddie LamCisco Systems, Inc.

ISO 9296:1998 Standard

• Section 4.4.2 - Determination of the declared A-weighted sound power level LWAd for an Individual machine.

• Formula: LWAd ≥ 1/10 (LWA + K)• K is equal to 2.5 dB (rounded up to 3dB )• ISO9296 assumes 3dB manufacturing

variance.

Opportunity to test multiple units

• July 2013 able to obtain large system which incorporated a good number of fans to test

• Three sets of fans.

Equipment tested

CRS 8 Router

Product Details

• 8 slots for 8 front and 8 rear cards• System delivers data, voice and video

services via optical and copper interfaces• Height = 97.8 cm, Width = 44.5 cm, Depth = 93 cm Weight = 294.8 kg (650 lbs)

* Actual Production samples used.

Constitution of the samples

• Chassis and Cards held constant

• 3 sets of fan trays and power supplies which were the sources of acoustic noise generators

Fans (air moving devices)

Airflow

Fan Details

• Fan Trays have four 48Vdc, 500 cfm, 200 mm diameter fans. Upper and lower fan trays.

• Power supplies have two 12Vdc, 5 cfm, 40 mm diameter fans. Each power supply has two fans.

• Total of 6 fan trays (two per measurement) and 24 power supplies (eight per measurement).

Sample details• Test Sample 1 consists of:• CRS-8-LCC-B Chassis with fabric and line cards• Fan Tray x 2 : serial numbers TBM15287366 and TBM15287359• DC Power Supply x 8: serial numbers DTM15031VV, DTM150301XJ,

DTM15030213, DTM150301W3, DTM150301 XW, DTM150301YF, DTM15030242

• Test Sample 2 consists of:• CRS-8-LCC-B Chassis with fabric and line cards• Fan Tray x 2: serial numbers TBA11330057 and TBA1330059• DC Power Supply x 8: serial numbers DTM1445038V, DTM144503B1,

DTM134701ZJ, DTM1348007T, DTM1348007U, DTM1445038K, DTM1344009

• Test Sample 3 consists of:• CRS-8-LCC-B Chassis with fabric and line cards• Fan Tray x 2: serial numbers TBM16331371 and TBM16237362• DC Power Supply x 8: serial numbers DTM144401JN, DTM144503BB,

DTM14450391, DTM14450382, DTM14450395, DTM1445038X, DTM1445039L, DTM1445038Us

Measurement Set Up

9 microphone parallel pipe – ISO3477:2010

Data Sound Power Results    

1/3 Octave Band

Sound Power (dB)  

Center Freq[Hz](re 1E-12 watts)

Notes

100 61.0  125 61.1  160 64.7  200 63.7  250 63.8  315 64.0  400 72.1  500 68.0  630 65.7  800 69.1  1,000 68.2  1,250 66.5  1,600 64.5  2,000 63.0  2,500 60.9  3,150 61.2  4,000 58.3  5,000 55.8  6,300 54.7  8,000 52.7  10,000 49.0  Lin 78.3  LWA 76.2  

Sound Power Results    

1/3 Octave Band

Sound Power (dB)  

Center Freq[Hz]

(re 1E-12 watts)

Notes

100 61.0  125 61.4  160 64.8  200 63.5  250 63.5  315 71.6  400 67.4  500 64.8  630 67.7  800 67.7  1,000 68.7  1,250 65.1  1,600 63.6  2,000 63.6  2,500 61.3  3,150 61.1  4,000 58.4  5,000 56.2  6,300 55.3  8,000 53.0  10,000 49.6  Lin 78.1  LWA 75.8  

Sound Power Results    

1/3 Octave Band

Sound Power (dB)  

Center Freq[Hz]

(re 1E-12 watts)

Notes

100 61.4  125 61.0  160 64.1  200 63.4  250 63.0  315 62.9  400 73.3  500 68.2  630 65.2  800 69.1  1,000 68.1  1,250 66.7  1,600 64.9  2,000 62.9  2,500 60.9  3,150 61.4  4,000 58.2  5,000 55.8  6,300 54.7  8,000 52.4  10,000 49.0  Lin 78.5  LWA 76.4  

Discussion of Data Measured Sound Power DataSample 1 76.2 dBSample 2 75.8 dBSample 3 76.4 dB

Measured data shows only 0.5 dB variance between the three samples.

Discussion

• Advances in manufacturing technology allowing for better quality and consistency between units.

• Actual variances may be less that the 3 dB assumed in ISO 9296:1998.

ECMA 109 6th Edition

• New definition of Declared Noise Emission Values

• Section 3.11 of ECMA 109 6th Edition under Acoustical Definitions:

• Declared noise emission value – the value of the mean A-weighted sound power level LWAm in bels (rounded to the nearest 0.05 B)

ECMA 109 6th Edition continued

New Edition still allows for an “upper statistical limit of A-weighted sound power value LWAc in bels. Sections 3.12 and 3.18 of ECMA 109 6th Edition.

Subscript C – stands for upper statistical limit.

Acknowledgements

Jeff Schmidt

Marc Mantelli

Thank you!