Personal Computer, Printer, and Portable Equipment Noise in Classrooms

Robert D. Hellweg- bob.hellweg@hp.com
Egons K. Dunens,
Terrance Baird,
John N. Olsen
Hewlett-Packard Co., MRO1-2/K15, 200 Forest Street, Marlborough, MA 01752

Popular version of paper 1pNCc1
Presented Monday afternoon, October 17, 2005
ASA/NOISE-CON 2005 Meeting, Minneapolis, MN.

INTRODUCTION

In order to improve learning conditions in schools, the American National Standard on classroom acoustics - ANSI S12.60-2002 - presents background noise criteria that apply to noise from building services and utilities, such as cooling, heating, ventilating and dehumidifying equipment, and from external noise such as highways and airplanes. Not all noise sources present in modern classrooms are covered by the criteria in the standard. Noises from portable or permanent built-in equipment used during the course of instruction (such as computers, audiovisual equipment, and printers = Information Technology [IT] equipment) are excluded. The fact that computer products and projectors are excluded from ANSI S12.60 does not mean that these sources cannot interfere with instruction. In fact, these sources could raise noise levels in the classroom.

In order to prevent adverse noise effects, we recommend sound power levels for IT equipment in schools that will result in acceptable learning conditions. Our recommended levels are based on the ANSI S12.60 sound pressure level criteria, on our experience, and on new and existing European environmental criteria. Products meeting these criteria are available today.

We recommend the following approach for schools to ensure that computers and instructional material are acceptable acoustically in classroom environments:

• When purchasing new equipment, specify acoustic noise emissions from the product based on our recommendations,
• Purchase products that meet those noise criteria, and
• Install and operate them in a manner to minimize noise emissions.

SOUND POWER CRITERIA FOR IT EQUIPMENT

The "declared A-weighted sound power level" (which is a statistical maximum per ISO 9296) is the proper quantity to use for IT product specifications since it does not change with installation conditions and it is a quantity that the manufacturer of those products can control. The manufacturer cannot control how or where the product is installed which affects the resulting A-weighted sound pressure levels in the classroom; thus sound pressure level in the classroom is not the appropriate noise quantity to specify when purchasing IT equipment. Sound pressure varies strongly with the distance of the observer from the noise source, while sound power is a measure of the sound energy being emitted by the source, so it is independent of the observer's distance or position.

When IT products are installed in classrooms, the important acoustical parameter for the student or teacher in the classroom is the A-weighted sound pressure level at their ears. Why? People hear sound pressure, not sound power. So even though sound power is best for specifying acoustic performance of an IT device, sound pressure is the best metric for what is happening in the classroom at a defined place relative to the noise source. In ANSI S12.60, the maximum A-weighted one-hour steady background noise levels are 35 dBA for typical classrooms and 40 dBA for larger learning spaces and for ancillary spaces. (If transportation noise dominates then these limits are increased by 5 dBA.) We developed transfer functions relating product sound power levels to the sound pressure levels at students' ears based on the relationship between the location of the product to the student or teacher.

These transfer functions were used to recommend sound power levels for computers and business equipment based on the sound pressure criteria contained in ANSI S12.60. Our recommendations also considered new European "eco-label" and purchase specification criteria for PCs, notebook computers and printers.

For PCs we recommend declared A-weighted sound power levels of 4.5 bels for the idle mode and 4.8 bels for the operating mode. These values are the same as or more stringent than the recently adopted values from Swedish Statskontoret 26:6 and the Nordic Swan eco-label. The sound pressure levels at a student's ear in classrooms resulting from operation of PCs meeting our recommendations would be 34 dBA during PC idle operation and 37 dBA during hard disk drive (HDD) operation. These sound pressure level values are consistent with the ANSI S12.60 criteria for background noises and will result in acceptable acoustical conditions in classrooms.

For printers, we recommend declared A-weighted sound power levels based on the speed of the printer and its location in the room. For small printers located near a student's desk we recommend a sound power value of 6.0 bels during printing. Noisier and larger printers may be installed in classrooms provided they are at a further distance and shielded to reduce noise received by the students. Since classroom printers are not used for long durations, the resulting sound pressure levels in the classroom are compatible with the one-hour criteria of ANSI S12.60.

Typically a projector in a classroom will be located on a table near desks, and in larger classrooms the projector will be greater than 3 meters from the nearest desk. We recommend declared A-weighted sound power values of 5.0 and 5.5 B, respectively. The sound pressure levels from the projectors at students' ears will be comparable to PC noise values in the idle mode. Furthermore, when projectors are operating the PCs should be in the energy save mode, so the PC noise levels are almost inaudible and are not contributing to background noise levels in the classroom.

A summary of our recommendations for PCs, notebook PCs, printers, projectors and servers are included in Table 1. The recommendations include both declared A-weighted sound power level criteria and restrictions on location based on the product noise emissions.

PURCHASE SPECIFICATIONS FOR IT EQUIPMENT

In order for schools to purchase products that are acoustically acceptable for classrooms, schools must use unambiguous purchase specifications with appropriate declared A-weighted sound power level criteria. The noise criteria should be selected from those presented in Table 1 for the conditions in which the school will install the products.

A manufacturer's declaration certifying that the data is in conformance with ISO 9296 and ANSI S12.10 (or ISO 7779) is sufficient to satisfy purchase specifications, and thus there is no need to measure sound pressure levels in rooms to verify compliance. If conformance of the products to the specification is questioned, then the procedures in ISO 9296 for verification of the noise values should be used.

INSTALL AND USE IT EQUIPMENT PROPERLY

To obtain the benefits of products with appropriate sound power levels, the users should install computers and instructional equipment in classrooms in a manner to minimize noise levels. More powerful printers should be installed away from students and teachers and behind acoustical screens depending on the noise emission values. Projectors should be located away from students and on acoustical mattes to isolate structure-borne-noise from the table and to absorb sound. Mini-tower PCs should be installed on the floor next to the desk instead of on top of desks. Noisier servers should be in a second room or installed with special noise control features behind a screen.

Inkjet printers have several modes of operation, which differ substantially in sound power output, and classroom users would have the option of printing in normal mode, which is much quieter (3 - 8 dBA depending on the printer). We recommend that inkjet printers should be operated in classrooms in the default or "normal" mode, and should not be operated in the fastest and noisiest mode.

SUMMARY

Schools should purchase equipment which meets the A-weighted sound power level criteria that we have recommended. Schools should then install and operate the equipment in a manner to minimize noise emissions - considering both location of the products and students and special noise reduction techniques. We recommend modifying ANSI S12.60 to include an annex that would contain a table of recommended A-weighted sound power values given in Table 1; a recommended format for purchase specifications; and guidelines for installing, operating, and locating these products in classrooms.

Our recommendations will ensure that computers, printers, projectors and instructional material are acceptable acoustically in classroom environments. Products are available today that are acoustically suitable in classrooms.

Table 1: Recommended declared A-weighted sound power L_WAd values and installation restrictions for computer and instructional products located in classrooms