J1-Attachment-Stereo-Headphones_final.pdf

J.1. ATTACHMENT – STEREO HEADPHONES SPECIFICATIONS

APPLICABLE DOCUMENTS/INFORMATION

1. HUMAN ENGINEERING

These headphones are intended for used by blind and print disabled patrons of the NLS talking-book program. To meet the unique needs of these patrons, the headphones shall comply with the following requirements:

A) The headphones shall not require any locking mechanisms, set screws, or other adjustments that may be difficult for patrons to operate.

B) No exposed metal surfaces used as electrical conductors shall be accessible during normal use.

C) The headphones shall be designed to minimize the risk of pinching, snagging or otherwise causing injury to patrons or damage to their clothing.

D) Structures incorporated in these headphones shall be provided with minimal protuberances.

E) All surfaces, edges and finishes shall be smooth and free from sharp edges, burrs, and other defects.

F) The headphones shall be rugged, durable, and capable of withstanding frequent use in home, hospital, library, and institutional environments.

2. MECHANICAL REQUIREMENTS

A) Weight

The stereo headphones shall have a maximum weight of 300 grams.

B) Headband

The stereo headphones shall have an adjustable headband with a minimum adjustment range of 1.5 inches on each side. The headband shall contain no exposed electrical conductors and shall be free of sharp edges, burrs, or other defects.

C) Ear Cups

One ear cup shall be permanently marked with the following text:

PROPERTY OF U.S. GOVERNMENT

LIBRARY OF CONGRESS

The marking shall be legible and durable for the expected service life of the headphones. The size, layout, and font of the text shall be submitted to NLS for approval prior to printing on the stereo headphones.

D) Ear Cushions

The stereo headphones shall be equipped with two supra-aural (on-ear) cushions securely attached to the headset. The ear cushions shall remain affixed during normal use and handling.

E) Cord

The stereo headphones shall have a single-sided insulated cord. The cord length, measured from the ear cup to the strain relief plug, shall not be less than 5 feet and not greater than 8 feet.

F) Plug and Strain Relief

The stereo headphones shall be equipped with a standard 3.5-millimeter right-angle stereo plug. The plug cover and strain relief shall be injection molded. A longitudinal tension of 4 kilograms shall be applied to the plug. After tension is released, the assembly shall be examined to ensure no slippage has occurred between the cord and the plug, verify sound integrity of both earpieces.

G) Random Drop Test

The complete headset shall be dropped from a height of 3 feet onto a concrete floor. The floor may be covered with a single layer of asphalt tile. The headset shall be dropped once in each of three different planes, for a total of three drops.

Following the drop test, the frequency response of the headphones shall be measured. The measured values shall not vary by more than 3 dB from the pre-test measurements. Any physical damage affecting the functionality, performance, or integrity of the headset shall constitute a test failure.

3. ELECTRICAL REQUIREMENTS

A) Sensitivity

The stereo headphones shall be capable of producing 100 dB sound pressure level (SPL) with a maximum of 500 millivolts rms input at 1.0 kHz.

B) Impedance

The stereo headphones shall have an impedance of 32 +/- 3 ohms.

C) Harmonic Distortion and Noise

The stereo headphones shall have an A weighted total harmonic distortion plus noise (THD+N) not exceeding 3% at 1 kHz +/- 100 Hz when producing an output of 100 dB SPL.

D) Frequency Response

When normalized to 0 dB at 1.0 kHz and measured with an weighted pseudo-random band-pass source, the frequency response of each earpiece of the stereo headphones shall not vary more than +/- 10 dB from 100 Hz to 8 kHz.

Note: Final acceptance limits for the measured frequency response shall be agreed upon by the Library and the contractor prior to start of production. These limits shall be based on the results of subjective listening evaluations and performance testing.

4. METHODS OF INSPECTION

A) Test Environment

All measurements and tests shall be performed at an ambient temperature of 70 degrees F +/- 5 degrees F and a relative humidity of 35 to 65 percent, unless otherwise specified herein.

B) General Examinations

Test units shall be visually and aurally examined for proper operation and conformance to the applicable requirements of sections C.4.3, C.6.1 and C.6.2.

C) Sensitivity

Using an artificial ear (B&K 4152) with a 1” condenser microphone (B&K 4144) fitted with a flat plate adapter (NLS drawing #LC606-2) (this is done by removing the acoustic coupler), measuring amplifier (B&K 2610 or equivalent) and Audio Precision System One or equivalent. Center one earpiece on the flat plate adapter.

Drive the headphones with 1 kHz +/- 100 Hz sine wave from System One generator. Measure SPL with measuring amplifier while adjusting voltage across the headphone channel to reach 100 dB SPL. The input voltage should not exceed 500 mVrms per channel. Repeat test for the other earpiece

Note:

1. Set Audio Precision signal source impedance to 50 Ohms

2. To reduce acoustical leakage a static load shall be placed on the earpiece without loading its acoustic impedance.

D) Distortion

Using an artificial ear (B&K 4152) with a 1” condenser microphone (B&K 4144) fitted with a flat plate adapter (NLS drawing #LC606-2), measuring amplifier (B&K 2610 or equivalent) and Audio Precision System One or equivalent.

Center one earpiece on the flat plate adapter. Drive the headphones with 1 kHz +/- 100 Hz sine wave from System One generator. Measure SPL with measuring amplifier while adjusting the input voltage across the headphone channel to reach 100 dB SPL. Measure the A weighted total harmonic distortion of the measuring amplifier output. THD+N should not exceed 10% between 100 Hz and 8 kHz.

Repeat test for the other earpiece

E) Frequency Response

Using an artificial ear (B&K 4152) with a 1” condenser microphone (B&K 4144) fitted with a flat plate adapter (NLS drawing #LC606-2), measuring amplifier (B&K 2610 or equivalent) and Audio Precision System One or equivalent.

Calibrate the system to read dB SPL as described above. Center one earpiece on the flat plate adapter. Drive the headphones with pseudo random bandpass noise from System One generator. Normalize the 1 kHz output to 0 dB SPL. Record the output of the measuring amplifier with System One. Output shall be 100 dB +/- 10 dB for 100 Hz and 8 kHz. Repeat test for the other earpiece

F) Sound Quality The stereo headphones shall be subjectively examined. Naturalness of voice reproduction shall be a basis for judging the acceptability of the headphones.

G) Maintenance and Technical Data

The contractor shall provide a copy of a technical data sheet. This document shall contain:

1. The circuit diagram of the headphones

2. A list of parts

3. Assembly drawings

4. Technical specifications

5. APPLICABLE DOCUMENTS

1. American National Standard

Sampling Procedures and Tables for Inspection by Attributes:

ANSI/ASQC Z1.4-2003

2. U.L. 94 HB Flammability requirement

Copies of U.L. Standards may be obtained from:

Underwriters Laboratories 333 Pfingsten Road Northbrook, IL 60062

6. Sample Shipping Carton

7. Sample Over Pack Carton

8. Flat Plate Coupler

9. Unit Carton & Text

10. Overpack Carton & Text

11. Sample Carton

J.1. ATTACHMENT – STEREO HEADPHONES SPECIFICATIONS APPLICABLE DOCUMENTS/INFORMATION