Shure 488A, 488B User Guide

A.To modify the 488A for a normally open microphone switch, proceed as follows:

1. Remove the three #5-40 round head screws

from the back of the microphone case. (Caution: the microphone cartridge is spring loaded, and care must be taken to hold the two halves of the microphone case firmly together).

2.Separate the case front and back and remove switch button. See Figure C.

3.Remove the #5-40 round head switch mounting screw and lock washer, holding the switch assembly in the case back.

4.Disconnect or clip the white cable lead from the switch solder lug.

5.Strip the insulation from the white lead approximately 6 mm (VI in.) and solder to unused lug at the bottom end of the switch.

NOTE: In certain instances, if switch sequence is critical, it may be necessary to remove the effect of the shorted switch on the cartridge. This can be done by insulating the shorting contacts with a piece of "spaghetti" tubing or a piece of insulating tape.

6.Re-assemble the switch in the case back, using screw and lock washer removed previously.

7.Replace switch button in case back. Also be certain that the cartridge-shield retaining springs are in the proper position.

8.Place case back on case front and firmly press cases together. Fasten with the three #5-40 screws and washers previously removed.

The Model 4888 is supplied with the microphone circuit opened by the switch in the normal position of the switch. The microphone may be modified for use in applications requiring the microphone circuit to be shorted in the normal position of the switch.

B.To modify the 4888 for normally closed microphone switch, proceed as follows:

1.Remove the three #5-40 round head screws from the back of the microphone case. (Caution: the microphone cartridge is spring loaded and care must be taken to hold the two halves of the microphone case firmly together).

2.Separate the case front and back and remove switch button. See Figure C.

3.Remove the #5-40 round head switch mounting screw and lock washer, holding the switch assembly in the case back.

4.Disconnect or clip the white cable lead from the switch solder lug.

5.Strip the insulation from the white lead approximately 6 mm (1/4 in.) and solder this white lead to the switch blade next to the blade with the green lead connections. This is the blade that the switch button pushes against. The outside solder lug may be bent out of the way to aid soldering.

6.Re-assemble the switch in the case back using screw and lock washer removed previously.

7.Replace switch button in case back. Also be certain that the cartridge shield retaining springs are in the proper position.

8.Place case back on case frogt and firmly press cases together; fasten with the three #5-40 screws and washers previously removed.

ACOUSTIC CONSIDERATIONS

The important characteristics contributing to the total noise reduction of the 488 Series Microphones are shaped frequency response, directionality and distance and direction discrimination.

The acoustical elements are arranged to optimize performance in the frequency range of 200 to 4000 Hz. The results achieved are the elimination of all sounds outside of the desired frequency range and proper control of those sounds within the desired range.

The 488 microphones reject noise through their inherent directional properties and discriminate against unwanted sounds arriving from a distance in favor of sounds arriving from a near source.

The microphones operate on the pressure-gradient principle and have two sound entry ports, spaced a small distance apart.

In order to obtain the best noise cancelling performance with the Model 488 Series, the microphone must be used as "close talking." The lips should be as close to the microphone grille as comfort will permit, with a distance of approximately 6 mm to 25 mm ('/4 in. to 1 in.) providing the greatest discrimination between the voice sounds and background noise.

No special precautions beyond ordinary care are necessary in operation of the 488 Series microphones. They will operate very satisfactorily under all ordinary conditions of humidity, heat, and cold. Dropping the microphones or other severe mechanical shocks should be avoided.

SPECIFICATIONS

Frequency Response:

200 - 4000 HZ

Output Level (at 1000 Hz):

Model 488A

Open Circuit Voltage . .. ...- 17.0 dB* (.141V)

EIA Microphone Rating

Gm (Sensitivity) ........- 147.0 dB***

Model 4888

Open Circuit Voltage ... .. .- 37.0 dB* (.014V) Power Level (into 200 ohms) - 56.0 dB**

EIA Microphone Rating

Gm (Sensitivity) ........ -148.5 dB* *

*O dB = 1 volt per 100 microbars "'0 dB = 1 milliwatt with 10 microbars

***Reference, EIA Standard SE-105, August, 1949.

Microbar = one dyne per square centimeter. Measurementsat 9.5 mm (% in.) from sound source.

Recommended Load Impedance:

Model 488A . . . . . . . ... . . ...100,000 ohms or more Model 4888 .. . .. .... . . . . .. . ... .I50 to 250 ohms

Cables:

Attached, recoils to 0.3m (1 ft) extends to 1.5m (5 ft)

Case:

High impact gray "Armo-Dur"

Dimensions:

See Figure D

Net Weight:

340 grams (3/4 Ib)

Shipping Weight:

510 grams (1'YE Ib)