A portable battery-operated analyzer was chosen 

 because it can be used in a variety of situations. It can be 

 used in a semipermanent installation where data are taken 

 at periodic intervals. It can also be used for a system 

 requiring a completely portable system, such as would be 

 needed in a small boat where no ac power is available, and 

 will operate for about 30 hours on its battery. The battery 

 can be recharged using the built-in charger. The octave 

 band filters of the analyzer provide the means of doing an 

 on-the-spot frequency analysis of the noise. The "A" 

 weighting position is useful for pre -equalization when 

 recording noise with predominant low frequency content. 



Tape Recorders 



The kind of tape recorder to be used depends on 

 where and how the noise-measuring system is to be used. 

 When the measurements are being taken from a relatively 

 large ocean-going research ship a good quality ac -operated 

 tape recorder can be used. For use on a small boat, where 

 portability is essential and ac power is not available, a 

 battery-operated tape recorder is necessary. The tape 

 recorders described below are the ones used in this system 

 and serve as examples of the two types. 



The Ampex model 350-2P is a two-channel recorder 

 which uses 10-1/2-inch reels of tape. Two tape speeds of 

 3-3/4 and 7-1/2 ips are available. The frequency response 

 extends from about 15 Hz to 8000 Hz at the slower speed, 

 and from about 10 Hz to 15, 000 Hz at the higher speed. 



The Uher 4000 Report -S is a portable battery- 

 operated tape recorder which uses 5-inch reels of tape. 

 Four speeds are available, 15/16, 1-7/8, 3-3/4, 7-1/2 ips. 

 The measured frequency response for one of these tape 

 recorders is shown in figure 11. These curves may be 

 found to vary from the manufacturer's specifications 

 depending on the condition and maintenance of the recorders. 



The effective response can be extended below the 

 low-frequency limit by using a high playback-to-record 

 ratio for the analysis of the data. 



18 



