The frequency range of the playback is flexible and dependent on the capabilities of the sound card and PCMCIA card and the amplifiers and speakers. Playback can be performed during data acquisition by using the signal directly from the DAT recorder (7 Hz – 22 kHz) or during analysis by using the output from the computer PCMCIA card (.01 Hz – 100 kHz) or computer sound card (20 Hz to 20 kHz). Research that we have completed in the field has played back signals from 10 Hz to 28 kHz. Edited signals can be played back very quickly (10 s or less) from the computer, via either the sound card or the PCMCIA card.
The subwoofer is a V-I-B-E Pulse 3 Series PT120 12 inch, (300 mm), 440 watt, 4-ohm speaker housed in a V-I-B-E BA120 3-chamber bandpass box with dual venting. The speaker is capable of producing frequencies from 10 Hz to 300 Hz. At 10 Hz the maximum SPL is 115 (+/- .05 dB), 125 (+/- .05) at 90 Hz, at 1 meter. The maximum SPL for the PT120 is 133.2 dB at 63 Hz, at 1 meter. The subwoofer weighs 20.4 kg and measures 300.4 mm x 330 mm x 660.04 mm.
For frequencies above 90 Hz, a pair of Kenwood KFC6907 2-way 6 x 9 inch (150 mm x 230 mm) speakers are used. These speakers are light, 2.2 kg each, and have frequency specifications from 28 Hz to 28 kHz at 100 dB (+/-3) at 1 meter.
2. Amplifiers and equalizer/crossover
In order to power the speakers in the field, two types of Rockford Fosgate automobile audio amplifiers are used. To power the subwoofer, a Punch 2-channel amp is used. The G500a2 is bridged for 500 watts on one channel. The frequency range for this amplifier is from 10 Hz to 20 kHz (+/- .05dB). The dimensions for this amp are 60.6 mm high, 240.3 mm wide, and 330.7 mm long.
To power the other two speakers, a Punch G160a2 is used, creating 80 watts for two speakers, 20 Hz-20kHz. +/- .05dB. The dimensions for this amplifier are 60.6 mm high, 240.3 mm wide, and 260 mm long. The amplifiers are normally powered by a deep cell 12-volt battery that provides power for a period of several hours to overnight, depending on the number of amplifiers used and the decibel level of the playback. The dimensions of the deep cell are 300 mm x 250.4 mm x 250.4 mm and it weighs 19 kg.
An equalizer crossover, the Audio Control Three.1 was used to crossover frequencies of 90 Hz and less to the V-I-B-E subwoofer, and 91 Hz and above to the Kenwood speakers. The Three.1 is a 4-band stereographic equalizer with para-bass and a 4-channel 2-way 24 dB octave electronic crossover. It is capable of working with frequencies from 10 Hz to 100 kHz.
The amplifiers and crossover are housed in a wooden box. The total weight of the amplifier system is 6.8 kg.
The playback system was field tested by playing recorded signals produced by the Bruel and Kjaer 4226, which were then analyzed by Polynesia. The system was also tested at Dashboard Stereo by using readily available music industry tone CDs made for automobile audio speaker testing. The system was also tested using a portable Radio Shack digital level meter with a range of 50 dB to 128 dB (+/- 2dB) by the playback of animal sounds previously analyzed by the LabVIEW software, mentioned in section II.