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A new concept in underwater high fidelity low frequency sound generation

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This article reports on a new type of system for high fidelity underwater sound generation (patent pending PT105474). The system includes an underwater sound actuator and the corresponding electronic driver. The sound is generated by a rigid plate that is actuated (both for positioning/dumping and excitation) using purely electromagnetic forces, thus, avoiding the use of any elastic membrane. Since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure. Characterization of the frequency response, the radiation characteristics, and the dynamic range of this new device for underwater sound generation is presented.
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REVIEW OF SCIENTIFIC INSTRUMENTS 83, 055007 (2012)
A new concept in underwater high fidelity low frequency sound generation
Paulo J. Fonseca and J. Maia Alvesa)
Faculdade de Ciências Universidade de Lisboa, Centro de Biologia Ambiental and SESUL,
Lisboa 1749-016, Portugal
(Received 19 November 2011; accepted 28 April 2012; published online 18 May 2012)
This article reports on a new type of system for high fidelity underwater sound generation (patent
pending PT105474). The system includes an underwater sound actuator and the corresponding elec-
tronic driver. The sound is generated by a rigid plate that is actuated (both for positioning/dumping
and excitation) using purely electromagnetic forces, thus, avoiding the use of any elastic membrane.
Since there is no compressible air inside the device, which is flooded by water, the operation of
this device is independent from depth, broadening its applications to any water pressure. Charac-
terization of the frequency response, the radiation characteristics, and the dynamic range of this
new device for underwater sound generation is presented. © 2012 American Institute of Physics.
[http://dx.doi.org/10.1063/1.4717680]
I. INTRODUCTION
Many fish communicate with acoustic signals mostly
in mating and agonistic contexts.15These signals are often
pulsed low frequency sounds with fast transients.6,7Playback
experiments, a widespread tool to study the function of an-
imals’ acoustic signals,8have been hampered in fish due to
limitations of commercially available underwater loudspeak-
ers, which do not reproduce fish sounds appropriately.
Most devices for underwater sound playback use either
(i) a moving coil associated to a diaphragm, as in traditional
loudspeakers; (ii) a piezoelectric effect, which is appropriate
to produce medium to high frequency sounds above 1 kHz,9
or (iii) a system that incorporates both a diaphragm and an
axial deformation mechanism.10
Commercial acoustic devices allowing low frequency
sound playbacks in water are relatively scarce. Underwa-
ter loudspeakers developed for swimming pools, such as the
UW30 from Lubell Labs (one of the most used in under-
water playback experiments) or the Clark Synthesis AQ339
Aquasonic Underwater Speaker, although suitable to play-
back music, do not represent appropriately low frequency
sounds with fast transients, such as the sounds of many fish
species. Although these devices can generate low frequency
sounds, usually above a few tens of Hertz, the equilibrium
position of the sound emitter is dependent on elastic compo-
nents, and so prone to resonation at certain frequencies as can
be clearly seen in Figure 1.
In addition, some of these devices are sealed and incor-
porate air, creating a further constraint caused by increased
pressures due to water depth. This is the main reason why
the UW30, for instance, cannot be used at depths in excess of
3 m. Moreover, the power output of these commercial loud-
speakers is often affected by depth, a further complication for
experiments requiring sound playback in places were the wa-
ter level changes significantly, as in the cases of sea shores and
estuaries. To the best of our knowledge even the higher quality
underwater loudspeakers available today have poor responses
a)jma@fc.ul.pt.
and/or are non-linear at low frequencies (below 100–200 Hz)
and cannot be used at depths beyond 20 m.
Several devices falling in categories (ii) and (iii) were
created to produce underwater sounds, some of them de-
scribed as appropriate to overcome some of the above men-
tioned problems. These include moving coil devices,11,12 or
hydraulic devices13 that use a piston and plate to drive oil that
is circumscribed by an elastic membrane responsible for ra-
diating the sound into water. Since all these devices not only
incorporate several elastic components but also keep some air
inside, it is expected that they are prone to resonances and
may be affected by water pressure, i.e., depth. Other devices
incorporating speakers kept in watertight containers14 are ex-
pected to be not only limited in water depth but also its fre-
quency response is probably affected by the air volume and
by the container itself. Thus, there was a need to develop a
device that could overcome these limitations.
II. DEVICE DESCRIPTION AND CHARACTERIZATION
An expanded schematic representation of a cross section
of the new device for underwater sound generation is pre-
sented in Figure 2.
The sound is generated by a rigid plate attached to a
cylinder that contains a permanent magnet inside. The vibra-
tion of both the cylinder and the plate is accomplished by ap-
plying a variable electrical current to a pair of coils surround-
ing the cylinder, wound in opposite directions (one clockwise
and the other anti-clockwise). A second pair of such coils,
both wound in the same direction, is used for setting the equi-
librium position of the cylinder. This is accomplished simply
because the magnetic field created by each coil will force the
permanent magnet located inside the cylinder in opposite di-
rections, the equilibrium position being the point along the
axis of vibration where these forces balance out to zero. The
intensity of the direct current applied to this pair of coils is
used to control the dumping effect on the cylinder and plate.
It should be noted that this prototype was developed to meet
the needs for playback experiments with small fishes. For this
0034-6748/2012/83(5)/055007/4/$30.00 © 2012 American Institute of Physics83, 055007-1
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055007-2 P. J. Fonseca and J. M. Alves Rev. Sci. Instrum. 83, 055007 (2012)
Acoustic signal produced by the device
time
100 ms
Acoustic signal produced by the fish
time
100 ms
Acoustic signal produced by UW30
time
100 ms
FIG. 1. Comparison of a fish signal with the playbacks of the same sound obtained using both the new device and a commercial underwater loudspeaker UW30.
reason the dimensions of the device were kept considerably
small. However larger devices should, in principle, perform
even better, because larger discs will be more efficient in low
frequency sound generation.
This unique combination of both electromagnetic exci-
tation and positioning/dumping makes it possible to exclude
any elastic component(s), such as membrane(s), from the ac-
tuator, and thus avoids unwanted resonant modes that char-
acterize all the existing equipment for underwater sound gen-
eration, as can be clearly seen in Figure 1. It should also be
noted that, since there is no compressible air inside the de-
vice, which is completely flooded by water, its operation is
independent from depth, broadening its applications to any
water pressure/depth.
The electronic driver developed to operate the device is
mainly composed by (i) a voltage controlled direct current
source to be applied to the positioning/dumping pair of coils;
and (ii) a transconductance amplifier whose output current is
applied to the excitation pair of coils. In normal use the po-
sitioning/dumping current is of the order of a few tenths of
ampere, and the peek excitation current is of the order of a
few ampere.
A suitable characterization of a sound playback device
(i.e., the actuator and its control electronics) includes its
frequency response, the radiation characteristics, and the
dynamic range. In order to measure these parameters an FFT
based transfer function was computed as the ratio of the cross
spectrum between the input (i.e., the electrical signal input
f
rigid plate
excitation coils
permanent magnet
positioning / damping coils
FIG. 2. Schematic diagram of a cross section of the device for underwater sound generation.
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055007-3 P. J. Fonseca and J. M. Alves Rev. Sci. Instrum. 83, 055007 (2012)
-30
-20
-10
0
10
20
0 500 1000 1500 2000 2500 3000
Frequency (Hz)
Magnitude (dB)
-180
-90
0
90
180
0 500 1000 1500 2000 2500 3000
Frequency (Hz)
Phase angle (degree)
1.7 cm
3 cm
6 cm
12 cm
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500 2000 2500 3000
Frequency (Hz)
Coherence
Magnitude (dB)
Phase angle (deg)
Coherence
Frequency (Hz)
-180
-90
0
90
180
0 500 1000 1500 2000 2500 3000
Frequency (Hz)
Phase angle (degree)
Centered
disc edge
at disc plane
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500 2000 2500 3000
Frequency (Hz)
Coherence
Magnitude (dB)
Phase angle (deg)
Coherence
Frequency (Hz)
(b)(a)
-30
-20
-10
0
10
20
30
FIG. 3. Device characterization: (a) Frequency response as a function of position; (b) frequency response as a function of distance.
to the playback device driver) and the system’s output (i.e.,
the sound produced by the device), to the power spectrum of
the input. For this purpose, the sound produced by the device
was recorded by a reference hydrophone Bruel&Kjaer 8103
(B&K 8103, frequency response 0.1 Hz–180 kHz, sensitivity
211 dB re 1 V/μPa) connected to the conditioning electron-
ics of a Bruel and Kjaer Sound Level Meter 2238 Mediator
(B&K 2238 Mediator). The input signal was a sine sweep
(0–3000 Hz, 20 ms) allowing the evaluation of the frequency
response within this range. The output of the transfer function
gives both the gain and the phase responses as a function
of frequency, flat functions meaning that the response of
the system (output) is similar to the input signal in gain and
phase across frequency. A zero value of the transfer function
gain (dB) and phase (degree) means no amplitude difference
and no phase shift of the output relative to input, respectively.
Moreover, a coherence function, allowing an estimation of
the portion of the output power spectrum that is related to the
input spectrum was simultaneously computed. The coherence
function is normalized and a value of 1.0 means perfect coher-
ence, which in turn is a powerful statistical indication that the
transfer function result is valid, since the output is correlated
with the input. A value close to zero indicates that the result
of the transfer function at that frequency is not related to the
input and is therefore meaningless. Both functions were sub-
jected to a 25 stimulus presentations averaging. All stimuli
were delivered and recorded simultaneously with a through-
put rate of 100 kHz (National Instruments NI USB-6251
Multifunction I/O board). The recording (output) was delayed
(precision of ±0.005 ms at 100 kHz) relative to the stimulus
(input) to account both for the electronics and the propagation
time interval from the moment the stimulus was generated
to the instant when it was recorded, thus, preventing phase
change artifacts on the measurement. All functions were
computed using a 2048 points FFT based program made in
LabVIEW by the authors. Additionally, the responses at
discrete frequencies were measured by comparing the am-
plitudes of pure tone stimuli recorded both at the input of
the instrument chain (electric signal) and at the output of
the sound emitting device (sound recorded in water with the
hydrophone B&K 8103 connected to B&K 2238 Mediator).
This procedure confirmed the frequency response at very low
frequencies.
As observed in Figure 3(a), the frequency response mea-
sured from the sound recorded in front of the playback device
is not only very smooth and relatively flat (10 Hz–3 KHz,
±3 dB) but its characteristic does not change significantly
with distance, both in magnitude (gain) and phase angles
(Figure 3(b)), that are astonishingly even and close to zero.
The quality of the measurement is attested by the values
of the coherence function that remain close to unity within
the frequency range considered. Notice also the good agree-
ment with single frequency calibration data of two differ-
ent devices, represented by the circles and the triangles in
Figure 3(a).
Since the actuator disc is expected to act as a dipole, mod-
ifications of the sound field are predictable when measure-
ments are obtained progressively away from the axis. Addi-
tionally, the body of the device may interfere itself with the
sound waves. In fact, when recordings are obtained towards
the plane of the disc (Figure 3(a), blue line), the frequency re-
sponse changes not only in magnitude, but especially in phase
angles due to interactions of opposite phase waves generated
in both sides of the disc. The field is however very stable in
the region in front of the disc both in its gain and phase com-
ponents. Again here coherence close to 1.0 attests for the sig-
nificance of the measurements. Therefore, the device presents
a radiation diagram with an even sound field in the volume
in front of the disc, becoming considerably disturbed when
approaching the plane of the actuator’s disc.
In order to test the behavior of the device when reproduc-
ing fast transient sounds, a need for many researchers willing
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055007-4 P. J. Fonseca and J. M. Alves Rev. Sci. Instrum. 83, 055007 (2012)
-90
-80
-70
-60
-50
-40
-30
-20
0 500 1000 1500 2000 2500
Frequency (Hz)
Amplitude (dB rel)
FishTalk playback
Fish Sound (electrical signal)
20 25 30 35 40 45 50
10 ms
(a)
-90
-80
-70
-60
-50
-40
-30
-20
0 500 1000 1500 2000 2500
Frequency (Hz)
Amplitude (dB rel)
noise
10 ms
(b)
FIG. 4. Device characterization: (a) Comparison of spectra of painted goby
sound (Pomasthoschistus pictus) and its playback with the device (both
recorded with B&K 8103); (b) representation of power spectra of a fish
sound (painted goby, Pomasthoschistus pictus) generated using the device,
and attenuated in 6 dB steps (recorded using a B&K 8103 hydrophone).
These results show that the dynamic range is greater than 36 dB. Notice that
the playback amplitude was not increased further because, at the represented
maximum, it was already above the amplitude generated by the fish.
to make playback experiments with fish, we used a pulse of
an agonistic sound of the fish painted goby (Pomasthoschistus
pictus). The device reproduced with very high fidelity the
fish sound wave as shown in Figure 4(a). The superimposed
oscillograms of the fish sound and the device playback (inset
in Figure 4(a)) are very similar, as are the power spectra
computed from a sequence of these signals.
Similar measurements were made to assess the dynamic
range of the device. As depicted in Figure 4(b) the power
spectra of recordings of the same sound reproduced with am-
plitudes decreasing by 6 dB steps shows a dynamic range in
excess of 36 dB and in the whole range down to the noise
level. In fact, the power spectra closely follow the sound am-
plitude decreases by the same 6 dB steps (cf. Figure 4(b)).
Notice that in these measurements the playback amplitude
was not increased further because, at the represented maxi-
mum, it was already largely above the amplitude of the sound
generated by the fish. It should be emphasized that a high dy-
namic range is desirable since it guarantees a proper represen-
tation of elements with different amplitudes within a sound
sequence.
III. CONCLUSIONS
A new concept in underwater sound generation was de-
scribed. The device presented does not keep any air inside,
and thus its operation is water depth independent. The equi-
librium positioning, excitation and dumping of the rigid plate
used to generate the sound is purely magnetically actuated.
Consequently, the resonances are almost absent, allowing low
frequency sounds to be reproduced with very high accuracy
from about 10 Hz up to 3 kHz, even when they present fast
transients as is typical of many fish communication sounds.
We believe that this device overcomes most of the limita-
tions of available emitters of underwater sound, and for this
reason may become an important tool in studies of fish be-
havior or other applications in deep water where low fre-
quency signal playback, namely of complex sounds, may be
requested.
ACKNOWLEDGMENTS
This research was funded by the Science and Technology
Foundation, Portugal (Project PDCT/MAR/68868/2006) and
pluriannual program UI&D 329.
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Anthropogenic noise is globally recognized as a stressor for animals. However, despite evidence of detrimental effects of noise exposure on fish, knowledge about chronic effects on critical early life stages is still scarce. Using a split-brood design to exclude the genetic effect, African cichlids (Maylandia zebra) from the same brood were exposed to boat noises (~120 dB) and to control condition (~100 dB) for 12 weeks, starting when mouth-brooding females released their young. Treatment fish were exposed to motorboat noises from 9 a.m. to 6 p.m. to mimic a typical daily boating activity. Larvae total length and foraging activity were measured in weeks 1 and 12. The study did not find a significant effect of chronic boat noise exposure on these variables. However, whether noise has any impact within the studied period or after week 12 is not clear. Future work will focus on analyzing the data weekly over the 12 weeks exposure period to further substantiate the current results. Addressing the effect of anthropogenic noise on early life stages may have implications for our understanding of the effect of this pervasive stressor on aquatic organisms.
... Furthermore, they are often limited in their use to shallow water depths. Due to these limitations, Fonseca and Alves (2012) developed a new reliable underwater sound source capable of generating sound with high accuracy in the frequency range between 10 and 3000 Hz. The system includes an underwater sound generator and the corresponding electronic driver. ...
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The record of seismic, hydroacoustic, and infrasonic waves is essential to detect, identify, and localize sources of both natural and anthropogenic origin. To guarantee traceability and inter-station comparability, as well as an estimation of the measurement uncertainties leading to a better monitoring of natural disasters and environmental aspects, suitable measurement standards and reliable calibration procedures of sensors, especially in the low-frequency range down to 0.01 Hz, are required. Most of all with regard to the design goal of the Comprehensive Nuclear-Test-Ban Treaty Organisation’s International Monitoring System, which requires the stations to be operational nearly 100% of the time, the on-site calibration during operation is of special importance. The purpose of this paper is to identify suitable excitation sources and elaborate necessary requirements for on-site calibrations. We give an extensive literature review of a large variety of anthropogenic and natural sources of seismic, hydroacoustic, and infrasonic waves, describe their most prominent features regarding signal and spectral characteristics, explicitly highlight some source examples, and evaluate the reviewed sources with respect to requirements for on-site calibrations such as frequency bandwidth, signal properties as well as the applicability in terms of cost–benefit. According to our assessment, earthquakes stand out across all three waveform technologies as a good natural excitation signal meeting the majority of the requirements. Furthermore, microseisms and microbaroms allow a calibration at very low frequencies. We also find that in each waveform technique man-made controlled sources such as drop weights or air guns are in good agreement with the required properties, although limitations may arise regarding the practicability. Using these sources, procedures will be established allowing calibration without record interrupting, thereby improving data quality and the identification of treaty-related events.
... These results appear to be consistent with interactions between individuals separated by larger distances. Notice however that the loudspeakers used by Jordão et al. (2012) did not reproduce well frequencies below 100 Hz (Fonseca and Alves, 2012), thus simulating a stronger attenuation of the fundamental frequency of boatwhistles with distance (Alves et al., 2016;Amorim and Vasconcelos, 2008;Vasconcelos et al., 2010). Further experiments with playbacks at different amplitudes and simulating different levels of frequency attenuation should be made to further investigate the males' interaction behaviour. ...
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Males of several fish species aggregate and vocalize together, increasing the detection range of the sounds and their chances of mating. In the Lusitanian toadfish (Halobatrachus didactylus), breeding males build nests under rocks in close proximity and produce hundreds of boatwhistles (BW) an hour to attract females to lay their demersal eggs on their nest. Chorusing behaviour includes fine-scale interactions between individuals, a behavioural dynamic worth investigating in this highly vocal fish. Here we present a study to further investigate this species' vocal temporal patterns on a fine (individual rhythms and male-male interactions) and large (chorus daily patterns) scales. Several datasets recorded in the Tagus estuary were labelled with the support of an automatic recognition system based on hidden Markov models. Fine-scale vocal temporal patterns exhibit high variability between and within individuals, varying from an almost isochronous to an apparent aperiodic pattern. When in a chorus, males exhibited alternation or synchrony calling patterns, possibly depending on motivation and social context (mating or male-male competition). When engaged in sustained calling, males usually alternated vocalizations with their close neighbours thus avoiding superposition of calls. Synchrony was observed mostly in fish with lower mean calling rate. Interaction patterns were less obvious in more distanced males. Daily choruses showed periods with several active calling males and periods of low activity with no significant diel patterns in shallower intertidal waters. Here, chorusing activity was mainly affected by tide level. In contrast, at a deeper location, tide level did not significantly influence calling and there was a higher calling rate at night. These data show that photoperiod and tide levels can influence broad patterns of Lusitanian toadfish calling activity as in other shallow-water fishes, but fine temporal patterns in acoustic interactions among nesting males is more complex than previously known for fishes.
... The playback chain consisted of the custom-made underwater speaker and a driver (Fonseca and Maia Alves, 2012), which are able to reproduce low-frequency pulsed fish sounds with great accuracy (Fig. 1B). Sound stimuli were fed to the driver through a D/A converter (Edirol UA-25, Roland, Japan) controlled by Adobe Audition 3.0 (Adobe Systems Inc., Mountain View, CA, USA) on a laptop. ...
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Information transfer between individuals typically depends on multiple sensory channels. Yet, how multi-sensory inputs shape adaptive behavioural decisions remains largely unexplored. We tested the relative importance of audio and visual sensory modalities in opponent size assessment in the vocal cichlid fish, Metriaclima zebra, by playing back mismatched agonistic sounds mimicking larger or smaller opponents during fights of size-matched males. Trials consisted in three 5-min periods: PRE (visual), PBK (acoustic+visual) and POST (visual). During PBK agonistic sounds of smaller (high frequency or low amplitude) or larger (low frequency or high amplitude) males were played back interactively. As a control, we used white noise and silence. We show that sound frequency but not amplitude affects aggression, indicating that spectral cues reliably signal fighting ability. In addition, males reacted to the contrasting audio-visual information by giving prevalence to the sensory channel signalling a larger opponent. Our results suggest that fish can compare the relevance of information provided by different sensory inputs to make behavioural decisions during fights, which ultimately contributes to their individual fitness. These findings have implications for our understanding of the role of multi-sensory inputs in shaping behavioural output during conflicts in vertebrates.
... In addition, commercially available speakers are often too large to be used in smaller set-ups and complicated to deploy in the field. Fonseca & Alves (2012) have developed a relatively small device that can not only produce low-frequency sounds, but also reliably reproduce fish sounds for playback experiments independent of water depth. Regrettably, this device is not yet commercially available and difficult to build without specialized technical knowledge and equipment (P. ...
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Studying the effect of anthropogenic noise on animal behaviour and physiology is a field of growing scientific and management interest. Anthropogenic noise is internationally seen as major environmental concern, but knowledge of the response of animals to noise and its ecological and evolutionary consequences is disparate. Even though fish and invertebrates form the majority of aquatic taxa, the effects of noise on these taxa are largely understudied. Especially the consequences of noise for short‐range communication and behavioural interactions are yet unknown. While experimental studies on this subject are thus greatly needed, the expense of the equipment can be a main factor limiting data generation. Speakers that produce low‐frequency sounds under water are currently either too large or too expensive to allow for sufficient replication in many research set‐ups. Here, we describe a device that can produce a low‐frequency sound, which can be used as an experimental source of noise both in aquaria and in the field. The device is completely self‐contained and costs around 10 euros per ‘noise egg’. The sound created consists of frequency bands (harmonics), which has the advantage that broadband and pulsed sounds, such as sounds produced by vocal fish, are easily detected in a spectrogram. Because the sound from the egg attenuates quickly, it can be used in aquaria and in the field to target certain study species or individuals without affecting a large part of the surrounding area. We have developed the device to study the effects of noise on communication and behaviour in small aquatic animals; however, it could be used for other purposes, such as testing the propagation of certain frequencies in shallow‐water habitats. We hope the described method will facilitate the generation of experimental data on the effect of noise on behaviour and communication in aquatic animals in a wide variety of study systems and study areas.
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The streaked gurnard Trigloporus lastoviza produced only one sound type, a growl, lasting up to 3 s and consisting of repeated groups of typically one to three pulses. The foraging fish followed two different strategies. In the first, the fish circled the feeding area, grasped a food item and fled, sometimes displaying aggressively to competitors. With this foraging strategy, fish usually made sounds as they circled, grasped and fled. Fish that growled while circling were more likely to grasp a food item subsequently than were silent fish. The second feeding strategy occurred when a fish had already ingested food or failed to get any. In this case, typically fish searched for food on the substratum or approached and touched other individuals that were feeding, sometimes grabbing food that was spat out during food handling by the other fish. Although payback experiments would be needed to draw firm conclusions on the communicative function of growling during competitive feeding in the streaked gurnard, the results suggest that sound production confers advantages Co individuals competing for limited food resources. (C) 2000 The Fisheries Society of the British Isles.
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Signal attributes should show different degrees of variability depending on the information to be conveyed. Species identity is usually associated with stereotyped features of a signal, whereas other types of information such as individual quality and motivation are associated with signal plasticity. Lusitanian toadfish males form aggregations during the breeding season and emit a tonal advertisement call (the boatwhistle) to attract mates to their nests. We test the hypothesis that the boatwhistle can convey information both on individual identity and motivation by checking how signal parameters vary with time. We study how the physical (tide level) and social (calling alone or in a chorus) environments and male calling rate affect this advertisement signal and how all these external and internal factors (environment, social and male motivation) blend to modulate the Lusitanian toadfish’s advertisement call. Boatwhistles of each male were very stereotyped in short periods of time (minutes), but intra-male signal variability greatly increased in a longer time scale (days). Nevertheless, significant differences among males could still be found even in a long time scale. Pulse period was the acoustic feature that most contributed to discriminate among males. Tide level and male calling rate modulated boatwhistle characteristics, and there was a differential effect of tide on call attributes depending on male calling rate. Social acoustic environment only affected calling rate. These results suggest that inter-individual differences in call characteristics and call plasticity may mediate both male–male assessment and mate choice. KeywordsAcoustic communication–Individuality–Signal plasticity–Batrachoididae–Teleost fish–Tide effects
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The codfish family, Gadidae, contains many vocal species. The sounds produced are species-characteristic and relatively simple. Unusually within this family, the haddock Melanogrammus aeglefinus, produces a range of sounds in different contexts. Both male and female haddock produce short sequences of repeated knocks during agonistic encounters. During the spawning season, however, male fish produce sounds which vary in their characteristics as courtship proceeds. The repertoire of the male fish consists of a graded series of sounds ranging from a short series of slowly repeated knocks to long sounds of rapidly repeated knocks. The fastest sounds are heard as a continuous humming. Different behavioural acts leading up to the mating embrace are associated with particular sounds, the sounds becoming longer and faster as the level of arousal of the male increases. It is suggested that the sounds serve to bring male and female fish together in the same part of the ocean, and that the sounds also play a role in synchronising the reproductive behaviour of the male and female.
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Courtship and agonistic interactions in an African cichlid species present a richer diversity of acoustic stimuli than previously reported. Male cichlids, including those from the genus Pseudotropheus (P.), produce low frequency short pulsed sounds during courtship. Sounds emitted by P. zebra males in the early stages of courtship (during quiver) were found to be significantly longer and with a higher number of pulses than sounds produced in later stages. During agonistic intrasexual quiver displays, males produced significantly longer sounds with more pulses than females. Also, male sounds had a shorter duration and pulse period in courtship than in male-male interactions. Taken together, these results show that the acoustic repertoire of this species is larger than what was previously known and emphasize the importance of further research exploiting the role of acoustic stimuli in intra- and interspecific communication in African cichlids.
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A sound reproducing apparatus is provided with a circuit comprising a first secondary phase shifter in a front stage of at least one of channels among a first power amplifier, a second power amplifier and a third power amplifier, and a second secondary phase shifter and an adder in at least one of remaining channels for providing an output by adding output signals of a music signal source and the second secondary phase shifter. The apparatus of this structure eliminates phase interferences between a center speaker and right and left speakers by controlling sound waves generated by the center speaker, thereby achieving excellent reproduction of music.
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Many fish species emit sounds in agonistic contexts. During direct confrontations sounds are typically produced during the display phase in conjunction with visual exhibitions. Here we studied sound production during territorial defence in captive painted gobies, Pomatoschistus pictus, and related acoustic parameters with male traits and the date of recording (Julian day, i.e., with the approach of the peak of the breeding season). Territorial males emitted drumming sounds during displays that involved darkening the chin and fins, spreading fins and quivering the body. Drums were trains of low frequency pulses (≈23 pulses) repeated every 27 ms and usually lasting under a second. Drums were produced in short sequences of sounds (bursts). All acoustic parameters differed significantly among males. Drum and burst duration, and drum number of pulses increased significantly with male size. Calling duration (including drum, burst duration and drum number of pulses) also increased significantly with Julian date and presented a high intra-male variability, suggesting that these parameters may also depend on the individual's motivation. We provide the first report for agonistic sound production in sand gobies and give evidence that sound parameters contain information that can be used during mutual assessment in contests over territories.
Article
The streaked gurnard Trigloporus lastoviza produced only one sound type, a growl, lasting up to 3 s and consisting of repeated groups of typically one to three pulses. The foraging fish followed two different strategies. In the first, the fish circled the feeding area, grasped a food item and fled, sometimes displaying aggressively to competitors. With this foraging strategy, fish usually made sounds as they circled, grasped and fled. Fish that growled while circling were more likely to grasp a food item subsequently than were silent fish. The second feeding strategy occurred when a fish had already ingested food or failed to get any. In this case, typically fish searched for food on the substratum or approached and touched other individuals that were feeding, sometimes grabbing food that was spat out during food handling by the other fish. Although payback experiments would be needed to draw firm conclusions on the communicative function of growling during competitive feeding in the streaked gurnard, the results suggest that sound production confers advantages to individuals competing for limited food resources.
Article
Male signals are frequently studied in a single behavioral context, but in some cases they may assist multiple functions, namely for both male–male competition and female mate choice. Boatwhistles are known as the mate attraction calls of toadfishes typically produced during the breeding season. However, recent observations with the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae) indicate that the emission of boatwhistles is not restricted to this period, which suggests a function in other behavioral contexts such as agonistic territorial interactions. We experimentally manipulated the social context of toadfish males to investigate whether boatwhistles are produced during territorial defense, by introducing ‘intruders’ in an experimental tank containing nesting ‘resident’ males. Furthermore, we examined whether parental care (eggs in the nest) affected the behavioral responses of resident males during territorial defense. Resident males defended their shelters producing sounds, mostly boatwhistles, towards intruders. Parental males revealed higher aggression levels, exhibiting additional threatening and attack behaviors. Boatwhistles registered during agonistic events were compared with the mate advertising boatwhistles recorded from small aggregations of nesting males in a natural breeding intertidal area. Agonistic boatwhistles were produced in lower and variable calling rates comparing with the advertising ones that were typically emitted in long series of calls. Agonistic boatwhistles were similar in duration and frequency harmonic structure (with a middle tonal phase) to the advertising calls, but presented less amplitude modulation, and lower dominant and fundamental frequencies. These acoustic differences were probably related to differences in calling rates and broadcast demands associated to the distance to the intended receiver. We provide first evidence that, apart from attracting mates, the toadfish boatwhistles also function as active ‘keep-out’ signals during territorial defense.
Bent type wave transmitter-receiver,” patent JP2001333487
  • S Hiroshi
S. Hiroshi, "Bent type wave transmitter-receiver," patent JP2001333487, 30 November 2001.