Aquarian Audio
H3n Hydrophone User’s Guide
H3 product family overview
The H3 uses a unique high-sensitivity, dual-sensor, mechanically-balanced transducer assembly that
offers exceptional signal-to-noise performance in the human auditory bandwidth. The fully-shielded design
inherently rejects EMI and RFI noise, making it useful in the studio, lab or shop. Its low mass and full polyurethane
rubber encapsulent make it highly resistant to damage caused by impact. Its small size allows users to fish it
inside of pipes and other tight spaces, making it excellent for leak finding. Though designed primarily for
underwater listening and leak finding, it is also useful as a waterproof microphone for tool room applications, such
as monitoring cutting in waterjet and other CNC tooling
.
The
H3nP
and
H3nB
are sold as passive hydrophones, terminated with 1/4” TS and BNC output plugs
respectively. These can be useful with DAQ and test equipment or high-impedance audio preamps.
H3dM and
H3dX
configurations include signal conditioning that is built into the hydrophone, which make them compatible with
standard consumer and professional microphone circuits. They are identical, other than the output connector. The
“n” in the part number designates the signal conditioning board used—in this case, none. The piezo sensor array
is connected directly to the cable. Please reference correct manual for each version.
The H3 hydrophone can be optionally assembled with our WT150g sliding stainless steel weight assembly
for maintaining negative buoyancy. There are several advantages to placing the weight on the cable, rather than
building it into the hydrophone. When the hydrophone is dropped, the cable flexes and absorbs any stress from
impact, making the hydrophone more durable. The weight can be moved if needed to allow insertion into a pipe.
Both of these attributes are especially useful to the leak finding specialist. Moving the weight away from the
hydrophone dampens acceleration noise that is transmitted down the cable from handling and it also minimizes
response irregularities caused by material resonances and sound reflections. It can also be used for mounting a
shroud tube to minimize flow noise over the hydrophone. To move the WT150g weight, turn the black plastic
thumbscrew counter-clockwise to loosen the internal rubber compression sleeve and slide the weight where
needed. Wet the cable if this is difficult. Secure again by turning the thumbscrew clockwise.
Be Advised
: Finger-
tighten thumbscrew only and always leave a minimum spacing of 5cm (2 in.) between hydrophone and weight!
Using the H3n
When using a passive piezo sensor, input impedance of the hydrophone preamp should be considered.
Impedance is the load that your preamp puts on the hydrophone. The low-frequency response of a piezo
transducer, such as that used in the H3, will be limited by the input impedance of the preamp. Higher input
impedance will result in extended low-frequency response. Very low frequency response can be troublesome
because it is most often noise from acceleration or thermal change, or sound that is dominated by machinery, so it
is often desirable to filter low frequency using the input impedance of your amplifier. If your hydrophone response
is unstable (seems to be cutting out) it is very possible that you are saturating the input of your preamp with
infrasound.
This relationship can be calculated for the H3 with the following formula:
Fc
= 1 / 0.000000094 *
R
Fc
is the frequency at which electrical output is 3dB below nominal and
R
is the input impedance of your preamp,
measured in ohms (Ω). Therefore, using a preamp with an input impedance of approximately 500 KΩ will give you
a low-frequency cutoff of 20 hertz—the low end of what humans can hear. Many high-impedance audio preamps
have input impedances of 1MΩ or more. Test equipment, such as oscilloscopes and spectrum analyzers have
typical input impedances of 10MΩ or more.
Aquarian does not guarantee compatibility of rubber and plastic materials used in its hydrophones for anything other than natural aquatic
environments. Prospective users should test compatibility with machine coolants and lubricants in production environments.
