Speaker Placement; Vibrations; Heating Pads - TDT Medusa4Z User Manual

Speaker Placement

Most enclosures have some amount of acoustical reflection or interference during open field
stimulus presentation. The effects will vary depending on the size of the enclosure, the angle at
which the speaker is positioned, and the materials used or added for sound dampening. To
minimize the effects of distortion or interference, position the stimulus speaker on the same
plane as the subject's ear and set at an angle from the sides of the enclosure. See
Chamber Fundamentals

Vibrations

Vibration from nearby large equipment is another common source of noise. If this is a problem
in your lab, the cage and subject can be positioned on an air table or anti-vibration table.

Heating Pads

When the subject is sedated for testing, it cannot generate enough body heat to maintain core
temperature. When the subject loses body heat, its hearing system is not as responsive which
can artificially raise hearing thresholds. A heating pad is typically used to maintain the
subject's temperature. Heating pads that require AC power inside the chamber are not suitable
for ABR recordings.
Below are two alternative types of heating pads used for this purpose:
An Isothermal Pad contains a phase change material that changes state near the subject's
body temperature. It can be heated in a microwave and can typically hold a constant
temperature for an hour or more.
Example: http://www.braintreesci.com/images/DP.pdf
A Warm Water Recirculator moves warm fluid through a small subject heating pad to keep the
subject's body temperatures stable. Because this method uses an external heating element
and pump to transfer water to the pad via non-ferrous tubes, the recordings will not be
affected.
Examples: http://www.braintreesci.com/prodinfo.asp?number=HTP-1500
www.braintreesci.com/prodinfo.asp?number=TP-700
for more information on speaker placement.
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