Abstract: An apparatus for modifying a responsive liquid held in a barrel or other liquid container includes a transducer for producing vibration energy within the audio frequency range in response to an audio signal input and a coupler affixed to the transducer such that vibration energy produced in the transducer is transferred to the coupling device. The coupling device has a pusher end that extends beyond the front plane of the transducer and that contacts and pushes against the barrel wall when the apparatus is tied to the barrel wall. By determining the resonances of the liquid-filled barrel, audio input signals having sufficiently high levels at determined resonant frequencies can be chosen to achieve a maximum response in the liquid contained in the barrel. The apparatus is particularly suited for the sonic aging of whisky.