This information is outdated and should only be used on old versions of CrossOver and Linux. Please see our sound troubleshooting guide
Wine triggers a bug in older Pulseaudio versions (older than version 1.0) that cause games to lose sound. If your machine has up-to-date PulseAudio (PulseAudio >= 1.0 and alsa-plugins >= 1.0.24, which is libasound2-plugins on Ubuntu & co) the following information will not be useful to you.
This bug prevents Wine from interacting properly with the ALSA Compatibility plugin for PulseAudio. Therefore, Wine needs to access the audio device directly (bypassing PulseAudio), but cannot do so because PulseAudio has a "hold" on the audio device. The solution is to suspend PulseAudio's hold on the device so Wine can use it directly.
The workaround is to first open Wine Configuration (inside Crossover's Manage Bottles>Control Panel), head to the "Audio" tab and set both Output Device dropdowns to be the desired hardware device. This will have the format "Sound Card Name - Sound Device Name", for example, "HDA ATI SB - ALC889 Analog". If you are presented with both Analog and Digital options you will probably want the Analog device. Make sure to press OK in winecfg after selecting.
Next, Wine (and the windows game you're trying to run) needs to be run from pasuspender. This tool is a part of the "pulseaudio-utils" package and should already be present on your machine.