Comment 1 for bug 305750

"options snd_hda_intel model=mbp3"

This is posted to the end alsa bug report, but I figure since I wrote it, then I should be able to post it where ever I like :)

On my Macbook 4,1, running a stock Ubuntu 8.10, kernel 2.6.27-11-generic, alsa version 1.0.17
The magic options bit that makes bass work on mine is a kernel option when inserting the snd_hda_intel module:

model=asus-a7m

The PCM level seems to control some(all, maybe) of the bass woofer. I'm not sure if all of the woofer is entirely all there though. Might be, would need to get two macbooks next to each other with the same piece of music to see. My hunch is that it isn't. Its more bassy than than the auto detected config, however.

To make this change permanent, do this
sudo gedit /etc/modprobe.d/options
Add the line:
"options snd_hda_intel model=asus-a7m"
Save, Quit
Reboot

Sound should work.

I'm not promising that it's perfect, either. I have no idea about recording, or iec playback, or even if plugging in a headset turns off the speakers, or causes global thermonuclear war, only that it increases the bass somewhat.