either you disassemble the backplace and remove the wires of the woofer by cutting it or you bring it to an electric shop to repair it for bass~

disable the woffer is just simply cut off the wire i guess lol...troubleshoot just try to open up the woffer box see the amplifier got any bad cap or not

Does the sound appear when you disconnect the sound source (ie. unplug the audio cable and leave it disconnected)? Is there any scratchy/rumbling/crackling sounds when turning the bass control knob?

To disable the wooder, simply open up the subwoofer enclosure and disconnect the wires to the woofer either by cutting or de-soldering. Remember to use wiring tape to cover the ends of those wires to prevent short circuit across the woofer power amplifier output. With only the satellites running, the speakers will sound like those el-cheapo RM20 speakers (all highs and hardly any bass at all). Anyway, before deciding to disconnect the woofer, check for any signs of failed components such as badcaps...

As long as all the correct wires are still in place...

Not talking about the power button as that "crack" is quite common in budget speakers. The one in concern is the bass control knob. Is there any other sound when turning the knob? As for the problem, as mentioned earlier, first have to visually check for failed components. Not sure whom you've spoken to about that problem, but that is not the correct answer given at all. Even without any sound source, the speaker should not be humming or generating the "wooooo" sound as you had described. If you're still not familiar then try sending it for repair.

Just remove the screws at the back, then slowly pull out the back piece assembly containing the circuit board attached. Here's an example from a review: Neoseeker : Articles : Audio : 3 Piece Systems : Altec Lansing VS4121 Review...  

Your speaker is just 2.1 system only thus considered easy (less cables and connections to deal with). Imagine 7.1 system, with multiple cables and boards, such as my repair example here: Special Interest -> Home Entertainment -> Audiophiles -> Creative GigaWorks S750 7.1 speaker repair, A short guide and info with pictures... (PC Audio) , if you had missed it...

That means there are no effect with the bass control potentiometer. Sometimes if one side of the potentiometer is disconnected from GND line then you may get some humming problem (e.g. if you ever study audio circuits then you should know that often one side of any sound level controls is usually connected to GND). Rather than badcaps, very often the humming and/or buzzing problem was due to broken GND connection usually at the input side. This creates floating inputs with no virtual return GND and when connected to a sound source then the humming/buzzing will occur (which is the reason I asked about disconnecting the sound source earlier). Its not uncommon to see broken GND problems, as I've fixed quite a number of them before. Below is an example of a recent one...

Nope, unfortunately from the symptoms described you may have to open up the speaker system to check. As for possibility of broken GND problem, you can try checking them at the audio connectors. At least a digital multimeter is required to troubleshoot. If you feel its "too technical" for you then as I've mentioned earlier send it to repair...

Some snapshots will help. Make sure your camera is in macro mode (for very close up shots). And yes, I do repair speakers. Just PM me for details... 

Not sure what is your budget. If not so high end, then can try Edifier M3300 or Edifier M3300SF which has a sub-bass control.

Can do repair, upgrades and modifications. 

Those Edifier speakers are more suited for music and movies. Its bass is a little different than current Altec Lansing generation ones. Edifiers are more of a thumper (tight bass) than a boomer (loose bass) like Altec Lansing. If you're fed up with Altec Lansing over-top boomy bass, then the Edifier is very surprisingly different and welcome change. As for bass control, its on the subwoofer itself unfortunately. Just turn it to your prefered settings and leave it there.

The satellites for M3300SF are slightly higher wattage but less "bright" than the M3300. Excerpt from a review here: Overclock3D :: Review :: Edifier M3300SF 2.1 Speaker Set Review :: Testing and Conclusion:...

Did you mean the ACS45.1? Played/toyed around with these before, even fixed/repaired one belonging to one of my friends.

An example would be Klipsch ProMedia 2.1, which has subwoofer bass control on one of the satellites.

the powerfilter cap is dead (25v 4700uf)
if problem still persist after replacement...its the transformer (common problem)
but i think it will be not economical to repair it in any event unless you are diyer yourself
please go to a electronic repair shop or buy a new set =)

use the recommendations section above if you are looking for a something
and nope, no multimedia speaker will sound good if you disconnect the subwoofer
if unsure or you don't have any knowledge, please don't save rm30. go to the electronic repair shop...
don't risk your life trying to save rm30

The M3300 is way better than the ACS45.1 in terms of clarity, and also bit better when it comes to deep bass (e.g. can clearly hear sound effects such as low rumbles and "thuds", unlike the Altec which can be kinda soft).

That Klipsch speaker has a subwoofer bass control (ie. set the volume of the subwoofer bass), and not a generic bass control. I don't remember seeing any multimedia speaker systems out there that has an on/off for its subwoofer bass control.

That "wooo" is actually due to faulty speaker system. Usually there should not be any sound from the subwoofer at all if there is no audio signals. Thus if there is a hum, buzz and/or crackling sounds then very likely some problems already (such as broken GND, bad capacitors, etc)...

If not mistaken, that Altec Lansing VS4121 uses a 6800uF capacitor instead. Plus the power supply board is actually mounted on the transformer itself (separate from the main power amplifier board). If transformer problem then the whole unit would be dead (e.g. no power at all, and no sounds from any speakers).