It sounds possible that both your problems (In reply to comment #0)
> In my setup I have a Squeezebox Boom (Firmware rev. 47) coupled with a Tivoli
> Model Subwoofer. Of course I have the Line Out mode set to Subwoofer, but this
> causes a couple of problems:
> 
> 1. I have to turn the volume up really high on the sub (about 80% of full
> volume) for the music to sound right (this could just be the sub having a weak
> amp, but it would be nice to ajust this on the SB).
> 
> 2. More importantly, I'm having problems with the subs auto off feature
> (there's no permanent "on", only "off" and "auto"). When the sub switches from
> "on" till "auto-off" mode, there is a small noise from the sub (mecanical
> sounding).

This is your fundamental problem.  It seems very likely that you have a bad cable connecting your devices, with a bad ground connection.    It could explain both the low signal level, and the noise that keeps your sub on.

Does your cable have gold connectors?   Do you get noise when you wiggle the connector in the back of Boom?

Are both your sub and Boom connected to the same AC jack?  If not, try that.

If you still get noise after plugging both into the same AC jack, and you're sure you have a solid connection, you can check out  http://www.jensen-transformers.com/an/an004.pdf, but it's a bit technical.


> 
> The problem is, when I use the "sub-out" mode on the Boom, the signal sent to
> the sub seems to put it right on the threshold for auto-off, resulting in the
> sub putting out a constant (very annoying) noise.
> 
> I've done some experiments to find out if the problem is related to the
> squeezebox or the sub, and it seems to be the squeezebox.
> 
> 1. Often the noise occurs after I've paused a song or turned the squeezebox
> off. When this happens, I've unplugged the sub mini-jack. The sub will then go
> properly into auto off. When I reinsert the mini-jack, the noise comes back.
> 
> 2. If the noise occurs while squeezebox is off, I've pulled the power on the
> squeezebox and the noise disappears.
> 
> 
> I'm guessing two things could be at the root of my problems:
> 
> 1. The "sub-out" jack isn't completely shut down when the squeezebox is paused
> or off. I.E. some signal is created that keeps the sub half-alive.
> 
> 2. The volume sent to the sub is too low. I'm guessing the louder the signal
> sent to the sub, less chance it turns off when it shouldn't.
> 
> I should also add that some specific songs (like "la femme d'argent" by "Air")
> causes the sub to turn auto-off or enter "limbo" (i.e. making noise) because
> most sound is above the 100Hz limit of the sub-out filter. I think this problem
> would be reduced if one could adjust the volume of the sub-out line.
> 
> Also, I think this bug might be related:
> https://bugs-archive.lyrion.org/show_bug.cgi?id=10868

Cato: have you been able to isolate this issue based on Caleb's comments?

Sorry for the late reply. I've been meaning to do some thourogh testing, but I'm not sure how or what to test :(

I've tried two different mini-jack to mini-jack cables from the Boom to the sub:

1. The cable that came with the Boom: This cable is short, has gold connectors and appear to be good quality.

2. The cable that came with the sub: Long (about 3m), no gold connectors, seems solid.

The problem appears with both cables, although my testing today suggests that the problem is _much_ less frequent when the line-in (from my computer soundcard with very bad ground) is disconnected.

I've also done some thinking, and I'm guessing my first idea (to boost the line-out signal) won't work. Since the sound still occurs when the squeezebox is turend off, it must be some signal caused by the sub or the Boom (right?)

I guess it's also possible that, if a bad grounding is causing the problem, it could be in the sub? But how would I test that? I've tried connecting my iPod to the sub directly to see if the same thing happens, but I haven't been able to recreate the problem. (should I try other audio sources?)

It also appears that the Booms volume and the type of music I play makes a difference. First I tried with some music that was heavy on the bass, and almost never got the annoying sound. Then I tried some softer music with long parts without bass, and the sound problem was easier to recreate (more frequent).

I'll try to upload a recording of the sound tomorrow. I'll also try to find a more reliable way to recreate the problem.

Thank for the help so far.

Oh, btw:

1. The sub and the Boom is connected to the same AC outlet.
2. I've tried reading the referenced paper, but had trouble understanding it. When I have some time I'll try harder :)

(In reply to comment #1)
> This is your fundamental problem.  It seems very likely that you have a bad
> cable connecting your devices, with a bad ground connection.    It could
> explain both the low signal level, and the noise that keeps your sub on.
> 
> Does your cable have gold connectors?   Do you get noise when you wiggle the
> connector in the back of Boom?
> 
> Are both your sub and Boom connected to the same AC jack?  If not, try that.
> 
> If you still get noise after plugging both into the same AC jack, and you're
> sure you have a solid connection, you can check out 
> http://www.jensen-transformers.com/an/an004.pdf, but it's a bit technical.

Did you try wiggling the cable Cato? Caleb do you have anything to add? Can you suggest any other tests for Cato or QA?