[CUBE] Cube speakers/amp

[atoa at krak.net]

Thanks for this information. But three questions.

1) Does the USB spec limit the power that a port can deliver?
If so, I can't find it. If not, it is wrong to say that a port that 
delivers more than 500mA is non-standard, at least if you use "standard" 
to mean "meeting the specs".

2) Does USB Prober show _actual_ usage, or just what it is rated as? I 
show different values for some of the devices than you do. For example, my 
keyboard shows up as 50 ma, not 15, and the speaker amp as only 500ma, 
even though it is plugged into an approved monitor port.

3) This is the first I've heard of a "booster mode". Do you have any more 
details on it?

I don't think there is any controversy about whether the Cube speakers 
will work with an unpowered hub. But do they work with non-enhanced power 
hubs? Perhaps it boils down to what we mean by "work". Does my car work, 
if it will only go at 35 mph? Perhaps more importantly, is there any 
danger of blowing out a hub by making Cube speakers "work", albeit at 
reduced output?

On Sat, 7 Aug 2004, Steffen Barabasch wrote:

> Guys, stop the speculation and do your homework. Really. This guessing 
> doesn't help anyone.
>
> Here are the facts:
>
> Every (standard) USB port is specced to deliver 500 mA of power.
>
> Low power devices like mouse/keyboard etc. can share this power supply by 
> using an unpowered hub. Usually this hub takes it share for its own needs, so 
> if you've got an unpowered 4-port hub that claims 100mA itself, you can use 4 
> 100 mA devices with that hub, resulting in a rated power use of 500mA total.
>
> The Cube amp is a high power device, rated 500mA. So you can only use it 
> plugged directly into a computer or on a powered hub.
>
> But now make your calculations, 5V x 0.5A, that's a measly 2.5 Watts input, 
> resulting in a max. audio wattage of max 1.5W. That's not quite much, and 
> since Steve Jobs is a bit deaf Apple engineers decided to "expand" the USB 
> specs on the Cube a good bit.
>
> If plugged in into the Cube, the amp gets switched into "booster mode" and 
> draws a LOT more power than the actual USB specs allow. That's why the Cube 
> speakers are a lot louder if plugged directly into the Cube.
>
> That doesn't mean that the speakers won't work on a powered hub, it just 
> won't be as loud since it uses just the rated 500mA max. to behave like a 
> nice citizen in USB land.
>
> The amp will not work on a unpowered hub, since the rated 500 mA plus 
> whatever the unpowered hub claims is more than the max 500 mA.
>
> If it DOES work (=the computer doesn't complain about too much power usage) 
> then you've got one of those weird critters like I did. I've got an 
> *unpowered* hub that claims (to the computer) to be a *powered* hub. That 
> means, you could use 4 500 mA devices plus the hub drawing all their power 
> (thats more than 2A in the worst case!) from one 500 mA port. Even with the 
> Cubes "high-power-ports" this could be very dangerous. Be careful if you 
> stumble across an unpowered hub that behaves like that!
>
> And if you still don't believe me, I made actual measurements on some of my 
> USB devices to see how much power they draw in real life:
>
>
> Low power devices (rated from 50 to 100 mA):
>
> Apple Pro Keyboard (not using the built-in hub)
> 15 mA
>
> LeadData Kartenleser (not using the built-in hub)
> 60 mA
>
> Keyspan TwinSerial
> 70 mA
>
> iMate + Apple Extended KB plugged in (LEDs on KB dark)
> 30 mA
>
> unpowered Hub + Logitech Mouse + Logitech Trackball + PowerMate (total)
> 120 mA
>
> This shows that the ratings here are really conservative. The last 
> combination is rated to a total of 314 mA, actual use is far less than half 
> as high.
>
>
> Now some high-power devices, rated 500 mA:
>
> Roland UA-30
> 320 mA
>
> Cube USB-Amp plugged into Cube port
> 800 mA
>
> The Roland USB audio interface is once again well below the rated value, the 
> Cube amp on the other hand is far over the actual USB specs, if allowed 
> (=plugged into Cube). If the Cube amp would have to be rated, and if you'd 
> use the same conservative rating as on the other devices, this would have to 
> be called a 1500 mA ultra-high-power device...
>
> BTW, to get the rated power usage, don't use the System Profiler, it doesn't 
> have a clue. Use USB Prober (part of the Developer Tools/Xcode) instead.
>
> Steffen
>
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