Originally Posted by Bill Fitzmaurice
Again, depending on the topology of the summing it could have higher sensitivity. But as for how loud it will play that's determined by the amp power supply rail voltage and driver excursion limit, and neither is altered by how many inputs are used.
This is true, and is why I think a Y-splitter is an unnecessary expenditure. But since we're all geeks here, and since I'm stuck in Djibouti with nothing better to do, let's explore this further.
IF somebody experienced an issue where they turned up their LFE channel all the way up in their receiver, and they turned their sub all the way up, and their sub had an amp which would be at -3db with just one input (which is a poor design, and explains why the newer subs aren't like this), and they ended up 1-3db shy of whatever level they were trying to calibrate to, then a Y splitter might seem like the answer.
I still wouldn't recommend a Y splitter. If they have to turn both the LFE channel and the subwoofer all the way up, and they are still 3db shy, the sub is way too small for the room. If they did get a Y splitter to get to that target, that sub would not have anywhere near the headroom to play any louder. A larger sub is the answer.
Now, let's say that we ended up in a situation where our sub does calibrate fine, but we ran sweeps, and found that we are only attaining 112db peak loudness, instead of the 115db which is the loudest peak we're ideally supposed to have in a calibrated setup. (although depending on bass management, and how well/poorly a movie is mixed, our peaks could theoretically be higher, but that's a different debate in a different thread) Should we use a Y splitter to get to 115db (again assuming the poorly designed sub amp)?
I would again have to say no. If we added a Y splitter and gained 3db, when we run our calibration we would have to turn our sub back down by 3db, and we'd be where we started. The issue this time is availabler headroom - our sub does not have the oomph to hit 115db. So like in the last scenario, a larger sub is the ultimate solution.
Now, if one were to not calibrate their setup, and they did nothing else but add a Y splitter, and they had the amp in question, they would experience a louder sub with a Y splitter. But in that case, adding the Y splitter had the same effect as turning up the LFE channel, or the sub's master volume.
All that to say I agreed - while in some instances a Y splitter would provide the amp 3db more signal, it would be essentially the same thing as adjusting either the LFE out on the receiver or the master volume on the sub. But ultimately, it would have no effect on the absolute loudness of the sub unless something else was drastically wrong.