Does this mean I should leave the limiter off? Do I risk damaging my sub? Right now I always leave the limiter on and rumble filter off. I still have not figured out, in stupid people terms, exactly how these things are related. If they are even related at all.
We seem to have misunderstanding here.
This is the EQ 2 position, both ports opened, recommended by Dr Hsu.
Now the EQ 2 position has the high pass filter second order roll off at 30 Hz. The EQ 1 position does not have the filter.
This from Paul's review.
Before proceding we felt it necessary to point out that the HSU VTF-15H has two switch positions on the amplifier back panel called "EQ 1" and "EQ 2", respectively. EQ 1 essentially runs the sub fullrange while "EQ2" employs a 30Hz second order HPF filter for better mechanical protection of the subwoofer driver. HSU recommends running "EQ"2 with both ports open for maximum output while they recommend running the sub in EQ1 for 1 or both ports plugged for maximum extension mode. In this report, we test both positions and show their respective tradeoffs associated.
Now note in the above graph before roll off, there is a hump. I think that Paul is correct and from the driver exceeding linear excursion and the voice coil starting to leave the gap.
So why the filter. We have been over this ground many times before. Once the driver frequency drops below the roll off frequency in a ported enclosure, the driver decouples from the box. You get large cone excursions and little to no sound produced. If you power the driver below that point, yes, you will damage it. So that is why you want to use EQ 2 with both ports open.
Now note there is smooth roll off below 30 Hz at all levels below over drive, with good performance above 30 Hz.
Now lets look at the extended bass alignment. One port closed, which will lower the box tuning frequency. It uses EQ 1, no high pass filter at 30 Hz.
What we see is reduced output above 30 Hz, and the roll of frequency has moved up a few Hz. What is gained is a shallower roll off between 20 and 30 Hz, but the driver exceeds mechanical limits and makes a frightful racket below 20 Hz, as you can see in hash on the graph in that region.
So the trade off was not worth it, and for the vast majority of drivers it is not worth it. An extended bass alignment versus an optimal alignment is not a good idea for most drivers, especially cheaper ones.
So now lets look at the sealed, both ports plugged. This graph shows sealed alignment and one port open. Both alignments are shown with Q control at 0.7 and 0.3.
Roll off starts at 100 Hz but now the enclosure is sealed roll off is second order at 12 db per octave. Note there is no port reinforcement so output is lower than both ports open EQ 2.
Now a sealed enclosure could have bass boost applied, but the driver has to have the excursion available and the power handling. From the above graphs, I doubt that driver would have the spare excursion.
So this is a nice demonstration of how sacrificing spl for bass extension is not worth it. It also shows that a sealed sub needs a very formidable driver and lots of amp power.
However you cut it, getting any speaker with high spl to and below 20 Hz is a formidable and costly affair.
I would say for all but very expensive reference systems the cost is not justified. The money would be much better spent improving performance above 80 Hz, which for most systems is nowhere near optimal, or in far too many cases not even acceptable.
I don't thin there is anything to gain debating this further. Either you get it or you don't.
