Blog › Forums › DIY Speakers and Subwoofers › Max-X High Excursion 15" Subwoofer for only $200 – Build Ideas › Reply To: RE: Max-X High Excursion 15" Subwoofer for only $200 – Build Ideas
@123toid Under advanced in winisd is an option marked “simulate voice coil inductance”. Generally, this isn’t important, but with these high excursion subs the voice coils are huge and can have a decent amount. This sub has an inductance of 5.51mH, which is pretty substantial. Fortunately, it isn’t that important for a home theater application with dsp. When you simulate it, you’ll notice a hump form around 70 hz, a low pass drop above that, and a small loss in low-frequency output. This is likely the problem you are having with xmax. I’ve included the same simulation, one with inductance and one without. I’ve also included the values I inputted. I leave a few blank to fill in naturally to see if dayton is stretching their values. The variance shouldn’t make a significant difference overall.
As for port velocity, I did show it with the 13hz high pass filter.
The last and most complicated difference is the cabinet. I try to estimate the theoretical value for cabinet volume caused by the box lining and incorporate it into my design. I find that pink insulation works best. Some people are wary to use it on ported subs because it might spread particles, but I put a thin stretchy material over it to prevent that.
So originally, my box was 4 cubic feet with a 1.5×17″ port which was 45″ long. This gets you a box with a tuning of 19hz. This is the response.
Then I added the insulation to all the walls, not covering the port in any way, and the port tuning changed to 16.5ish hz. For this to happen, the psuedo box volume had to increase through some sort of fancy science thing I don’t fully understand. We know this because we didn’t change the port in any way, only the box. To simulate that I entered the tuning I had after the insulation and adjusted the box volume until I had my initial port length. This ended up being 5.5 cubic feet, a 37.5% increase. I was surprised at the large increase in such a big cabinet until I saw that the response was accurate. I then did all my simulations off that value. This is that response.
When I design cabinets I generally make multiple simulations. One with the true volume, and a couple with larger volumes with the same port length up to 30% larger, sometimes hoping I’ll get to that, sometimes just in case.
I hope this makes sense and I hope my assumptions are right. Through all my builds I have always found them to be true.
I use a minidsp 2×4 for my dsp. It works fine because my crown has an input sensitivity of .774Vrms or something. It has an output voltage of .9Vrms. I’m not very familiar with the xti amps, but I’m assuming they are similar, but with the DSP built-in? Here’s my simulation with the dsp filters I used so you can compare.