@ben
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You have discovered the trade-off of SPL vs. LF extension. It’s just harder for drivers to push those low frequencies at high volumes. That’s why live events need a wall of subs to get usable levels that low in frequency. The Meyer VLFC is even made just for that very bottom end because regular subs don’t do it well. You can get that low in theatres because it’s a much lower SPL required for a small space. They also tend to have multiple subs to achieve that result.
A highpass filter is definitely recommended as a safety for subs even if it starts at 20-25Hz. You don’t want them trying to play lower than that without a limit on the excursion from a HP filter. Personally 102dB would be plenty for my listening but that’s subjective. Stuffing is a bit complicated. I’m wary of broad statements like “this much stuffing makes the box seem this big”. I think sam_adams from this forum explains it well (https://www.audiosciencereview.com/forum/index.php?threads/is-all-speaker-fill-created-equal.47151/) You need dense material to limit airflow but everything in speaker building has a tradeoff. In this case you are sacrificing efficiency.
I see what you are saying about the RSS not going as low in WinISD as their graph. My only observation is an efficiency gain. Using less wattage to get the same SPL maybe means you can bump the low end more before cone excursion? Not sure there
What kinks in the graph are you referring to?
I checked out the file you linked. I think your main problem is trying to add low end below what the driver can do. If you follow the recommended Vas from that driver’s spec page of 248 liters and put no filters in you can see that the response in WinISD matches pretty close to the published graph on that spec sheet. Even using the full 1200 watts RMS as advertised you will not hit cone excursion. Because of the impedance curve the fact is that the driver can only play so low and so loud. You can tune that bottom end up if you’re running at lower wattage or you can leave the natural roll off and go up to the rated RMS wattage.
Chiming in as a novice. Some big idea things I’m noticing:
That driver you listed for this test has an Fs of 33Hz. My understanding is that a driver’s response tends to fall off quickly after that number so it might not be the right choice if you’re looking to get to 20Hz.
Don’t ignore the cone excursion graph. I missed that on my first one and was confused that my speaker wasn’t playing as low as the SPL graph showed. When you pass the red line it will not play those frequencies. I haven’t built a sealed sub yet but I’m pretty sure If you want it to go lower before hitting cone excursion the box needs to be bigger. Those guidelines for how big of a box fits that driver is just a starting point. Feel free to adjust it to suit your preferred outcome
Cone excursion is based on input wattage though. If you won’t run it that high then you can back off the wattage and see how low it goes at quieter volumes
Thanks for the reply. I probably should have looked at the stock response more and built around that. Is there a part of the spec that gives an idea of what’s required to achieve that? Is Vas related to the box size?
