Seeing as how the Willsenton R8 has no pre-amp output and the Starke SW12 has no speaker level input you are going straight from your dac to the subs, correct? Are you controlling the volume level with the dac and just using the R8 as an amp only? What you describe sounds an awful lot like you are using a fixed volume output from your dac. "They are way too loud even with the volume set almost to off". I am willing to bet you are sending a full power signal to the subs and over driving their amps. This will cause all of the problems you are having.
Is this how a Subwoofer Crossover is supposed to work?
I bought two Starke SW12 subwoofers that I installed. So far I'm not particularly happy with them. They are way too loud even with the volume set almost to off. More importantly, I'm having trouble integrating them into my system and I'm wondering if that is because their crossover setting is really functioning as I understand a crossover should. Attached please find measurements from Room Equalization Wizard with SPL graphs of the two subs (no speakers) taken at my listening position with the crossover set at 50 Hz, 90 Hz, and 130 Hz. Ignore the peaks and dips which I assume are due to room nodes. All of those settings appear to actually have the same crossover point of 50 Hz. All that changes is the slope of the rolloff in sound levels. This isn't how I thought a properly designed crossover was supposed to work. I thought the frequency the levels would start to roll off would change, i.e. flat to 50 hz then a sharp drop, flat to 90 hz then a sharp drop, etc. etc.. But Starke says this is how a subwoofer crossover is supposed to work.
https://www.dropbox.com/s/8x4cr32pagwg48i/Two%20Subs%20Different%20Crossover%20Points%20No%20Speaker...
Any experts on here with an opinion about this? Is it possible to buy an inexpensive active crossover that I could use in place of what is built into these subs?
https://www.dropbox.com/s/8x4cr32pagwg48i/Two%20Subs%20Different%20Crossover%20Points%20No%20Speaker...
Any experts on here with an opinion about this? Is it possible to buy an inexpensive active crossover that I could use in place of what is built into these subs?