Post by Steve Deckert on 01/23/23 at 04:08:23
What do you do with a super exotic 10 inch full-range driver? I have one that has an FS of around 29Hz if I remember right. Fairly low Qts as well and high efficiency.
Sounds pretty good so far! But when I measured it, I discovered that the impedance peak at resonance is 500 ohms. That is so extreme that phase angle shifts 180 degrees at that frequency.
I'll let you think about that for a minute...
If the phase shifts 180 degrees in time at 29Hz then it is going to cancel everything for half an octave above and below it. It also means that if there are other low frequency drivers involved the low bass is going to be canceled by this driver.
The driver is exotic. A crossover is not acceptable. Even a digital crossover is not acceptable. The driver must be allowed to move through it's full range of excursion to get into its zone.
So how are we going to deal with this?
Hours of exotic box modeling with all the tricks, from high order boxes, passive radiators, and everything I could model there was no good way to get bass below 100Hz with this driver. The lowest I was able to model was around 50Hz but I had to use a really high Q and it was gettin ugly.
A cabinet could be made to achieve 60 or 70 Hz with some complexity, but why? If we can't get to 29Hz what is the point? Why not use a smaller driver instead of a 10 if we can't have bass?
It's been my experience in audio that when something is stressed to the point of becoming almost dysfunctional in one area, something incredible happens in all the other areas. That is what I think will happen with these exotic tens I have.
So the question is what are we going to do...
That 500 ohm peak has to come down naturally somehow, but how? That peak comes from bottled up energy, the result of the ultra strong magnet. It needs a place to go.
My plan would be to give it place to go since it is an 8 ohm driver I will parallel it with a 4 ohm load from 100Hz on down. I can do this by using two 8 ohm 15 inch drivers. One driver crossed over at 50Hz and the other driver crossed over at 100Hz. This should drop the impedance spike to less than half at 100Hz and again as much at 50Hz. That in turn should be exiting to measure and compare to the original impedance plot.
This would be done in an open baffle so as to maximize image size and have zero colorations in the midrange from the exotic driver. The estimated response would be 30Hz to 20kHz. The lack of internal reflections and resonances also keeps things cleaner since moving the speaker cone with a reflection creates a voltage impulse that fights against the incoming signal and the other drivers involved.
I'm just posting these original thoughts so I don't forget them. I would start tonight but I literally have no place to put these... story of our lives right?
Steve