I got a chance to place an early order for four of the upcoming Funk Audio UH-21v1 drivers. This driver is an underhung design, similar to the Focusworks GUJ18V1 and GUJ21V1 drivers, but it uses the magnet structure from the TSAD21v2 driver featured in the Funk Audio FW21.0 powered sub. I requested coils with lower resistance for a better match to my choice of amp and for getting the most motor strength possible.
Here are some pictures of the finished product:
Forgive me for my pictures are not the best. Here is a driver undergoing inspection:
My cat likes bass and sine sweeps but doesn't like dynamic movie sounds or music with horns. Here are a couple more:
The carbon fibers have a mirror like reflection when viewed from the right angle. None of the pictures I've seen do the motor/magnet assembly justice. It's about 10" diameter like the spider:
And of course, they deserve nothing less than an SP2-12k drive them all:
These are T/S specs taken by Funk Audio, using the lower DCR coil:
- Fs: 22.32 Hz
- Re: 4.65 ohm
- Qms: 5.52
- Qes: 0.235
- Vas: 296 L
- Mms: 590g
- Bl: 40.4 T*m
- Le (1 kHz): 2.93 mH
The (BL)^2/Re comes in at 350 putting it among the top brass for motor strength, approaching the Rockford Fosgate TS3-19 and the B&C IPAL-21. It appears to have a more compliant suspension than either of these, which aids low frequency efficiency in medium to large size boxes. Compared to the TS3-19, the mass of the UH-21v1 moving assembly is lower, and the driver has greater upper frequency efficiency. It also requires less mounting depth. Compared to the IPAL-21, the UH-21v1 has more cone travel and a much more usable DCR.
I plan to install the drivers dual-opposed in two boxes with about 4-5 cuft per driver. They will be designed to fill the spaces I have on each side of my equipment racks up front, about 40" wide, 28" deep, and 24" high. At 4.5 cuft per driver, the Fb models at around 35 Hz and a low Qtc of around 0.4. Each box will be run with a channel from a SpeakerPower SP2-12000 with drivers wired in parallel. After a lot of research, these drivers appeared likely to offer the most ULF bass of any driver for the space I had to work with, and they should still be usable to frequencies well beyond 100 Hz. They will also be insanely efficient above 20 Hz and a good fit to my room gain profile.
I also have an upgrade path if for some reason I find the headroom in the deep bass to be insufficient. I can add a second SP2-12k amp and run each channel on a pair of coils in parallel for DCR of 1.25 ohm and then use frequency selective limiting to avoid over-driving them at the lowest frequencies. I doubt I'll opt to go this direction, especially since I'm not even one to run my bass hot. I just want as much ULF as I can get in this fairly large space, and lots of headroom for realistic high SPL peaks. As it is, the numbers I'm looking at are quite absurd. I can also envision moving these to horn-loaded cabinets at some point in the distant future but probably not for my living room.
Dual-opposed Sealed Cabinets
Here is one of the cabinet sides attached to the bottom, with dados for the opposing front baffles, and for internal braces:
Here is one of the internal braces along with one of the front baffles:
Here is the inside of the cabinet, right after gluing the major panels together. The cabinet is actually divided into separate chambers for each driver. I'm not sure what's up with the weird camera lens flare on the left.
This is with the braces installed parallel to the axis of the drivers, connecting the baffles:
Here is a cabinet after patching and sanding, ready for Duratex application:
Here is look at the inside of the fully finished cabinet, without the driver:
I also ordered hand-machined anondized aluminum trim rings from Funk. Each piece fits the frame profile perfectly and interlocks with the adjacent pieces:
The resonance comes in at around 39 Hz and with a Qtc of 0.33. Wow! These things appear to be absurdly efficient. The DCR is 4.75ish ohm, and I measured impedances of 8.5 ohm at 10 Hz and 14 ohm at 20 Hz .
This was measured approximately 6" from the cone, and a signal level normalized to 2V. It should not be taken as quantitatively accurate but reveals the approximate native response shape:
Here are in-room sensitivity measurements, normalized for 2V (more precisely than above) and taken at the main listening position:
The sum just assumes I send each sub an identical signal. I can likely get a bit more output in some spots with help from some phase corrections.
My amp is rated for 126V maximum with 240V supply, so if the subs are capable, the amp can supply the current, and there's no compression, I'll see +36 dB with full power. (NoteAt this time, I'm running on 120V power and can probably do closer to +33 dB.)
The impedance is 7 ohm (for two drivers in parallel) at 20 Hz, so the amp is unlikely to have any problem at or above there. It appears that I now possess ridiculous output capability.
Edit: Added lots more pictures.
Edited by SME, 25 April 2017 - 07:01 AM.