DRIVE UNITS BY MANUFACTURER:
SB21RDC-C000-4

UK STOCK ITEM - EXCELLENT REPLACEMENT FOR VIFA / PEERLESS XT19TD00-04.
The SB21RDC-C000-4 by SB Acoustics is a 21mm ring radiator tweeter. The centre of the diaphragm is inverted and bonded to an internal dimple on the pole piece, this innovation negates the need for a front phase plug and gives excellent extension to above 20kHz.
| Resonant frequency (fs) | 760 Hz | Nominal impedance (Zn) | 4 Ω |
| Effective diaphragm diameter | 21mm | DC resistance (Re) | 3.0 Ω |
| Ferrofluid ? Y/N | Yes |
Max power handling | 60 W |
| Recommended crossover | 2.6kHz/12dB | Faceplate diameter | 92mm |
| Sensitivity (2.83V/1m) | 90dB | Cutout hole diameter | 64mm |
Firstly, thank you for the excellent service!
I wanted to replace a pair of old 92mm faceplate Scan-speak D2008/8203 tweeters I've been using with KEF B100B bass driver for many years. The replacement D2008/8511(now discontinued) would 'drop in', although isn't a perfect replacement efficiency or sound wise (the 8203 was heavily doped). The wonderful Hiquphon OW1/92 would be first choice but sadly out of my price range!
The SB21RDC-C000-4 required a little modification to the cabinet, simply to accommodate the connectors, and has four screw holes rather than three - but fits flush with the baffle.
I've had to re-work the crossover somewhat (this is a 4ohm tweeter), but the results are very promising using a third-order high-pass with an l-pad (1.5/2.7 ohm based on the 3 ohm DCR). Currently using a 5.6 and 16 microfarad capacitors and a 0.125mH inductor, which seems to blend rather well. I'm sure I'll tinker more, but there's really nothing to dislike as it is.
Thankyou for your review Peter!
Will & Caroline
Friendly technical support
40+ years in the trade
UK family run business
Excellent customer service
Quick dispatch
The crossover was constructed well, I just need to figure out the best way to attach it to my Kef Concertos as they are bigger than the ones supplied by Kef that are mounted on the front of the baffle board.
Very nice deep bass look amazing with my custom made speaker
Great speedy delivery and very easy to fit. The plastic in my drivers had perished and they had suffered one too many parties! No need to make any adjustments (someone above did suggest that). I just screwed them in and the foam compressed into place. Before and after below (before I changed speaker number 2). Thank you!
Thanks you very much for the kit. I found back my kelidh after nearly 27 years. The filter were really dead and one tweeter damaged. Very happy to decide to repair/ upgrade rather than change. I found back tone and stereo stage like in the old days probably even better.
I didn't know soldering material was so important thanks for providing some.
Quite easy to recap filter and change tweeters.
Also wanted to thank you for this little note hand writen in French just for me. Very nice attention to see.
Next step is the next question do I change first the drivers with the monacor as I ve lost dust caps but they still work properly or do I change my old arcam alpha 8. Is there really something to gain moving to an newer arcam sa10 or Radia a5? Are newer amplifier much better than the old days one?
In addition to my post from 17/11/2025, here is some information on the final status of the project: Saving the Mission 752 loudspeakers.
Once it was certain that it would be possible to revise the loudspeakers (thanks to Willy), the desire to also replace the low-midrange drivers and convert the crossover to a high-quality version quickly arose. I was fortunate enough to be able to purchase two Burmester 949 MKII midrange drivers from Audax to replace the existing low-midrange drivers (52LFHDA – still available and can be sold). They are practically identical in design, but significantly more refined and powerful. Revising the crossover proved somewhat more difficult because the values of the coils were not printed on them. However, they can be determined by measuring the originals. Mundorf resistors, coils and capacitors of the two highest quality grades were installed. These are not exactly cheap, but once the speaker is finished, the difference is clearly audible. The crossover was also modified slightly. A shunt was integrated into the high-frequency branch. Following a tip in a forum, the crossovers were also moved to the outside. They are currently still on the speaker without a housing. The metal housing provides perfect shielding. As the Willys tweeters are very efficient, they were ‘damped’ slightly. The final cost of the conversion was approximately £600. In return, the speakers now perform at a level that far exceeds their original condition. An exciting project that was only made possible by Willys – thanks to Caroline & Will ❣️
