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DRIVE UNITS BY MANUFACTURER:
SB65WBAC25-4

UK STOCK ITEM
The SB Acoustics SB65WBAC25-4 is a 2.5 inch 4 ohm full range loudspeaker drive unit featuring a profiled aluminium cone and a neodymium magnet assembly. The geometrically furoughed cone and copper capped pole piece help control breakup and improve the high frequency response.
| Resonant frequency (fs) | 115 Hz | Nominal impedance (Zn) | 4 Ω |
| Mechanical Q factor (Qms) | 6.0 | DC resistance (Re) | 3.6 Ω |
| Electrical Q factor (Qes) | 0.77 |
Max power handling | 20 W |
| Total Q factor (Qts) | 0.68 |
Sensitivity (2.83V/1m) |
83.5dB |
| Equivalent volume (Vas) | 0.43L | Chassis (square) |
64mm |
I’m no expert when it comes to speakers, but after some research (and a strong recommendation from ChatGPT), I went with the SB Acoustics SB65WBAC25-4 as a reference full-range speaker in this size range.
Having now tested them, I can confidently say they’re probably the best speakers I’ve ever owned. The clarity is outstanding—every detail comes through with incredible precision. The bass is surprisingly full and punchy for a speaker this size, and they handle power impressively well. For anyone looking for a high-performance compact full-range driver, these are hard to beat.
Thanks for the review !
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 ❣️
