replacement midrange driver

[yewneek]

Picking up a speaker restoration I started last year, but had to stop due to a death in the family.

Technics SB-R3 rebuild thread

Midrange driver on one of the pair is deffo sub-optimal, and I'm looking to replace it/them. There's only so much you can patch up, rebuild, refoam, recolour, relacquer, re-ferrofluid...

I've totally rebuilt the crossover networks with new capacitors. Rebuilt the cabinets, terminal plates, and finishing up replacing the grille cloth. Done a quick confirmatory recalibration with new crossover components too.
Added another 25 or so hours work over 4 days.

Seeking recommendations of MF driver replacement, please chip in and link away!

I'm so invested into the speakers I can't really satisfactorily abandon them, so balls-deep and more.

Cheers and TIA

GB

 

[staticV3]

Without T/S parameters of the stock driver, finding a replacement that'll work well with the stock crossover is going to be a challenge..

 

[DVDdoug]

Since you're "serious" about this, it's worth checking into r-coning. If the speakers are well known or common/popular there's a good chance they can bring them back to factory spec. It doesn't hurt to check and get a quote.



...If it was me, I'd probably just try to find something similar that fits, or that I could "make fit", and give it a shot. (I'm cheap!)

 

[alex-z]

Did you measure both mid-range drivers with the crossover bypassed? It looks ugly but I don't see anything that would cause obvious performance loss. Doing driver swaps is always a challenge, you need something with identical frequency response, impedance curve, and sensitivity if you don't plan to redesign the crossover.

 

[yewneek]

I'm cheap. I want something that fits. I'm not serious, just buried to the hilt.
The drivers I have no idea about the tech specs, it's a guesstimate and something that's good enough is sufficient!

LEFT speaker is the one with the MF driver that's duff(more duff). Maybe I shouldn't have doped the HF with ferrofluid, but since my hearing is shit in the HF range due to age, it probably compensates!

The speakers are nothing of historical importance, but I found them in a loft, recapped them twice now, second time properly scoped out etc. So, they're mine, I like them, and we've got an assimilation of some of the best objective and experienced audio nerds going here. Where better to ask!

I'm still learning how to do this, and the polymath in me wants all the knowledge I can get!

More than happy to exchange for any photography, computing, teaching/autodidactic/pedagology/journalism tips and tricks if respondents wish to pick my brain back!

GB

 

[yewneek]

I'll do a FR of each MF driver on its own in the morning. Looks like the sligtly lower-power version, the SB-R2 has a part number EAS10PM128S. Same 6.2ohm impedance.

Thoughts on this unit?
MF driver replacement possibility

 

[alex-z]

I'm cheap. I want something that fits. I'm not serious, just buried to the hilt.
The drivers I have no idea about the tech specs, it's a guesstimate and something that's good enough is sufficient!

If you want to be cheap then do an impedance sweep of the mid-range driver you know is working properly, see if the Lavoce driver is close. If so it would be a good swap choice.

Impedance Measurement

If the sensitivity is too high there is a little trick to fix that, add some mass to the cone. Clear epoxy is my preferred choice, but anything non-resonant with a strong adhesive will work.

 

[Chrispy]

All this time and effort for a frankenstein speaker? You are a brave soul!

 

[alex-z]

I just looked at your measurement files, my first impression is that the tweeter portion of the crossover is poorly designed, there is 5-7dB of peaking above 4000Hz. There is also the usual 200-600Hz stored energy, seems like the cabinets would benefit from extensive bracing. The mid-range actually looks like the best part of these speakers.

 

[yewneek]

MF Drivers from BlueAran didn't fit, sadly. Looks like I'm stuck with the original drivers being imbalanced until I can find OEM replacements on ebay or somewhere.

Cabinets rebuilt and re-covered and laquered, crossovers rebuilt twice, grilles rebuilt and re-covered, drivers refoamed and rebuilt, tweeters upgraded with ferrofluid, internal wadding upgraded, protection circuits bridged out, rear terminals replaced, just the sealing foam to replace and then I'm done.

They may be a little peaky in the HF but that probs compensates for the falloff in my 50+ hearing, so it's moot.

I can't really demonstrate the sound, but it's pretty nice, quite full and more than acceptable when listening to classical, pop, or rock, on CD (Philips CD650) or vinyl (Rega Planar 2/3 hybrid upgraded)

Played thru a Rotel RA-921 which I got on Freecycle and repaired the buzzing transformer with a deshielding, clean and shield restick with carpet glue .
Recapping/upgrading the main filter caps and a couple of other sets of big capacitors is pretty straighforward.

Sorry if this is a little rambling, but I thought to get down on record in case anyone else wants to go thru this process or searches any of the items or processes I've undertaken.

Videos aren't my thing but documenting is my thing, and the more basic things in restoration are sometimes a little daunting to people working out how to approach it first time.

Loft finds, free stuff, hand-me-downs, it's all still very able to perform and even easier with such good materials we have so freely available now.

GB

PS safety precautions, checks, materials science, test equipment, theory and research, proper chemical handling, all that level of techie fun, has been dilligently undertaken.

PPS the bracing I can't do much about, unless I retrofit some damping for car audio which should do the same thing, if one considers constrained layer damping being the gold standard. May be up next and I can't see it doing much wrong, tho the amplitude difference of the cabinet vibrations may well be up to 60dB less than the cone driver itself.