Here, we have a brief overview of the complete restoration and upgrading of a legendary pair of JBL4311 loudspeakers.  These, reportedly, have sold more pairs world-wide than any other loudspeaker, and whilst these are an original pair fro the early 1970s (they first made an appearance in 1969), new versions are still being manufactured today.   However, many purists favour the original 4311 speakers with their ALNiCo magnet drive units, so early pairs are holding value well.  Finding a pair in good condition, like many of these things, is becoming more difficult.  These were originally designed for use in recording studios (hence the tweeter location, designed for horizontal speaker placement), the domestic equivalent being the JBL -L100.

 

Original pair arrived rather the worse for wear!

JBL 4311: original grilles beyond repair

JBL 4311: original grilles beyond repair

Original JBL 4311

Original JBL 4311

Damage to JBL 4311 cabinet corner

Damage to JBL 4311 cabinet corner

 

 

 

A brief examination revealed:

  • serious cabinet damage requiring repair
  • tweeters damaged and new tweeters required
  • veneer in very poor condition requiring the cabinets to be re veneered
  • internal fibreglass wadding considered a health risk so requires replacement with acoustic foam
  • cabinets poorly damped so bitumastic damping to be added internally
  • existing crossovers out of specification (electrolytic capacitors past their best) and rudimentary design runs all three drivers to overlap too much in the mid band, so a new three way crossover is really required for serious hifi use
  • front baffles need re-painting
  • new grilles required

Cabinet work:  removal of drive units and internals:

JBL 4311 cabinets

JBL 4311 cabinets

Name plates being carefully removed so that access to crossover holding in bolts can be made:

Removal of name plates

Removal of name plates

JBL 4311 name plates removed

JBL 4311 name plates removed

Existing crossovers removed:  Note, bass runs full range with simple roll-in capacitors for mid and HF units.  Potentiometers are for altering sensitivity of mid and HF units but hey also change corner slope profile between drive units!

JBL 4311 crossover

JBL 4311 crossover

Cabinets ready for restoration.  Note, all internal galss fibre wadding removed except for mid range (sealed tube):

Stripped out JBL 4311 cabinet

Stripped out JBL 4311 cabinet

Damaged cabinet corner repaired:

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Cabinets then re veneered:

Re veneered JBL 4311 Cabinets

Re veneered JBL 4311 Cabinets

Next, cabinet internals tackled with new bitumen damping sheets applied to all surfaces except front baffle, and new 40mm acoustic foam panels glued into place.  Following measurement and testing of drive units, a new crossover design (supplied by others) for the equivalent L100 was deemed an exact drop in, so a crossover was built based upon the design for the L100 and inserted into the back speaker panel:

New crossovers constructed for JBL 4311

New crossovers constructed for JBL 4311

Restored Loudspeakers final assembly and cabinet finishing:

 

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Restored JBL 4311 with new grille

Restored JBL 4311 with new grille