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Technical report on the repairing of a JBL 4350

Technisches Bericht der Instandsetzung einer JBL 4350

Relazione tecnica della riparazione di una JBL 4350

Serial Number 11300A - 11311ASeriennummer 11300A - 11311ANumeri di serie 11300A - 11311A
Mestre, 7 June 2010Mestre, 7 Juni 2010Mestre, 7 Giugno 2010

Target to be achieved

Zielsetzung

Obiettivo da raggiungere

The customer is fascinated by classical loudspeakers. These are able to deliver extreme dynamic even if the frequency response do not extend to the limit.
Goal was to realize the feeling of a stage in the living room, made for the listen of Punk, Hard Rock, Industrial Metal music. Impact music made for high volume at exceptional quality.
The loudspeaker needed to deliver high sound pressure and handle high power. In the end not an audiophile system but a music oriented system, able to deliver a true live sound stage.
JBL 4350 to be repaired

The loudspeaker candidate for repairing

Der zu reparierende Lautsprecher

Il diffusore da riparare

Analysis of the components

Analyse der Komponenten

Analisi degli altoparlanti

The woofer seem to be reconed in the proper way and the mid-bass driver appear to be in very good conditions. At first listening the right high-frequencies driver sounded a lot softer than the left one, this impression has been confirmed from laboratory measurement. Both of the super-tweeter are in perfect shape.

Internal analysis of the cabinet

Analyse des Gehäuse

Analisi interna del mobile

The structure of the cabinet is intact, but due to the age, the screws of the bracings were loose. Furthermore the stiffening separations for the front panel were wrong positioned and loose. The metal support of the right tweeter was missing.
It was clear that the loudspeakers had been already approximatively overhauled: there were wrong soldered wires, some modification at the terminals and bass reflex tubes out of their place.
Internal analysis of cabined of the the JBL 4350

Internal analysis of the loudspeaker

Analyse des Innenlebens des Lautsprecher

Analisi dell'interno del diffusore

Cross over

Die Weiche

Il cross over

The original components of the cross over were still in good shape, but the target to make it as performing as possible, all caps have been substituted using other caps bearing same capacity and higher quality from well known brands, like, e.g. Mundorf, Jantzen, Obbligato.
Furthermore the resistive selector of the right tweeter driver has been renewed to have the same level like the left. It was still not possible to have a perfect match, due aging of the components, but the difference has been considerably reduced to a level, which can be ignored in a normal listening environment.
The crossover of the JBL 4350

The cross over

Die Weiche

Il cross over

External electronic cross over

Externe elektronische Weiche

Cross over elettronico esterno

The original 2-Ways 12dB electronic cross over, which was needed to cut the frequency range between woofer and mid bass driver at 250Hz, was not available and, even if available on the 2nd hand market for a reasonable amount of money, it has been substituted with a modern cross over, which can deliver fairly higher performance. The choice was a StageLine professional cross over. This StageLine Crossover has been tweaked with more performing components.
The connections to the preamplifier and the power amplifier will be balanced to exploit even more the dynamic of the system.

Internal wiring

Interne Verkabelung

Cavi di interconnessione interni

The Loudspeakers have ben re-wired with the 12-AWG cable from Transparent. American cable for an american loudspeaker. The soldering have been made with Tin-solder enriched with 4% silver

Others

Verschiedenes

Varie

The terminals have been substituted with a more modern gold plated terminal, able to accept bananas, forks and barbed wire.
In the basement of the loudspeakers have been inserted steel spikes to improve the quality of the bass reproduction.
The new terminals fo the JBL 4350

The terminals

Die Anschlußklemmen

I terminali

The measurement

Die Messungen

Le misure

The measuring equipment used for the JBL 4350

The measurement equipment

Die Meßinstrumente

Il laboratorio di misura

Frequency response of the left JBL 4350 without woofer and supertweeter

Frequency response of the left midrange

Frequenzgang des linken Mitteltöners

Risposta in frequenza del medio sinistro

Frequency response of the right JBL 4350 without woofer and supertweeter

Frequency response of the right midrange

Frequenzgang des rechten Mitteltöners

Risposta in frequenza del medio destro

Measurement parameters
- Frequency response for the mid-bass range
- Tweeter and super tweeter set to 0dB
- Vertical scala: 5dB per segment
Some measurement differences are due to the positioning of the loudspeaker in the measurement room and their symmetry

The result

Das Ergebnis

Il risultato

JBL 4350 repaired

The repaired loudspeaker

Das reparierte Lautsprecher

Il diffusore riparato

Follow up

Weitere Schritte

Passi successivi

6 November 2011

6. November 2011

6 Novembre 2011

The StageLine active Cross over has been substituted by a Bryston 10B with completely balanced design.