JBL-2245J Replacement work for the Surround

Some sort of surround materials have shorter life time. After three or four years usage, the surround is broken or worn out depending upon the condition of environment and or usage. In the PA industry, they usually ask makers to repair. The maker replace all the diaphragm assembly. If the speaker is for personal usage, it is also good idea to ask maker to repair for keeping original product quality. However, some amateurs may challenge to repair it by him or herself on their own risk.

In most of the case, the surround is worn out faster than other components which have relatively longer material life. There are 3rd party surround replacement kits sold in the street which gives us longer life. This page shows how to repair surround from flat sheet material. For the material, refer to the following site.
http://www.labsp.net/

The repair work was done for JBL-2245 in this example. However, it is important to know that the replacement of speaker materials will damage original speaker property in some case. Also makers product support is terminated.


December 1990, MJ Magazine
Repair process

Broken or worn out
surround
(Urethane made)
Removal of the surround
by a cutter knife
Removal of the edge from
the frame and keeping it
for re-use
Removal of the surround
material from rear side
of the diaphragm
Removal of the surround
residual material by the
alcohol/bensine cleaner
Completion of surround
removal process
Drawing two circles by a
compass on new
surround sheet
(Urethane rubber)
Cutting out of the
surround by a scissors or
a cutter knife
This process is the most
important portion.
The mass on the diaphragm
must be well balanced
and no contact between
the voice coil and the
magnet is assured.
The photo I used was the
small speakers as a
weight.
Application of adhesive on
the edge side of the frame
and placement of new
surround on it
Making some slits inner
side of the surround
and bringing those into
the rear side of the
diaphragm
An adhesion process of
the surround to rear side
of the diaphragm with
adding constant mass
Then, an adhesive is
applied between the
surround and rear side
of the diaphragm.
Removal of the weight
yields a curve on the
surround sheet to
support reasonable motion
of the diaphragm.
Final adhesion process
for the rear side of the
diaphragm and inner side
of the surround
Completion of repair work
.(rear side view)
Completion of repair work
. (front side view)

Measurement of TS Parameters

Major TS parameters in
JBL-2245 catalogue are
as follows.

Fs=20Hz
Qts=0.27
Vas=820Liters
After the repair, TS
parameters measured
are as follows.

Fs=22.45Hz
Qts=0.2715
Vas=424.26Liters
Comments: It is very fortunate that the parameters are not so far away from the catalogue number. Numbers move depending upon 1) Unit by unit variation, 2) Environment of usage and 3) Way of measurement such as how many wattage applied.

Notice:

The surround is one of the most delicate component in a speaker driver. Replacing this component means that we , most probably, change the compliance. This leads out the difference of Fs, Qts and Vas values at minimum. This potentially impacts the low frequency property of the speaker enclosure.
Therefore, we have to know about original TS parameters and also the TS parameters after the repair work is done. Then, we can recognize the magnitude of the differences. We can sometimes re-tune the enclosure resonance

One more important matter is the "Quality of work". The "Curve" of the surround relates to Xpeak and Xmax. Diaphragm motion exceeding Xmax generates distortion. Where Xpeak is physical maximum of the diaphragm motion and Xmax is maximum motion with linear domain.

Good luck!!

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