Surround Replacement of JBL LE15A
This driver is historic JBL LE15A which JBL Paragon uses. You can visit heritage JBL world at
http://www.audioheritage.org/

Also, visit JBL Pro site for JBL drivers specifications including TS parameters for low frequency drivers.

Specifications and TS parameters for LE15A
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Diameter: 38cm
Frequency range: Fs to 500Hz

Fs: 20Hz, Qts: 0.21, Qms: 5.5, Qes: 0.22, Vas: 736.2 Liter,
Eff: 2.6%, PE: 100 watts, Xmax:4.06millimeters, RE: 8.8ohms,
LE: 2.2mH, Sd: 0.088m^2, Bl: 22, Mms: 97grams, Flux: 0.9tesla


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Surround Repair Kit:
Hino Aidio
http://www.hino-audio.com/SHOP/hyse01.html

July 2012, MJ Magazine
Repair process

Heavily damaged surround and other components The surround is almost gone and the gasket is detached. Removal of residuals from
the gasket by the sand paper for re-use.
Removal of the surround and adhesive from the frame.
Removal and cleaning up the frame and the corn to prepare replacement of the surround.
Cutting out of the surround material. Outer size have to be accurate.
Putting of the surround for fitting and adjustment work if needed. Apply adhesive for the gasket setting.

Place the front side of the diaphragm up on the floor. Adhesive is applied in the rear side of the diaphragm and fix the surround on it one by one. Locations have to be degree 0, 180, 90, 270, 45...order. Make sure that the voice coil does not contact with the magnet gap in every step. Provide 7cm long column with dust cap diameter and temporary fix by the tape. Place the driver upside down. Apply adhesive for every piece and fix. Locations can be random to avoid unnecessary force applied to the diaphragm.

Measurement of TS Parameters

JBL low frequency driver spec. and TS parameters are at
 http://www.jblpro.com/catalog/support/getfile.aspx?docid=1075&doctype=3

In this experiment, there is no major adjustment applied. I have to say that it is very fortunate.
If Fs is higher than expected, you can scrub the surround by the paper Number 100 or around, gently. The Fs value may go down.


Measurement conditions are 1): constant current method and 2) approx. 20 deg-C. Clio is used.

----- Target Parameters ----
Fs: 20Hz
Qts: 0.21
Qms: 5.5
Qes: 0.22
Vas: 736.2L
-------- Measured --------
Fs: 20.29Hz
Qts: 0.21
Vas: 567.7L

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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