Falcon Acoustics posted about White Belly Disease in 2021 on the LS3/5A Facebook page. This information is important to warrant a page all to itself.

Their post said, “B110 White Belly Disease.

We don’t do many refurbishments of classic LS35a’s but in the past couple of months we have helped a couple ex-BBC Engineers with their own personal pairs of LS3/5a’s.

A few weeks ago, we had a mid-1980’s pair of faulty Rogers 15-ohm LS3/5a’s come into us from an ex-BBC engineer who said they didn’t sound right.

On receipt of the speakers the first thing we always carry out is a visual inspection to look for anything simple. In this example, the first obvious fault was the infamous B110 White Belly.

White Belly is a progressive B110 driver deterioration of the coating of the B110 in the critical dust cap/neck region, where the Plastiflex/binding coatings have failed, coming away from the cone underneath.

This creates a cavity between the Plastiflex coating and the Bextrene cone, and causes a resonance peak in the frequency response in the vital 1.2 khz region resulting in a very mid-forward presence in the speaker voicing.

The next step was to take a frequency response of these Rogers speakers, we were fully expecting a peak in the 1khz region but this pair exhibited a 10db rise in this critical area. It also collaterally showed that the T27 on one of the speakers was now down in output.

Both pairs of B110’s and T27’s were replaced with matched pairs of Falcon drivers, crossover components changed to match Falcon B110 specification, and all tested and resealed.

The accompanying response curve shows the original response plot (Red) and clearly shows the effect of the +10dB White Belly peak at 1.2 KHz compared to the post-repair response (blue).