old Jbl's distorting

my Jbl 4313's sound "cracked" when heavier bass is being played......They surrounds were replaced not too long ago and appear ok from the outside.....tried other sets of modest type speakers and they don't break up at all.......any thoughts?
Dynaco hum, Dynaco hum, where's this Dynaco comin' from? I dun' spent.......

Sorry, got off on a little tangent there.

It is important that the voice coil/bobbin assembly was aligned properly when applying the new surrounds. If they were not, the voice coil/bobbin will rub against the magnet assembly causing a "rubbing" or "cracking" sound with high excursion passages.

Have you noticed this condition since the surround replacements?

Also, if the speakers were played for any extended period of time with the surrounds in bad condition, more than likely (because the woofer cones were not properly supported), the voice coils are damaged.

The 4313s 10" woofer incorporated a 3" voice coil. The voice coil wire in those drivers was actually a square wire vs. a round wire. JBLs term for their square wire was called "Edgewound". Because of this configuration, the voice can be severely damaged very easily if the voice coil was allowed to run misaligned to the magnet.

I know this by experience. I destroyed the voice coils in my L112s by playing them with bad surrounds. It was a VERY costly mistake. It cost me over $500 to have the drivers rebuilt with new voice coils.

Now the speakers are sitting in a closet. Go figure.
I guess that substantial repair money would be better spent on a more "modern " type speaker system.....
I had a pair of Dynaco A-25's that I kept stored in a hot attic for several years. When I decided to re-animate them they seemed fine for about the first half hour. After that they both exhibited scratchy sounds. Pushing gently on the cones with outstretched fingers revealed the voice coils were scraping. Curiously, once they cooled the scraping ceased. Unfortunately it came right back after using them a little. I replaced the woofers with non-OEM ones. It solved the scraping problem but ruined the A-25's tonal balance.

My guess is that during their prolonged non-use some kind of corrosion or rust grew in the voice coil gap. Did your JBL's sit for a good while before you replaced the surrounds?

On the other hand, if your JBL's are making a loud crack like a pistol shot it means the voice coil it smacking against the bottom of its frame basket. Eventually something's got to give. If that's the case you're either playing them too loud or the replacement surrounds may be more elastic than the originals.
Dynaco, it depends on your tastes. Until this day, I have still not yet found speakers that have that "JBL" sound.
If you really enjoy the sound of your JBLs, have them repaired. Voice coil replacements would not be $500.00. Mine cost that much because I had the surrounds replaced at the same time.

Maybe $250.00? You would have to check.

Although, if your interested, I happen to know where there is a set of completely restored L112s w/stands that are absolutely perfect/gorgeous......

Take them to an authorized JBL repair center and have the cones replaced. I use Eastern Cinema Supply in Mass. The repair kit has cone, voice coil, surround as one piece. Like brand new!