What goes wrong with RT16 Drivers and how to fix it!
Gretsch6136
Posts: 80
Hi all,
I bought a great pair of Polk RT16 speakers from 1997 earlier this year. They have been absolutely wonderful, but recently I noticed one of the bass/mid drivers starting to act up.
Every once in a while I would hear a little crackle and sometimes a bit of a buzz or scratchy sound. It would come and go, not a consistent problem.
To try and find the issue I ran a slow frequency sweep through the system and immediately found the driver exhibited a flapping sound on very low bass, and as the sweep rose in frequency there were moments where that buzz/scratchiness came and went.
I removed the driver and carefully pushed the cone in and out. Depending on where I pressed, I could feel a rub. A classic voice coil rub where the coil was touching against the magnetic pole in the middle under the dust cap. Left unattended, it would get worse, leading to a thin, hot spot in the coil that would eventually short out and fry the speaker for good.
I took the driver to my audio/guitar amp tech for further investigation. What he found was that the glue which holds the spider to the basket had broken down and had given up its bond. The spider was lifting away from the basket and was completely detached through 180+ degrees of its circumference.
This meant that the geometry of the speaker wasn't correct and the very fine tolerances of the voice coil around the magnetic pole were off. This caused the coil to rub when it moved. It wasn't doing it all the time as the spider wasn't completely detached. The geometry would vary a little bit as the speaker responded to signal. Sometimes it would rub, sometimes it didn't!
It was lucky I caught it early. There were no visible rub marks on the voice coil itself.
Anyway, the fix was to remove the dust cap and shim the voice coil correctly around magnetic pole. The spider and cone was then raised a little within the basket and the old glue residue removed. New glue was applied to the basket and the spider was carefully bonded back in place. When dry, the shims were removed and the dust cap also glued back in place.
My friendly tech suggested I check the other three drivers. Sure enough they all had lifting spiders to varying degrees, none as bad as the first one. They all got repaired and now my speakers are singing their sweet tune once again.
During this process I researched the RT16 driver and found many instances of drivers exhibiting this type of problem. Many people simply bought replacements, but these have been unavailable for quite a few years now. So if your RT16 drivers are acting up, take a good look at your spiders.
I also found reports of the rubber surrounds separating from the cones. I can only conclude that there was something wrong with the glue used to assemble these drivers.
In either event, fear not, they can be easily fixed by a competent speaker repairer.
Hope this helps!
I bought a great pair of Polk RT16 speakers from 1997 earlier this year. They have been absolutely wonderful, but recently I noticed one of the bass/mid drivers starting to act up.
Every once in a while I would hear a little crackle and sometimes a bit of a buzz or scratchy sound. It would come and go, not a consistent problem.
To try and find the issue I ran a slow frequency sweep through the system and immediately found the driver exhibited a flapping sound on very low bass, and as the sweep rose in frequency there were moments where that buzz/scratchiness came and went.
I removed the driver and carefully pushed the cone in and out. Depending on where I pressed, I could feel a rub. A classic voice coil rub where the coil was touching against the magnetic pole in the middle under the dust cap. Left unattended, it would get worse, leading to a thin, hot spot in the coil that would eventually short out and fry the speaker for good.
I took the driver to my audio/guitar amp tech for further investigation. What he found was that the glue which holds the spider to the basket had broken down and had given up its bond. The spider was lifting away from the basket and was completely detached through 180+ degrees of its circumference.
This meant that the geometry of the speaker wasn't correct and the very fine tolerances of the voice coil around the magnetic pole were off. This caused the coil to rub when it moved. It wasn't doing it all the time as the spider wasn't completely detached. The geometry would vary a little bit as the speaker responded to signal. Sometimes it would rub, sometimes it didn't!
It was lucky I caught it early. There were no visible rub marks on the voice coil itself.
Anyway, the fix was to remove the dust cap and shim the voice coil correctly around magnetic pole. The spider and cone was then raised a little within the basket and the old glue residue removed. New glue was applied to the basket and the spider was carefully bonded back in place. When dry, the shims were removed and the dust cap also glued back in place.
My friendly tech suggested I check the other three drivers. Sure enough they all had lifting spiders to varying degrees, none as bad as the first one. They all got repaired and now my speakers are singing their sweet tune once again.
During this process I researched the RT16 driver and found many instances of drivers exhibiting this type of problem. Many people simply bought replacements, but these have been unavailable for quite a few years now. So if your RT16 drivers are acting up, take a good look at your spiders.
I also found reports of the rubber surrounds separating from the cones. I can only conclude that there was something wrong with the glue used to assemble these drivers.
In either event, fear not, they can be easily fixed by a competent speaker repairer.
Hope this helps!
Comments
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Good info, thanks for sharing. Any idea on the cost of this type of repair vs just buying a new driver? I know someone mentioned Chinese replacement drivers on eBay before.
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My tech normally charges $35.00 per driver for this kind of repair.
