blown drivers

doc25 · February 2003

I would like to get an opinion concerning two blown drivers in one of my RT-16 series speakers.

I noticed quite a bit of distortion from one side recently and realized that both drivers in that speaker were making noise and crackling. This was especially apparent during certain types of music (sometimes at low enough volumes they seemed fine). Since both drivers seemed bad, I didn't know if the crossover was at fault. I swapped one of the bad drivers into the other speaker and the driver still was bad (real easy to hear next to the normal sounding driver).

Additionally I have recently noticed that my Panamax surge protector is not working anymore. It now reads overvoltage when plugged in.

My question is this. Could a power spike have caused the damage to the surge protector and also the drivers? Could the surge protector somehow by going bad, in of itself injure the drivers? Because both drivers went bad at the same time, should I be concerned about the crossover? I certainly would not want to replace the drivers and be a setup for a repeat event if the original problem wasn't fixed. I don't really play my music/movies too loud (I have an Adcom amp/preamp, but a fiance whose a light sleeper!). Thanks for any help you can give.

harley92 · February 2003

sure seems like the driver to me , surge could cause driver to go if you had the system on but i dont think so the amp or receiver would be the first thing in line for destruction

doc25 · February 2003

Thanks. I know what your saying I just found it weird that both drivers went bad at the same time. I'm not sure if that's a relatively common occurrence.

jcamin · May 2003

Strange, one of the drivers on my set or RT16's just died as well. I noticed the same thing, at low volumes there is lots of scratching and distortion. I pulled it all apart and found that the rubber surround is no longer holding the cone in the proper alignment. When you physically move the cone with say a finger, you can hear the coil scratching the magnet. Interestingly, it only scratches on one side of the speaker. Movement is free and clear on the other side. With low volumes, there is not much magnetic force driving the speaker, so friction takes a much larger role in the sound (ie, if there is friction, you'll hear it much clearer at low volumes). Higher volumes produce much higher magnetic forces and hence the friction force it proportionally lower and hence quiter.

Question, did you do anything to fix it? I checked and replacement drivers are about $75 a wack. I'm guessing this is my only option right now, except for just running one speaker.

-John

burdette · May 2003

Originally posted by jcamin
Interestingly, it only scratches on one side of the speaker. Movement is free and clear on the other side.

Given that the VC is circular, suspended within a circular magnetic gap, ONLY one side could touch at a time unless the VC was deformed.

Originally posted by jcamin
With low volumes, there is not much magnetic force driving the speaker, so friction takes a much larger role in the sound (ie, if there is friction, you'll hear it much clearer at low volumes). Higher volumes produce much higher magnetic forces and hence the friction force it proportionally lower and hence quiter.

Technical correction... the *magnetic* force doesn't change. That is set up by the magnet structure of the driver. As the electrical energy going through the VC increases, the interaction between magnetic and electrical can increase, but the magnetic force itself is constant.

Question, did you do anything to fix it? I checked and replacement drivers are about $75 a wack. I'm guessing this is my only option right now, except for just running one speaker.

-John [/B][/QUOTE]

Watch the Flea Market forum for used drivers.

jcamin · May 2003

OK, but the question still remains... why/how did it fail? Is the surround deteriorating or was there a defect in production that is pulling the coil to one side?

These drivers have been babied since I've gotten them. It is definitely a mechanical failure, and not a typically 'blown' speaker from abuse.

A 'technical - technical correction' actually the magnetic force does increase. True, there is a constant earth magnet creating a static magnetic field, but the 'interaction' you mentioned is an electromagnetic force that is equal in frequency of the electricity in the coil and proportional to the current in the coil. So With increased volume (increased current) there is much more magnetic force acting on the coil. If the total magnetic force remained the same, the coil would not move.

burdette · May 2003

Your assertions don't refute what I said - and in fact after you told me I was wrong you proceed to essentially say the same thing I said.

The original implication was that a change on the volume control somehow changed the *magnetic* force.. and it does not. A change on the volume changes the electrical current, and the interaction between the constant magnetic power and the changing electrical current can produce changing electromagnetic interaction. But the ONLY variable in that interaction is the current... changing the volume does NOT add a magnet or take away a magnet. The electromagnetic forces can change, but the physical magnet and the magnetic energy it provides to the VC gap does not. Now, an *electromagnet*... its magnetic energy would change as a function of input current and frequency... but the magnets on drivers are not electromagnets.

jcamin · May 2003

Yes we're basically saying the same thing.

Some terminology corrections, however... Magnetic fields are created by either perm magnets OR by electromagnetics. The voice coil is effectively an eletromagnetic, and as such creates magnetic fields as well. The total magnetic field is a function of both the static perm magnetic field and the dynamic electromagnetic field in the coil. So, the magnetic force (which is the product of the current in the coil and magnetic field) does increase with current, or volume.

So your correct, changing the volume does not add or subtract a magnet. BUT, it does add or subtract from the total magnetic field. And as such, what I said about the friction force being less proportionally at higher volumes is correct.

My question, that hasnt been answered, is how/why the surround holding the coil in the proper position deteriorated/changed and is now holding the coil slightly off-centered?

jaster · May 2003

Pull the drivers out of the RT16's and see if the spider has come apart from the basket. I had some similar sounds in mine and what I discovered almost made me cry. All 4 drivers in my RT16 are trash. The spider has come completely apart from the basket. The speakers are not blown and still work, but they make some noise.

Here's what mine look like.
http://www.hesterinc.com/polkaudio/

jcamin · May 2003

Well... thats encouraging.

I spoke with customer service and they said that even though the 5 yr warenty is up on mine, to send them in if I thought it was a defect. They'd take a look, and see what they could do. Worth a shot anyhow.

I checked the spiders and they appear fine. Still no clue... perhaps they are degrading and pulling the cone to one side.

F1nut · May 2003

jcamin,

While I'm not familiar with the RT16, one of the great things about Polk speakers is that they use a rubber surround. There are plenty of 20 year old Polk's that still have the original surrounds in them because of that. I really doubt that's your problem.

filleul · May 2003

I had a similar experience with my LS-fx, one of the midrange/woofer driver caused scratching and distortion. This was already a replacement 3 years ago. I took it out of the speaker box this time to check and there it was : the spider had totally come loose from the part that houses the voice coil and the magnet. It was going to cost me US$ 60 to have it replaced again since it came out of warranty 2 years ago. My dealer suggested they could reglue the part. So that's what I did : I used some Pattex (contact cement) to glue the spider back onto the plastic speaker case and so far OK.
It's a cheap alternative but with some imagination, patience and a few tooth pics I was able to carefully glue the parts back together.
This brings me to the conclusion that Polk Audio must have used some bad glue on the parts starting "97, since that's when my replacement woofer was assembled, 30 oct. 97. The others seem fine... for now... they were assembled arround may '95.
As for my RT16's they seem to be fine as well... maybe they were assembled in '95 too? 8-)

joe logston · May 2003

try to turn the driver upside down the reverse of the weight will align the comb & magnet, this mite help

jcamin · May 2003

Interesting... as in just set it face down, or play it while its facing down?

I was wondering if it just might need to be removed and rotated. I guess gravity 'could' eventually pull it down. Sounds strange though.

blown drivers

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