15" RCF bass driver - cause of ticking sound?

I bought two beautifully made Neo magnet bass drivers that came from a Mackie active speaker, so it is probably safe to assume they were made by RCF. The previous owner sold them as defective with scraping coils after an overload. However, when I received them, I carefully moved the cone up and down and could not detect any scrape. Actually, the wiggle rome for tilting the cone or moving the VC laterally was a lot bigger than in most new factory drivers I have com across.

The next test was to run 20 Hz. Both drivers exhibited a slightly metallic ticking sound but none of the scraping or metallic thud usually associated with a burned or deformed VC. It sounded a lot like tinsel slap or a poorly glued surround, but these phenomena usually start at a certain excursion whereas both my drivers exhibited it even with barely detectable drive level.

Thanks to the generously vented spider, I had a clear view of the VC. I was even able to pull all windings out of the gap thanks to a large maximum excursion. Their outside showed no signs of burned resin or other deformity. The coil was dull black with the exception of the upper winding (which happened to be on the inner layer), so I assumed it was blackened to improve heat dissipation.

Having checked all soft parts for loose glue joints, I finally removed a dustcap, but there were no loose particles or faulty joints underneath.

So pretty much the only explanation I have is that the resin that holds the turns in place on the former has come loose, allowing the individual windings to chatter against each other. I have seen older (15L200?) and fairly recent (L18S801) drivers where the turns have become unwound so that you can see a nest of wires through the sieve in the pole bore. Is it possible that my drivers are exhibiting a similar conditions except that the windings look like they are still securely in place?

If so, would a drop of fairly thin high temperature epoxy solve the situation? Should I let it cure cold or apply some DC current to speed curing?

Thanks
 
Im no expert so dont shoot me down!
Even though the VC isnt showing signs of damage there could be an intermittent connection that will only show at full excertion... however, have you tried this 20 Hz test on a different amplifier ? it could be an amplifier clip or a poor audio source.

Furthermore, it could be the fact that the speaker is in open air (im assuming) try the speaker in an enclosure where the speaker is getting the correct amount of back pressure on the cone.

again im just suggesting things to try, please dont shoot me down :)
 
The voice coils are not normally black and I suspect the resin has been burnt and become loose.

Not normally, but they can be. I have a couple of mint P-Audio recone sets (for a pretty humble driver with a steel basket) and they have blackened copper wire.

The VCs in question look very similar, but I will take a second look.

The amp is the one that I normally use for testing drivers, and I hooked up a known working speaker afterwards, so this is not the issue.
 
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A voice coil *may* be black (although I never saw one) but it will never be black for part of the winding and enamelled copper colour for another section of same winding.
In that case the copper coloured is the good one, and black is toast.
Meaning *the VC* is toast.
That metallic ticking sound is some loose part (caused by overheating or mechanical abuse), either a couple turns, VC partially separated from cone, you name it.
The speaker looks very good, but you'll have to recone it.
Hope you paid peanuts or nothing for it.
And no, dripping some adhesive down the coil will not repair it, sorry.

You probably have something similar to this:
[IMGDEAD]http://img144.imageshack.us/img144/1395/burnt002nr6.jpg[/IMGDEAD]

this one also bottomed so it's slightly crushed:
[IMGDEAD]http://img83.imageshack.us/img83/3636/burnt001sv8.jpg[/IMGDEAD]

Compare these:
3863592563_5e6a166897.jpg
 
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A voice coil *may* be black (although I never saw one) but it will never be black for part of the winding and enamelled copper colour for another section of same winding.

Thanks, those pictures are helpful. I would say the transition is more aprupt in the case of my VCs, consistent with black paint applied with some sort of roller so it couldn't get to the first turn that happens to sit on the inner layer. As I said, I will look more closely.
 
Maybe you can get a recone kit (or spare parts) and recone it for relatively low cost.
*Somebody* in Europe must sell speaker parts .
In USA you can try MWA Speaker Parts
Speaker Parts Voice Coils Speaker Repair Kits - MWA Speaker Parts, Inc.
In theory they only sell to established speaker reconers, and they have "exclusive area" agreements, so they have "one" reconer in each area, but if you write from Germany as "the" reconer in XXX City who has a problem with a customer and Mackie or RCF doesn't help, they probably will sell you.
As of freight cost, kit will be very light but bulky.

Alternatively write RCF themselves.

Personally, being in Argentina and quite away from supply sources , not because of distance but because of obnoxious Customs, problems with funds transfer, etc. , I have repaired such speakers by disassembling them and making new voice coils.
Even rewinding on the same form, how's that?
But it's not for the faint of heart.
 
I'll take everything back. Looking at the VCs in bright daylight, I have to agree they were toasted even if no single turn is sticking out. I removed one of the dust caps so I can use my fingers to expand the VC former. When I do this close enough to the pole, the chattering stops whereas it doesn't when I do it a few mm above the uppermost turn. So I suppose there are indeed some loose turns.

One of the coils measures at 3.9 Ohms which is almost high for a 4 Ohm driver. The other one measures about .35 Ohms lower so I am not sure if this is regular tolerance or I am facing one or several shorted turns.

Since the venting underneath the spider is quite generous, I was hoping to apply some sort of lacquer with a paintbrush or a pipette. I have found some alkyde based lacquer for electronics use that is good to at least 125°C which should be fine for home use. The advantage compared to epoxy is that the lacquer can be removed with acetone, should I screw up.

By the way, do professional VCs rely only on the tension of the wire after winding or do they usually have epoxy or some other resin to keep the turns from moving?

Yes, rewinding on the existing former is something I might try should the lacquer not work. It might be a whole lot easier with square wire but I have not found a source yet.

In case I have to remove the soft parts, some are glues with clear stuff that will normally turn opaque and softer when exosed to water. However, the dustcap and spider are glued with glossy black glue that does not absorb water. Any ideas how to tackle that?

Thanks again for all the input so far!

(two pics of the toasted VC and one brand new black P-audio)
 

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Save money and frustration and send it back. :)

By the way, do professional VCs rely only on the tension of the wire after winding or do they usually have epoxy or some other resin to keep the turns from moving?
Usually winding tension is low, only as much as needed so wire follows the form curve, it's held with adhesive.
Standard is a special Epoxy but modern wires come with a pre-applied dry adhesive to simplify winding in high speed machines.
 

Mid Low

Member
2013-03-14 4:20 pm
I hate when speakers act like that once i have some 15" Celestion mid bass drivers in my car and one day i started to notice that they sounded strange when they hitted lower frequencies but they where sounding on higher frequencies normally. Turns out that when i take'd them out the VC was like shattered on the lower side a lil bit, making them to do a scraping sound i keeped using them until it completely broke =\
 
I hate when speakers act like that once i have some 15" Celestion mid bass drivers in my car and one day i started to notice that they sounded strange when they hitted lower frequencies but they where sounding on higher frequencies normally. Turns out that when i take'd them out the VC was like shattered on the lower side a lil bit, making them to do a scraping sound i keeped using them until it completely broke =\

Well, you may hate *the speakers* if you wish, I bet they hate you more :D
The "VC shattered on the lower side" means you drove them with *way* too much bass in a poorly loaded enclosure, so they "bottomed out".

i blew a coil on some 3000 watt DVC drivers where something got under the dust cap where the heat from last summer melted the adhesive Smoke everywhere....
I very much doubt even staying under the Sun at noon had anything to do with it.
Don't you think your 3000W amplifier maight have had even a tiny little something to do with your speakers bursting in flames?
Just sayin' :p
 
I very much doubt even staying under the Sun at noon had anything to do with it.
Don't you think your 3000W amplifier maight have had even a tiny little something to do with your speakers bursting in flames?
Just sayin' :p

the amp outputs 5000watt at 1ohm (monoblock) into 4 parallel wired voice coils (4 ohm each) providing a 1ohm load for the amp. The speakers are 2x DVC (Dual Voice Coil) ~3000Watt Peak (1500 RMS) @ 2ohms for 2coils wired parallel into one.

The sun comment was a joke.... what happened to banter people !!!!?!?! :)

Please read the comment before replying Mr JMFahey.

Me and my team did the maths smarty pants :)

(Didnt mean to come across nasty btw :):):) im in it for the laughs)

-Steve
-European Mobile Media Association
 
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