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RCF L18S800 cloth surround not doped after repair?
RCF L18S800 cloth surround not doped after repair?
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Old 28th January 2015, 10:39 AM   #1
athlon64 is offline athlon64  Croatia
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Default RCF L18S800 cloth surround not doped after repair?

Hello guys. So i'm running 4 EV T18 boxes with RCF L18S800 drivers. Recently someone from the club i rented them clipped and fried all 4 of them so they payed for the rapair. One driver had allready been repaired a long time ago (they are 17 years old) so the guy couldn't repair it again, he had to order a recone kit for that one. He reconed it and it looks beautifull and works fantastic now.
The other 3 drivers did not need a recone, he just ordered a new coil from RCF. And a new upper suspension (cloth surround) because the old one started falling apart from age. The guy that i gave these drivers to for a repair is doing this job for 25 years and is the best in city.

Now these 3 drivers that he repaired are working well, but he didn't put any glue/doping material on the new cloth surround. So it looks yellow and you can see it's completly dry, there is nothing on it. I forgot taking a picture but it looks the same as this: http://www.diyaudio.com/forums/blogs...ound_small.jpg

So as you can see, the air can now go trough the cloth material and it's very soft. You can feel , when you are touching the driver, how it's softer then the reconed one. When you give it some low frequencies you can tell it's moving more then the reconed one just by looking at it. When playing music they seem to sound similar, but when you give them a sinewave between 45 - 60hz. The reconed one is about 10dB louder. I listened to it and measured it. The guy in the store told me he never puts doping on the sorround because it just slows the cone down and isn't necessary. He repaired hundreds of S800 (and he is not lying, he is really known as one of the best in this job). He told me that the reconed one needs some braking in and they are going to sound the same later. But it still seems to me i should dope the cloth sorround since i have never seen an RCF 18 withouth doping on the cloth sorround.

What do you think about this?

https://www.youtube.com/watch?v=5CJx...ature=youtu.be

Last edited by athlon64; 28th January 2015 at 01:42 PM.
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Old 28th January 2015, 12:40 PM   #2
bear is offline bear
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Wonder where he gets the undoped cloth surrounds? Hmmm...

If these are bass bins, then I would definitely put some doping on the surrounds. If air can go through the surrounds and/or the dustcap then the effective parameters are altered somewhat. Otoh, if the performance is ok, then it may not matter.

It makes little sense that the recone is 10dB louder at 45-60hz, except that there must be a difference in the cone mass and/or the VC is different (more turns in the gap).

There are very light compounds that can be put on the surround, so that is not an issue as far as changing the compliance of the surround enough to be concerned about.

Glue should never be used on a surround unless the goal is to stiffen it, and even then glue is not exactly what is called for anyhow. (imo)

If the new surrounds are less stiff than the old, then at LF the TS parameters are changed. Probably it will not handle quite as much power, as it is likely to have less excursion control at LF, especially *below* Fs or F3 (in the box). So bottoming out the driver becomes a concern in live sound situations, unless there is a HP applied to keep the subsonics out.

It will also have an effect on what the cone will do at higher freqs as the termination of the cone at the outer edged is changed. Could be better or worse - likely different somewhat.

All merely my opinions...

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Old 28th January 2015, 12:48 PM   #3
athlon64 is offline athlon64  Croatia
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By what he says he gets it directly from RCF Italy. I'm quiet sure this might be true. Every audio tehnician i know recomended the guy. What do you think is the other possibility. That he got aftermarket cloth?

These are Electro voice T18 boxes. Bass bins yes. I usually low cut them at 35hz and high cut them about 100hz. The boxes are horns so drivers move quiet free. But these repaired ones without doping a bit too free from what i see. From what i hear i think they start reaching xmax sooner now. They get that ringy/too much membrane movement sound earlier then the reconed one. They are just too soft and move to free. They have less excursion control yes. I have recorded a one minute video showing the reconed one running at 50hz. And then the repaired one at 50hz with the same input power. I'll upload it now so you can take a look and listen.

Questions, where do i buy the right doping material?
Can i buy a black doping material? Yellow cloth looks a bit silly.
Doping shouldn't be hard to do right?
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Old 28th January 2015, 01:41 PM   #4
athlon64 is offline athlon64  Croatia
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https://www.youtube.com/watch?v=5CJx...ature=youtu.be

Here. Take a peak at the video. The first bass bin in the video is the reconed one.
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Old 28th January 2015, 06:03 PM   #5
zettairyouiki is offline zettairyouiki  United States
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I reconed a 3015lf myself and was worried I had done something wrong when they sounded horrible. Then I realized you could blow right through the surrounds. I bought this stuff to dope the surrounds and seal it up.
Speaker Repair Adhesive, Sealer, Cloth Surrounds, Foam Surrunds, MI-1291
Works great now.

This video shows that stuff being used.
http://youtu.be/x6CCrLz-Zts?t=38m11s
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Old 28th January 2015, 06:06 PM   #6
athlon64 is offline athlon64  Croatia
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Thank you. I really can't believe, every audio guy in the city told me, get them streight to the "xyz" guy, he is the best in reconing and repairing. And he puts absolutley nothing on the yellow surround. The driver is so soft now.
Can i get this glue in black? I'd really like to see my surround black, it looks alot better.
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Old 28th January 2015, 07:50 PM   #7
epa is offline epa  Netherlands
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Quote:
Can i get this glue in black?
you can put some black dey( ofarbati)in it .
it would be wise the weaterproof the cones aswel.
i think original rcf cones are stiffer.
i don't know how costly the repair was,buty you can alwais put an original recone kit in.
edit / the repaired one hes a lighter conus an lighter suspension.
maybe in your box they preform "better" > then you can do the last one also.
edit2/original rcf
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Last edited by epa; 28th January 2015 at 08:13 PM.
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Old 29th January 2015, 12:02 AM   #8
athlon64 is offline athlon64  Croatia
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Well what he put in is the original recone kit. The package arrived from RCF Italy. I saw it myself. I don't think they sell exactly the same cones as 20 years ago.

Also what can be the cause of one driver clipping slightly earlier then the other one even when the amp is getting a mono signal. Can over excursion be the cause of this?
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Old 29th January 2015, 12:35 AM   #9
bear is offline bear
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There are many types and grades of sealers in the speaker industry. Unfortunately only a few make it to consumers, like the one cited above. It dries clear. So you could color the cloth itself. That's what I would do. Could be as simple as grabbing the guts of a permanent marker with a surgical glove and wiping one or more coats to make it black.

When you say a driver is clipping, what exactly is the thing you are calling "clipping"?

Btw, the stuff shown may or may not add enough stiffness to equal the original's characteristics. But more than one coat may be applied.
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Old 29th January 2015, 01:15 AM   #10
conanski is offline conanski  Canada
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Quote:
Originally Posted by athlon64 View Post
These are Electro voice T18 boxes. Bass bins yes. I usually low cut them at 35hz and high cut them about 100hz. The boxes are horns
The T18 is a manifold design and they really only load the driver down to 50hz so your 35hz lowcut likely contributed to your driver failures, I'd suggest you raise that up to 45hz. Did you get a definitive cause from the reconer? Were the voice coils burnt or physically damaged from over excursion?
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