Film-Tech Forum ARCHIVE: Dry rot in speakers

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Posted by Allison Parsons (Member # 2728) on 11-14-2004, 02:47 AM:

Recently, when tearing down my old theater, we noticed that A) many of the sub woofers in our surround sound speakers were missing thanks to old janitors stealing them... and B) most of the rest of our surround sound speakers had dry rot. Thank god the speakers in the two theaters that we had which had MONO sound in it worked [Eek!]

Yeah. I said MONO sound.

Question too older theatres: Do you annually check your speakers for dry rot/stolen sub's.?

Posted by Steve Kraus (Member # 476) on 11-14-2004, 09:50 AM:

Theft is a problem sometimes; search the forums for "speaker" and "theft" or "stolen" and you'll see some earlier discussions.

Grand Theft Speaker

Locking Screws for Speakers

But don't you bet that speakers are more likely to be taken by young ushers than old janitors? [uhoh]

Posted by Mark Gulbrandsen (Member # 72) on 11-14-2004, 12:40 PM:

Actually torx anti-theft screws rarely stop anyone any longer and I've stopped using them for the most part. The anti-theft bits are easily available at Home Depot these days. Back when Steve was working for me at Midwest Theatre Supply we did manage to stop speaker theft at an Elgin theatre location by using them... these days its another story as hardware places like Home Depot stock the special bits as fast as new anti theft hardware emerges on the market.... so anyone has easy access to them. I do still use anti-theft torx set screws but just for locking the shutter blade in DP-70's as normal allen screws heads strip out too easily.

As for dry rot.... It normally happens to any foam surround in any woofer at about 7 to 10 years time. Like all foam it literally desintegrates when it gets old. Paper cones can also dry rot in about the same time and become VERY brittle and will disentegrate to pieces during the next Lucas Film engaugement of high level sounds. If you use higher quality speaker systems, JBL or E-V, it is not as much of a factor as the paper for the cones is specially produced so they will not dry rot any time soon. Generally you get what you pay for in cinema speakers life span and performance!! So if you bought some cheap speakers such as Peavey don't expect a long life span from them. It is possible to replace those cheap drivers with higher quality longer lived parts though.....

The good thing is that foam surrounds on woofers are easily replaced by simply sending in the driver to a qualified speaker re-cone service. Once there they will replace just the foam surround with newer type foam surrounds that won't rot nearly as fast. Drivers that have rubber surrounds on the cone rarely fall apart like the foam type do but they are much more expensive and are rarely used in cinema applications.

Mark @ CLACO

Posted by Allison Parsons (Member # 2728) on 11-14-2004, 02:07 PM:

Steve,

hehe, actually, when I said 'old' janitors, I ment janitors from 7-9 years ago. Not old aged janitors [Smile]

Posted by Steve Kraus (Member # 476) on 11-14-2004, 02:14 PM:

Your old theatre went 7-9 years without noticing? No wonder they closed!

Send those recone jobs to Steve Guttag; it keeps him off the streets and out of trouble! [Big Grin]

Posted by Allison Parsons (Member # 2728) on 11-14-2004, 04:23 PM:

Lets just say the even if we noticed the speakers were gone/rotted, no one from home office would have spent the money to replace them. Sad, but true.

Posted by Mike Babb (Member # 1379) on 11-14-2004, 05:09 PM:

I know of several theatres that have lost subs but was interested to hear of one theatre where the thieves got up in the speaker lofts and stole one 15" driver from each cabinet that had two, the tech apparently noticed it when checking the b-chain.

Posted by Wolff King Morrow (Member # 2226) on 11-14-2004, 05:29 PM:

quote: Allison Parsons
Lets just say the even if we noticed the speakers were gone/rotted, no one from home office would have spent the money to replace them. Sad, but true.

That reminds me of an old (and now shut down) UA theater I worked at. They had gone 20 years at the place without replacing the speakers. After I got promoted to manager there, I got a ladder and pulled the speakers down to inspect them. ALL of the paper cones turned to dust at the slightest touch. I had to go over the head of my boss (whom wouldn't spend a dime on the place) and get the district manager to replace them. I naturally got busted by my boss the next day, but the theater got new speakers and the difference was incredible. It was worth getting busted to have them replaced.

Posted by Edward Jurich (Member # 1787) on 11-14-2004, 09:27 PM:

I once heard of rats eating out cones, wire screening had to be used to cover baffel openings.

Posted by Allison Parsons (Member # 2728) on 11-14-2004, 11:55 PM:

I dont know why getting something like new woofers is so difficult for a theatre chain to do. We would always complain about the surround sound being crappy but home office would always say 'well, your an old theater.' and would leave is at that. I hope more of you work at better companies then I did/do. I know sub-run theatres are the bottom of the food chain but still, at least give a damn!

Posted by William Hooper (Member # 71) on 11-15-2004, 01:21 AM:

Yes, they rot.

The worst case I saw was visiting a church that had 5 years earlier sold the theater organ it had bought as its original organ, & replaced it with an electronic chuchy-like organ.

I went up to the old pipe chambers to look for missing parts of the removed theatre organ, & the large speaker cabinets for the presently-used, 5 year-old electronic organ were installed there behind the grilles. The cones were all dry & rotted; several of the speakers had cones that had fallen apart. That electronic must have sounded awful through that junk.

Posted by Frank Angel (Member # 248) on 11-15-2004, 09:54 AM:

I understand that reconing services are readily available and any speaker exhibiting that kind of damage should either be sent for service or replaced, hopefully BEFORE it turns to dust.

I have 8 15in woofers and 8 midrange speakers in 8 BSR 3-way systems where I see the foam surround beginning to deteriorate, yet the cones are fine -- impregnated paper on the woofers and a transparant plastic of some kind for the mids. I was thinking of trying to repair the surround foam myself, not so much for the cost of reconing, but rather more for the labor of having to physically extricate the speakers from the boxes.

The foam is just beginning to go and I thought if I got strips of rubber and just glued the strips over the foam with rubber cement, that might be a preventative and easy fix. I have no idea how that would affect the performance of the speaker, but I figure I could try -- if it works, I am ahead of the game; if it doesn't, I just will have to pull them and have them reconed.

I knew a reputable audio engineer (he worked in a big NYC recording studio) who said that with his any of his speakers that had paper cones, after 5 years he would paint the paper with rubber cement as a preservative. He claimed it did not affect the speaker response but that it actually improved the speakers damping. I have no way of knowing if that actually is true or not, but I figure if he can apply a coating of rubber cement to the entire cone, my applying just a bit around the edges couldn't hurt. In fact, the only reason I thought I would try rubber cement is because of this guy's tale. I actually first thought of using silicone cement as the bond for the rubber strips as silicone has great bonding power while remaining flexible after it dries. Although I don't think I'd be able to apply it as evenly as the thinner rubber cement which can be brushed on more uniformly.

Anyone know who might supply rubber sheets of various thicknesses? I was considering cutting up condoms as the joining material for want of anything more easily accessable. I figure they should be pretty tough and resilient, no? Then again there is the embarrassment of having to dump twenty-five 100 count cases of Trojans on the counter.

Posted by Edward Jurich (Member # 1787) on 11-16-2004, 09:54 AM:

quote: Frank Angel
I knew a reputable audio engineer (he worked in a big NYC recording studio) who said that with his any of his speakers that had paper cones, after 5 years he would paint the paper with rubber cement as a preservative

It's not every day rubber cement, I have some of that stuff downstairs somewhere and have used it to repair paper cones that were starting to tear. It does a great job of repairing paper cones but I doubt it'll work on foam. I thought that new foam edge could be bought for replacement, you might check with a speaker supplier.

Posted by John Pytlak (Member # 331) on 11-16-2004, 11:34 AM:

When I worked at the drive-in, spraying the cones with silicone water-repellant treatment (similar to what is used to waterproof boots) seemed to help the in-car speakers cope with the weather better. Didn't seem to hurt the sound quality from a cheap 4-inch speaker. [Roll Eyes]