Film-Tech Forum ARCHIVE: New speakers to replace old dryrotted relics

This is topic New speakers to replace old dryrotted relics in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Lee Eady (Member # 6411) on 12-16-2011, 09:01 AM:

We Have a few auditoriums in our theater with old dead dryrotted speakers all along the walls. Some buzz and some are just dead.
Well, some used ones have popped up from a sister theater closing down the road and I was just wondering if i could get the forums expert input on how to get these switched out and functional without blowing anything up. Is this strictly some tech- only work? Or can the projectionist do it with help? Thanks much.

Posted by Mitchell Dvoskin (Member # 751) on 12-16-2011, 09:19 AM:

Make sure that the amplifiers are turned off. Turn off the breaker to the sound rack if possible. Note which wire is connected to the plus/minus terminals on the old speaker, and connect the wires to the same terminals on the replacement speaker.

Posted by Scott Norwood (Member # 30) on 12-16-2011, 10:29 AM:

Are you just replacing the drivers (same make and model?) or the entire cabinets?

I would suggest leaving replacement of the cabinets to the professionals, unless they are the same type and can use the existing mounting brackets. If they are different models, the coverage angles may be different. And, even if they are the same type, you might still not want to be involved, unless you have knowledge and, ideally, professonal qualifications for carpentry and/or rigging. Do you really want to be responsible if a speaker falls off the wall and hits someone on the head?

Replacing the drivers should be easy if they are of the same as the originals. Note that surround speakers may be wired in one of several different ways (series, parallel, series/parallel, or 70v). If the previous installation has been done correctly and the impedence of the drivers and amplifer type remain the same, you can just follow the existing pattern. Make sure to keep everything in phase with everything else.

Posted by Randy Stankey (Member # 64) on 12-16-2011, 12:17 PM:

If they are the exact same model of speaker they aren't hard to replace. Just get a ladder, go up and observe how the originals are installed and take notes if you have to, before you start working.

From there it is just a matter of mounting the speakers and connecting the wires. Any person who knows enough to make home repairs should be able to do it if he pays attention and works carefully.

However, it is probably worth it to get a technician or contractor to come and do it for you.

About a year ago, the Genie Lift that we use on our stage started malfunctioning. I was pretty sure I knew what the problem was. (A stuck hydraulic valve.) I was 99% certain that I could do the repair and do it correctly. However, I still refused to make the repair even when my boss told me to do it. When I finally explained the reason why he agreed to call a contractor.

Using a Genie Lift creates some important life safety issues. If any part of that equipment fails it could cause a person to be injured or killed. If I was to repair that equipment and it failed and somebody got hurt, it would be ME who is called into question.

Even if I made a 100% perfect repair. Even if the problem happens ten years from now. People would still blame me if somebody got hurt.

If you hung your own speakers and one of them came down, causing somebody to get hurt, you would be the one standing in your bosses office explaining what happened.

It's a whole lot easier to simply pay somebody else to do the work. Besides, peace of mind is worth the money spent.

Posted by Rick Raskin (Member # 1561) on 12-16-2011, 02:13 PM:

Listen to Randy! What he says is spot on.

Posted by Justin Hamaker (Member # 2165) on 12-16-2011, 03:35 PM:

I just finished replacing the surround foam on a bunch of speakers in my smaller auditoriums. There were all Boston Acoustic A70 speakers from about 1990 and the foam that holds the cone to the frame and completely deteriorated. Fixing this was just a matter of unscrewing the wolfer from the box and unplugging the two wires. It took about 2 hours total to remove the remnants of the old foam and glue on new ones.

I don't know if this matches what you're dealing with, but the expense would be much less than the cost of hiring a tech to mount and EQ new speakers.

This is what the speakers looked like before I replaced the foam surrounds.

Posted by Steve Guttag (Member # 268) on 12-16-2011, 04:16 PM:

It took you 2-hours each driver to remove the foam leavins' and glue on new foam (and replace the gasket)? How many speakers did you do?

-Steve

Posted by Louis Bornwasser (Member # 3063) on 12-16-2011, 04:19 PM:

By shear coincidence, the monitor speaker we made for 25 years used an exact replacement speaker for the A70t. It was made by Eminence Speaker Co in Eminence KY. No more foam.

Sounds good, too!. Sold several hundred of them over the years for surround woofer use.

Posted by Justin Hamaker (Member # 2165) on 12-16-2011, 05:05 PM:

Steve: Most of that 2 hours per speaker was letting it sit for the glue to dry. It was maybe 20 minutes of labor per speaker - including removal from box, cleaning, gluing, re-installing.

Posted by Jeremy Weigel (Member # 4208) on 12-16-2011, 11:37 PM:

Speaking of the A70t's, does anyone know if there is an aftermarket replacement diaphragm for the the tweeters? Boston said they are a discontinued unit. I have 2 of them that are none functional.

Posted by Steve Guttag (Member # 268) on 12-17-2011, 12:16 AM:

Wow...I've never had a refoam go that quick. It is normally pretty nasty getting rotted foam off since it goes all sticky. The gaskets can also have a few surprises when trying to get them off. Then, setting the new foam in...when they go under the cone (as it appears to be shown in the picture) the foam never wants to sit in the shape of the cone, the lip wants to sit flat. It is one reason I gave up on doing re-foams...they generally became harder than recones.

Did your cement resemble contact cement or Elmer's Glue (I've seen it done both ways)? I'm guessing that you did the contact cement method if you only let it cure 2-hours...Elmer's (Polyvinyl Acetate) takes much longer to cure.

-Steve

Posted by Justin Hamaker (Member # 2165) on 12-17-2011, 12:56 AM:

The foam laid over the top of the cone and the inside is angled so that it almost can't help but line up correctly. I ordered from two different places just to see if there was a difference in quality - both appeared to be identical. One place sent glue that was about equal to Elmer's; the other sent something that was not much different from model glue.

I don't know the complete history of these speakers, so I don't know if they had been redone in the past. Several of them seemed like the old glue was the Elmer's and it came off very easily. The others had some kind of black cement that was very difficult to get off - cleaning was by far the most time consuming part of the process.

I got the frame perfectly clean, but I didn't spend a lot of time trying to clean the old cement off the cones for fear of damaging them. I just made sure to get all the old foam and made sure there was no loose debris. I used the cement to glue the inside of the foam to the cone and the "Elmer's" to glue it to the frame.

All in all it was a relatively painless process. I would pull a speaker before a show and usually had it read to put back before the next show. It took me about a week to take care of 7 speakers spread between two auditoriums.

In the 6+ years that I have been at this theatre, we have never been able to get the sound right in these two auditoriums. Now that I know about this issue, I can't help suspecting those foams may have been bad for a long time. Or it could be that switching from analog to digital causes the cones to move more and the weak foams to break apart. I just finished a couple days ago, so I still need to spend time listening to see if the sound is noticeably improved, but it sounds better from the few minutes I spent in each house.

What prompted me to investigate the speakers was customers complaining that it sounded as if there was something rattling inside one of the speakers. The picture above was the first one I checked, and the most intact of the 7 bad ones. In most cases, the foam was completely gone.

Posted by Lee Eady (Member # 6411) on 12-17-2011, 10:19 AM:

Well its basically new JBLs- well not new but used from the closed sister but the old ones were dryrotted and out of use for soooo long- site- replcing old crappy noname- they actually look like the old wood speakers my dad had with the living room stereo in the 80s-and those auditoriums were basically just running in mono- and now that the new ones are going up theres nothing at the projector to power them! these 4 auditoriums have no racks- just an old hi-fi deal on the lamphouse that flips open to reveal eq. this stuff is all foreigb to me. but he demands they all go up, and attach the wires, to see what they do! god help me!

Posted by Steve Guttag (Member # 268) on 12-17-2011, 10:21 AM:

Kudos for your efforts. Clearly the foam companies are doing a better job of forming them since I last gave it a try...they didn't angle the foam for the cone and it was a paint to set with the Elmers.

The A70 was really a bookshelf speaker that was not too efficient as it was geared towards home audio of the '80s. It isn't a bad speaker, just not efficient for surround use. For digital, they can be a liability since they combine low efficiency with low power handling. As I recall (and it has been quite some time) they only had about 75-watts of power handling and their efficiency is in the upper 80s

For optical sound, surrounds only had a 100-7KHz bandwidth with lower power demands. In digital (film or DCinema), the surrounds have as much or more asked of them than the stage speakers...this will tax lesser speakers quite a bit.

I'm sure you greatly improved the sound as a failed woofer is an annoying thing (as is a failed tweeter).

With the new foam in, the room should definitely be retuned.

-Steve