Weird behavior from CP650

[Peter Foyster]

Well... the reason that I asked about other sources being the cause is because, more often than not, a problem is not what you expected it to be.

There is a peak limiter in the line to help prevent spikes from damaging the speakers. We found that bypassing the limiter on the centre channel the sound returned to normal. A subsequent sound test confirmed that the problem was resolved.

In any event, the tech copied the settings from one CP650 to the spare, just in case.

I guess it pays not to just assume that something is the problem.

[Tony Bandiera Jr]

Well... the reason that I asked about other sources being the cause is because, more often than not, a problem is not what you expected it to be.

There is a peak limiter in the line to help prevent spikes from damaging the speakers. We found that bypassing the limiter on the centre channel the sound returned to normal. A subsequent sound test confirmed that the problem was resolved.

In any event, the tech copied the settings from one CP650 to the spare, just in case.

I guess it pays not to just assume that something is the problem.

A suggestion for your next tech visit is to have the tech rewire so that your booth monitor looks directly at the CP650 line outputs, BEFORE the limiter. Since the processor is a key component (as are the amps and speakers of course), and the limiter is a non essential add-on, you should only look at what the CP650 and the amp's outputs are doing.

This way, it would have narrowed down the culprit immediately, using simple flow logic. In your case, if it had been wired as I suggest, you would have known that the output from the CP650 was normal, and the loss was happening before the amp (or in the amp itself.) Then next step would have been to engage the bypass on the limiter, which would have ended the problem right then. (If the problem continued, then of course the next step was the amp, and finally if the amp out was ok, the speaker driver(s).

To address the elephant in room, who decided to install peak limiters? They are totally unnecessary in a properly designed and tuned sound system. Unless you are running crap speakers and amps like Peaveys or TOAs and Radio Shack speakers, take those limiters out completely. As you have discovered, they are simply another failure point. And since one has already failed, the others aren't far behind.

What speakers and amps are you running, and who installed them?

[Peter Foyster]

The limiters were put in by the previous owner, soon after the cinema switched to digital. The speakers were “crap”, as you put it, and, being outdoors, the choice was limited.

I have since added more substantial speakers, which have to be covered or taken in each night, apart from 4 18” subs in their own weatherproof enclosures.

The original amps were custom built for a large Australian cinema company in the film days. I am now using older model QSC amps on all channels, apart from the subs which don’t like them.

As a small family owned business, I simply don’t have the resources to install an expensive cinema sound system. Even the projection system is living on borrowed time. We take whatever precautions are necessary to protect our modest investment.

[Leo Enticknap]

Just as a very general rule, and not in any way meaning to criticize Tony, I am very cautious about jumping to the "this is unnecessary - get rid of it" conclusion, either when working on a system myself, or advising others. It was put there for a reason, and I want to be sure that the reason either no longer exists, or never existed in the first place (i.e. it was put there as the result of an error or misunderstanding) before I remove it.

Example - I once had a complaint from the new owner of a mom-and-pop owned single screen in a touristy town up in the mountains, complaining of a dim picture. This was about a 150-seat auditorium, with a 50ft throw to a screen that was only about 20ft across in scope. When I arrived, I found a projector with a 6kW bulb in it (that was way over hours, black, and flickering like the proverbial candle), and ND filter glass glazed into the (removable) port frame that was so dense you could barely see through it and into the auditorium, even with the house lights fully up! Why the f*** would anyone want to do that?!

It turned out that the reason was that the previous owner had rented the place out to a school as an overflow classroom, which liked to do Powerpoints using the projector. By simply removing the port glass for school use, it gave them a nice, bright picture, even with the house lights fully up. For movie theater use, they put the ND filter glass back in. As the new owner did not feel comfortable handling xenon arc bulbs and the rental agreement with the school was ongoing, we had to continue with this arrangement, though my first thought was to suggest having the glass swapped out for regular port glass and going back down to a 3kW lamp (the smallest that an NC3200 with the bigger lamp power supply unit can take).

The annoying thing is that if their projector had been a Barco, they could have had two lamphouse modules and swapped them in and out without having to handle bulbs. But my point is that there was a good reason for doing something that, at first glance, looked to be certifiably insane.

[Marco Giustini]

I’m with Leo here.
not everyone can afford the latest and greatest of the equipment. And calling ‘crappy’ someone else’s sound system without knowing much about them is, imho, disrespectful.
As Leo, I’ve also seen many ‘technicians’ over time removing amp protections or re-wire amplifiers so to get ‘more power’ and ‘better sound’ which inevitably ended up in speaker damage because they didn’t know how to do the math about SPL (in some cases it was just common sense to be honest but I digress).

Yes, limiters should not be necessary. And if you really need to limit, I guess a compressor would be more suitable. But it’s a short blanket, there is no perfect solution here.

what’s important is to make sure it’s clear that a properly designed sound system won’t need limiters. But if a sound system has been set up with limiters, then it takes a bit more than ‘yank them out’ before someone removes them.

[Marcel Birgelen]

I guess it pays not to just assume that something is the problem.

They say assumptions are the mother of all screw ups. I think that's mostly true.

Still, if you have some experience in a particular field, assumptions often help you to assert a certain problem and help you to limit the initial search for a solution to a limited domain. Since chances are you've encountered the exact or a similar problem before, chances also are, that previously taken measures will also help in this particular case.

The real trouble often starts when initial assumptions are false and the problem at hand is beyond the experience of those involved...

[Peter Foyster]

Had I the presence of mind at the time I could have easily bypassed the Limiter and immediately seen the result on the monitor VU. Unfortunately, panic sets in and common sense takes a break.

As long as it is as simple as pressing a button to bypass something in the line after the processor, I would prefer to have it that way rather than having to go out to the auditorium to check the results.

[Tony Bandiera Jr]

Peter, please understand my original comment wasn't intended as an insult to you or what equipment you have, and I apologise if it came off the wrong way. I perhaps should have first asked what equipment you have, and in what type of setting. As Marcel said, my experiences in systems with limiters (the assumptions he spoke of) was the basis of my comment. Nothing good ever resulted from the use of limiters in my experiences.

That said, I can see the need for the limiters in an outdoor setting, but still stand by the premise that a properly designed system shouldn't need them. I have experience in both live sound and cinema, and in my live sound days (three years worth) we had limiters in both the house PA and monitor racks, but can count on one hand the number of times we actually had to use them. In my cinema days I had some theatres in my route that had the "crap" equipment I spoke of, and some had limiters, some did not, but both cases suffered frequent failures due to poor design. So the limiters were obviously not helping, and thus introduced the additional breakdown point I mentioned.

Your last two posts do have me a bit confused though, in the first reply you mention the speakers being outdoors, then this last one you mention an auditorium. Do you also run live sound events? Or are you running a Drive-In?

Oh, and don't feel bad about the presence of mind clouding your troubleshooting. There is a post of mine in the FT forum Archive where I had an odd problem with a CP-200, where I spent HOURS checking all of the wrong things based on my assumptions, where the actual cause was a dumb installation choice by the original installer. (They cut the plug ends off of all the power cords and connected them to a screw terminal strip. One loose screw on the CP 200's power cord termination made it randomly shut down and reboot.) It was in a 70mm large auditorium playing the original "Top Gun" to sold out crowds. Was a learning experience for sure.

[Mark Gulbrandsen]

Tony,

Back when the BW Broadcast was making the 1, and 5 watt transmitters, those had limiters. They could be shut off by moving a couple of jumpers. In the cases of drive in's that had ramp speakers... I left the limiters in. In cases of FM transmitters only, I left them off. The small 70 volt speakers, which some still use, likely survived because of the limiters. FM only places always had a lot of cars show up with big sound systems in them.

[Peter Foyster]

Thanks Tony,

I used the word auditorium to describe the area where the audience is seated. Although outdoors, it is fenced off and there is semi permanent seating. I could not think of another word to use at the time.

In order to accommodate many of the modern digital soundtracks on blockbuster titles, and musicals, I had to upgrade the sound, primarily the centre channel, to ensure vocal clarity and to be able to handle the moments of increased sound levels that occur, e.g. battle scenes, car chases etc. The limiter helps to prevent speaker damage as a result of severe peaks.
The original "sub" was an 8 or 10 inch powered unit stuck inside a bass bin. That lasted about 5 minutes. It was replaced with four 18" JBL subs.

[Jim Cassedy]

( slightly edited )Per my notes, the current software versions are 2.3.6.3 for the regular (5.1) version of
the CP650, or 2.3.6.6 for the 7.1 upgraded variant. If you have anything earlier than 2.3.6.3, your unit
could possibly do with upgrading, though if the bug fixes and additional features that the upgrade would
bring are not relevant to your use case, it's worth asking yourself if it's worth the risk of upgrading a
machine in which the firmware is stored on flash memory, given the risk of bricking it if the procedure
goes wrong; especially if there is no more OEM support for the machine in question..

Just curious: I've got 2½ spare CP650's here at home that I use for various reasons- -none of them commercial
My main one (the one I'm not using as a door stop) is equipped with both CAT 773 & CAT 790 cards, but is only
running Software V2.2.5.0.
> So, since it completely meets my needs & purposes, would there be any advantage at all for me upgrade to
newer software? There's zero chance I'll ever need to pump 7.1 thru this unit.
> Although I probably know the '650 better than any other Dolby possessor, I've never actually done a software
upgrade- although I've seen it done while working at various venues
> So, "how risky is it" - - I've got all the necessary cables & software, but is it worth mucking around with?

(Generally speaking, I'm a "if its working, don't f-ck around with it" guy- - so maybe I've just answered my own
question)

[Leo Enticknap]

My suggestion would be to look at the bug fixes and new features that came between 2.5.5.0 and 2.3.6.3, and decide if those are worth the risk of upgrading the units. I can't give you that info right now (I'm on vacation with only personal, not work, laptop with me, which doesn't have all my cinema software files and saved login to dolbycustomer.com), but if you have a login to dolbycustomer.com, this info should be easy to find.

With really old flash memory, there is always a slight risk that the upgrade process will try to write to a bad sector (or whatever you call its equivalent in flash memory), leave you with a corrupted program code file, and the unit is dead in the water. Unusual, but not unheard of, to the extent to which I would always want to do a risk vs. reward think through before going ahead.

[Marco Giustini]

With the 650 you really need a reliable serial port - either hardware or a good adaptor. I've never had a 650 update failing on me but it's always been a possibility. The good news is that the EEPROMs are on a separate little daughterboard (which features very fragile pins!) so if the worst happens, you can still remove the ICs and flash them again.

However, you'd need an EEPROM programmer (cheap tool nowadays), de-solder the ICs (I believe they are soldered on the daughterboards) and also somehow obtain the images of the two separate EEPROMs as it's not like the CP500 where - I think - the update file is basically the only EEPROM image.

What I am saying is that if the update fails you can recover the unit. What is important is that if it fails you don't power cycle the 650 but you try again instead.

[Jim Cassedy]

Can confirm the NS will get robotic occasionally as well..

I'm not saying your wrong, but I'm a bit surprised to hear that because I would have assumed that NS was
strictly handled in an analog domain. I mean, you don't even need to have the cat 773 & 790 cards installed
for NS to work. Or am I missing something?

THANKS Leo & Marco for your thoughts on my question. I do have dolby customer access and I've probably
already got copies of all the release notes & software versions on a thumbdrive a Dolby tech shared with me
a while back. I was asking more out of curiosity than actual need. In worst case,if I decide to go ahead with
trying to update and run into a problem, I know a few theaters with unused CP-650's sitting around that have
been partly cannibalized for parts. (mostly power supplies & the control shaft encoder) -that I could probably
talk their owners into letting me have, for nothing or dirt cheap. but I know those retired units still have the
EPROM boards inside if I really needed one, and I've actually even seen them occasionally show up on e-bay.

EXHIBIT "A"
Dolby650ROM.jpg

[Marco Giustini]

Ah I had forgotten they come in that package, that is why I don't have a copy of them saved on my disk! A bit more complex to DIY re-program then. Well, you'd need to de-solder those chips which are in the middle of plastic things. Better to have a spare 650 indeed