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Author Topic: Subwoofer is humming...help! Aaron Garman Phenomenal Film Handler Posts: 1470 From: Toledo, OH USA Registered: Mar 2003 posted 07-24-2003 02:25 AM                     Hello all. For awhile, one of our auditoriums has had a distinct low frequency hum emminating from the subwoofer and it will not go away. The only reason it is still there is because most people don't notice it, but it is blatantly there. Anyhow, I'm trying to figure out what it could be. Our system for the auditorium is as follows: USL JSX 1000 Processor USL Monitor DA20 with Cat. 700 reader Peavey CS 800 amps Not sure on speakers Anyhow, I thought it may have been a lose cable or dirty cable. So I checked everything upstairs and all was good. The only thing I could imagine it would be would be one of the cards in the JSX 1000. Our tech was in this week, looked into the problem, and said he got rid of the hum. Well, I went into the auditorium on my shift tonight (after he left) and lo and behold the hum is STILL there. I saw his report and it said it was a loose card, and he said he fixed it. Any thoughts? This used to be our best auditorium, if not the best in the whole area, but now it is a shadow of its former self. I just want it to sound the way it used to, but no one seems to really care. Maybe someone here will. AJG [ 07-06-2004, 01:20 AM: Message edited by: Aaron Garman ]  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-24-2003 03:33 AM                     That's not enough info to fully diagnose your problem, but you've got to start troubleshooting somewhere, so do this first. Turn the fader to 0. Is the hum still there? If the hum remains it is post processor. If the hum varies in volume with the fader, then it is inside the processor. Odds are though that you have a grounding issue with the way the rack was wired. Anyway, first things first, let's rule out the processor and go from there.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-24-2003 09:19 AM                       If it's a powered s/w, like a Kintek KT-90, go backstage and unplug the audio cable feeding the unit. If the hum remains, the amplifier in the sub is out. If that is the case, also check the speaker cones because they may be blown. A common failure mode for those amps is they go square wave, and quickly blow the speakers.  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 07-24-2003 09:41 AM                     Brad, Doesn't this sound suspiciously like that old problem where a "certain company" pre-wired all of the racks and grounded both ends of the shields? I've had that happen a lot of times. Unhooking one (upstream) end of the shield solved the problem many times for me.  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 07-24-2003 10:52 AM                    Randy is right about the ground loop problem, it can cause such noise. We took all of our racks and removed that ground connection on one end and removed the terminal strips and wired all speaker wiring straight in. The other possable problem, and you listed it in your equipment, is the peavy 800amp introducing hum into the subs. remove the amp and try conecting the subs to another amp that is working fine and see if the problem is still there. If it goes away get your amp repaired. If it is still there it could be something else.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-24-2003 10:58 AM                     Unplug the input to the sub amp and see if it goes away Also since the peavey used 1/4 jacks they may be a bit less than ideal in the quality of connection Also if this rack was built by the unamed company I think then also try disconnecting the sub from the monitor both the processor and the speaker connection to the monitor  |  IP: Logged Adam Fraser Master Film Handler Posts: 499 From: Houghton Lake, MI, USA Registered: Dec 2001 posted 07-24-2003 12:36 PM                        We have had thew same problem, turning off the subwoofer amp until after the xenon is struck solves the problem (either the disturbance when striking or a grounding problem is our guess). Although not a permanent solution it has worked until we can get our tech up here for the routine maintainence instead of spending the money for the 7 hour roundtrip to fix one small problem. Our Equipment- Peerless Magnarcs with Kniesley conversion Altec 944? amps for subs and surrounds. Ashly for stage channels JBL Speakers  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 07-24-2003 02:02 PM                     quote: since the peavey used 1/4 jacks they may be a bit less than ideal in the quality of connection Gord, the Peavey CS800 also had XLR jacks. -Aaron  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-24-2003 02:06 PM                     hopefully then they had used them as 1/4 phone is the most unreliable connector I have seen  |  IP: Logged Aaron Garman Phenomenal Film Handler Posts: 1470 From: Toledo, OH USA Registered: Mar 2003 posted 07-24-2003 02:09 PM                     Thanks guys. I'll try to check this stuff out as soon as I can. Again, no one really cares that much about this problem there and if they see me tinkering with one of the racks, they may assault me with questions. Brad, I think it's in the processor because when I flip the USL monitor to processor, I can hear the hum out of the monitor too. But I'll give what you said a try and see what I can do. Thanks again everyone! AJG EDIT: I chose to get rid of my angry comments. Looking back, they weren't necessary. [ 07-06-2004, 01:22 AM: Message edited by: Aaron Garman ]  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-24-2003 02:18 PM                     It could also be on the input to the processor in a connection to the nonsync to the digital player to the projector ground related hum is a bitch to find and takes a lot of time Best is break the system in the middle and that will eliminate 1/2 the possibilities  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 07-24-2003 05:09 PM                     All of the above is good advice. You're basically trying to isolate the source of the hum first and then deal with the problem. However, I am compelled to add a few words of caution. quote: ...if they see me tinkering with one of the racks, they may assault me with questions. Which makes me wonder if you are venturing into an area where you aren't supposed to. Sure, it's a simple problem and you could probably solve this but there is something to be said for having proper prior approval to alter the setup. quote: I'm so fed up I'm just gonna do whatever because the situation is ridiculous along with other booth problems. Actually, this is the part that made me raise an eyebrow. Two wrongs don't make a right. Go ahead and do the simple tests like the one Brad suggested and if you manage to isolate the problem then you should talk to your manager before changing anything. quote: If I told my tech, something tells me he won't care. This is an example of mind-reading. Even so, if you really cannot give your tech the benefit of the doubt then I still have to point out that two wrongs don't make a right. Deal with your manager. Show him/her that you have respect for the chain-of-command and point out that you've only (a) noticed and (b) researched the problem. It's a simple problem and, depending on how it is handled, it could be the difference between a commendation or a letter of warning. The best way to be smart is to be right.  |  IP: Logged Aaron Garman Phenomenal Film Handler Posts: 1470 From: Toledo, OH USA Registered: Mar 2003 posted 07-24-2003 05:17 PM                     Oh, forgot to mention, I did run a show in there once with the two sub amps off. This did eliminate the hum however. It appears that all conections for speakers on the amps use bare wire, and the line connections use 1/4" phono plugs. Also, the LCR channels are being biamped with a crossover on each of them. Again thanks for the help and I'll try to check the system out when I go in tonight. AJG  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 07-24-2003 05:26 PM                     Maybe it's humming because it doesn't know the words. Sorry, I just couldn't resist.  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 07-25-2003 02:37 AM                    swap your format card with another format card and see if the problem follows it. Volume for the subs is controled on these cards. One easy way to find out if it is that card is by opening the port and listen then turn the volume up and see if the hum gets louder. this is with no film running and the processor in stereo mode. Since you are using two amps to power the subs I would say you have a total of four behind the screen turn one amp off go down and listen to the sound or just listen to the subs with nothing playing and see if you still hear the hum. then do the same for the other amp. If you hear the hum in both amps then there is a processor problem if only one of them it could be just the amp.  |  IP: Logged

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