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[Timothy Tucker]

I have recently run into an issue with our sound system at church and I'm having a hard time troubleshooting it.  The audio signal from the microphones  appears to be clear (monitoring via headphones) but the speakers have developed an issue where they just don't sound good.  The audio is not very loud and it appears to be distorting and thin sounding with the occasional increase in volume that is sometimes rather startling.  Plosives have also started become rather severe with some of the ones using the microphones.  This is a straight forward system that is used for spoken word (accapella singing only).  I have listed the components below that I'm working with.  I did the install (I have done several 70v installs w/o issue) but I can't nail down the culprit.  I have checked the speaker taps and also the wiring @ each speaker to make sure my connections are correct and secure.  Any suggestions would be greatly appreciated. 

2 powered mics
1 wireless lapel
1 overhead powered audience mic (not directed to the speakers..for streaming/recording only)
Yamaha MG16 mixer>dbx 131s graphic EQ>EV PA2400T Power Amp (using one output channel 70v for the auditorium speakers and the other 70v output to the classroom speakers downstairs, which are having no issues)>14AWG wire>8-JBL control 18c/t ceiling speakers (2 tapped at 7.5 watts and 6 tapped at 15 watts) and one EV-ID-S5.2T tapped at 15 watts...all wired in parallel on Channel 1

[Erik Jerde]

I have recently run into an issue with our sound system at church and I'm having a hard time troubleshooting it.  The audio signal from the microphones  appears to be clear (monitoring via headphones) but the speakers have developed an issue where they just don't sound good.  The audio is not very loud and it appears to be distorting and thin sounding with the occasional increase in volume that is sometimes rather startling.  Plosives have also started become rather severe with some of the ones using the microphones.  This is a straight forward system that is used for spoken word (accapella singing only).  I have listed the components below that I'm working with.  I did the install (I have done several 70v installs w/o issue) but I can't nail down the culprit.  I have checked the speaker taps and also the wiring @ each speaker to make sure my connections are correct and secure.  Any suggestions would be greatly appreciated. 

2 powered mics
1 wireless lapel
1 overhead powered audience mic (not directed to the speakers..for streaming/recording only)
Yamaha MG16 mixer>dbx 131s graphic EQ>EV PA2400T Power Amp (using one output channel 70v for the auditorium speakers and the other 70v output to the classroom speakers downstairs, which are having no issues)>14AWG wire>8-JBL control 18c/t ceiling speakers (2 tapped at 7.5 watts and 6 tapped at 15 watts) and one EV-ID-S5.2T tapped at 15 watts...all wired in parallel on Channel 1

If you swap the loads on the amp outputs does the problem follow the load or the amp output channel?  Are both zones getting the same signal?  If so via the same cable and an amp configuration switch or some other method?

[John Roberts {JR}]

Disconnect speaker wiring. Connect only one speaker, if that is clean, reconnect speaker system in stages, until it gets nasty.

JR 

[Mike Caldwell]

In addition to Erik's and John's suggestions.....
Has anyone done any work in ceiling that could done something to the speaker cabling?
When the speakers are popping and making noise do you see any peak lights on the EV amp?
Is there a lot of low end  boost on the EQ channel that is feeding the main speakers?

Post a couple pictures, the back of the amp, the EQ and mixer.

[Timothy Tucker]

In addition to Erik's and John's suggestions.....
Has anyone done any work in ceiling that could done something to the speaker cabling?
When the speakers are popping and making noise do you see any peak lights on the EV amp?
Is there a lot of low end  boost on the EQ channel that is feeding the main speakers?

Post a couple pictures, the back of the amp, the EQ and mixer.

Yes, there has been some work in the ceiling (new AC unit installed).  I have checked the wiring, but would likely benefit from giving another look.  I am not seeing any peak lights on the EV, so I don't believe it is sending an overloaded signal.  As for the low end, I had it rolled off.  For right now, I've actually bypassed the EQ (via the bypass button), so it is just getting the signal from the board, which only has EQ for each channel.  I will try the provided suggestions and will reply with my findings.  I'll also grab some photos to attach.  Thanks for the help. 

tt

[Timothy Tucker]

If you swap the loads on the amp outputs does the problem follow the load or the amp output channel?  Are both zones getting the same signal?  If so via the same cable and an amp configuration switch or some other method?

Hi Erik,
I will try swapping the loads and see what happens.  It did cross my mind that it might be one of the amp channels, so we'll see.  Yes and no on the zone signals.  The classroom speakers get their signal from the same mixer and amp, but I don't have any microphone signal going to those speakers as I use it for the end of class bells that go from my PC to the mixer to the amp.
tt

[Timothy Tucker]

Disconnect speaker wiring. Connect only one speaker, if that is clean, reconnect speaker system in stages, until it gets nasty.

JR

Thanks, JR.  I will add this to my troubleshooting list and see what happens.

tt

[Mike Caldwell]

70 volt systems need to be high pass filtered, I would leave the EQ in place and activate the high pass filter and cut the low end up around 100hz at least as well as using the high pass filters on the board input channels. That amp has a couple of high pass filter options, can't remember what they right now but if one of them is 70hz or so make sure it is turned on.
Doing that you would not need to get so aggressive on the EQ filter cuts.

As for the AC work in the ceiling double check that the speaker line or lines has not been scored through at some point and one or both of the conductors is in contact with some metal frame work of the building, even the metal grid of the suspended ceiling that is if the room has a suspended ceiling.

You can check for that by disconnecting both of the + and - speaker lines from the amp that feed the main speakers, take volt ohm meter put it on a low ohm scale, then measure between each speaker line and the building ground, the building ground can be any metal properly wired outlet box or even the chassis of a piece of equipment with a grounded electric cord.
You should not read anything doing that from either the + or - speaker lead. 

[Timothy Tucker]

I really appreciate the help from everyone.  Fortunately, the first thing I tried seemed to indicate what the issue was.  Per Erik's suggestion, I tried the easiest test first, which was to swap the outputs on the amp.  I had a test speaker which I hooked up to both output A and B of the power amp.  There was a definite difference in the two.  Output B sounded like it should and output A (which was the output for the auditorium speakers) sounded bad.  I hooked the auditorium speakers up to output B and everything sounded like it should, so I'm guessing output A is compromised in some way. 

While this has told me what the issue is and how I can correct it for the time being, should I be concerned that there might be something about the way the speakers were hooked up which caused output A to be compromised? 

I'm not sure if the amp is still within the warranty period, so if I happen to need to buy a new power amp, are there any recommendations based on my current needs and your experiences?  I don't anticipate needing anything more powerful that what I have now, but I will need two inputs and two outputs.  Thanks again. 

tt

[Magnus Högkvist]

I really appreciate the help from everyone.  Fortunately, the first thing I tried seemed to indicate what the issue was.  Per Erik's suggestion, I tried the easiest test first, which was to swap the outputs on the amp.  I had a test speaker which I hooked up to both output A and B of the power amp.  There was a definite difference in the two.  Output B sounded like it should and output A (which was the output for the auditorium speakers) sounded bad.  I hooked the auditorium speakers up to output B and everything sounded like it should, so I'm guessing output A is compromised in some way. 

While this has told me what the issue is and how I can correct it for the time being, should I be concerned that there might be something about the way the speakers were hooked up which caused output A to be compromised? 

I'm not sure if the amp is still within the warranty period, so if I happen to need to buy a new power amp, are there any recommendations based on my current needs and your experiences?  I don't anticipate needing anything more powerful that what I have now, but I will need two inputs and two outputs.  Thanks again. 

tt

You should also to be safe switch the inputs to eliminate that Your signal to the amp channel is bad.

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