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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Andrew Cole on May 14, 2019, 09:18:19 AM
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Hello,
I've been running sound at various churchs for around 10 years but over that time I've not had much experience with power amps and passive speakers. The church's I've been at with that set up were already set when I joined and the one I did set up was a church that met at the local high school and we used powered speakers/subs.
So at my current church we were looking at our system and I've never seen wiring like this before. I've had one guy tell me we were running stereo and another say mono. Well it turns out it's mono but the speaker wiring confuses me. I've tried to get at the speakers themselves to see what they are but they're contained in these strange boxes I can't get into. Can anyone tell me from the pictures I've attached what exactly is going on here in regards to the wiring and our current wattage/ohms?
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The amplifier is being used in "Bridged Mode".
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And with cheesy light speaker wire and banana plugs when there is a speakon right next to it... that setup seems to be just looking for trouble to me.
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Looks like in bridged mode that amp puts out 1800W at 8ohms, not sure if that's peak or RMS output, their documentation is pretty sparse but I'd lean heavily towards it being peak. The fact that the manual doesn't even list the 4ohm bridged output makes me think that its performance at that load will be either less or roughly equal to the listed 8ohm load.
I'd pull off those banana plugs and put a multimeter to it to see what kind of load you're actually getting. Since you can't actually get access to the speakers and find their specs that will at least let you know if the amp is being stressed at all. When you say strange boxes are they just framed off into little nooks in the wall, or do the speaker enclosures themselves a strange configuration? My next step would be figuring out what cabinets you have to be sure they're able to handle the power being given to them.
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Looks like in bridged mode that amp puts out 1800W at 8ohms, not sure if that's peak or RMS output, their documentation is pretty sparse but I'd lean heavily towards it being peak. The fact that the manual doesn't even list the 4ohm bridged output makes me think that its performance at that load will be either less or roughly equal to the listed 8ohm load.
I'd pull off those banana plugs and put a multimeter to it to see what kind of load you're actually getting. Since you can't actually get access to the speakers and find their specs that will at least let you know if the amp is being stressed at all. When you say strange boxes are they just framed off into little nooks in the wall, or do the speaker enclosures themselves a strange configuration? My next step would be figuring out what cabinets you have to be sure they're able to handle the power being given to them.
Speaker impedance is not a simple resistance that can be easily measured with VOM.
Question has already been asked and answered.
JR
[edit OP can google "amplifier bridge mode" for more information about the technique. /edit]
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Speaker impedance is not a simple resistance that can be easily measured with VOM.
Question has already been asked and answered.
JR
Very true, but since the cabinets appear to be sealed off, it's the best method of determining any kind of cabinet specs without ripping walls out. Is it an ideal test method? Of course not, but we rarely work in ideal situations.
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Looks like in bridged mode that amp puts out 1800W at 8ohms, not sure if that's peak or RMS output, their documentation is pretty sparse but I'd lean heavily towards it being peak. The fact that the manual doesn't even list the 4ohm bridged output makes me think that its performance at that load will be either less or roughly equal to the listed 8ohm load.
I'd pull off those banana plugs and put a multimeter to it to see what kind of load you're actually getting. Since you can't actually get access to the speakers and find their specs that will at least let you know if the amp is being stressed at all. When you say strange boxes are they just framed off into little nooks in the wall, or do the speaker enclosures themselves a strange configuration? My next step would be figuring out what cabinets you have to be sure they're able to handle the power being given to them.
Yeah, the documentation is vague at best and since I'm not super familiar with amps it makes it worse for me! haha. I would imagine the amp isn't being stressed as the level is around 9 o'clock and it's still loud for our building.
Regarding the speakers, from the sanctuary the speakers are hidden in wall behind a screen which is framed with trim. From the attic space the speakers are contained within homemade plywood boxes. The speaker wires terminate at the boxes at speaker connections. I don't know if the whole thing is homemade or if on the other side of the speaker connections, the wire goes to a commercially available enclosed speaker. Given my pessimistic tendencies, I'm starting to think the plywood boxes I see are the actual speaker enclosures.
I have a meeting tonight with some guys who might know a little more about it but the people who set the system up (years ago) are no longer attending.
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Yeah, the documentation is vague at best and since I'm not super familiar with amps it makes it worse for me! haha. I would imagine the amp isn't being stressed as the level is around 9 o'clock and it's still loud for our building.
Regarding the speakers, from the sanctuary the speakers are hidden in wall behind a screen which is framed with trim. From the attic space the speakers are contained within homemade plywood boxes. The speaker wires terminate at the boxes at speaker connections. I don't know if the whole thing is homemade or if on the other side of the speaker connections, the wire goes to a commercially available enclosed speaker. Given my pessimistic tendencies, I'm starting to think the plywood boxes I see are the actual speaker enclosures.
I have a meeting tonight with some guys who might know a little more about it but the people who set the system up (years ago) are no longer attending.
If the system is working as designed (i.e., it ain't broken), what are you trying to accomplish? Other than learning about amplifier bridge mode and why some of us think it's a bad idea in many situations (and fixed installs are not among them), what do you think needs inspection?
What you're seeing is common in sound system installations... so if it's working, don't mess with it.
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Think I'd still want that lot replaced with an SpeakOn connector. Banana plugs like these are not for PA applications.
Also, the speaker wiring on the next amp down needs tidying up.
Chris
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If the system is working as designed (i.e., it ain't broken), what are you trying to accomplish? Other than learning about amplifier bridge mode and why some of us think it's a bad idea in many situations (and fixed installs are not among them), what do you think needs inspection?
What you're seeing is common in sound system installations... so if it's working, don't mess with it.
I'm not fully saying I want to change it but something in this system isn't right. My wife and I are taking over as worship directors and I'm trying to get an idea of how things are set up so I have the knowledge. I work in IT and I'm used to knowing what systems I work with in case something goes wrong. Plus, it serves as an excuse for me to finally learn how power amps and speakers work.
No one truly seems to know how things are set up and the mixer doesn't work the way I'd expect it to. For instance, during a normal service that's run a little loud; the channel and group faders (incl mains) are set around -20, the gain for the channels are not set high, the mixer shows main output at around -16, and the power amp level is set at 9 o'clock where the lowest possible is 8 o'clock. Needless to say it doesn't give the sound tech a whole lot of "room" to work with on the mixer when mixing near -20 and most gain knobs set to 0. Just seems like the whole system was set up for a rock concert as opposed to a house of worship.
So this started with me just being curious/wanting to learn and the deeper I dig the weirder things seem. :o
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Think I'd still want that lot replaced with an SpeakOn connector. Banana plugs like these are not for PA applications.
Also, the speaker wiring on the next amp down needs tidying up.
Chris
I agree that speakons are better, but it seems to me, that if the banana plugs weren't adequate, the amp builder would not have put them on their amp.
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I see your point, but I more meant the fact that they're gold-plated all the way along. If you put a little weight on the top one, I bet you could get it to short the amp's output.
Chris
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Aside from some gain staging aspects of how your system operates, it seems to me that all is fine. Being at -20 on the faders isn't a huge deal, but that is relative to what other things are going on. If the master fader is down to -20 as well and you have that kind of volume, it could be because of the way the channels are grouped. If you group the channels into multiple groups and buss all those groups to the main you gain +3db for every buss doubling. With a 4 group console that means you have a potential 9-12db boost just from double bussing.
My answer would be to have the system run either in stereo or simply mono, but not bridged mono. The bridging of the amplifier may very well add more wattage than is needed to meet your NAG (Needed Acoustic Gain ). By making the amp run in the more common mono mode, you would have half the potential wattage being produced. This may allow you to run the level of the amp up more and still have a reasonable adjustment at the mixer.
If you don't need any kind of grouping, it would behoove you to simply eliminate that part of the signal flow. What many operators do is run the channel to both the group and the main L/R in order to get a little more volume. If you don't want added volume, then getting rid of the groups will help. You can turn the master volume down as far as you need to in order to get the channels up to where you want them. In some cases, this helps greatly with record feeds and other feeds that come off the mixer that do need to have a hotter signal.
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Aside from some gain staging aspects of how your system operates, it seems to me that all is fine. Being at -20 on the faders isn't a huge deal, but that is relative to what other things are going on. If the master fader is down to -20 as well and you have that kind of volume, it could be because of the way the channels are grouped. If you group the channels into multiple groups and buss all those groups to the main you gain +3db for every buss doubling. With a 4 group console that means you have a potential 9-12db boost just from double bussing.
My answer would be to have the system run either in stereo or simply mono, but not bridged mono. The bridging of the amplifier may very well add more wattage than is needed to meet your NAG (Needed Acoustic Gain ). By making the amp run in the more common mono mode, you would have half the potential wattage being produced. This may allow you to run the level of the amp up more and still have a reasonable adjustment at the mixer.
If you don't need any kind of grouping, it would behoove you to simply eliminate that part of the signal flow. What many operators do is run the channel to both the group and the main L/R in order to get a little more volume. If you don't want added volume, then getting rid of the groups will help. You can turn the master volume down as far as you need to in order to get the channels up to where you want them. In some cases, this helps greatly with record feeds and other feeds that come off the mixer that do need to have a hotter signal.
The Samson SX series amps say 8 ohm only in bridge mode any lower and you risk damaging the amps. The fact they are stacked, unless they are 16 ohms you are in a bad spot.
The concept that the amps are "not working hard" because they are set at 9 o'clock is a false premise. It simply means a larger signal must be applied to drive the amp to full power.
That speaker cable is woefully inadequate. No way this was a pro install.
Sent from my VS996 using Tapatalk
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I'm not fully saying I want to change it but something in this system isn't right. My wife and I are taking over as worship directors and I'm trying to get an idea of how things are set up so I have the knowledge. I work in IT and I'm used to knowing what systems I work with in case something goes wrong. Plus, it serves as an excuse for me to finally learn how power amps and speakers work.
No one truly seems to know how things are set up and the mixer doesn't work the way I'd expect it to. For instance, during a normal service that's run a little loud; the channel and group faders (incl mains) are set around -20, the gain for the channels are not set high, the mixer shows main output at around -16, and the power amp level is set at 9 o'clock where the lowest possible is 8 o'clock. Needless to say it doesn't give the sound tech a whole lot of "room" to work with on the mixer when mixing near -20 and most gain knobs set to 0. Just seems like the whole system was set up for a rock concert as opposed to a house of worship.
So this started with me just being curious/wanting to learn and the deeper I dig the weirder things seem. :o
This sounds like a console gain-staging issue, mostly, but there could be other things going on and we'll need a LOT more info to suss it all out.
First, what console? If it's a digital mixer with metering in DBFS (dB full scale), -18 is the close equivalent of an analog mixer mechanical meter reading at 0 dB Vu.
{quick story} When our shop got our first Yamaha M7, my Olde Analogue Guy boss wanted to play with it in the shop. He got a CD to play through it and and microphone to work. He called me, happy that he'd gotten the new technology to work, but told me "these things have LOTS of gain and the faders need to be down really far." He's an old analog guy with a practice of "PFL the input, set the channel gain so the meter reads 0 dBVu". The M7 has metering in DBFS, which is almost 20dB hotter at -0- (at that point the console has no more "1s" in the digital inventory). Once he understood that -18 DBFS is the new "zero VU" the console operation was normal for him. {/quick story} Could this be what you're seeing?
Seeing input gains all set at the "zero" or "unity" (I could eviscerate Greg Mackie's marking people for that BS concept of setting input gain) means someone bought into the Mackie marketing hype from 25 years ago and the BS still has impact.
If the input gains are set more or less as I described in the story (but so the inputs peak at -18ish on the meters, if DBFS metering), the problem is down stream of the console, and that will require answers to more questions, some pictures and maybe a signal flow diagram.
The Samson amps would not be my choice for anything except a frat house basement PA, broke musicians playing bars, etc. but my standards are fairly high. If it's working, there is no need to replace it.
Is your issue with the system 1) held by others and 2) based solely on the observed fader positions?
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The Samson SX series amps say 8 ohm only in bridge mode any lower and you risk damaging the amps. The fact they are stacked, unless they are 16 ohms you are in a bad spot.
The concept that the amps are "not working hard" because they are set at 9 o'clock is a false premise. It simply means a larger signal must be applied to drive the amp to full power.
That speaker cable is woefully inadequate. No way this was a pro install.
Sent from my VS996 using Tapatalk
The whole system is probably...20 years old with various smaller "upgrades" done along the way. I'm guessing it may have been a pro install and then modified over the years. Thanks for the info on the amp signal! Also, how far east does your company go? I'm over in Geauga county and if we try to upgrade in the future I can keep you guys in mind.
This sounds like a console gain-staging issue, mostly, but there could be other things going on and we'll need a LOT more info to suss it all out.
First, what console? If it's a digital mixer with metering in DBFS (dB full scale), -18 is the close equivalent of an analog mixer mechanical meter reading at 0 dB Vu.
Seeing input gains all set at the "zero" or "unity" (I could eviscerate Greg Mackie's marking people for that BS concept of setting input gain) means someone bought into the Mackie marketing hype from 25 years ago and the BS still has impact.
The Samson amps would not be my choice for anything except a frat house basement PA, broke musicians playing bars, etc. but my standards are fairly high. If it's working, there is no need to replace it.
Is your issue with the system 1) held by others and 2) based solely on the observed fader positions?
Tim,
The console is an old Allen & Heath GL2200 so it's not using DBFS. I've heard Samson amps don't have a glowing reputation but maybe they'd be OK in the future serving for monitors?
In response to input gains @ 0 and my issue: FWIW I was taught to set gain by putting the fader at 0/unity and bring the gain up to where the level meter shows near 0. At that point use the faders/groups to adjust the mix. So seeing how this board ran with most gain @ 0 and faders super low just through me for a loop especially since if I tried to set the gain my way I'd have to turn all the input gains way way down. Maybe the way I've always done it/ been taught is wrong? Also, I've spent most of my mixing time on a X32 and not an analog. So I suppose my issue was that the setup (which seems to work ok) is completely different from what I'm used to.
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The Samson SX series amps say 8 ohm only in bridge mode any lower and you risk damaging the amps. The fact they are stacked, unless they are 16 ohms you are in a bad spot.
That's interesting since his first photo shows a little "4ohm min" annotation nested in the bridging diagram by the screw terminals.
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The whole system is probably...20 years old with various smaller "upgrades" done along the way. I'm guessing it may have been a pro install and then modified over the years. Thanks for the info on the amp signal! Also, how far east does your company go? I'm over in Geauga county and if we try to upgrade in the future I can keep you guys in mind.
Tim,
The console is an old Allen & Heath GL2200 so it's not using DBFS. I've heard Samson amps don't have a glowing reputation but maybe they'd be OK in the future serving for monitors?
In response to input gains @ 0 and my issue: FWIW I was taught to set gain by putting the fader at 0/unity and bring the gain up to where the level meter shows near 0. At that point use the faders/groups to adjust the mix. So seeing how this board ran with most gain @ 0 and faders super low just through me for a loop especially since if I tried to set the gain my way I'd have to turn all the input gains way way down. Maybe the way I've always done it/ been taught is wrong? Also, I've spent most of my mixing time on a X32 and not an analog. So I suppose my issue was that the setup (which seems to work ok) is completely different from what I'm used to.
Hi Andrew-
Your method is close to the "PFL to 0 vu" that the resulting input gain should be close to the same. Give it a try both ways and see if there is a difference. Good to know you're familiar with the differences in metering scales; you a couple steps ahead.
Yeah, it probably would be a good idea to call a team rehearsal and take a look at levels. Does the console feed other down stream items like lobby or nursery? A recording or streaming feed? Hearing assistance system? Particularly if the sends are derived pre-fader, reducing input gain will require that lost level be made up elsewhere.
At 20 years old I think your review of the system is understandable. Other than console operation being inconvenient what aspects of the system are you questioning?
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Hi Andrew-
Your method is close to the "PFL to 0 vu" that the resulting input gain should be close to the same. Give it a try both ways and see if there is a difference. Good to know you're familiar with the differences in metering scales; you a couple steps ahead.
Yeah, it probably would be a good idea to call a team rehearsal and take a look at levels. Does the console feed other down stream items like lobby or nursery? A recording or streaming feed? Hearing assistance system? Particularly if the sends are derived pre-fader, reducing input gain will require that lost level be made up elsewhere.
At 20 years old I think your review of the system is understandable. Other than console operation being inconvenient what aspects of the system are you questioning?
It also seems the system just plain has too much gain. The first thing I would do is get rid of the bridged mode on the amp. Switch it to parallel instead of bridged and put one banana plug in ch1 and the other in ch2. You will lose 6dB of unwanted gain just by that.
If excessive noise is not an issue can certainly run the mic input gains a little lower as well.
Mac
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It also seems the system just plain has too much gain. The first thing I would do is get rid of the bridged mode on the amp. Switch it to parallel instead of bridged and put one banana plug in ch1 and the other in ch2. You will lose 6dB of unwanted gain just by that.
If excessive noise is not an issue can certainly run the mic input gains a little lower as well.
Mac
Mac, that was where I was going next, depending on the OP's input gain findings.
The use of that amp isn't fully clear, either, but we're presuming it powers 2 full range loudspeakers and I'm in full agreement about not bridging.
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The first thing I would do is get rid of the bridged mode on the amp. Switch it to parallel instead of bridged and put one banana plug in ch1 and the other in ch2. You will lose 6dB of unwanted gain just by that.
Mac
And while you are at it. Fix/correct the banana plug colors.
Every speaker should have one black and one red plug attached.
The fact that whoever installed/upgraded this chose to use that color scheme combined with the wiring on the bottom Amp and the fact that the amplifier is probably way overpowered for this use makes me wary of this installation.
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Tim, Mac, Joe,
The console does technically feed an overflow area but the area apparently hasn't been used for this purpose for years. I'm not sure of the wiring, but as far as I know this channel outputs to two main PA speakers and somehow the smaller overflow speakers are connected into the same channel with a volume control on the wall. I wouldn't mind removing them from the system until the time comes where we need them or upgrade the amps & speakers.
So I had a meeting with a guy last night who knows a bit more about the system and according to him if we turn up the amp to maybe 12 o'clock we get lots of noise. I suppose that's not too surprising given what I hear about Samsons...
Being that I haven't been able to figure out anything regarding the speakers being 4, 8, or 16 ohm; I'm assuming we'd be fine switching from bridged to parallel with no worries right? Also, given that it's a stereo amp and I believe there's an unused xlr cable from the board to the amp area are there any issues with maybe switching to stereo? I don't have anything against mono, just exploring possibilities.
Tim - I'm not really questioning the system beyond the awkward console setup and now the speaker set up.
Thanks everyone for all your input! I'll probably try and get a better look at the speakers on Sunday and maybe I'll have more info then.
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The noise can probably also be at least partially attributed to the wonky gain structure going on that Tim and Mac helped you with. Any time you send a super hot signal out you're going to get a much higher noise floor down the chain. Also pots get dirty sometimes, so try giving the gain knobs on the amp several rotations back and forth and see if that knocks out whatever crud/lint/corrosion has gotten inside, if any.
The only thing you'll lose by going to stereo operation is a bit of power (and gain as Mac mentioned), but given that we're not talking about throwing rock concerts in this space you should be fine. Worst case you run a couple tests with it in stereo and put it back to mono if you don't get the performance you need. Just be sure to flip the switch on the back of the amp to the correct amplification mode.
Sounds like you've got a solid gameplan, let us know how things go over the weekend with your changes.
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The noise can probably also be at least partially attributed to the wonky gain structure going on that Tim and Mac helped you with. Any time you send a super hot signal out you're going to get a much higher noise floor down the chain. Also pots get dirty sometimes, so try giving the gain knobs on the amp several rotations back and forth and see if that knocks out whatever crud/lint/corrosion has gotten inside, if any.
The only thing you'll lose by going to stereo operation is a bit of power (and gain as Mac mentioned), but given that we're not talking about throwing rock concerts in this space you should be fine. Worst case you run a couple tests with it in stereo and put it back to mono if you don't get the performance you need. Just be sure to flip the switch on the back of the amp to the correct amplification mode.
Sounds like you've got a solid gameplan, let us know how things go over the weekend with your changes.
Don't forget to turn off the bridge switch in the amp. You can leave the input in parallel so you only have to feed one channel.
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Sorry for the late update but I do have an update. The speakers are indeed homemade enclosures that are screwed to building structure. From what I can tell there are three speakers...One on the left, and two on the right. The two on the right are different sizes. There's not a ton of access so I didn't really get a good look at them and I forgot to bring my phone into the attic to take pictures. I'd like to figure out the speaker setup before I try switching from bridged to parallel. I'm going back in a few days and maybe I can take some pics and maybe try and figure out the wiring. I know for the left speaker it has two wires connected to it (as in two blacks and two reds). I'm not sure where the second set of wires goes yet.