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Author Topic: Power Amp Speaker Wiring Question  (Read 1434 times)

Andrew Cole

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Power Amp Speaker Wiring Question
« on: May 14, 2019, 09:18:19 am »

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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Tim McCulloch

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Re: Power Amp Speaker Wiring Question
« Reply #1 on: May 14, 2019, 09:29:22 am »

The amplifier is being used in "Bridged Mode".
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Mal Brown

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Re: Power Amp Speaker Wiring Question
« Reply #2 on: May 14, 2019, 10:02:20 am »

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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Taylor Hall

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Re: Power Amp Speaker Wiring Question
« Reply #3 on: May 14, 2019, 10:04:41 am »

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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John Roberts {JR}

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Re: Power Amp Speaker Wiring Question
« Reply #4 on: May 14, 2019, 10:15:44 am »

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]
« Last Edit: May 14, 2019, 10:18:37 am by John Roberts {JR} »
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Taylor Hall

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Re: Power Amp Speaker Wiring Question
« Reply #5 on: May 14, 2019, 10:21:58 am »

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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Andrew Cole

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Re: Power Amp Speaker Wiring Question
« Reply #6 on: May 14, 2019, 10:52:46 am »

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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Tim McCulloch

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Re: Power Amp Speaker Wiring Question
« Reply #7 on: May 14, 2019, 01:22:28 pm »

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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Chris Grimshaw

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Re: Power Amp Speaker Wiring Question
« Reply #8 on: May 14, 2019, 02:03:09 pm »

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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Andrew Cole

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Re: Power Amp Speaker Wiring Question
« Reply #9 on: May 14, 2019, 03:08:35 pm »

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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Re: Power Amp Speaker Wiring Question
« Reply #9 on: May 14, 2019, 03:08:35 pm »


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