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Discussion Starter · #1 ·
I think I have an unique problem. My a/v receiver shuts off, but why?


History:


-I have ran together my Denon 3808CI with two Focal Chorus 826V fronts, a Focal CC800 centre, two subs and 4 surrounds for over a year now. No problems at all until about 6 weeks ago. After pushing the a/v receiver for the first time for over an hour, it shut off. I understand that is normal, due to it warming up, and had no problem with that happening.


-The problem is that now the 3808CI shuts off at much lower volumes, and does it with the amp still being cool (ie seconds after turning it on) So I figured I fried something.....


-I had the amp sent to Denon tech centre, where they performed tests on it to confirm that I fried something. Problem is, (or not a problem really) that there turned out to be nothing wrong with amp. SO.............


-I decided that, (according to Denon tech anyway), that this avr isnt completely suitable to run my Focal speakers. (NOT what the salesman I bought all my home audio from claims, but that is a different story) So I bought an Emotiva external power amp (XPA-3) to run the focals, and figured that would solve all my problems.


-It didnt. The XPA-3 shut off as well as soon as I increased volume to around -15 Dbs on avr (which is not that loud, about as loud as a tv on full.)


-So I checked my 12 gauge speaker wires from end to end again, took off banana plugs and hooked wires directly with no shorts to terminals. This never helped. I checked the resistance of speakers : 4.5 ohms. (4.6 ohms thru 22' of wire)


-I checked the ohms while music was playing. At low volumes the meter bounced around 5.5 to 13 or so, at higher it went down between 2.2 to 30 ish. At the highest I can go before it shuts off, the meter displayed everything from 0.0 to 177. (bounced around like crazy) This is where I need help, I have no idea what this means. I basically have to assume the only thing left that could cause me problems is the speakers are 'broke'. They sound great however.


-Is there any other thing I can check regarding the speakers? The amp doesnt shut off at high volumes with my paradigm surrounds loud.
 

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Just spitballing here cause I'm not All that good, but learning....


Most avr's are not meant to drive 4 ohm speakers. But the emotiva shut off too? Is this really bass heavy content?, they may drop even lower than the 2.2 ohms you saw on the meter. Focal lists the min. Impedance of the 826 at 2.9 ohms at 118 hz and the cc800 at 4 ohms at 210 hz but I'm not sure to trust that. The emotiva is only stable to 4 ohms. Are the amp and avr in a cabinet? Enough ventalation?


How does the denon or the emotiva deal with just one speaker connected? Do you have any 8 ohm speakers to hook up and try?


Like I said I don't know much but maybe I can be of a little help


also maybe try taking the denon out of the mix and run the emotiva right from a cd player and see what happens. Will it still shut off at a higher crossover?


Good luck and there are many good minds around here that I'm sure can help figure this one out.
 

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Discussion Starter · #3 ·
Technically, these are 8 ohm speakers, with sensitivity of 95. My avr ran them fine for over a year. That is why I think something happened recently with the speakers themselves.


I was assured the XPA-3 would have no problem with these speakers.


Its not a heat issue with avr or XPA-3.
 

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It seems you've covered most bases. I agree that one of your speakers is causing the problem. I can only think to disconnect each of your speakers for a while to try to localize the problem.
 

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Discussion Starter · #5 ·
So here is the question. Can a speakers rated ohm change over time? Mine were rated to drop to 2.9 ohm at certain freq. Do they now drop lower, and thus cause avr and external amp to shut off?
 

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Quote:
I checked the resistance of speakers : 4.5 ohms. (4.6 ohms thru 22' of wire)

The "Ohms" on the back of the speaker is it's impedance, usually at 1KHz. You cannot measure impedance with an ohmeter.

Quote:
-I checked the ohms while music was playing. At low volumes the meter bounced around 5.5 to 13 or so, at higher it went down between 2.2 to 30 ish. At the highest I can go before it shuts off, the meter displayed everything from 0.0 to 177. (bounced around like crazy) This is where I need help, I have no idea what this means. I basically have to assume the only thing left that could cause me problems is the speakers are 'broke'. They sound great however.

You cannot, and should never measure resistance with a voltage applied. These meter readings are meaningless, and could damage your amp. Again, impedance cannot be measured with an ohmeter.

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-Is there any other thing I can check regarding the speakers?

What is the stated impedance of the speakers? are your amps capable of driving it?
 

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I have been having the same problem. I have the yamaha RV 3800, I use it as a pre amp/ processor for my Rotel amps RB1080 and RMB 1075. the yamaha will kick off at high volume levels. I went through the same process as you ie. checking all connections, put my yamaha in the shop for repair etc. the yamaha reciever was ok as per the repair shop. Ifound out the tweeters were blown on the 826s and my center channel speaker 918cc. I was told that clipping was the problem.I am looking to replace the 826s with klipsch, i hear you cannot blow the horn tweeters in their speakers. Check the tweeters by putting your ears to the tweeters.
 

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Discussion Starter · #8 ·

Quote:
Originally Posted by duvetyne /forum/post/18151600


The "Ohms" on the back of the speaker is it's impedance, usually at 1KHz. You cannot measure impedance with an ohmeter.



You cannot, and should never measure resistance with a voltage applied. These meter readings are meaningless, and could damage your amp. Again, impedance cannot be measured with an ohmeter.
Thanks, this is what I needed to know.





What is the stated impedance of the speakers? are your amps capable of driving it?
8 ohms, and it was able for over a year.
 

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Discussion Starter · #9 ·

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Originally Posted by darskar /forum/post/18152270


I have been having the same problem. I have the yamaha RV 3800, I use it as a pre amp/ processor for my Rotel amps RB1080 and RMB 1075. the yamaha will kick off at high volume levels. I went through the same process as you ie. checking all connections, put my yamaha in the shop for repair etc. the yamaha reciever was ok as per the repair shop. Ifound out the tweeters were blown on the 826s and my center channel speaker 918cc. I was told that clipping was the problem.I am looking to replace the 826s with klipsch, i hear you cannot blow the horn tweeters in their speakers. Check the tweeters by putting your ears to the tweeters.

I think you are on to something here. I just listened to speaker tweeter and heard nothing. I changed music, turned it up slightly, and then heard a faint 'hum' or 'scratch' at very low volume.


So a blown tweeter can cause an avr or external amp to shut off? Wow.....


If I disconnect the tweeter - will this solve the avr shutting down?
 

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Discussion Starter · #12 ·
I have. Both fronts shut down avr. Centre doesnt.


My paradigms can run on any channel without shutting down avr.


However, after more looking into it, I found that the tweeters on the fronts really dont work. Is there any way to check to see if it is the tweeters causing a short by being blown, or if something is fried in the crossover hardware?
 

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It sounds as if something is damaged with the speakers. Since you are able to run some of your other speakers and it does not shut down. You said you measured 4.4 ohms on the speaker. At idle, meaning not plugged into your amp you should get about the nominal ohm reading for the speaker. In this case the spec sheet says 8 ohms. Unfortunately without pulling drivers out of the box and checking each one you will not be able to tell if it is a speaker or internal crossover network. If they were my boxes, I would pull that top 6.5" out and see if I could get to the wire leads of the tweeter. If I could I would unhook them and then put a meter on the tweeter. If I got an ohm load of like 1 or less, or anything above like 16 I would say that is the problem. However, a blown driver does not cause this kind of problem. Once you start adding power to the box it could be lowering the overall ohm load of the box down to something that the amp cannot take. The reason you cannot measure the impedance of the box with an ohm meter is that while the speakers are producing sound, the impedance changes.


Sorry that was long. I don't claim to be an expert, that is just how I would go about figuring this out.
 

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Quote:
You said you measured 4.4 ohms on the speaker.

that would be the resistance of the input to the crossover, not the speakers impedance.

Quote:
At idle, meaning not plugged into your amp you should get about the nominal ohm reading for the speaker.

No likely, you cannot measure impedance with an ohmeter

Quote:
If I got an ohm load of like 1 or less, or anything above like 16 I would say that is the problem.

If the resistance of the tweeter is very low, it's most likely shorted and would cause the problem you're describing. If the resistance is very high, ie. open circuit, then it won't cause the problem you're describing.

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However, a blown driver does not cause this kind of problem.

That depends on what you mean by 'blown'.

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Once you start adding power to the box it could be lowering the overall ohm load of the box down to something that the amp cannot take.

No, impedance is dependant on frequency.

Quote:
The reason you cannot measure the impedance of the box with an ohm meter is that while the speakers are producing sound, the impedance changes.

No, impedance is the vector sum of resistance, capacitive and inductive reactance, you can only measure resistance with an ohmeter, not reactance.


The impedance does not change 'while producing sound'.
 

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Let me clarify a little. He got 4.4 ohms at the terminal, which is the overall ohm load of the whole box. Who knows what the crossover network is doing to that. I have hundreds of raw speakers in my shop. If I put an ohm meter on any of them, they will give me the nominal ohm rating, 8 ohm, 4 ohm and so on. If he measured 4.4 and it should be 8 then it sounds like something is wrong. You are right that if the ohm load is below 1 then it is probably shorted out, but most crossovers I have used would protect against this. Blown as in slightly gone, totally gone. I have huge concert PAs that don't do this anytime someone blows a driver, as in stops working or just puts out bad sound.


Adding power to the box and producing sound is what I meant by changing the ohm load. If he is playing music or other sources that has more low end then anything else, he could be pushing the ohm load down to something the amp cannot take. Impedance changes all the time while producing sound. I have processors that monitor what my amps see and they constantly show a changing impedance even with just someone talking. Normally it is not enough to cause a problem, however I have seen everything from .5 to 100.
 

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Quote:
He got 4.4 ohms at the terminal, which is the overall ohm load of the whole box.

it's the resistance of the crossover input. "Ohm load" is a term used by people who don't understand this


Quote:
If I put an ohm meter on any of them, they will give me the nominal ohm rating, 8 ohm, 4 ohm and so on.

Some will some won't , it's not the impedance of the speaker you're measuring though.

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If he measured 4.4 and it should be 8 then it sounds like something is wrong.

I disagree

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Adding power to the box and producing sound is what I meant by changing the ohm load.

At the rist of repeating myself, Impedance changes with frequency, not applied power, as you're suggesting.


I'd suggest you google impedance for a primer.
 

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Ok, just so I am clear, maybe I am missing something. I have a speaker sitting here. It has no crossover network in it. Why then when I put an ohm meter on it, why do I get 8 ohms? All of the 8 ohm rated speakers in my shop will give me 8 ohms. I don't even have some of them in boxes, just raw drivers. All the 4 ohms will give me 4 ohms. The slightly used ones give me .1 or so off of what they are rated. How do speaker manufactures rate a speaker load? Meaning why do they give a nominal impedance. Your last point is just me not being able to communicate. I totally agree that impedance changes with frequency not power. I was trying to say that when he is listening to music or something, the frequencies the speaker is trying to produce is causing a low load on the amp. Does that make more sense?


Sorry for the confusion.
 

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Why then when I put an ohm meter on it, why do I get 8 ohms?

It means that the resistance of the voice coil is 8 Ohms.

Quote:
How do speaker manufactures rate a speaker load?

Impedance is measured by applying a known voltage at a known frequency and measuring the current drawn and the phase angle, The impedance is calculated using Ohms law.
 

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Ok, I should just stop trying to help. To me, you and I just said the same thing. If he was seeing a 4.4 ohm reading, but the nominal load of the box should be 8, would that not suggest that one of the drivers might be damaged, or the crossover network itself is damaged? So if he metered the tweeter, and say it is suppose to be an 8 ohm tweeter, and his meter said 2 or 100, would that not suggest that it is bad? Granted, I don't know what the nominal rating for the tweeter is, lets just say it was 8. I do appreciate you correcting me. Resistance of the driver I guess is more the correct term then impedance.
 

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Quote:
To me, you and I just said the same thing.

I didn't, you seem to think resistance and impedance are the same thing.

Apparently there's a crossover involved as well, so measuring the resistance at the speaker terminals really doesn't tell you anything.


It's impedance that we're interested in, resistance is only a part of it.
 
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