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QUESTION: Hello. I have looked everywhere for an answer to my problem, but have found none. When I power my home stereo system down i get a delayed popping sound in one of my speakers. I have isolated the problem to a particular mid-range speaker within my Paradigm Speakers. Here is what I have and here is what I've done. I have the following Adcom components : CD Player. Tuner/Pre Amp. Two GTA 555ii amps for main speakers. A GFA 2535 amp for Paradigm rear and center speakers. A Velodyne Sub Woofer. An ACE 515 power/surge protector with switched and unswitched outlets for the amps and components. The main speakers are Paradigm Sudio Monitors. On the backs of each are amp inputs for the tweeters, inputs for the midrange and imputs for the bass. I have the midrange and tweeters bridged. So One of my 555's powers the midrange/tweeters of each and the other 555 powers the bass of each. I have isolated the problem to one midrange speaker. At first I thought it was the amp. I switched amps and still got the same noise. Then I thought maybe the speaker was blown, but good sound comes out of it. So when I turn the system off, the amp power indicator lights fade off and then quick pop pop pop pop pop pop pop from the midrange speaker. I turned off the 2535 amp and the subwoofer to eliminate them. I purchased everything in 1993. The system was in storage from 2005 until two weeks ago. I was always pretty mellow with the voume. Occassionally I would " Crank " it up just to see what it sounded like, but only for a few seconds. All components were stored in a climate controlled environment. I  hooked it up with all new wires and cables and attachments--no bare wires. I went back to the place where I purchased the system and they showed me how to hook everything up again. However, when I first got the system out of storage I wanted to just hear a speaker. I was thinking that it used to be wired with one amp per speaker, so I had the right output going to the bass input and the left output going to the midrange/tweeter input. Also,I could have had the right preamp out going to the left input on the amp--not sure. Anyway, everything sounds as good as I remember its just this problem. It can't be good and it can't be good for the speaker. I sincerely appreciate you taking the time to try and solve this problem. I hope I have given you all the information you need.

ANSWER: Have you swapped speakers?  Switch the amp connections to each speaker; left to the right and right to the left. Then check to see if the pop trades places or stays on the same side.  This will help you decide if it is a speaker problem or amp problem.  (I know you switched amps but if both amps have identical power down cycle it may not give you true results).

You could have a bad electrolytic cap inside the amp.  You could have a speaker driver that has a rubbing voice coil or popping spider during the off cycle of the amp driving that speaker.

Quite common among amps is a relay or sometimes a special circuit to power up and down in a way that masks out the "bloop" that often comes with the process. The "bloop" or transient comes during the dc buildup from the amps power supply. For example, a relay is used at the speaker terminals. The safety circuit closes the relay to activate the speakers only after the power supply has come to full voltage.  Same during power down; the relay disconnects from the speakers first then after that is accomplished it allows the power off from the mains.

A speaker unit can have a rubbing voice coil - which is very common.  Sometimes the rubbing generates a popping sound from the coil grabbing the pole piece and jerking as it settles down.  Also, the surround and the spider diaphragm, due to age, will start clicking or popping when the speaker gets a big dc pulse such as when the amps power off  (amps without the impulse eliminator feature explained above.)

So, these are some of the things you can look at to get closer to the cause and the solution..

Let me know what you find out if you need another iteration.

---------- FOLLOW-UP ----------

QUESTION: Thank you so much for your time. I truly appreciate it. I understand what you mean by switching speakers. I will try that. By switching amps,though, if it was an amp problem wouldn't the sound then come from the bass driver ? Or could it affect the drivers differently, ie not produce the same noise. I don't understand everything you said but the big DC pulse made sense. It sounds like ELECTRICAL " crackling/popping ". I didn't say this before but there usually is a single " pop " from the other speaker. I didn't try to isolate what driver it was coming from  because it is so minor compared to the other. As far as rubbing voice coils and  clicking spider diaphragms, are these signs that the driver is failing ? Can drivers be replaced ? Would I gain any knowledge if i bridge the 3 drivers together and then run one amp to the speaker in the Bridged-Mono out put mode. ? If you had one guess, what would you say it is ? I realize i am asking more than one question. Again, thank you for your time

ANSWER: By swapping speakers I was saying to swap the speaker channel.  In other words with your system wired normal biamps that you have just switch the left speaker system with the right, everything else remaining the same. (With woofers not energized.)

The thing we MUST do is determine exclusively if the problem lies with a speaker or with an amplifier.

Another test you can conduct on your own is pull the front covers off the speaker box and manually depress the mid range speaker. Do it gently so as not to damage it but listening up close and depressing the cone - make sure you are depressing it linearly by applying equal pressure on the cone.  If you hear scraping or crinkling sounds that may be where the problem is coming from. Compare the 'good' speaker cone with the 'bad' one.

You would gain the most wisdom by disconnecting all speaker except for the pair with the popping problem. That way you have removed all but the suspect channel.  Now you have a stereo pair being driven exactly the same.  No other speakers are fired up except for the left side mid/tweeter and the right side mid/tweeter.  Then you can do speaker swapping, speaker listening to see if there are distortions or voice coil rubbing, etc.  You can also switch amps around to see if the stereo pair are behaving differently with different amps.

Keep struggling.  I think you will find the problem.

---------- FOLLOW-UP ----------

QUESTION: Hello again. Tonight I ran every combination of AMP channels to speakers to bass drivers  midrange drivers  tweeters. I wired each driver separately and listened to each.  ALL sound fine.  It is the AMPS.  BOTH AMPS. Seems like both left channels do it more than the right ones. The tweeters make the sound lightest.  pop pop pop pop.  THe midrange is loud POP POP POP POP POP POP.  The bass is softer and just one POP. The AMPS are GFA 555 ii's by Adcom.  I wired an Adcom 2535 amp  (which has an A amp and a B amp for rear and center channels.) to the speakers and got absolutely no pop. Both 555's are 20 years old as are the speakers. So what would you recommend ?  Have the Amps serviced or cleaned or something else ???  Once again I thank you for your time. I realize you do this voluntarily and I sure do appreciate it.

I am beginning to wonder if you have an interference of some kind that is getting into the amplifier.  Are you near a radio transmitter or hospital or something with lots of rf energy floating around?  Have you tried the 'bad' amp in another room or at a friends house?  A real nuisance to do but maybe helpful in making a diagnosis.

A good audio technician may be able to identify the problem but you would have to lug the amp in to the shop.  TV repair techs are not usually knowledgeable for high fidelity audio so you should try to find a tech with good audio experience.  One who can hear the popping sounds and look inside the amp during the popping jag would help find the gremlin..

All the best.  

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Audio Design Engineer; systems, loudspeakers, cd/dvd players, etc. I am knowledgeable in all high end audio equipment and installations. MAKE SURE YOU GIVE A MAKE AND MODEL NUMBER AND CAR IF IT IS AN AUTO QUESTION. Note: I am getting some who ask good questions that take a lot of time to research but then the questioner fails to read the answer. Please don't ask questions unless you are seriously looking for an answer. If you find an answer to your question otherwise then let me know with your reply. Thank you.


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