01-30-2013 05:35 PM
Good Evening -
Posting here because I think this situation best matches recording rather than live sound... not sure.
I have been using a pair of Crest 15" Powered Speakers for 6 years in my studio. They have only been out of the house 4-5 times. My acoustic group rehearses by running everything into a MOTU interface then into a MacPro (GB) and then out thru a Mackie mixer to the speakers. The connections rarely get touched - we just leave everything connected.
Over the 6 years, 2-3 times ONE of the speakers seems to partially lose its connection. The 15 speaker drops out but we still have the horn. It's only ONE of the speakers and it's the SAME speaker each time. In the past the situation has eventually corrected itself. One time I had called the folks at Peavey and was about ready to pack up this beast and send it to them for a look-see when it came back to life.
It has happened again. Any thoughts on what I should do to get this piece back on track?
01-31-2013 05:12 AM
Electrical connections are just the pressure of two contacts together. They are not soldered to a perminant joint so they are exposed to the air. This means dust and oxidation can get in the contacts making for a faulty connection.
In a speaker cab you often have press on connections that can loosen from vibration. You can also have solder connections to the speakers and crossover circuit boards with solderd components vibrate loose from their connections especially if those connections werent wave soldered well.
I had one of my monitors start doing what your did and it wound up being a dirty/fatigued circuit breaker that was in there that prevented overcurrent from blowing the horns. A little contact cleaner and it was back to working like new.
You can also have wire that gets over heated. Once the insulation gets hot enought, the insulation separates from the copper wire and oxygen gets in and the copper oxidezes. Once that happens the wire gets crackely. instead of the individual strands working as a single wire, the copper strands each get oxidized and each strand gets a tarnished skin on them. This causes all kinds of noise when a signal is passed through them. Its also why you should never ever use a guitar cord for a speaker application. The plastic insulation is low temp and low voltage designed for less than one volt. Pass 70+ volts from a speaker jack and the insulation melts away from the copper and lets oxygen in and the cord becomes noisy and microphonic.
Temp too makes metal expand and contract. Copper and lead expand and contract at two different rates so what once may have been a good solder bond, can become cracked, especially in a speaker cab where the constant vibration is occuring. Thas why they usually use clip on connections to allow for the metal contractions.
You also have cable connectors that fail over time even though they arent on the road on a daily basis. Oxygen, heat, moisture dust and aging are all factors in failure. I notice more cable failures in my studio during the hot humid summers because of the moisture getting into contacts. Pot sliders and switches too have more issues with humidity than the cold as well.
It can also be the speaker itself. When I used to do equipment repairs for a living I'd find ndozens of speakers that just blow themselves appart through normal use. Speakers are and electro mechanical device thats basically just glued together. The wires between the connector and cone are usually the first things to go. You can also have the surrounds crack, mounting screws loosen and the speaker basket loosen and twist and cause binding.
The cables, amps Mixer etc can be easily ruled out by swapping the two sides. If the problem moves you know its not in the cabinet. If it stays, Best thing you can do is open the cab and inspect and clean all electronic connections. Start at the jack and move along towards the crossover and speakers cleaning all connections. I suspect its just a dirty connection because when a speaker blows it doesnt come back and work properly again. Its likely a connection or a solder joint fault colse eyed inspection should be able to find.
02-02-2013 07:18 PM
I want to follow up on this because of the curious nature of what "fixed" this problem.
When my techie bandmate showed up for rehearsal and learned that one of our powered PA speakers had no working speaker he began a hopeful workaround by asking me for a 1/4 inch cable. His intention was to plug a cord into the LINK OUT jack of the malfunctioning powered speaker and connect to a secondary speaker. The moment he touched the cords metal jack (male) to the LINK OUT output there was an electrical click and the previously non-functioning powered speaker began to work just fine!
I was very grateful for the easy, non-invasive fix and at the same time felt a bit silly. It appeared that all was well.
Tonight I went to play and once again the same speaker had dropped out. I reached for a cord, touched the plug to the LINK OUT jack and BINGO - sound on.
What's going on here?
02-03-2013 05:19 AM
Like I said in my writeup. You need some lubricating contact cleaner and clean all jack contacts.
Jacks get dusty and dirty and all they need is a piece of dust in the contacts and you loose connectivity. The specific jack you spoke of is a switching jack. When you plug something into it it breaks the contact to one speaker and provides contact to another. From your symptom the contact is dirty and it has intermittiant contact. Get some lubricating contact cleaner, spray it inside the jack then pus a plug in and out of it several times to work the connections clean.
You may have a cable starting to go bad but try the contact cleaner first. Just be sure its lubricationg contact cleaner. Zero residue cleaner can make issues like this worse because it can oxidize the metal.
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