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Thread: Speaker amp problem

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    Speaker amp problem

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    Our church was robbed and now we have 2 sets of speakers running off one amp. The amp is a behringer a500. 500 w, 8ohm as mono. 350w 4ohm as stereo. 2 speakers are bose 32se, 32w 6 ohm. Short run. The other 2 are unknown on a very long run to our kids rooms. Wired parallel stereo. The volume is very low. The Bose should be louder for sure. Is this a situation where i need another amp to separate the speaker pairs?

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    I am assuming that the amp is running stereo 4ohms per channel.

    Two many speakers, you also need to find out what the ohms is for the kids room speakers, a simple multi meter will do this.

    Even the Bose speakers wired 2 each side of the amp will be a bit low for ohms, 3ohms, but will probably not hurt the amp. If you know what the kids speakers are there may be a way to series parallel wire the system to give a good ohms. Running the wrong ohms will eventually blow the amp up, it worries me that the volume is low, also the long run needs some good quality wire not some skinny cheap speaker wire.

    Alan.

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    Power Dynamics PDV040 PA Amplifier 40W 8-Ohm/70V/100V Line

    Get something like the above to run the kid's room. The cabling can be very light in fact if the church is "networked" you could pinch pairs 7/8!

    The 70volt* amp can be slaved from the Behringer feed. Mixer? Or you could use a DI transformer across the speaker output. You mention "stereo"? Not usually a lot of point for PA especially in a church where 50% perhaps of the congregation will not be in a "sweet spot".

    You will need 70V transformers for the remote speakers but these are only a few $$s if you just need low levels. 10 watts would for instance be plenty I would think.

    See, "back in the day" churches and factories had sound systems installed by people who knew WTF they were doing! and they would have rigged a 70volt system. Today kit is cheap and there is always "somebodie's dad that knows a bit about "hi fi"..."

    *In EU we use 100V line speaker systems but for some unaccountable reason the USA went 70 volts?

    Yup, found 15W 70V traffs under 10 bucks. BTW that Behringer amp only has a spec of 125W into 8 Ohms. If perchance "stereo" means you are running it in bridge mode? DON'T! That must see an 8 Ohm minimum load.

    Dave.
    Last edited by ecc83; 08-12-2019 at 22:59.

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    To complicated just use 7amp wiring like used in mans cables as speaker cables for the long run.

    Alan.

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    Quote Originally Posted by witzendoz View Post
    To complicated just use 7amp wiring like used in mans cables as speaker cables for the long run.

    Alan.
    Good heavens Alan! Yonks ago ELECTRICIANS used to install factory PA systems! Surely not beyond the wit of anyone who can run a computer?

    Then, people always miss the point of 100/70V systems? They are not really about avoiding cable loss, more about being able to set the sound levels needed at various locations in a building. You can even get "lossless" volume controls that contain a mini variac.

    OP needs to buy another amp, he WILL blow up the Bellringer eventually as he is going on. Might as well install at least a semblance of a professional system?

    Dave.

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    You are talking about someone that does not have a multimeter?

    I know how to do the 100/70v system, but this is a setup in a home and I would think that the long run is actually not that long.

    What we need to know is the impedance of the unknown speakers.

    Alan

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    Quote Originally Posted by witzendoz View Post
    You are talking about someone that does not have a multimeter?

    I know how to do the 100/70v system, but this is a setup in a home and I would think that the long run is actually not that long.

    What we need to know is the impedance of the unknown speakers.

    Alan
    Oh! I was not questioning YOUR expertize Allan! The Z of the remote (HOW remote?) speakers is, IMHO immaterial, what the chap needs is another amplifier to set a different level for the kids.

    He could in fact send the signal down back to back, cheap ass' DI boxes and use a bog S receiver from a charity shop at the kids end.

    Trying to balance speaker levels with various impedances is bound for failure. It is the very reason why 100/70 systems were invented (they came to their zenith with the Wireless Relay where the streets were wired and there was a shop with some BIG MOTHER tooob amps at the back with a constant flicker from the Mercury arc rectifier supplying the juice (were they on 3 phases I wonder?)

    Fooling about with one amp and multiple speakers is going to end in smoke. AND! If the church does not already posess a DMM tell them to get one!

    Pity the guy's a Texan, I would cheerfully GIVE him all the bits to fix this.

    Dave.

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    Waking up a bit...So, the Bose's are 6 Ohms so the amp can stand no more load since even 8R will push the Z below 4 R (he could JUST get away with 16 Ohms) .

    Loads below 4R might not wreck the amp immediately but continuous operation could cause eventual failure. For sure there will be VI limiter distortion. The "low level" OP speaks of could be the amp going into a "limp" mode?

    Dave.

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    The thing we're not mentioning is simply speaker sensitivity. So four speaker of the same brand and model wired in series parallel with identical feeder lengths will be all the same volume. If you mix two Bose 8Ohm speakers with two xYZZ 8 ohh boxes, they will be different. If you used two small Bose speakers and two 15" max power handling 500W speakers, then the Bose will be louder - probably much louder. So as Dave said - getting the impedance right is as important as the speaker sensitivity. If you then add in short and long cable runs, you could find the distant speakers miles down in volume - 8 Ohm speakers with 4 Ohms of power wasted heating up thin cable means a significant drop in volume. Your choice is a planned and proper system or a bodge. Bodges can be great and long lasting too.

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    Quote Originally Posted by rob aylestone View Post
    The thing we're not mentioning is simply speaker sensitivity. So four speaker of the same brand and model wired in series parallel with identical feeder lengths will be all the same volume. If you mix two Bose 8Ohm speakers with two xYZZ 8 ohh boxes, they will be different. If you used two small Bose speakers and two 15" max power handling 500W speakers, then the Bose will be louder - probably much louder. So as Dave said - getting the impedance right is as important as the speaker sensitivity. If you then add in short and long cable runs, you could find the distant speakers miles down in volume - 8 Ohm speakers with 4 Ohms of power wasted heating up thin cable means a significant drop in volume. Your choice is a planned and proper system or a bodge. Bodges can be great and long lasting too.
    Plus, you NEVER put speakers of any semblance of quality in series! The amplifier mnfctr has worked hard to give the device a very low output impedance, putting resistance in series with that is just palin daft.

    Yes, calm down! I know 4 x12 guitar cabs are series pll but they are NOT "hi fi" and a valve guitar amp (as they were when the 4x12 came about) has buggerall damping factor. There was however a rare 4 x12 bass cab with specially wound 32 Ohm speakers so the resultant was 8 Ohms.

    Another often overlooked advantage of 100/70V op' is that done properly the speaker cabling is balanced and you can, if need be, run it alongside a balanced mic cable. It is also very RFI immune. Long speaker cables on direct amp outputs make splendid aerials!

    Dave.

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