Speaker amp problem

zepfan59

New member
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?
 

witzendoz

Senior Member
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.
 

ecc83

Well-known member
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.
 
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witzendoz

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

Alan.
 

ecc83

Well-known member
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.
 

witzendoz

Senior Member
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
 

ecc83

Well-known member
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.
 

ecc83

Well-known member
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.
 

rob aylestone

Well-known member
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.
 

ecc83

Well-known member
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.
 

rob aylestone

Well-known member
Hang on Dave? The series parallel combination is surely perfect for many situations, and damping factor isn't really an issue with most modern amps unless its crazily bad, and the amp poorly designed. It's pretty common for there to be series split boxes laying around. I've certainly got some, and never ever noticed a sonic problem with them.

I'm really intrigued by why it's such a bad idea - for me, needing to plug in an extra pair, or often even more speakers using them works pretty well.
 

ecc83

Well-known member
Hang on Dave? The series parallel combination is surely perfect for many situations, and damping factor isn't really an issue with most modern amps unless its crazily bad, and the amp poorly designed. It's pretty common for there to be series split boxes laying around. I've certainly got some, and never ever noticed a sonic problem with them.

I'm really intrigued by why it's such a bad idea - for me, needing to plug in an extra pair, or often even more speakers using them works pretty well.

What do you mean by "series split boxes" Rob and do you have schematics? What are the speakers you are plugging into them?

There is another problem with seriesed speakers with valve amps? If you have a box that puts two 8R unots in series to get 16R and one is unplugged the amp is now unloaded and we all know valves do NOT like that! Valves are however very tolerant of lower loads. A 16R tap loaded to 8 even 4 R will usually be quite ok but a big amp, 50W+ might redplate and pop an HT fuse if you give it the beans.

Damping factors: Yes, transistor amps have a high one in the hundreds. DF is the ratio of amp output Z to speaker Z and a typical sstate amp will be 0.02 Ohms* or better so DF =400 for an 8R load. Valve op stages, even very "hi fi" ones rarely get better than 0.1 Ohms DF= 80. The "classic" AC30 type 4X EL84 has an opz of about 60 Ohms! A big mother 100 watter with a whiff of NFB might get down to 10 Ohms.

If you go back to the tranny amp with a DF of 400 and put two 4R speakers in series the DF is now ONE! High quality speaker design is based on the assumption that the drivers will "see" a very low source impedance, anything else will play ducks and drakes with the frequency response especially the lower octaves.

*Some sstate amp use "current feedback" to raise the opz and hope to mimic the action of valves. Good idea but this entails inserting a low, 0.22-0.47R resistor in the earthy end of the speaker circuit which again is fine IF they use a meaty resistor, often a wee 5W job is used, gets hot and the print joints go dry and can even burn!

Should say also that it is very difficult to measure such low opz's and it is done by indirect means.

Dave.
 

witzendoz

Senior Member
Gee I started it with my series parallel suggestion LOL. Series parallel is used regularly to get correct speaker to amp impedance using multiple speakers. Talk about a mountain out of a molehill.

Has the OP come back or just been scared off LOL.
Alan
 

ecc83

Well-known member
" Series parallel is used regularly to get correct speaker to amp impedance using multiple speakers"

Not by anyone that wants quality bass Al! WHAT is so hard to grasp here? You Allan and you Rob are top audio blokes! You KNOW a speaker needs to be driven from a very low source impedance. The exception as I have stated is where 1) the amp has little or no damping anyway and where people don't give a ***t about the response, i.e. Gitists!

Series speakers also means they are "protecting" each other as a fuse!

(do I need to draw diagrams?)

Dave.
 

witzendoz

Senior Member
" Series parallel is used regularly to get correct speaker to amp impedance using multiple speakers"

Not by anyone that wants quality bass Al! WHAT is so hard to grasp here? You Allan and you Rob are top audio blokes! You KNOW a speaker needs to be driven from a very low source impedance. The exception as I have stated is where 1) the amp has little or no damping anyway and where people don't give a ***t about the response, i.e. Gitists!

Series speakers also means they are "protecting" each other as a fuse!

(do I need to draw diagrams?)

Dave.

If they are wired in correct phase there is not bass loss? I don't get anything you are saying? The only thing that changes is the amount of power each speaker puts out depending on the resistance of that speaker. Heres an explanation LiNK

And here is an explanation on the wiring of Parallel, series and series parallel. LINK

I have used series parallel in a large PA system to get the best impedance for the Amps and never suffered bad bass.

Alan.
 

ecc83

Well-known member
Attached is an impednace curve for a single, GP drive unit. If that is put in series with another such drive unit surely it is obvious that the current is going to be modulated BY that curve? That is the impedance plot for a single speaker. Imaging the havoc a 3 way crossover would cause!

It is of course the current through the voice coil that produces the magnetic force, do we really want to make that proportoonal to some gahstly frequency dependant resistance? That is why speakers should be driven from a voltage source. The bass damping is a bit secondary since even if the amp had absolutely zero opz the voice coil has resistance, even so amplifiers help.

Anyone with a bass speaker and tranny amp can try this...With the speaker unconnected, tap the cone. You will likely get a "boing". Now connect to a decent amp an power it up, VC at min. Now tap the cone..Thud. The resonance has been all but eliminated (the bigger the speaker and the bigger its maget the more obvious its effect.)

I would not chaps, insult you by suggesting you got the speakers out of phase!

I cannot speak for large, s/p'ed arrays but then they might have sounded even better ALL paralled with some matching transformers!

But all this, hill or Everest is not my main point. That is that the OP needs another amplifier to drive the speakers in the remote room so he can set a proper level. (We used a mains variac on valve amps but DON'T put one on a tranny!)

Dave.
 

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witzendoz

Senior Member
Have you looked up the speakers he plans to use, all this theory is not going to make any difference.

I agree that the best way to do this is setting up a multi zone system using separate amps.

Anyway we seemed to have managed to loose the OP.

Alan.
 

rob aylestone

Well-known member
More confused Dave. I have a pile of EV SX300s - probably 12 or so, and we use them for all kinds of things. Just a few days ago, we had a row of brass players. Two saxes, trombone and trumpet and they each wanted a monitor, and all wanted the same feed. I've got some plastic boxes, each with three speakon connectors. One is input, so the 1+ goes to out socket 1, 1+. The 1- connection goes to the last socket 1+ and then 1- back to the input 1-. Plug in a speaker to each outlet and they both work and the amp sees 16Ohms, not 8. Do the same with the other pair and in parallel the amp then sees 8 and is happy. To be honest it's find seeing 16, you just need to drive it a bit harder. Or the other connection possibility is one splitter, then daisy chain two speakers from the first two - that's a 4 ohm load, but with the splitter box, it's back to 8. I've been doing this for years and it solves all the problems.

It can go wrong, when people don't think - you can have two in series, paralleled with one other - and that one is just louder, and this can sometimes even be useful. I don't use them as much now I have plenty of spare amps, but two in series with two in parallel works 100%, and the additional inductive load and the change to the damping factor doesn't upset the amps - most of which can drive down to 2 Ohms, so the occasional miswire to 4Ohms is never an issue. On occasions I've used the series splitter with 4 speaker, going up to a 32Ohm load, and it's strange to see a so much amp power producing so little output, but with a big amp, you can do this with no problems. 6 12" plastic boxes either side from a single stereo amp is a handy thing to be able to do.
 

ecc83

Well-known member
Yes Rob, it can be and is done, (4x12 gitcabs have been mentioned) and guys like you that know what you are doing will get good results but you cannot avoid the laws of physics and putting a frequency dependant resistance in serious with another one will screw the frequency response. Whether the resultant is noticeable in any given situation is moot. I guess those guts just need "some" foldback!

I would also be unwise to have a fairly complex series parallel setup where the unplugging of one speaker could kill sound on everything else. Then there is the fact that levels are all over the shop depending upon the Z of a particular speaker.

I will agree, 100V line systems ARE more common in fixed site setups (the AWOL OP's!) but yonks ago we used them for point to poin meetings, AGM reinforcement and small AmDram situation. The big advantage is that you can hang more speakers on the system with virtually no change in level. If the ASM whats a feed into a dressing room 100 ft away? No problem, we just ran out some 5A lighting flex and gave them a wee box . A more sophisticated system used multicore alarm cable and so the "star" could have a FOH feed with VC but there was a relay switched full wick over ride so he/she did not miss their call.

You have a shedload of speakers and S/Pll boxes. We had a few horns and line source speakers and big box of traffs!

I sometimes wonder if the audio world has advanced that much?

Dave.
 
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