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1200 watt powered mixer with 200 watt , 8 ohm speaker
jaynag
post Mar 2 2010, 01:33
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Hello all,
I am new to this forum and i hope i can get some valuable input from you all.
I bought a new powered mixer (Behringer 16 channel mixer 1st output - 1200 watt, 8 ohm in bridged mode and 2nd o/p 600 w , 4 ohm).
I have 2 scenarios
I can either use 600w watt , 4 ohm o/p of the power amp
1) with 2 or 3 speakers which are 200 w continuous power with 8 ohm impedance. Again there is a question of whether i have connected the speakers in series or parallel but not there yet and need answers as well.

2) with 13 speakers on the ceiling which are just 20 watt 8 ohm ones probably connected in series-parallel but not sure.

I am just trying to replace an existing system to see if there is a better quality.

Description about the existing system.
The current PA system has a 150 w 70 Volt power amp connected to these 13-14 speakers mentioned above.

Could someone guide me on

Whether i can use the new power amp(1200 w one) with either of these sets of speakers without damaging them.

Thanks




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DVDdoug
post Mar 2 2010, 02:25
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What's your application? Is this for speaking? For live or recorded dance music? How big is your room? Are you going to be "blasting" all 1200 Watts?

For dance music, I'd use the 2 "big" speakers. (This is not good for speaking. You usually end-up blasting-out the people up-front, and the people in the back can't hear... depending on the room, ambient noise, etc.)

For speaking, I'd use the ceiling speakers for even sound distribution and for reduced reverbration.

In some situations, you might want to use some main speakers up-front along with ceiling speakers (and 70.7V amp) to fill-in in the back or dead spots. This is something you'd have to experiment with. If you're setting-up a church PA system, I'd try using this approach.

Sophisticated systems in big auditoriums, stadiums, etc., sometimes use main front-speakers and then use delay lines to the distributed speakers to prevent echo and to make sure the sound from the front speakers hits the listener first, so the sound seems to come from the "stage".

QUOTE
1) with 2 or 3 speakers which are 200 w continuous power with 8 ohm impedance. Again there is a question of whether i have connected the speakers in series or parallel but not there yet and need answers as well.
Three might be tricky, but two should work fine. One rule-of-thumb is to use an amp with twice the power rating of the speakers. If you don't drive the amp into distortion, you should be OK with regular music (or speaking).

Two 8-ohm speakers (in parallel) on one "channel", and one 8-ohm speaker on the other "channel" should work. (Assuming a mono installation... It's a bit odd, but it should work...)

When you connect speakers in series the impedance is added. Three 8-ohm speakers is 24 ohms. (You are not going to get enough power at 24 ohms.)

When you connect speakers in parallel, the impedance is divided. Three 8-ohm speakers in parallel are 2.67 Ohms. That's too low and will "pull" too much current.

(You could go with a series-parallel 5.33 Ohm connection, but then one speaker is going to get 4x as much power as the other two.)


QUOTE
2) with 13 speakers on the ceiling which are just 20 watt 8 ohm ones probably connected in series-parallel but not sure.


I wouldn't connect a "regular" amplifier to the 70.7V ceiling speakers. You could probably "get-away" with it, with your high-powered amplifier, and you could calculate the voltage from the amp, and you can calculate the load... But I would NOT recommend it.

If you want to use the ceiling speakers with the mixer, connect the mixer's line-out to the 70.7V amp.

If installed correctly, each speaker has a transformer with various taps (connections). These will be marked in watts. i.e. If the 1W tap is connected, you get 1W at 70.7 Volts. These should all be wired in parallel, and the total wattage should not exceed the amplifier's rating. ePanorama.net has more information on constant-voltage set-ups.

This post has been edited by DVDdoug: Mar 2 2010, 02:50
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pdq
post Mar 2 2010, 04:07
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Those 13 20W speakers are each connected to a transformer that presents a load of 250 ohms (70.7 ^ 2 / 20) to the amplifier. All 13 in parallel then would present a combined load of 19 ohms. You will be driving all 13 to their maximum 20 watts if your amplifier can deliver 70.7 volts.

The bridged output, 1200 watts into 8 ohms, has a maximum output voltage of 98 volts (square root of 1200 * 8).

In other words, just connecting the bridged output to the existing system in place of the 150 watt amplifier will drive all 13 speakers to their maximum 20 watts each with very little effort. The only thing to be careful of is that the new amplifier will actually drive 38 watts (98 ^ 2 / 250) into each speaker if you turn it up, possibly damaging the speakers.

The 600W output would be safer to use since it would only deliver 49 volts maximum (square root of 600 * 4), but it would only be delivering 125 watts total, less than your current system.

As for the higher wattage 8 ohm speakers, I would never connect speakers in series. A speaker is far from a simple resistive load and there could be interactions between the series speakers. Two in parallel would be fine (4 ohms combined) and possibly three in parallel (2.7 ohms) depending on the rating of the amplifier. Or perhaps driving two speakers in parallel from one output and the third from the other output. You would need to balance the volume levels between the outputs.

Hope this helps.
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Arnold B. Kruege...
post Mar 2 2010, 13:58
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QUOTE (pdq @ Mar 1 2010, 22:07) *
Those 13 20W speakers are each connected to a transformer that presents a load of 250 ohms (70.7 ^ 2 / 20) to the amplifier. All 13 in parallel then would present a combined load of 19 ohms. You will be driving all 13 to their maximum 20 watts if your amplifier can deliver 70.7 volts.

The bridged output, 1200 watts into 8 ohms, has a maximum output voltage of 98 volts (square root of 1200 * 8).

In other words, just connecting the bridged output to the existing system in place of the 150 watt amplifier will drive all 13 speakers to their maximum 20 watts each with very little effort. The only thing to be careful of is that the new amplifier will actually drive 38 watts (98 ^ 2 / 250) into each speaker if you turn it up, possibly damaging the speakers.

The 600W output would be safer to use since it would only deliver 49 volts maximum (square root of 600 * 4), but it would only be delivering 125 watts total, less than your current system.

As for the higher wattage 8 ohm speakers, I would never connect speakers in series. A speaker is far from a simple resistive load and there could be interactions between the series speakers. Two in parallel would be fine (4 ohms combined) and possibly three in parallel (2.7 ohms) depending on the rating of the amplifier. Or perhaps driving two speakers in parallel from one output and the third from the other output. You would need to balance the volume levels between the outputs.


I think this is good advice with one caveat. 70.7 volt transformers are often the scunge of the earth, and when hooked in parallel, can present some of the oddest loads in the history of audio. I'd work into high power levels slowly, and back off quickly if the amp starts sounding weird.

Also, Behringer seems to be getting pretty aggressive with their power ratings. For example they suggest that the A500 might even be 500 watt amp, but 125 wpc/8 ohms is what it really is on my test bench. They recently came out with a so-called 4000 watt amp that is pretty much the same as what they called a 2500 watt amp last year. :-(
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jaynag
post Mar 2 2010, 17:43
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QUOTE (Arnold B. Krueger @ Mar 2 2010, 06:58) *
QUOTE (pdq @ Mar 1 2010, 22:07) *
Those 13 20W speakers are each connected to a transformer that presents a load of 250 ohms (70.7 ^ 2 / 20) to the amplifier. All 13 in parallel then would present a combined load of 19 ohms. You will be driving all 13 to their maximum 20 watts if your amplifier can deliver 70.7 volts.

The bridged output, 1200 watts into 8 ohms, has a maximum output voltage of 98 volts (square root of 1200 * 8).

In other words, just connecting the bridged output to the existing system in place of the 150 watt amplifier will drive all 13 speakers to their maximum 20 watts each with very little effort. The only thing to be careful of is that the new amplifier will actually drive 38 watts (98 ^ 2 / 250) into each speaker if you turn it up, possibly damaging the speakers.

The 600W output would be safer to use since it would only deliver 49 volts maximum (square root of 600 * 4), but it would only be delivering 125 watts total, less than your current system.

As for the higher wattage 8 ohm speakers, I would never connect speakers in series. A speaker is far from a simple resistive load and there could be interactions between the series speakers. Two in parallel would be fine (4 ohms combined) and possibly three in parallel (2.7 ohms) depending on the rating of the amplifier. Or perhaps driving two speakers in parallel from one output and the third from the other output. You would need to balance the volume levels between the outputs.


I think this is good advice with one caveat. 70.7 volt transformers are often the scunge of the earth, and when hooked in parallel, can present some of the oddest loads in the history of audio. I'd work into high power levels slowly, and back off quickly if the amp starts sounding weird.

Also, Behringer seems to be getting pretty aggressive with their power ratings. For example they suggest that the A500 might even be 500 watt amp, but 125 wpc/8 ohms is what it really is on my test bench. They recently came out with a so-called 4000 watt amp that is pretty much the same as what they called a 2500 watt amp last year. :-(


Thanks a lot all for replying.
This is for a church set up with high ceiling.
So, since i would like to bypass the 70 v amplifier and try to connect the new amp(using the output A 600 W) to the ceiling speakers, i ll bring the volume slowly up and see the o/p.
I HAVE ONE OTHER SIMPLE QUESTION:
Can i connect JUST ONE passive speaker of 8 ohm (200 w ) to the new amp(using the output A 600 W) and see the o/p. I just want to make sure i dont damage the speaker. I m little concerned since the amp impedance is 4 ohm and the speaker is 8 ohm, the amp watt is 600w and that is thrice of the continuous power of speaker.
Thanks again.
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pdq
post Mar 2 2010, 18:05
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The output that is rated for 600W at 4 ohms will supply somewhat less than that into an 8 ohm load, possibly as little as 300W. Be careful how high you turn up the volume, but otherwise you should be OK.
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DVDdoug
post Mar 2 2010, 19:59
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QUOTE
...since i would like to bypass the 70 v amplifier and try to connect the new amp(using the output A 600 W) to the ceiling speakers...
Why??? The 70V amp is designed to drive the 70V speakers. If I had an unlimited budget, I'd use a 70V amp to drive the distributed speakers and another amp to drive the main speakers. (but, I'd do some experiments first to see if it's best without the ceiling speakers at all, or if the ceiling speakers are only need in that back-half, etc.)


QUOTE
Can i connect JUST ONE passive speaker of 8 ohm (200 w ) to the new amp(using the output A 600 W) and see the o/p. I just want to make sure i dont damage the speaker. I m little concerned since the amp impedance is 4 ohm and the speaker is 8 ohm...
Yes! Power & current are inversely related to impedance.* Higher impedance means less power. (i.e. 8 ohms is OK, but 2 ohms will "pull" too much power from the amp and could blow the amp.)

QUOTE
...the amp watt is 600w and that is thrice of the continuous power of speaker.
You should be OK. Typically, you get half the power with an 8 ohm speaker compared to a 4 ohm speaker.

Are you going to push that amp to full power? ...Probably not! You could blow out the speaker, but you probably won't. The truth is, you could probably blow-out the 200W speaker with a 50W amp if you really tried! Speaker power ratings are based on program material (or pink noise). If you drive the amp into heavy distortion or if you run high-power test-tones into a speaker, you can you can burn it out. With normal program material the average level is much lower than the peak level... The average power will probably be far less than 100W.

If you hear distortion, you are probably pushing the speaker too hard. If you don't hear distortion, you are probably OK. I don't know if the Behringer's meters show "watts", but if they do you can use that as a guide. If you find that the meters are constantly "in the red" (or near the red), you might need more speakers, or higher-powered speakers. I have a feeling that you won't need to push the amp that hard. 500 Watts (through good-sized, efficient speakers) is probably plenty for a congregation of 2000 or more. (It depends on the room size, acoustics, the style of music, etc.)


* Power (Watts) = Voltage squared/impedance (ohms). The voltage from a solid-state amp is "constant". (It depends on the signal level and the volume setting. It is independent of the load.)

This post has been edited by DVDdoug: Mar 2 2010, 20:07
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jaynag
post Mar 3 2010, 00:13
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QUOTE (DVDdoug @ Mar 2 2010, 12:59) *
QUOTE
...since i would like to bypass the 70 v amplifier and try to connect the new amp(using the output A 600 W) to the ceiling speakers...
Why??? The 70V amp is designed to drive the 70V speakers. If I had an unlimited budget, I'd use a 70V amp to drive the distributed speakers and another amp to drive the main speakers. (but, I'd do some experiments first to see if it's best without the ceiling speakers at all, or if the ceiling speakers are only need in that back-half, etc.)


QUOTE
Can i connect JUST ONE passive speaker of 8 ohm (200 w ) to the new amp(using the output A 600 W) and see the o/p. I just want to make sure i dont damage the speaker. I m little concerned since the amp impedance is 4 ohm and the speaker is 8 ohm...
Yes! Power & current are inversely related to impedance.* Higher impedance means less power. (i.e. 8 ohms is OK, but 2 ohms will "pull" too much power from the amp and could blow the amp.)

QUOTE
...the amp watt is 600w and that is thrice of the continuous power of speaker.
You should be OK. Typically, you get half the power with an 8 ohm speaker compared to a 4 ohm speaker.

Are you going to push that amp to full power? ...Probably not! You could blow out the speaker, but you probably won't. The truth is, you could probably blow-out the 200W speaker with a 50W amp if you really tried! Speaker power ratings are based on program material (or pink noise). If you drive the amp into heavy distortion or if you run high-power test-tones into a speaker, you can you can burn it out. With normal program material the average level is much lower than the peak level... The average power will probably be far less than 100W.

If you hear distortion, you are probably pushing the speaker too hard. If you don't hear distortion, you are probably OK. I don't know if the Behringer's meters show "watts", but if they do you can use that as a guide. If you find that the meters are constantly "in the red" (or near the red), you might need more speakers, or higher-powered speakers. I have a feeling that you won't need to push the amp that hard. 500 Watts (through good-sized, efficient speakers) is probably plenty for a congregation of 2000 or more. (It depends on the room size, acoustics, the style of music, etc.)


* Power (Watts) = Voltage squared/impedance (ohms). The voltage from a solid-state amp is "constant". (It depends on the signal level and the volume setting. It is independent of the load.)

gr8. Thanks a lot for the replies again. This really saved me a couple hundred dollars .
I wanted to bypass the 70v amplifier since i see some clipping and distortion in o/p when i increase the master volume of the amp after a certain level.
not sure why, hence wanted to try the speakers with new and see.
Thanks again.
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DVDdoug
post Mar 3 2010, 02:50
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QUOTE
...to bypass the 70v amplifier since i see some clipping and distortion in o/p when i increase the master volume of the amp
1. What do you mean by "seeing clipping"? Is there a clipping indicator on the amp? Is it occasional with loud peaks, or most of the time at "normal volume"?

2. What did you mean by "20W speakers"? Is there a transformer on each speaker? And, are you connected to the 20W tap? Or, are you wired direclty to the 8-ohm voice coil with a series/parallel connection?

20 Watts per speaker is a lot for a "typical" distributed-speaker set-up. Standard 8" ceiling speakers (like they use in supermarkets) usually have transformers that go to 10 or 15W maximum, and they might be set for 5W.

And, if all 13 speakers are set for 20W, you are overloading the 70.7V 150W amp.

If you are getting lots of clipping, then yes, you need "more power". If you add the big speaker in the front, you can probably reduce the volume to the ceiling speakers, but I think you'll still need the ceiling speakers so that people in the back can hear clearly.

If it's occasional clipping... i.e. If your preacher's style is to occasionally shout... A limiter is probably the best answer (or part of the answer). If loud music is causing clipping, the answer is probably to send most of the music to the front speaker(s). A limiter is a really good idea for live music too. Without a limiter, you are very likely to get some clipping in most live situations (where input levels are unpredictable). A limiter would be a really great thing to have in a church system... if you have the budget, and if the additional technical complexity is managable.
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Speedskater
post Mar 3 2010, 13:47
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Rane Corp. has a good paper on using 70Volt systems:

"Constant-Voltage Audio Distribution Systems"
http://www.rane.com/note136.html


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Kevin
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jaynag
post Mar 4 2010, 02:29
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QUOTE (Speedskater @ Mar 3 2010, 06:47) *
Rane Corp. has a good paper on using 70Volt systems:

"Constant-Voltage Audio Distribution Systems"
http://www.rane.com/note136.html


Thanks again . I am so indebted to this group for helping.

Sir, whenever i increase the volume (either master volume or individual channel volume), i hear voice splitting and distortion. i dont have any reading for clipping but i assumed thats what it is. The amplifier is not able to give more power ?

Also, i only know the model of the speakers and not sure whether they have a transformer since they are on the ceiling.



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Notat
post Mar 4 2010, 15:44
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QUOTE (jaynag @ Mar 3 2010, 18:29) *
Whenever i increase the volume (either master volume or individual channel volume), i hear voice splitting and distortion. i dont have any reading for clipping but i assumed thats what it is. The amplifier is not able to give more power ?

The amplifier is not able to give more voltage. You typically need a step-up transformer between amplifier and distribution to drive this sort of system. That transformer was built into the old amp.
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pdq
post Mar 4 2010, 16:13
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QUOTE (Notat @ Mar 4 2010, 10:44) *
QUOTE (jaynag @ Mar 3 2010, 18:29) *
Whenever i increase the volume (either master volume or individual channel volume), i hear voice splitting and distortion. i dont have any reading for clipping but i assumed thats what it is. The amplifier is not able to give more power ?

The amplifier is not able to give more voltage. You typically need a step-up transformer between amplifier and distribution to drive this sort of system. That transformer was built into the old amp.

He was talking about the old 150 watt amplifier not being able to drive the speakers to full volume without distorting. This is not surprising since it is overloaded, i.e. the 150 watt amplifier is trying to drive 260 watts worth of speakers.
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DVDdoug
post Mar 4 2010, 18:41
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QUOTE
He was talking about the old 150 watt amplifier not being able to drive the speakers to full volume without distorting. This is not surprising since it is overloaded, i.e. the 150 watt amplifier is trying to drive 260 watts worth of speakers.
We don't know that. He seems to know that the speakers are rated for 20W, but he's been unable to access the ceiling speakers, so we don't know if they are set for 20W. If the installation was done correctly, the speakers are set for 10W or less.
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pdq
post Mar 4 2010, 20:05
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Connecting a 20 watt speaker to the 10 watt tap of the transformer is not something that I would expect to see, unless someone wanted to intentionally reduce the volume in one area vs. another.
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Speedskater
post Mar 5 2010, 00:05
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QUOTE (pdq @ Mar 4 2010, 14:05) *
Connecting a 20 watt speaker to the 10 watt tap of the transformer is not something that I would expect to see, unless someone wanted to intentionally reduce the volume in one area vs. another.


I think that it is often done in 70Volt systems.
You buy speakers that are the correct size, shape, color and price.
Then when you install the speakers, you set the taps so that the sum of the tap setting (Watts) is less than or equal to the power amplifier's rating.

Once again.
Rane Corp. has a good paper on using 70Volt systems:
"Constant-Voltage Audio Distribution Systems"
http://www.rane.com/note136.html


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Kevin
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jaynag
post Mar 5 2010, 00:31
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QUOTE (Speedskater @ Mar 4 2010, 17:05) *
QUOTE (pdq @ Mar 4 2010, 14:05) *
Connecting a 20 watt speaker to the 10 watt tap of the transformer is not something that I would expect to see, unless someone wanted to intentionally reduce the volume in one area vs. another.


I think that it is often done in 70Volt systems.
You buy speakers that are the correct size, shape, color and price.
Then when you install the speakers, you set the taps so that the sum of the tap setting (Watts) is less than or equal to the power amplifier's rating.

Once again.
Rane Corp. has a good paper on using 70Volt systems:
"Constant-Voltage Audio Distribution Systems"
http://www.rane.com/note136.html


Thanks again.... I ll go through this one.
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DVDdoug
post Mar 5 2010, 00:44
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QUOTE
Connecting a 20 watt speaker to the 10 watt tap of the transformer is not something that I would expect to see, unless someone wanted to intentionally reduce the volume in one area vs. another.
This is common practice. Many years ago, I worked for a company that did 70.7V installations.* I don't remember any indoor installation where we set the speakers for maximum wattage. I'm pretty sure we never set an "indoor speaker" for 20W, and most didn't have transformers that went that high! We never used distributed speakers for entertainment/music, and in the one church installation that I remember, we didn't use distributed speakers.

You're not using more speakers to make it louder... The idea is to get even coverage. It's perfectly acceptable to spread the 150W (or 130W) among 13 speakers or more. [/b] Of course, it is NOT acceptable (with this amplifier) to set 13 speakers for 20W each.

In this application, it might help to get a bigger amplifier and set each speaker to it's maximum. But, I expect better results from adding a big speaker up-front, and perhaps supplementing the sound with the existing distributed speakers & amp.



* We were doing lots of supermarket/retail installations. We rarely (if ever) used a 100W amplifier. And, 2 Watts per speaker was usually plenty for paging and background music. If you are 20 feet from a speaker, 2 watts is plenty to hear a page... And, nobody cares if you can't hear the elevator music! biggrin.gif (This probably isn't enough for a church, where you probably want it louder and you need "cleaner" sound.)
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