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Old 17th February 2013, 11:32 AM   #1
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Default Help to select amplifier type

Hi, am new to forum, hope I'll be accepted by your team...Please anybody could help...Let me explain what help I need from your team...
With 9 speakers (8 ohms - 50 watts each) in series/parallel (8Ω X 3 = 24 / 3 = 8Ω) with Resultant Impedance 8 ohms per channel, the max demand output per speaker is 15 watts with 20 watts PEAK from time to time, depends on speech rates. Would like to know the following:-
What will be the type of amplifier output : RMS or other?
What power output per channel ?
What size of wire from amplifier to one group of speakers when the length required is 24 meters ?
What will be the major problem in this ser/para wiring system ?
SPEAKER:- 8ohms 50watts but volume needed is 15-20 watts
NO Woofer or Sub woofer - Just midrange/ medium
Bass control will set at ---
Treble control will set at haft
Speakers mounting height 2.5 meters from floor.
TEST TONE:-
2.5v (please note that NEVER the volume be set at that high intensity) Then I make another test tone with a higher volume that we will set the system and the voltage tested was 1.2v.
ROOM:- 15 X 15 meters X 3 meters Height
MUSICAL TASTES:- Classic at reasonable sound level (9 minutes playing during 7 hours speech)
AMPLIFIER CHOICE: is it possible to use a HI-Fi amplifier for this system ?

If need add. data, kindly let me know.

Please and thanks for help.

Last edited by Steeveax; 18th February 2013 at 08:21 AM. Reason: Adding requested data
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Old 17th February 2013, 11:50 AM   #2
Mooly is online now Mooly  United Kingdom
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Have you seen this ?
A Test. How much Voltage (power) do your speakers need?

Its well worth a try and a test to see exactly what power requirements you might need.

The main problem with series/parallel combinations of speakers is that you alter dramatically their behaviour because each is not driven from a low impedance voltage source anymore. They all interact and modify each others response. For PA applications and voice it may not be much of an issue as overall clarity is what counts.
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Old 18th February 2013, 01:01 PM   #3
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Thanks for assistance
SPEAKER:- 8ohms 50watts but volume needed is 15-20 watts
NO Woofer or Sub woofer - Just midrange/ medium
Bass control will set at ---
Treble control will set at haft
Speakers mounting height 2.5 meters from floor.
TEST TONE:-
2.5v (please note that NEVER the volume be set at that high intensity) Then I make another test tone with a higher volume that we will set the system and the voltage tested was 1.2v.
ROOM:- 15 X 15 meters X 3 meters Height
MUSICAL TASTES:- Classic at reasonable sound level (9 minutes playing during 7 hours speech)
AMPLIFIER CHOICE: is it possible to use a HI-Fi amplifier for this system ?
I already inserted this part in first topic
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Old 18th February 2013, 01:31 PM   #4
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Have you considered the classical way of driving a lot of loudspeakers ?

It is usual to use the 100V line system. A 100V line output transformer is placed at the output of the amplifier and then all the speakers are fiited with a 100V line transformer and then the transformers wired in series.

As already mentioned, for voice a parallel / series combination will work but will not be good for Hi-Fi music.

As far as the amplifier is concerned, any amp will do as it only sees the combined impedance that it is driving.
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Old 18th February 2013, 02:03 PM   #5
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Quote:
Originally Posted by KatieandDad View Post
Have you considered the classical way of driving a lot of loudspeakers ?

It is usual to use the 100V line system. A 100V line output transformer is placed at the output of the amplifier and then all the speakers are fiited with a 100V line transformer and then the transformers wired in series.

As already mentioned, for voice a parallel / series combination will work but will not be good for Hi-Fi music.

As far as the amplifier is concerned, any amp will do as it only sees the combined impedance that it is driving.
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I greatly appreciate your advise too, So I want to help this association, these speakers has already been purchased before I get involved, I just need help to set the system, we have some time to establish the schematic and advise.

Please note that Speech/Talk is only soft speaking, NO pop music, Just Religious music playing at 15 watts / 20 watts PEAK

Note that a tiny system already exist in a permanent way in small church:- 6 speakers (15watts each) with drive amp 45 watts x 1 channel. since over 1 year.. Just to tell you that we don't need a loud system, Thanks for understanding..

I need answers to questions on first topic, any advise will be mostly apreciated.
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Old 18th February 2013, 02:41 PM   #6
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Steeveax
your profile doesn't give any info as to where and who you are.
as far as i can tell from the limited info you've shared you would need an amplifier that is capable of at least 400w or less depending on final volume but headroom in terms of availability to overcome potential losses such as losses from long cable runs despite uprating wire gauge should be considered also speaker sensitivity is a factor.
are you planning to cluster the new speakers or are they being distributed each approach requires different wiring techniques and each will have strengths and weaknesses that can be utilized in obtaining a final result.
as far as using a hi-fi amp in this application ask your self if the price/quality ratio will lead to any significant benefit.
in this situation there are a lot of good commercial amps for reasonable cost that you should certainly consider
protection features, types of output's (70 v and or low impedance 8,4 ohm) input source selection and balanced or unbalanced inputs

Last edited by turk 182; 18th February 2013 at 02:53 PM.
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Old 18th February 2013, 03:20 PM   #7
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Is 400 watts / 2 channel or per channel ? We have 2 channel of 9 sp each.
Cluster ? Yes, NO :- 9 speakers install surrounding 2 central concrete column.
Wiring 50/0.25mm as mains to each speakers circuit and further with 30/0.25 to other speakers.
Not really interested with HI-Fi amp for this system, am just solicited your valuable advise.
For 70v -we certainly take this advise during this year as we have this type of conference twice on yearly basis, If this series/para combinations fail our satisfaction, we probably choice 70v system.

Anyway all of you kindly help me find the good or the best way of helping others.
Thanks for all, May God bless all of you.

Last edited by Steeveax; 18th February 2013 at 03:35 PM.
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Old 18th February 2013, 03:23 PM   #8
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With three stacks of three speaker in series in parallel, each needing 20 watts, the current is 4.8 amps. For that you would need minimum 18 ga, for long runs you would need 16 ga wire. The amp has to deliver 4.8 amps which leaves out single output transistor pair designs, it has to have at least 2 maybe 3 pairs. Each speaker needs 11 volts at 20 watts, a stack of 3 needs 33 Vrms. Amps are usually rated at 4 ohms these days, so an amp rated at 273 watt (4 ohms) should be able to deliver that much voltage.
Non-hifi amps are called PA amps these days.
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Old 18th February 2013, 04:01 PM   #9
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Thanks, The continuous wattage will be 12 - 15 watts with Peak 20 watts...You suggested an amp 273 watts (4 ohms) That means that the following circuits >> With 9 speakers (8 ohms - 50 watts each) in series/parallel (8Ω X 3 = 24 / 3 = 8Ω) with Resultant Impedance 8 ohms per channel << must be modified to 4 ohms, Please advise.
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Old 18th February 2013, 05:23 PM   #10
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A standard PA amp rated 273 watts/ channel won't deliver 273 watts to your strange circuit. If you want 180 watts (33 volts rms) into your strange load, you have to buy an amp that will deliver 33 volts, which is 273 watts into a 4 ohm load. For example, a PV4 which is 200 watts per channel into 4 ohms, probably won't develop enough voltage.
If you really want to hear some low fidelity sounds, try to get 180 watts out of a transistor based amp that won't develop enough voltage. Clipping is what they call it, a very nasty sound on music. The sine waves get the tops chopped flat, which is awful sounding.
The wire gauges mentioned are for american wire gauge. You have since listed your location, which I don't recognize but your suppliers probably sell metric sized wire. I don't have wire amp tables for metric wire, you'll have to look up the wire manufacturer's website.
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Last edited by indianajo; 18th February 2013 at 05:28 PM.
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