I am looking at changing an amplifier in a church hall. The speakers they have are 2 x 100v TOA speakers wired at 20 watts, and 3 x speakers in other rooms with individual controls and can be switched to various wattages, but they are currently set to 30 watts.
Sorry to sound stupid, but will a 30 watt amplifier be enough for all these speakers (as they are set to 30 watta or below) or do I have to add up the wattages of all the speakers (i.e. 20+20+30+30+30)?
Thanks.
Sorry to sound stupid, but will a 30 watt amplifier be enough for all these speakers (as they are set to 30 watta or below) or do I have to add up the wattages of all the speakers (i.e. 20+20+30+30+30)?
Thanks.
Firstly an understanding in 100v line systems would be an advantage. If you have say 6 30w speakers and they are all set to 30w being fed by a 30w amplifier, you will get 1/6th of 30w per speaker. If two are set at 30w and the other 4 set to 2w you will get about 10w per 30w speaker and 2w per 2w set speaker.
If I were doing the project, I would want to test out the system for power but most empty rooms with speakers placed high up need low power to be heard. I would try and get a 50w amp but if funds are too tight a 30w will be fine and of course you can easily add another on as a slave.
If I were doing the project, I would want to test out the system for power but most empty rooms with speakers placed high up need low power to be heard. I would try and get a 50w amp but if funds are too tight a 30w will be fine and of course you can easily add another on as a slave.
"Sorry to sound stupid, but will a 30 watt amplifier be enough for all these speakers (as they are set to 30 watta or below) or do I have to add up the wattages of all the speakers (i.e. 20+20+30+30+30)?"
You must add the power, plus about 1.5dB for headroom.
A 30W rated amplifier is generally not run harder than about 20W.
Set all the taps to 5W or so for a 30W amplifier.
You must add the power, plus about 1.5dB for headroom.
A 30W rated amplifier is generally not run harder than about 20W.
Set all the taps to 5W or so for a 30W amplifier.
As they are already set to a given power and that seems to be working fine (You didn´t complain about that) then you need at least the sum of al individual power, or 130W; I`d
Buy at least a 150W amplifier, 200 to 300W wouldn´t certainly hurt, either to have more clen headroon, set them somewhat louder or in the future add more speakers,
Buy at least a 150W amplifier, 200 to 300W wouldn´t certainly hurt, either to have more clen headroon, set them somewhat louder or in the future add more speakers,
Yes you have to add up all the "wattages" All your speakers total 130W which on a 100V line is roughly 76 Ohms total for the whole line.
Your little 30W amp won't like an impedance lower than 333 ohms (approx) on the 100V output tap so something would eventually fail in the amp.
(it would be like trying to run a 1.8-ohm load on an amp that can only handle a minimum of 8-ohms!)
So either change your speaker taps to total around 25W (for headroom and to compensate for line and transformer losses) or get the bigger amp.
The rule generally is to add up all the wattage taps and buy an amp capable of that amount plus a bit larger.
You need to look at the wall volume controls. If they are transformer types then when set down in volume the power draw is reduced. My suspicion is that they are never turned up all the way. If that is the case then you should turn down the loudspeaker taps.
With 40 watts being used for the main coverage room, the normal use has this being most of the power. So if the volume in the remote rooms is adequate at 5 to ten watts then a standard 120 watt amplifier size is fine. If 5 watts per remote loudspeaker then a 60 watt model.
An amplifier with a 70 volt output of 60 watts would drive the system if the transformer style volume controls were used at less than full volume setting.
One problem can be that using a large amplifier such as 150 watts with all the transformer style volume controls turned off is that the load may be too low. In some amplifiers this can also cause failure.
So the first issue is to determine how the remote loudspeakers are used and their type.
"You need a HELL of a lot more than 1.5 db headroom!"
You have no understanding of what I said.
You need 1.5dB of headroom on the sum of the power taps, that is an impedance.
You have no understanding of what I said.
You need 1.5dB of headroom on the sum of the power taps, that is an impedance.
And i think we are assuming because they have room speakers set at 30w and main speakers set at 20 watts, they are actually coming even close to those power levels. Those are maximum power levels for when the system is cranked full out. yes, we should add all those powers, but they mainly represent the ratios between the speakers in this church environment. A classroom ceiling speaker actually putting 4 watts into the speaker will be LOUD. 30 watts would be real annoying at best. 100v system for five seemingly low level speakers seems like overkill to start with.
A low power system like this would be suited to spoken word, but not likely live music. Having said the above, I would prefer a higher power amp than 20 watts, just so it can work "effortlessly" in the system. And have reserve capacity for future needs. Besides, commercial low power constant voltage amps probably cost as much as or even more than common medium power amps like most PA systems use.
A low power system like this would be suited to spoken word, but not likely live music. Having said the above, I would prefer a higher power amp than 20 watts, just so it can work "effortlessly" in the system. And have reserve capacity for future needs. Besides, commercial low power constant voltage amps probably cost as much as or even more than common medium power amps like most PA systems use.
"first time I've ever heard of impedance headroom. ???? "
You need some headroom on the minimum load the amplifier can drive.
Speaker transformers may have a much lower input impedance that what is implied by the wattage rating marked on the part.
They either cheat on the power delivered to the driver, of the impedance presented to the amplifier (reflecting the insertion loss of the transformer).
Altec used to have some good application notes on the subject.
http://alteclansingunofficial.nlenet.net/publications/techletters/TL_106.pdf
You need some headroom on the minimum load the amplifier can drive.
Speaker transformers may have a much lower input impedance that what is implied by the wattage rating marked on the part.
They either cheat on the power delivered to the driver, of the impedance presented to the amplifier (reflecting the insertion loss of the transformer).
Altec used to have some good application notes on the subject.
http://alteclansingunofficial.nlenet.net/publications/techletters/TL_106.pdf
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Headroom, headroom, headroom!!! 1 watt RMS of actual power requires at least 25 watts to avoid clipping!
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