# 100v Line connection?

#### calpe

Looking for some explanation about 100v Line speaker connections.
E.G. We have 'x' amplifier giving out e.g. 250 watts and also 4 x 100v Line speakers.

These must be wired in parallel?

What needs to be considered with regards to the amp output and the wattage ratings of the speakers?

#### Keith Taylor

100V line speakers are wired in parallel.

It is common practice for the speakers to have tapped transformers, meaning that the wattage to be fed to the speakers can be adjusted by selecting the appropriate tapping.

The main amplifier consideration is that when all the speakers are connected they should present an impedance that does not load the amplifier beyond its power rating. Power equals E squared over R R equals 100 squared over 250 which is 40 Ohms.

Note the 40 Ohms is an AC impedance, not a DC resistance. It is possible to buy an impedance measuring aid. You need a source of audio tone, maybe 1KHz to feed into the amplifier to produce a modest output of a few Watts. Insert a decade resistance box in series with the one leg of the load. We are going to adjust this box until we have equal AC Voltage being dropped across the R box and the speaker load as read on a digital multimeter reading AC Volts.

Based on the idea that equal voltage drops equate to equal impedances we simply read the dials on the R box to give us our speaker load impedance.

If the speaker ratings are properly described by the manufacturer all the above should be unnecessary. Simply add up the watt ratings.

Keith

1 user

#### calpe

I'm trying to understand an issue with some JBL speakers.
They are of course wired in parallel and the JBL's are switched to 100V.

E.G. we have a 1,000 watt amp.
4 speakers to be connected in parallel to the 100V Line on the amp on one channel and 4 speakers to the 100V Line on the amplifiers other channel, also in parallel.

What is the correct wattage of each speaker to be used?
Is the impedance affected by connecting them in parallel?

#### Keith Taylor

What is the correct wattage of each speaker to be used?
In 100Volt constant voltage distribution there is no "correct" wattage. After selecting taps to give power levels appropriate to the situations the speakers are in the only thing that matters is that the sum of the power settings of the speakers connected to an amplifier should not exceed the amplifiers output power rating.
Is the impedance affected by connecting them in parallel?
If you mean the impedance presented to the amplifier the answer is yes. Two 1,000 Ohm speakers in parallel will load the amplifier with 500 Ohms.

The whole idea of constant voltage distribution is to avoid having to pay attention to impedances such as having series and parallel combinations of voice coils to end up with (say) 8 Ohms. I suggest you do a search of "constant voltage audio distribution" Don't be confused by the word "constant" There is only 100 Volts coming out of your amplifier when it is being driven to full output by a tone or some unchanging signal. In electrical engineering the word "constant" is often omitted; so we just say voltage source to describe a generator that has zero Ohms source impedance. It is the source impedance/resistance that determines how much the output is going to "sag" under load.

Keith

1 user

#### calpe

Thanks again.
So if I'm to understand then...
A 1,000 watt per channel amp, should have connected (as example given) to each channel not more than 4 x 250 watt speakers, per channel?
So if you had 4 x 300 watt speakers, i would have thought having more watts would have been ok?

As for the impedance this too is a bit bewildering.
So if the amp was say 8 Ohm output per channel then the 4 speakers should not be measure in total less 8 Ohms?

I wasn't sure about the use of a 100V Line and speakers impedances.
I assumed that if you had 4 x 250 watt speakers connected to the 100V Line then the impedance would not matter.
And also that 4 x Loudspeakers do not have a higher total in wattage than the amps output.

Thanks

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#### Keith Taylor

A 1,000 watt per channel amp, should have connected (as example given) to each channel not more than 4 x 250 watt speakers, per channel?
That is correct.
So if you had 4 x 300 watt speakers, i would have thought having more watts would have been ok?
4X300 watt speakers in parallel (1,200 watts) presents the amplifier with a load that is lower impedance than the amplifier was designed for. We need to remind ourselves that watts rating and impedance are directly related. On a 100 Volt system a speaker on a 2 watt tapping has an impedance of 5,000 Ohms. Voice coil impedance is of no interest to users of constant voltage distribution, only the watts figure. The transformer transforms the voice coil impedance, typically to a much higher value.
So if the amp was say 8 Ohm output per channel then the 4 speakers should not be measure in total less 8 Ohms?
That is correct. To make this observation we have changed the subject from constant voltage to impedance matching.
I assumed that if you had 4 x 250 watt speakers connected to the 100V Line then the impedance would not matter.
That is basically correct. In 100 Volt line practice a "speaker" is the combination of the speaker driver AND the transformer.
And also that 4 x Loudspeakers do not have a higher total in wattage than the amps output.
You have hit the nail on the head!

Keith

1 user

#### calpe

Thank you kindly Keith for all your explanations, greatly appreciated

#### chienmort

As a rule of thumb, I never load a 100V line amp over 80% of its rated power.