Speaker Impedance

[jakeselectronics]

Before I ask about hooking up speakers and their impedance;

Is it possible to parallel the L & R output of a radio to achieve a mono output.
(To get all sound out of 1 speaker, or multiple in parallel. Its for a retail shop application where 2 speakers are spread out in the Front Of House; therefore i do not want them stereo, rather all sound fed to both.)
Will this damage a solid state stereo amp chip?

 

[Jon Wilder]

You NEVER want to join amplifier outputs together. That being said...you CAN join the INPUTS together and just feed identical signals to both inputs.

 

[Nigel Goodwin]

You NEVER want to join amplifier outputs together. That being said...you CAN join the INPUTS together and just feed identical signals to both inputs.

Not strictly true, as long as the amps are absolutely identical, and you join both input and output - you can get away with it. It's pretty common these days on 'chip amps' - but no need to do it with larger descrete amps really

 

[Diver300]

On a Crown amplifier that I recently repaired, it had a mode for paralleling the outputs where only one of the feedback circuits was used.

If you don't know how the amplifiers will respond, paralleling them can cause them to fight. I would agree with Nigel that it is less likely to be a problem on smaller amplifiers.

 

[Jon Wilder]

You're speaking of "bridged mode". Only if the amp has a selectable bridged mode, you can then connect your load across the positives of the two amplifiers provided you don't use a load too low for bridged operation.

However, it sounds like what the OP wants to do is just mirror the same signal to the inputs of two separate amps.

 

[Diver300]

It wasn't bridge mode. That was available as well.

I thought that the parallel mode was just the inputs paralleled, but I later found that the feedback for both was from one channel. In that mode, the user was expected to parallel the outputs.

I think that mode is very rare in amplifiers.

 

[jakeselectronics]

However, it sounds like what the OP wants to do is just mirror the same signal to the inputs of two separate amps.

Not Quite.

Alright here's the senario:
I've been asked to set up a speaker system in a fast food resturant.
I've been supplied a Small Sony Stereo HIFI, It comes with 2 x 6Ω Speakers and the Minimum output impedance is also 6Ω on the HIFI.
Also, the resturaunt has 2 x 8Ω speakers spaced out in the Front Of House.

It would be simple if all the owner wanted was to use the 2 x 8Ω FOH speakers that are already installed.

But, he also wants to connect the speakers that come with it, and place them in the Back Of House with the steroa so the employees have music out the back.

Still fairly simple,
I could connect the L&R channels up, 1x6Ω and 1x8Ω each, in series (not parallel becasue the impedance would drop to about 3.4Ω and cook the Amp in the Stereo).

But, he wants a switch in the BOH to be able to turn the BOH speakers on and off during store open hours.
Music is only for employees before open and after close when preparing/cleaning up.

This is one senario I have:

But the problem I think will be becasue of the significant impedance changes, this will effect volume.

 

[Jon Wilder]

OK...why make it harder than it needs to be?

Run the FOH speakers in series on the Left Channel.

Run the BOH speakers in series on the Right Channel.

Mirror the source signal to both inputs (or set the stereo up for Mono mode).

Use the balance control to kill either FOH or BOH (or you can install a switch that shunts the signal at the Right side input).

 

[jakeselectronics]

Sounds like a great idea..

But what if the input is from the radio.

And there is a 4Ω Z difference when connected like that between each channel. Do you think there will be noticeable volume difference between channels?

 

[Jon Wilder]

If the input is from the radio then you would use the balance control on the hi fi.

If one side had 1/2 the impedance of the other side, one side would put out double the power of the other. In that scenario there would only be a 3dB difference in perceivable volume between the two sides which is barely audible. The balance control can compensate for that.

 

[audioguru]

Modern speakers are designed to be fed from the extremely low output impedance of a modern amplifier to damp their resonances. The output impedance of a modern amplifier is 0.04 ohms or less. When speakers are connected in series then they are not damped and resonate like a bongo drum.

With speakers in series then each one gets reduced level. If one speaker is shorted then the remaining speaker is louder.

Some homes use speakers in every room. Each speaker has a switched transformer. When all transformers are connected in parallel and at max volume then the total impedance is the rated load for the amplifier. The output level of a modern amplifier remains the same if it has hardly any load up to its rated load impedance. Then the volume at speakers that are connected does not change when the volume of other speakers is changed or if the other speakers are switched off.
The transformers have a switch as a stepped volume control.

"Hi-fi" stores sold the transformers long ago. Now maybe "home entertainment" stores sell them.