Basic questions on speakers, power amps and how to combine everything - AVS Forum
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post #1 of 3 Old 11-18-2012, 10:37 AM - Thread Starter
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Hello everyone,

I recently bought an Onkyo TX-8050 receiver. The main reason for this choice was the fact that it is multi-zone (2) and that it can be controlled via a mobile application (so you don't need to run to the receiver to pause, change source/volume, etc.).

Since I know very little about receivers or amplifiers, I ended up buying this unit expecting it to drive the speakers in both zones. Apparently few do, so now I have some questions.

First some basic information on my speakers:
- zone 1: two 8 Ohm speakers
- zone 2: two 6 Ohm speakers, recommended amplifier power range 10 - 80 W

The manual of the Onkyo TX-8050 says the following on connecting the speakers:
- When you connect one set of speakers to either SPEAKERS A or SPEAKERS B terminal posts, or when you connect two sets of speakers to both speaker terminal posts and output sound only from either speaker set, use speakers whose impedance is 4 to 16 Ω, and set the speaker impedance setting on the receiver to 4 or 6 Ω. When the impedance of the speaker to be used is less than 6 Ω, set the speaker impedance to 4 Ω.
- When you connect speakers to both SPEAKERS A and SPEAKERS B terminal posts and output sound from both speaker sets simultaneously, use speakers whose impedance is 8 to 16 Ω. Set the speaker impedance setting on the receiver to 4 Ω.

I now have the following questions:
1. What are the practical differences between 4, 6 or 8 Ohm (or other impedance) speakers? I'm assuming that the receiver will output a given voltage, meaning that the current will be higher or lower, depending on the impedance (so higher power with lower impedance). What I do not necessarily understand, is why it would not be possible to connect both speaker sets (one to the A terminal, the other to the B terminal) and decide whether I want to listen to A, B or A and B (providing I do not push the receiver when outputting via A and B).
2. If I want to use the real "Zone 2" functionality, it seems that I will need to add a power amplifier. Since I am currently on a budget and didn't calculate it in, I would like not to spend too much. Since the volume can be controlled from the TX-8050 (pre-outs for zone 2), I do not need a volume control and would like it to turn on when there is a signal coming in and off when not.
It seems that the AudioSource AMP-100 is what I need, although it states that it will need 8 Ohm speakers (which takes me back to the first question).

All information would be greatly appreciated!


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post #2 of 3 Old 11-18-2012, 06:04 PM
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This is a "powered" single zone stereo receiver with the A and B speaker posts sharing the same single amp. The Zone 2 speakers would be connected to a second amp which would be connected to the Zone 2 pre-outs on the 8050.

1. The lower the impedance, the harder it is for the receiver to drive that speaker. Think pushing water through a 1/2" hose at X velocity being equivalent to powering an 8-ohm speaker, while pushing water through a 2" PVC pipe at the same velocity would require a whole lot more water pressure being equivalent to powering a 4-ohm speaker. When you power both A+B speakers at the same time the receiver sees all 4 of them as < 4-ohm speakers (ie. much more difficult to power).
2. Yup.

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post #3 of 3 Old 03-02-2013, 06:48 AM - Thread Starter
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Thank you for the answers, much appreciated!

Best regards,

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