Single receiver/ multi room setup question - AVS Forum
Audio Theory, Setup, and Chat > Single receiver/ multi room setup question
quadrophenia's Avatar quadrophenia 01:06 PM 08-19-2013
Hey folks, moved into a new home recently with built-in speakers throughout the home but no outdoor speakers. I'd like to add outdoor speakers but don't understand ohm resistance calculations, wattage, etc. and want to be sure I'm not going to damage my receiver by doing so.

Here's my setup: everything runs through a Pioneer VSX 1020, which is a 7.1 surround receiver with 110 watts per channel. It's hooked up to 5.1 speakers in the main living area. There are two sets up built-in speakers in other areas of the house, each of which runs through a Niles in-wall volume controller. I hooked both of the in-wall speakers up to a cheapo 6-channel speaker selector from Monoprice (http://www.monoprice.com/products/product.asp?c_id=109&cp_id=10903&cs_id=1090305&p_id=8229&seq=1&format=2) and hooked the speaker selector up to the "Speaker B" output on the Pioneer (the receiver lets you use the last two speaker terminals as either 7.1 channel surrounds, a second zone, or a stereo mix of the source going to the 5.1 system -- I use the last option). The Niles controllers don't appear to have any jumpers or switches for impendence matching, but the speaker selector apparently won't let the resistance drop below 5 ohms to protect the amp/receiver.

My thought was that I could hook up the outdoor speakers to the speaker selector and a new exterior wall-mounted volume control. But, I have a few concerns: (1) is this safe for the amp? (2) do I need to get an impendence-matching volume control? (3) do I need to get a better speaker selector? and (4) do I need a more powerful amp/receiver?

I don't really know anything about ohms and parallel/series wiring so any input is much appreciated. Thanks in advance!

Don3931's Avatar Don3931 04:41 AM 08-20-2013
Hi. I hope that I can be of some help to you.
Speaker impedance is quite simple to calculate. Basically, amplifiers are designed to deliver power to a minimum design load. Typically, single speakers or speaker systems will have an impedance of 8 ohms. The lower the impedance, the more power will be sent to the speakers. The problem is that power amplifiers are designed to deliver maximum power to a minimum load. If the load is too low, and many professional amplifiers can deliver high power to loads of 2 ohms or less, the amplifier will quickly clip and may be damaged.
The rule then, is to look at the minimum load that your amplifier is designed to see, and keep you speaker designs within those limits.
For speakers connected in series, you simply add the impedances. So if two 8 ohm speakers are connected in series, the load seen by the power amplifier output will be 16 ohms.
For speakers connected in parallel, use this formula:
1/Imp Total=1/Imp 1 + 1/Imp 2 + 1/Imp 3 ...etc.

So. If you have three 8 ohm speakers connected in parallel, the total impedance will be:
1/Imp=1/8 + 1/8 + 1/8
= 3/8
3Imp=8
Imp = 8/3 = 2.66 ohms.

I am not a fan of using external volume controls unless you know exactly how they effect the load seen by the amplifier. You should be able to control levels of different zones at the amplifier. Anyway, that is your choice. I just wanted to explain how to calculate impedance for series and parallel connections.

Cheers, Don.
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