At our old house, I pulled some wires where I could and mounted some speakers on the walls, but for this to be what I really wanted it needed to be an in-wall speaker in each room as well as a volume switch. I researched existing whole-house systems, and generally they were pro level, which I could not afford. However, I did find some impedance matching volume switches that allowed me to use an old stereo tuner instead of purchasing something new.
Impedance? Let me explain if you're unfamiliar. Impedance is basically resistance, except over a range of frequencies. At its simplest, you can think of it as resistance. Then this equation applies:
V = I*R
So let's take an amplifier designed to drive an 8ohm speaker, and you connect a 4ohm speaker to it. The voltage generally remains constant, so you end up with:
8 * (current designed for) = 4 * (actual current)
(actual current) = 2 * (current designed for)
What this means is you will make the amplifier push twice as much current through that speaker as it was designed to do. At low volumes this may be okay, but at higher volumes you will burn up the amplifier.
Two 8ohm speakers connected in series add their impedance together and look like a 16ohm speaker to the amplifier, which probably won't hurt the amp but may be half the volume, and you can't control the speakers independently, while two 8ohm speakers connected in parallel (i.e. all of the red wires tied together, all of the black wires tied together) look like a 4ohm speaker to the amp, which doubles the current load.
So what is the solution? Well, pro amplifiers have multiple speaker outputs to deal with this, or some of them use so-called 70V systems which are a different deal altogether. But in my house if I want to be able to put in 12 speakers (and counting) with a separate volume knob for each, I need to connect them in parallel. If I do the math, 12 8ohm speakers in parallel end up giving me a 2/3ohm load, which is way too low for my stereo, which says it can do 6-16ohms on the back.
The solution is an impedance matching volume knob, like this one:
These knobs have transformers that adjust the impedance up to where it needs to be. You generally set a switch telling it how many speakers are connected overall, and it adjusts accordingly.
Okay, so back to my story. In a weekend I ran wire (approved for in-wall use, not just regular speaker wire) to every conceivable place I could ever want a speaker. Front porch, back deck, bathrooms, bedrooms, hallways, you name it. I put in boxes for volume switches, ran the wires from my coat closet (where the stereo sits) to the box, then to the general area where I wanted the speaker. I think I ended up going to 20 different places, some of which we will probably never use. After the drywall went up, I covered all of the boxes with blank faceplates, and over the years I've added volume switches and speakers here and there. I have made a couple of mistakes:
1) I installed 14 gauge, 4 conductor wire. I wanted to go overkill so that I would be future proof. The truth is I will *never* pump the kind of wattage through these wires to *ever* need 14 gauge. 16 gauge would have been cheaper and easier to deal with. And while 4-conductor is nice, I'm not sure it was worth the extra money (although it would allow me to put the stereo in a different room if I wanted to, which is nice).
2) I let my wannabe audiophile-ness for home theater speakers take over my common sense for whole house speakers, and I bought Polk and Yamaha. Later on I added a few that I got from parts express. The truth is I can't tell any difference. The inside of a wall is not an acoustical chamber, and we typically listen at such low volume that any bonus clarity that may come out of the expensive speakers is lost. I wish I had saved my money and gone with the parts express house speakers. They sound good, and cost about 1/4 as much
3) I bought stereo volume switches because I wanted to be future proof in case one speaker in each room didn't cut it and I ended up wanting two (again, since I put in 4-conductor wire I could do that). I didn't end up needing this. One speaker is plenty, and two may even give phasing problems in different parts of the room. I run my whole system in mono anyway, so there's no advantage to a stereo switch.
I bought a wiring connector at Home Depot that allowed me to connect all of the wires into nice wiring jacks. I put all of the downstairs speakers on the left channel of speaker set "A", and the upstairs speakers on the right channel of speaker set "B". As with most consumer stereos, the A and B speaker outputs are in parallel, meaning you can't really use them with 8ohm speakers (since it says it only goes down to 6ohms, not 4). But luckily for me my stereo is made in such a way that the amplifier and the tuner are separated, and so I combine left and right before connecting them to both sides. This isn't the perfect way to handle stereo signals, but I have most of my inputs configured to send a mono signal to the tuner anyway. This allows me to use the left and right amplifiers inside of the tuner to power half of my speakers each, rather than using only one side to power them all.
We don't use the system as much as I would like to, but I must say I love walking around the house when the same music is playing everywhere. It's especially useful when there's a game on that I want to listen to while I'm doing things around the house. And since I can turn the upstairs or downstairs speakers on and off, it's easy to use the system on only one floor without having to go turn the volume down in every room.
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