I'm installing a whole house audio system. I'm using a 200 wpc amp and Audioplex VC200DIOPT 200W volume controllers. Tonight When I added a 2 pair of speakers, my amp played for a few minutes then went into protect mode. The speakers that I am using are DCM KX212s and DCM KX6s. I believe that my speakers are 6 ohm speakers. The volume controller install manual refers to 8 ohm speakers. It never mentions 6 ohm speakers (I found the ohm rating for the DCM's on the internet). Tomorrow, I will go over all the wiring and just try the new set of speakers by themselves. Some ideas would really be helpful now.
Thanks for all your help so far.

Anthony

I couldn't tell if you just have two pair or added two pair to the speakers already connected. Two pair is max on an amp (one pair is max on cheaper amps) and if you keep adding pairs you drop the impedance below safe limits. If your speakers are all 6 to 8 ohm, the total impedance the amp sees is that impedance (say 6 ohms) divided by the number of speakers per channel. Two pairs of 6 ohm speakers = 3 ohms; 3 pair = 2 ohms, and so on.
Better designed amps will just shut down (but don't keep trying and pressing your luck); other amps will just go up in smoke.
More than 2 pairs of speakers? Add a speaker switch box, which usually includes built in protection for more speakers at once. Another cure with no switch box is impedance matched volume controls but that's a topic for another time.
=Tom

Actually, the VC200DIOPT is an impedence matching volume control. I would suspect that you either have the IM OFF, or se wrong. Refer to the guide chart that came with the VC200DIOPT to determin the correct settings for the impedence and number of speakers hooked up to the circuit.

Impaqt,
I have the instructions for the volume controller in front of me right now. The instructions state what settings to use for 4 ohm or 8 ohm speakers. It doesn't tell you what settings to use when using 6 ohm speakers. There in lies the problem.

If 2 pair of 6 ohm speakers are hooked to an amp. Does the amp see a 3 ohm load? If 3 pair of speaker are hooked up does the amp now see a 1.5 ohm load?

For the most part yes.

Actually, it's 3 and 2, respectively.

Larry
www.fineelectricco.com

Thanks larry and DavidatAVX and every one else that gave input.

Larry

Actually it depends on the freq. so that is why I said for the most part.


Dave

You should treat the 6 Ohm speakers as 4Ohm for impedence matching sake. Always default on the side of caution. You'll lose a couple watts of power, but its better to be safe than sorry.

Next time use an OC-12 and standard volume controls (Or some other impedence matching switch box)

Impedence matching volume controls are always a pain... Expecially when adding onto a system thats in place... Gotta go around and change ALL the volume controls instead of just hooking up another pair to the OC-12

I second that. The oc-12 is one heck of an impeadance matching device. I connected 14 pair of 8 ohm speakers and it remained cool to the touch with every zone at peak levels. As mentioned, be sure and use their direct path v-ctrls.(non impeadance matching)
CMack

Yup, just make sure you have the volume control stop inside set for 4 ohm speakers and you'll be good.

If you draw out the system you can figure out what you need them to be set at if you have difference impedances on each pair of speakers. If you have three pairs of speakers, muliply the impedance until you get 24 ohms at each volume control. These in parallel will give you 8 ohms at the amplifier. The paralles resistance is easy with all speakers the same, but a bit more involved with unequal impedance, but not that tough. Here's the parallel resistance formula.


1 / 1/x + 1/x + 1/x and so on. (x = impedance)

Once you have all of that under your belt, you can look at the impedance matching a little differently and adjust the impedance matches to control how much overall volume you get out of certain speakers.

A concept here is this: if your design has four speakers and you set up the volume controls as though you have eight speakers, all speakers will be a little quieter and even less power will be pulled from the amp. In fact, this particular setup would look like sixteen ohms to the amp, so it would just loaf along.
But then you could get even more volume out of the outdoor speakers by putting them back to the X4 setting, and you will not be overloading the amp...so you can use the settings on the impedance matching controls to help balance maximum volume levels as well as protecting the amp.

I always hook up the bathroom speakers with two times the called for rating (i.e. if calculation says X4 for these, I put them at X8). This lowers their volume, which is okay because they are in a small room and are never blasted.

At the other end of the scale, when the outdoor speakers call for X4, I put them at X2 after calculating to be sure that this will work with the entire system, or I change the way the others will work, all so that the outdoor speakers can stay at X4 and play louder than the indoors ones. Outdoors is where more volume is needed.

I can hear everyone objecting, but then you don't use the full power of your power amp! And they are right. In fact, if you design the system properly and use it normally, YOU won't use the full power of your amp either! The only time you will use the full power is when you set it up so that the amp occasionally clips, which is to say occasionally fries tweeters.

FYI, I'm sure a lot of you know this, but the speaker's impedance rating is a nominal rating. Actual impedance is frequency dependant and can drop below 2 ohms at certain frequencies so err on the low side when figuring out your impedance matching.

Actually, input clipping is more frequent in distributed audio than amplifier clipping. Actually, this is where all the damage is done (I don't think I've ever seen a speaker blow from a low amplifier impedance) This happens when the guy wants the sound louder in his house and turns up the preamp feeding the amplifier, or the volume controls on the receiver beyond it's input capabilities.

I wouldn't worry about running your amps at an 8 ohm level, I would worry about input clipping.