I know nothing about Ohms need compatibility advice

[Amon37]

If have a receiver that puts out 100watts per channel at 8 ohms but the speakers I want to pair it up with say 100watts at 6 ohms, is that okay?

[Matt X]

Originally Posted by Amon37

If have a receiver that puts out 100watts per channel at 8 ohms but the speakers I want to pair it up with say 100watts at 6 ohms, is that okay?

6 should be OK, but a more common 4 ohm speaker might be something to worry about - Ohms basically gives you an idea of how "resistant" ("resistive"?) a speaker is to the flow of electricity through it. The higher the ohms, the more resistant. lower the ohms, the more "free-flowing" the "juice", and the amp (rated @ 8ohms) might not be able to push the "juice" fast enough, and get damaged.

also realise that speakers never present a flat ohm reading to an amp - ohms will go up or down depending on the frequency of sound it is trying to produce, so what your amp sees is a range of resistance. an 8-ohm speaker will give the "healthiest" range for the amp, 6 should be OK, but lower might damage the amp (after long-term heavy usage, usually). higher speaker resistance is (AFAIK) always OK, but 16 ohm speakers are rare, if not nonexistent.

[Blue]

Assuming they are normal dynamic speakers (i.e. not some fancy esoteric speaker electrostatic, ribbon, plasma etc) and the amplifier is the average run of the mill solid state amplifier (not valve) there is no problem all.

[MouseRider]

Here's a simple outline...

Ohms is a measure of resistance. When you talk about amplifiers, if an amplifier says it outputs 100W at 8ohms, it means that when the resistance of the speaker is 8ohms, the amplifier will be sending 100W to the speakers.

So in your case, if your speaker is 6ohms, your amp will be sending 133.3W so if you're speaker's limit is only 100W, there is a very small chance that the speaker will go pop or you might also damage your amplifier as it is over rating.

The formula for your case would be 100W x (8 / target) = output power, where "target" is the ohm rating of the speaker you're using.

The other thing to note is that most of the time, the power rating of an amplifier is stated as the RMS power, or "root mean squared", a simplistic way to define it is it is a statistical average. So a common rule of thumb is you should select a speaker that is capable of handing 2x the rated RMS power output of your amplifier at the same resistance or ohm rating.

There are some amplifier manufacturers that use a real silly system they call PMPO (Peak Music Power Output), which basically means the maximum power the amp can pump out, so in those cases, you can just probably give your speakers anywhere from 10% to 50% safety margin.

Hope this helps.

[Footloose301]

Originally Posted by MouseRider

So a common rule of thumb is you should select a speaker that is capable of handing 2x the rated RMS power output of your amplifier at the same resistance or ohm rating.

Not exactly. You actually want to make the speaker and amp to be as close in watts as possible. Getting a speaker that can handle twice the power is also harmful because the amp won't be able to push that much power, thus creating distortion which heats up the voice coils and ultimately destroys your speaker. It is better to have more power than not enough. I have competed in car audio(yes, i know were talking about home theater) for some time now and won many local comps, so I know a thing or two about a thing or two, lol. Many people go out and spend $500 on a woofer that handles 1000 watts RMS, they get a 500watt RMS amp, and the speaker is a $500 paper weight in no time just because of distortion. As long as you don't turn the receiver up high enough to reach distortion then you'll be alright, but just because the speaker says 240watts and your amp says 120 watts, does NOT mean you can turn it to peak volume, you're only hurting your speaker. Many people think "YAY, I can turn it up louder because my speaker can handle more power than this thing can push", wrong! The speaker can handle the power..... but is the power provided without distortion?

But yes, you are on the right track with the ohm ratings. The lower ohm rating, the more power is pulled from the amp generally. For instance:

Hypothetically an amp will double its power if you cut the ohms in half and visa versa. Example:

300 watts @ 8 ohms
600 watts @ 4 ohms
1200 watts @ 2 ohms
2400 watts @ 1 ohm

If you have a speaker rated at 6 ohms then keep an eye on your 8 ohm receiver and make sure it doesn't generate more heat. Generally a receiver's ohm rating is what the manufacturer says the receiver can operate at without stability issues. Going below a manufacturers ohm rating can cause the amp to shut down or gain excessive heat and malfunction. You might be able to slip by with the 6 ohm speaker, just watch for heat.

[MouseRider]

Actually, you are correct Footloose, I stand corrected.

For some reason, my brain was working on the speaker rating as not based on RMS but peak.

You do want to match your amp with your speakers.

I'd check the faceplate on these things to make sure apples are being compared with apples RMS to RMS, Peak to Peak.

[Amon37]

I appreciate all the info. This temp setup is going to be in the bedroom where the receivers volume will never be very loud because of the small room size and placement of the speakers. The receiver will be in the open air not in any cabinet so I will monitor the heat. They are normal speakers and your basic HT receiver.

[Footloose301]

Originally Posted by Amon37

I appreciate all the info. This temp setup is going to be in the bedroom where the receivers volume will never be very loud because of the small room size and placement of the speakers. The receiver will be in the open air not in any cabinet so I will monitor the heat. They are normal speakers and your basic HT receiver.

Also, I just remembered. I used to have a Kenwood shelf system, just something to listen to music around the house, and I tried wiring up more speakers to it. It was only 2 channel running at 8ohms. I connected 2 more speakers, splicing them together with another set of 8 ohms speakers(This was years ago before I knew anything about ohms) and hooked them up and turned it on and the system wouldn't play anything, and would say "PROTECT" across the screen. By splicing those speakers together it cut the ohms in half. Putting 2 of the 8ohm speakers together gives you 4 ohms. So lucky for me the stereo recognized this and it had gone into safety mode. Just saying this in case you come across the same problem where the receiver won't do anything for you, it could go into a safe state. Which would be nice before it hurt something.

[Footloose301]

Originally Posted by Footloose301

Many people go out and spend $500 on a woofer that handles 1000 watts RMS, they get a 500watt RMS amp, and the speaker is a $500 paper weight in no time just because of distortion.

I have done many stereos installations, I competed for several years. I know whats going on. Everything I mentioned is what I have actually witnessed. The distortion ruins the speakers, NOT THE AMP! We used to have fun burning up woofers all the time on purpose. Each time the amp is NOT affected at all, only the speaker. The way you can tell that you burnt up the voice coils is if you cannot push the speaker in, it is frozen.

[Rup_Muk]

I'm going to pipe in with my $0.02 as well:

The 8 ohm (most common), 6 ohm, 4 ohm ratings on the speakers are what is termed "input resistance". The output resistance from the device driving the speakers needs to be exactly the same for minimizing distortion that can arise from an impedance mismatch (also called Schottky noise).

A classic example is trying to feed an analog video signal from a player device (VCR, DVD) to a TV using a 50 ohm coax cable (white and red plugs) instead of a 75 ohm coax cable (yellow plug). The picture on screen will be very distorted.

With an impedance mismatch, there remains a strong possibility that both the driver and the driven devices can sustain damage. However, with most modern electronics there should be overload protectors that limit signal output. But, that cannot always be assumed.

Again, my $0.02.

Rup.

[Amon37]

Well I'll hook it up and test at low volumes. If it doesn't seem safe I may have to get new speakers. It seems like the responses have gone from it should be safe to it won't be safe at all, it's a little confusing.