Impedence matching question

[Vaughan Odendaa]

Hi there,

I've heard a few people say that you must have amp and speakers which are impedence matched for home theater use. A speaker with a 6 ohm impedence must be used and one can't use an additional speaker of 8 ohms, for instance.

You can't, for example, use an 8 ohm pair of speakers with a 6 ohm center speaker etc. Now in the real world, how much of a concern is it to use different impedence loads on an av receiver ? Impedence obviously varies with frequency and the impedence load is not constant. It's dynamic because the AC signal is constantly in a state of flux.

Considering that the impedence fluxuates wildly, how "safe" is one using identical impedence matched speakers ?

--Regards,

 

[fmw]

I can't think of any reason that impedance matching speakers would be important. As long as you have control over the sound pressure level from speaker to speaker, it shouldn't matter what kind of load they represent to the amps.

 

[j_garcia]

I don't know where you heard this but it is completely false. It is because impedance varies with frequency that this doesn't really make a huge difference to your amp/receiver vs the nominal impedance of the speaker. Where it could be an issue is if your receiver can't handle lower impedance loads, but that is a completely separate issue.

 

[Vaughan Odendaa]

You know I thought this would be the case, but I just thought I would pose the question. I wonder where people got the misconception from in the first place ?

--Regards,

 

[Vaughan Odendaa]

I heard this in an audio shop. A customer wanted to buy a pair of 8 ohm speakers to match his other 8 ohm speakers. Not the same speakers but with an 8 ohm impedence. He said that for the best efficiency, all speakers need to be 8 ohm (in his particular case) and that using a lower impedence (6 ohm) would be less efficient and wouldn't sound as good.

Funny, impedence doesn't tell you how something sounds. It's an electrical metric. Although, to be fair, a very low impedence load could potentially clip the AC waveform and produce square waves (soft or hard obviously depending on the conditions) and produce additional harmonics which I'm sure would degrade the sound considerably, depending on where those harmonics are in the passband.

--Regards,

 

[j_garcia]

As I mentioned though, that would be assuming the receiver/amp couldn't handle the total load presented by all of the speakers. The customer didn't quite seem to understand how it works. There are other factors as well, such as speaker sensitivity, room size, the actual amount of current the given speaker draws, how loud and what is played, etc... that also influence what will happen and whether the amp can handle the load. You can have two 8 ohm speakers and one could require much more current to achieve a given SPL vs the other, so simply saying an 8 Ohm speaker isn't exactly achieving the intentions of the customer.

 

[Vaughan Odendaa]

I know.

--Regards,

 

[OttoMatic]

I wonder where people got the misconception from in the first place ?

Looks like there's good information in this thread, but I've seen all kinds of crap "facts" tossed around on this and other forums. Even uses that sound like they know what they are talking about are sometimes technically wrong, and sometime just out-and-out wrong.