Ohm, my receiver!

Last week we took a first glimpse at receivers vs. htib's. To keep it
short and understandable, I left out Ohms (thanks Michael Glenn for
noticing!). This week I want to discuss Ohm's because they are very
important to understand power.

Before we get to that, we need to understand what Ohm's are and how they
work.

Lets recall from last week: The Denon AVR-790 we found did 90 watts per
channel and we found the Panasonic HTIB to do 12.5 watts per channel.
While those numbers are great for explaining how the two systems
differ....they actually are not very accurate because we didn't take
Ohm's into consideration.

What are Ohm's?

Ohm is a measurement of electrical resistance and actually should be
connected directly to a wattage rating. To say, for example, the Denon
790 is 90 watts per channel is actually inaccurate and missing
information.

The easiest way to understanding is typically to think of it this way:
Ohm's are electrical resistance or "electrical weight". The larger the
number the more "weight" there is. Think of it like if you were working
out. How many reps can you do at a certain weight?...100 reps of 5
pounds, 50 reps of 50 pounds, 25 reps of 100 pounds, 12 reps of 200
pounds (this is not a completely accurate analogy but should do the job
for you). Thinks of the reps as ohms and the pounds as watts (in the
previous analogy). In the electrical world, the lower the ohm's the more
watts the receiver can let flow. The problem with this is the ohm's are
like a dam on a river. They keep the water flow exactly to what it
should be. For this reason, most receivers such as the Denon 790, are
6-8 ohm (the Denon being rated at 8ohms and the Panasonic HTIB is rated
at 3ohms).

So what does this mean for us?

It means that to directly compare wattage we need to be at comparable
ohms.

The Denon receiver produces 90 watts @ 8 ohms and the Panasonic HTIB
produces 12.5 watts @ 3 ohms. The rule of thumb is for every HALVING of
Ohm's we DOUBLE the watts output. For example, 90 watts @ 8 ohms is 180
watts @ 4 ohms and 12.5 watts @ 3 ohms is 6.7 watts @ 6 ohms.

Lets compare them both at 8 ohms to get a direct comparison:

Denon 790: 90 watts per channel at 8 ohms
Panasonic HTIB: 4.7 watts per channel at 8 ohms

Or we can compare them at 3 watts:

Denon 790: 240 watts per channel at 3 ohms
Panasonic HTIB: 12.5 watts at 3 ohms

So what does this mean in the real world?

Well, we do have direct comparison numbers now. And its even more
evident than before that a stand-alone receiver is light years ahead of
a overrated HTIB receiver.

However, receivers are meant to operate within their designed Ohm load.

This means, we would not want to hook any normal speaker to the
Panasonic HTIB. Only the speakers that come with the unit. Changing them
out to a Bose, Klipsch, etc. speaker could cause the receiver to be
stressed beyond what its capable thus damaging the amplifier.

On the flip side, we also do not want to hook the Panasonic HTIB
speakers up to a stand-alone receiver. The drop in Ohms could cause the
receivers amp to output more watts than its capable thus overdriving and
damaging the amplifier.

Do people do this? Do you do this? Sure. But it is not how the amps and
speakers are designed and can cause serious damage to your components or
could, at the minimum, shorten the life of your components.

As always, questions and comments are welcome. Next week we'll use this
information to look at speaker selectors and multi-zone audio.