Well there's really no way to explain the principle without writing a book
so for sake of the poor readers, and those of us with 28.8K modems I'll do
it quick and dirty.
Ohms is resistance. Higher the resistance, the less current flows, less
current, less heat. Real world experiment, take a 4 ohm speaker and set it
to a certain volume level. Notice the volume level, kill the power and
hookup another 4 ohm speaker in parallel - both (+) to amp (+) and both
speaker (-) to amp (-). This creates a 2 ohm load on the amp, turn to
volume to the same level as before. You will notice the volume is much
louder, approx. twice as loud, if the amp can handle it.
Heat kills amps. When the amp says 2 ohm stable, the MOSFETs used in the
amp can handle the current load and there is sufficient heatsink surface
area to dissipate the heat. If you drive them too hard too long without
adequate ventilation, they will go into thermal overload, some actually
latching the output high causing a high current draw which trips the
overload protection circuit killing power, till it cools down and
resets. While others use a thermal auto-resetting (and some manual reset)
circuit breaker to kill the power.
Now for wiring. To figure out resistance in series and parallel circuits
do the following:
For serial, as in amp (+) to speaker (+), speaker (-) to next speaker (+),
speaker (-) to amp (-) as an example, the formula is R1+R2+R3, and so
on. So two 4 ohm speakers in series makes an 8 ohm load, which means the
amp must deliver twice the power of a 4 ohm load to make the same volume level.
Parallel, use this formula: Total resistance = (R1 x R2) / (R1 + R2)
So if you have a 4 ohm speaker and an 8 ohm speaker, when connected in
parallel, the amp is seeing a 2.6 Ohm load. Two 4 ohm speakers in parallel
makes a 2 ohm load, etc.
If you have more than two speakers in parallel, use this formula:
Total resistance = 1 / ((1/R1) + (1/R2) + (1/R3)) and so on.
If the amp is rated for 8 ohm loads, and you have two 4 ohm speakers, run
them in series. Amp is 2 ohm stable, and you have four 8 ohm speakers, run
them in parallel.
Any questions?
Mike
At 07:47 PM 4/2/2000 , you wrote:
>Just curious, but I see alot of amps are rated at both 2 and 4 ohms. What is
>the difference and how is one used over the other, like is it how you
>install them and wire them up to create different ohm ratings? Also, what do
>'car audiophiles' think about MTX car amps? I see in the Best Buy ad they
>have an MTX 55x4 channel amp for $299, but I cannot find specs on the one
>the list, MTX#RT4240. Also, can most speakers handle 55watts per channel? My
>front Pioneer 6.5" 2ways are rated 2-35watts, and my rear Pioneer 5x7 3ways
>are rated 2-40. Should I look for a less powerful-per-channel amp? Thanks,
>Kyle
>93 Dakota 4x4 V6
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