crnchyfrog

Ok, I somewhat understand Ohms law. But the question still remains: How does this apply to subs?

I understand that VOLTAGE divided by CURRENT gives you resistance OHMS.

R = E/I

or VOLTAGE squared divided by POWER (watts) gives you resistance in ohms.

R = E^2/P


But, How can you tell the ohm load on an amplifier using the resistance of the speaker?

IE: what would the ohm load on an amp running two 4ohm speakers be?
And what is the equation?

In addition to this what is the difference between running in series and running in parallel? and how does this affect the ohm load on an amp?

(using standard 12v power supply)

RX-7-Tobi

Hi friend,

when you connect speakers in series (+,-,+,-), the sum will be the resistance of both speakers (Rt = R1 + R2 + R3 +...). If they have same res, (should be), so you have

2 in SERIES: 2 x R

When you connect them in parallel (+ to + and - to -), the res is 1/Rt = 1/R1 + 1/R2 + 1/R3 + ...
Two speakers same res:

2 in PARALLEL: R / 2

When you have a stereo channel, you might bridge them.
You connect the + of speaker to + of ch1 and - to - of ch2.
So every channel gets half of the res. Eg. a 4 Ohm speaker briged will make 2 Ohm for each channel.

When you put two 4 ohm speakers in parallel and then bridge it on 2 stereo channels, each channel will get 1 Ohm only. So some amps produce incredible power. But please be sure that the amp can handle that low impedances. If not, the amp will produce even less power and shut down quite early or it will smell badly and you need a new one.

Btw. speakers have no "resistance". The resistance is only the resistance of the voice coil. Measured with DC.
But music signals are AC (waves). The resitance gets higher to higher freq. We say the impedance.
The e.g. 4 Ohm is only a guide number. The DC res. (lowest) has to be only slightly under that guide number so that you know how the amp is loaded.

I hope I could descripe these things so that my English can be understood.

rgds
Tobias

schexy1

1/r1 +1/r2 +1/r3 +1/r4 +.........
you do not use current or voltage when figuring out total resistance of speakers. Measure the speakers unwired in their neutral position (as the speakers move their resstance changes).

It depends on what type of amp you have and how the speakers are wired.

Amps can be mono or stereo.
speakers can be wired one per channel of two per channel.
one per channel ohm load will be what ever the speaker is rated as (4ohm, 2ohm, 8ohm ......)
two per channel will be wired in series or parallel.
for series add the ohms together ( 4 + 4 = 8)
for parallel divide by 2 (4 / 2 = 2)

If you have a passive crossover running multiple speakers per channel the ohms law does not apply because each speaker will operate in a specific frequency range. An example of this is a three way crossover with a low pass cut (sub) off at 100hz, baqndpass (mid range) at 100 - 5000hz and high pass (tweeters) at 5000hz. Eventhough it may appear that you have three speakers wired in parallel which should give you a ohm load of 1.33 (assuming that all speakers are 4ohms), you will actually have a 4ohm load at the amp.