#39: Kiss your amp goodbye

The Question
T$ – No not Terrance says:
2005-07-04 11:39:28

Dearest McQuaid,

Why won’t you kiss me in public any more?

I just wanted you to know that I still care….On a serious note however I was hoping to get a little smoother sound unit shaking my car (and hopefully you 2!) this summer, but I just don’t understand how amp ohm ratings and that of the installed speakers will interact. For example if my 4 ohm amp is hittin a cheap 6 ohm speaker I found online, will it sound correctly? I know one can change up their wiring method between, say, a left and right amp out through parallel and series wiring to either ‘jump’ or ‘drop’ the ohm-rating. How do I do this and ensure that I won’t blow any of my new equip.

Sweetly yours,

Todd Hetrick
(love the site)

The Answer

A multi-part answer:

– Whatever your fevered imagination conjures up, I have no power over. Perhaps you should ask your own inner mental workings why, when you dream of me, I don’t enjoy public displays of affection. Remember, in the real world, things are different…

– Here’s the skinny on ohmage. It’s a rating of resistance (or load, depending on who you ask). The amp is rated by how much power it can deliver. Less ohms equals more power, since there is less resistance. For example, a 4 ohm amplifier is rated to power through 4 ohms of resistance. If there was less resistance (say, 2 ohms), more power would flow through the amplifier, and this could potentially damage the amp. Nowadays that’s a bit unlikely, but that’s the theory. The speaker’s ohm rating indicates the resistance it puts on the amp. Hence, if your scenario played out, and you hooked a 6 ohm speaker to a 4 ohm amplifier, you wouldn’t damage the system. The output, however. would be less.

You can drop the ohm rating by wiring your speakers in parallel. (Connect the + terminal from the amp to both of the + terminals on the speakers, and repeat with the – terminals). This lowers the resistance. The formula to calculate the new resistance is:

1 1 1 …… 1
– + – + – + + –
R1 R2 R3 Rf

Hopefully that’s readable. It’s 1 over the sum of 1 over each of the ohm ratings for each speaker wired in parallel.

Don’t run speakers in series unless the manual says it is acceptable. This will cause distortion. If you do, the total resistance is the sum of each individual resistance.

To increase the output of an amp channel, bridge it. This is when you take the + and – terminal from one output and wire them together to create a single channel. It will be approximately 3 times the original output.

I’m no expert in this field, but I can point you to a couple of audiophile electrical engineers if need be.

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