Question about Ohms

barry666 · Post by **barry666** » Thu Oct 12, 2006 6:47 am

Hi there.
This always confuses me and I wanted to pick your brains.
I have a Sovtek Mig 50 head and on the back it has sockets for 4, 8 and 16 ohms. I purchased a second hand quad yesterday. The 4 speakers are 100w and 8 ohms each. To avoid any messy mistakes, what input would I plug the speaker into the amp??? 4, 8 or 16???

cheers

g

Rog · Post by **Rog** » Thu Oct 12, 2006 7:03 am

Barry, it doesn't much matter what each individual speaker is in the quad, what matters is the overall impedance of the cab. It's probably 8 Ω, but is there not a plate on the cab with its impedance shown?

Do you have a multimeter?

Post by Bg » Thu Oct 12, 2006 7:04 am

beat me to it

barry666 · Post by **barry666** » Thu Oct 12, 2006 7:08 am

Unfortunately there isnt. Its a homemade cab with 4 x 12" 100w Beyma speakers. The speakers dont have much on them. The 8 ohms label is printed on the cone itself. I dont actually have a multimeter either.

Rog · Post by **Rog** » Thu Oct 12, 2006 7:13 am

Can you open the back?

Do you have a digicam?

barry666 · Post by **barry666** » Thu Oct 12, 2006 7:15 am

Its opened from the front. Last night I removed the grille and took out a cone, and thats where I got the info from. The back only has the plug socket plates. No digicam sorry.

Rog · Post by **Rog** » Thu Oct 12, 2006 7:17 am

Wow - making it hard to give you a definitive answer, mate!!

Best suggestion I can give is to find a friend with a multimeter and take a reading from the input of the cab.

Bear in mind that the readings from a multimeter will be lower than the actual impedance.

barry666 · Post by **barry666** » Thu Oct 12, 2006 7:20 am

yep, Im like that!!! Thanks anyway for your time. Ill see if I can borrow a multi meter from my local music store.

ash · Post by **ash** » Thu Oct 12, 2006 7:24 am

Assuming it was wired by someone with a clue, its almost certainly 8 Ohms. A combo of four 8 Ohm speakers can only be evenly wired a few ways. All in series is 32 Ohms, all in parallel is 2 Ohms and 2 series pairs in parallel (or vice versa) is 8 Ohms.

If you feel confident that you can trace the wires and decide that it is one of these, then you're good to go. Testing with a multimeter would be good insurance though.

barry666 · Post by **barry666** » Thu Oct 12, 2006 7:25 am

ok then, being a little clueless, how do I use a multimeter and where do i connect it.???

ash · Post by **ash** » Thu Oct 12, 2006 7:29 am

Might be best to get the person you borrow it from to show you.

Plug a speaker lead into the socket.
Switch the meter on and set it to measure resistance.
Touch one probe onto the sleeve of the speaker lead jack and the other probe onto the tip of the jack.

If all is well it should read about 6-7 Ohms.

barry666 · Post by **barry666** » Thu Oct 12, 2006 7:30 am

thanks for that!!!

Rog · Post by **Rog** » Thu Oct 12, 2006 7:30 am

Assuming it was wired by someone with a clue, its almost certainly 8 Ohms.

Agree!

That said I have found some strange wiring systems on home-built cabs.

Timi · Post by **Timi** » Thu Oct 12, 2006 9:17 am

Probably is 8 ohms but the multimeter could also let you know if there are blown speakers ect.

You can get cheap multimeters from Dick Smith, pretty handy thing to own I think.