Ohm in Marshall cab?

[MortenP]

I'm running my Laney GH100l through a Marshall 1960 cab, and I've become unsure on what Ohm-output to use..
When I'm running both sides of the cab(all four speakers), do I use the 4- or the 8-ohm output on my amp?

[MountainDog]

Depends how your cabinet is wired and what impedance the speakers inside the cabinet are. The older 1960 Marshall cabs had one input and usually had four 16ohm speakers wired in series/parallel that gave a 16ohm impedance rating out of the jack (hence using your 16ohm option on the marshall amp for 1 cab, the 8 ohm selector on amp for 2 cabs, and the 4 ohm selector on the amp for 4 cabs).

Current 1960 cabs show as 16/4 ohm in mono or 8 ohm in stereo. To use these, you put the speaker cable into the 4ohm input on left or 16 ohm on right an slide the switch to the mono side:

http://www.marshallamps.com/images/product_overview/cabfeatures3.jpg

According to the laney website, your amp has connections for 1x16ohm, 1x8ohm, 1x4ohm, 2x16ohm and 2x8ohm:

http://www.laney.co.uk/manuals/GH100L%20Manual%20-%202006%20-%20Issue%202.2.pdf

If your cabinet is a 16ohm cab, insert in the 1x16, if its an 8ohm, insert in the 1x8, if its a 4ohm cab, insert in the 1x4ohm.

If you don't know what your cabinet's impedance rating is or how its wired or what speakers are inside, you can get a rough idea by inserting a speaker cable in the cabinet jack, then using a electrical multimeter positioned on the ohms scale, connect the meter leads to the other end of the speaker cable (one to the tip, the other to the shaft body) and see what it says. A reading of like 12 to 16 would mean a 16 ohm cab, a reading of like 6 to 10 would be 8 ohm, a reading of 3 to 5 is a 4 ohm cab. (Using a meter like this, you are measuring the 'resistance' of the coil, whereas impedance is an interactive thing when the speaker is playing, but you can use the resistance numbers as a rough correlation).

[MortenP]

I'm sure I answered this, but hey - here goes!

So as long as I switch to mono, and I use 4 ohm out from amp/4 ohm into cab OR 16 ohm out from amp/16 ohm into cab I'm safe? Wich output/input-combo would give me the most "bang for the buck" then?

(I'm so sorry for the "noob-that-shouldn't-be-allowed-to-own-a-tube-amp"-question..)

[Cygnus X1]

Impedance roughly equals resistance. Roughly. Lower inductance generally
will give out more high end, and a punchier sound. More inductance will cut off the highs, and give a warmer, bass like sound.
So, 4 ohms=highs pass
16=lows pass.
It seems to me that 4 ohm would be the most efficient, giving the
most "bang for the buck". But there are enough variables invloved you should just try both, and let your ears decide.

[marcus]

Most likely both of these options will output the same amount of power. In a tube amp, if you are matching the speaker impedance to the proper tap on the transformer, you will get the same wattage approximately. In other words, 4 ohm tap into 4 ohm speaker (or cab), and 16 ohm tap into 16 ohm speaker (or cab) will yield the same wattage. Which one will be louder and/or sound better, I can't say. Probably in your case, it won't make much of a difference because you are going to be running the same amount of juice through each speaker for both settings. I am assuming here that the 4 & 16 ohm mono settings both utilize all 4 speakers, if I am wrong YMMV. Hell, YMMV anyway

[åron]

But there are enough variables invloved you should just try both, and let your ears decide.

Hit the nail on the head.

[scotty]

I am going to try this. I have an old Marshall cab (1977 w/30 watt green backs) that I rewired to 8ohms because I was using two cabs and the other was an 8ohm. I still have the original wiring harness and I only run one cabs these days. Lets see how good my ears are.

[Ace]

For no mathematical reason I can figure, I usually like running Marshalls at 16ohms instead of 4. Try both though, for sure.