speaker ohm question

[9 volts]

Slightly off topic...but I have an old rola speaker with an rating of 2 to 15 ohms......how does a speaker compensate for this? Its s a 12m model. I found info here
http://www.retrovox.com.au/rola.pdf//

I want to run this at 15 ohm through a valve amp. Is this safe?
Thanks

[Meanderthal]

 I would think that it's fine, especially if yer set up for 16 ohms.

[petemoore]

how does a speaker compensate for this?
  Ohmages divide or multiply when in series or parallel.
  an 8 ohm speaker = 8 ohms [no options here]
  two 8 ohm speakers at the same time' gives you 16ohm and 4ohm options.
  Two 8 ohm in series is 16ohms
  two 8 ohms in parallel is 4ohms
  Your speaker ohmage can be 'sort of measured' using an ohm meter, DMM. It'll give you an idea of the speaker ohmage..close enough for one speaker...ie a 15ohm speaker will show an ohmage on the meter in the neighborhood of 15ohms. For more than one speaker a 'percentages' view can be taken so that power is distributed evenly to each speaker.
  At 15 ohms, I don't think you'll be near exceeding an amps minimum ohmage, modern amp anyway, usually this min ohmage is printed by the speaker output of the amp, other times the speaker/amp are hardwired, just go by what speaker ohmage they had in there.