I have salvaged several speakers form different things. Some of the speakers are marked with the ohms and wattage on them and some are not marked at all.
I can get the ohms with a VA meter but don’t know the wattage.
Is there a way to find out the wattage of a speaker so that I will not ruin the speaker with to large of an amp ?
Thanks
Richard
Short answer is no. Your VA meter will not give you an accurate impedance rating either. Impedance is measured in Ohms, but it is not the same as resistance.
Smoke 'em if ya got 'em 
Speakers are cheap. I’d go with the marked ones. Safer.
Richard, that is not how things work. When you buy a car that has 200 horsepower, you do not use all 200 when you go the store for bread. Your speaker will not “blow” as soon as you turn things on. Your car is throttled. So is your sound card power output. The throttle is called a volume control. Power output of the amp is also a variable based on frequency. An EMD sound file has much more bass typically than an ALCO sound file. The output power will be different for each, on the same sound card at a similar volume setting, within a small variation. Finally, if you are using Phoenix sound, you can limit the output power in software, though going small is not always better, because it can increase distortion(see next). Some DCC decoders have this adjustment also, though not common.
Speakers fail because of an amplifier characteristic called clipping. Drive an amp too hard or too long and the output stops resembling audio and starts looking like a square wave. A square wave output can have HUGE harmonic content, well distorted, that will kill a speaker fast. This does not happen instantly unless really severe misuse is undertaken. The sound will sound VERY poor , either from amp distortion or speaker full cone excursion, an alternate method of distortion , before you get in trouble… if you hear poor sound, turn it down. If the system plays clearly at lower settings, but is not loud enough for your application, then change and upgrade.
Secondly, you Cannot measure speaker IMPEDANCE with a meter. Impedance is not resistance. They only use the same unit of measure. Speaker wattage ratings are a specified number based on a known impedance curve, along with some other design parameters such as voice coil size, type of wire, type of insulation , and more.
Go ahead and mess around, use what you have that fits. If you kill a speaker, let me know, I will send you a replacement , gratis.
jonathan/www.rctrains.com