amps - speaker cabs ohms?

[berkeleymando]

As I consider different amps /cabinets /amp heads to use with the emando I am a bit unclear on how ohm output relates to the capacities of various speaker cabinets.

If I understand correctly a 4 ohm head could drive a 8 ohm cabinet but not the reverse. Is this correct?

pardon my ignorance, but I am a recent arrival in the electric-amplified music world, having been an acoustic player up until very recently.

Thanks!

[berkeleymando]

OK, no one seems to be interested in this topic. However, can anyone point me to a good technical explanation of OHMs as they related to amp/speaker cab combinations? I would appreciate any ideas. Thanks.

[MartinD_GibsonA]

If you'll give me your email address, I've got a 36-page Word doc that might answer your questions.

Don Smith

[berkeleymando]

Thanks, Don. I just sent you a PM. I would be interested indeed. Thank you.

[MartinD_GibsonA]

Yeah, and in my stupidity, I managed to delete it rather than save it. Send it again please, and I *promise* to be more careful next time.

Don

[mandroid]

the drivers in the cabinet can be of a 4.8.16 ohm spec
and then there is the option of wiring them in series or parrallell all of which influence the combined impedance load
I think 2,16ohm in series is 8ohm
when impedance load combines too low, transistor amps go into overload, some are designed to handle 2ohm loads, some are toast at that point.

[Bruce Evans]

the drivers in the cabinet can be of a 4.8.16 ohm spec
and then there is the option of wiring them in series or parrallell all of which influence the combined impedance load
I think 2,16ohm in series is 8ohm
when impedance load combines too low, transistor amps go into overload, some are designed to handle 2ohm loads, some are toast at that point.
Sorry mandroid, but 2 16ohm loads in series (be they speakers or anything else) is 32 ohms. 2 16 ohm loads in parallel are 8 ohms.

The best situation is to exactly match the total speaker impedance to the output of the amplifier, e.g., 8 ohm speaker load to an 8 ohm amplifier output impedance. Some amplifiers have a selectable output impedance to make this easier.

[Lee]

Join at www.fenderforum.com There's lot's of amp people who will be very helpful. Over there they call it GAS (gear acquisition syndrome).

[mandroid]

See, its not simple, Bose has 9 speakers in some of their cabinets and I think 2 ohm per, and who knows how the whole set is wired>??
I tried a Galaxy audio 16 ohm cab in a 8 ohm output situation, and found the output was weak,[like 1/2] whereas A carvin PM5 8 0hm was OK, and an EV Sx80 made even more efficient use of the same 90W rms amp output.
http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wow.gif http://www.mandolincafe.net/iB_html/non-cgi/emoticons/cool.gif

[Dennis Schubert]

Try this backwoods explanation: When you hook up a speaker to a power amp, the amp "pushes" power into the speaker. Let's say this amp is rated for a 4 ohm minimum load. An 8 ohm speaker will resist or impede the flow of the power. If there are two 8 ohm speakers (total load of 4 ohms) there is less restriction, because there are now two places to push the power. The amplifier will work just fine with one or two speakers, but if you add two more 8 ohm speakers the total load is down to 2 ohms. Now, with four places to send the power, there is almost nothing to push against, so that the amplfier works too hard, overheats, and self-destructs.

[berkeleymando]

Thanks for all the info, its all very interesting and helpful!

[Bruce Evans]

Try this backwoods explanation: When you hook up a speaker to a power amp, the amp "pushes" power into the speaker. Let's say this amp is rated for a 4 ohm minimum load. An 8 ohm speaker will resist or impede the flow of the power. If there are two 8 ohm speakers (total load of 4 ohms) there is less restriction, because there are now two places to push the power. The amplifier will work just fine with one or two speakers, but if you add two more 8 ohm speakers the total load is down to 2 ohms. Now, with four places to send the power, there is almost nothing to push against, so that the amplfier works too hard, overheats, and self-destructs.
Ironweed, as an electrical engineer I shuddered when I read the first four words of your post. But you pretty much nailed it! That's a very good non-technical explanation of a very technical issue.

Good job.

Now tell me how to play Blackberry Blossom up to speed. #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

[Dennis Schubert]

I'm almost ashamed to tell, but I learned that EE lesson the hard way many years ago. My good friend the TV and amp repair guy explained it to me in simple terms, as he handed me the bill...

Regarding Blackberry Blossom, my advice is to simplify your arrangement to keep your pick moving in a steady up/down pattern as much as possible...and keep practicing.