| Author | Message | ||
| rklisme
Advanced Member Username: rklisme Post Number: 331 Registered: 5-2004 |
Hey guys In simple terms what would be the effect of using a 4ohm speaker with a 8ohm amp? Also if you reverse this situation what are the effects? Please remember I am a simple guy looking for a simple answer! Thanks in advance to any responses! Rory | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1978 Registered: 7-2004 |
Rory: Here is my understanding - I'm no electronics tech, so if I get something wrong, someone please chime in and put me in my place. Ohms is a measure of resistance, so an "8 ohm amp" expects to see a speaker with 8 ohms of resistance. Hook it up to a 4 ohm speaker and there is not as much resistance which results in bad things happening. If you're lucky, you will only blow the speaker. More likely, you may damage the amp. Hooking up a 4 ohm amp to an 8 ohm speaker is not as problematic. You will have to push the amp a little more and may lose some volume. This may also be dependant on the particular amp. Mesa Boogie has told me that ohmage (is that even a word?) is not critical for my Mark amps, at least whether to hook up an 8 ohm speaker to the 8 ohm jack on the amp, or the 4 ohm jack. Mesa says try both and use what sounds best to me. Bill, tgo | ||
| bob
Senior Member Username: bob Post Number: 799 Registered: 11-2002 |
A 4 ohm speaker will be louder than an 8 ohm speaker. Unless you're talking megawatts, or a really wimpy speaker, just start with lower volume and you probably won't hurt anything. There are really just two very simple things to look at. One is the output of the amp. Typically, you will see that the amp is rated to put out some number of watts (say 300) into 8 ohms, and much more, close to double (say 500) into 4 ohms. The other is the power handling of the cabinet. Often there are two numbers, continuous and peak, so a given cabinet might handle 200 watts continuous(ly), and maybe 400 for peak (brief) periods. It's actually considered safer to have more amp power, up to the peak rating of the cabinet or even higher, as long as you're not constantly playing at 11. So if you have the specs available, see how much power your 4 ohm cabinet is rated to handle, and then compare that to what your amp puts out into 4 ohms. Or if you don't know what your amp does into 4 ohms, take the 8 ohm rating and double it. As long as that number isn't grossly more than the peak speaker rating (even twice as much is generally fine), you shouldn't have any problems. Things get trickier when you get down to 2 ohm loads, since some amps don't like to go there. But most contemporary amps will handle 8 and 4 ohm loads fine, just putting out more power into less resistance. And remember they're only putting out their rated power when you have them cranked, and you play something loud or percussive, most of the time it will be much less. -Bob (no electronics whiz either) | ||
| inthelows
Advanced Member Username: inthelows Post Number: 269 Registered: 11-2006 |
Very nicely put Bill. That resistance is actually a simple way of explaining reactance, or the combined effects of the coil resistance of the wire and the effect of the coil when the dc and ac signal is applied to it. DC gives the power for the most part and the AC is the "sound material" applied. Generally speaking the less the ohmic value of the load, the more current can be applied thru the coil. Sooner or later some spike is going to have the amp sent a whole lotta love to your speaker and poof! Better to rewire the cab to 8ohms if possible( two 4 ohm speakers in series) would do it, or 2 four ohm cabs with a cable wired for series operation. Best not left to chance. I'm sure you are familar with Murphy's law, if something can go wrong, it will. Good luck. NLP | ||
| alembic_doctor
Intermediate Member Username: alembic_doctor Post Number: 115 Registered: 8-2002 |
If you're like me and you like to shake the walls of your place when listening to some heavy grooves, then you'll definately run the risk of having the amp go DC. The result will be at least thick, acrid smoke. At worst, Fire. I've seen it happen several times. I had a Vietnamese dude try to explain to me, in his broken English, that his speaker "it smok!! It Smok!!!" After 10 minutes of me trying to figure out what he was trying to say, his partner carried in two Bag End TA-6000 that they had previously bought. Problem, they hooked up to many speakers and drove the impedance down. The amp went DC when they cranked it up. All of the insides of the cabinets caught fire and burned up all of the components inside. And man did they stink. Just be careful | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1980 Registered: 7-2004 |
Bob: From what I've read, you are absolutely right if the amp is rated 4-8 ohms. But if the amp is rated for 8 ohms only (which is what I assumed Rory meant) aren't you taking a big risk running it into a 4 ohm speaker? Everything I've read says that it's usually o.k. to step up in ohms but warns to NEVER step down. Bill, tgo | ||
| bob
Senior Member Username: bob Post Number: 800 Registered: 11-2002 |
Bill, that's why I added the warning about 2 ohm loads. I've seen a few popular bass amps only rated to about 2.5, or "not recommended" for 2, but I believe you would have to look pretty hard to find one that won't handle 4. Maybe I'm wrong about that, and of course, Rory might just happen to have one of these... so it would be good to check. | ||
| rklisme
Advanced Member Username: rklisme Post Number: 332 Registered: 5-2004 |
Hey guys Thanks for all the good information and the amp in question is rated at 8 ohms. I was thinking of picking it up for a practice amp but my cabs are 4ohms this is why I am asking. I noticed that the cabs did not sound to good with this amp but when 8 ohm cab was used the amp sounded great! Once again thanks to everyone for taking your time to explain this to me! Rory | ||
| inthelows
Advanced Member Username: inthelows Post Number: 272 Registered: 11-2006 |
Rory.. What's the chance of just replacing or getting a 8ohm replacement speaker? How many speakers in the cab? If just for practice you could make your own mini wall of sound! NLP |
