• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

is running 8 Ohm speakers from 4 Ohm tap safe?

burnsyaz

burnsyaz

Active Member
Hello I was recently pushing my set of a/d/s/ L9e 4 Ohm speakers with my Dynaco St-70 amp. After listening for a while I wanted to compare my 8 Ohm New Large Advents to the a/d/s/. When I switched speakers I forgot to switch the speaker wire from the 4 Ohm tap to the 8 Ohm on the Dynaco. The Advents seem to be a bit fuller sounding this way especially at lower levels. Is it safe to run them like this? :scratch2:
I have also run stacked Advents wired in parallel from the 4 Ohm tap and the Dynaco seemed to have no trouble pushing all 4 speakers at 4 Ohms.
 
Register to hide this ad
I have been running 6 ohm speakers on my 8 ohm taps for a while with nothing but great results.


So go right on ahead and do it. But please, please enjoy.:music:







-Vic
 
Thanks to both of you. I figured it would be ok if I didn't push the amp too hard but I can't be too careful when it comes to the old Dynaco. Mine is an original (with a couple of mods) from 1960 and I want to keep it going for another 50 years if possible.
 
Tubes don't care all that much about stuff like that. You'll get less than optimal impedance on the plates, which will give either reduced output power, or slightly increased distortion but it won't cause anything to break.

If thats original, you'd probably do well to replace the capacitors. By now, they're not what they used to be. Old caps can be a safety issue too. If one shorts, you can burn out tubes or transformers.
 
been running stacked advents for years from a stock st70 on the 4 ohm tap. no problem. be aware that the large advents are better rated at 6 ohms.
 
From what I understand to be the case, running 8 or 6 ohm speakers from a 4 ohm tap or a 4 ohm setting on SS may only reduce the damping factor of the amplifier a bit. If it's even noticable, the bass may be a little less tight, i.e. fuller sounding? Impedance is actually inductance in speaker terms, which changes with frequency, right?
 
OK my Advents do rate at 6 ohms (just measured them). Wouldn't running the speaks from the 4 ohm tap be better for the amp than running them from the 8 ohm tap?

I am a guitarist and I have been told that it is bad to run a smaller ohm cab than what your amp is putting out. For example running a 4 ohm cab from the 8 or 16 ohm output of my Marshall amp is not good for the amp. I have been told that it is just fine to go the other way. For example running an 8 or 16 ohm cab from the 4 ohm output of my Marshall wouldn't be the most efficient but would not strain the amp. Wouldn't this be a very similar situation with my ST-70?
 
6 ohms resistance doesn't mean 6 ohms impedance. Its a rather different measurement that unfortunately uses the same unit and causes a lot of confusion. 6 ohms dc resistance is probably closer to 8 ohms impedance.

And yes, running an 8 ohm speaker on the 4 ohm tap mostly makes for less efficient operation. It wont damage anything.
 
See the attached graph of a typical 8 ohm speaker. See how the impedance changes with frequency? See the "nominal" line? That's how all conventional cone type speakers react to input due to coil inductance. So 4, 6, 8 or 16 ohm impedance is relative.

If it sounds good and nothing overheats or blows up it's probably okay.:thmbsp:
 

Attachments

  • graph.jpg
    graph.jpg
    58.4 KB · Views: 21
Last edited:
hey thanks for the graph Jim. Athough I've produced similar graphs with woofer tester I didn't know that the low point there was what was used when a speaker states 8 ohm nominal or 6 ohm or whatever.
 
cubby01 said:
hey thanks for the graph Jim. Athough I've produced similar graphs with woofer tester I didn't know that the low point there was what was used when a speaker states 8 ohm nominal or 6 ohm or whatever.
Click to expand...

That's a woofer graph for sure, although I've seen some that barely spend any time around the 8 ohm nominal impedance in a frequency sweep that are still rated "nominal 8 ohm".

The behavior of a particular speaker system factors the low, mid and high frequency drivers along with the crossover components to determine the nominal impedence. The actual impedance will be all over the range with any given piece of music.
 
You must log in or register to reply here.
Back
Top Bottom