Confused about Ohms and speakers

chabby · January 11th, 2008, 12:45 PM

With regard to my new amps extension speaker jacks, there is one jack with a lever to select either 4 or 8 ohms. I have a epiphone Valve Junior Cabinet that reads 16 ohms on the back. Can I use that Epi cabinet as an extension speaker cab? If so, which do I select on the back of the new amp 4 or 8 ohms? It say the toal load must be 4 or 8 ohms so what load would the 8 ohm speaker in the amp and the 16 ohm speaker in the Epi cabinet put on it.
I'm hoping it will equal either 4 or 8.

chet · January 11th, 2008, 01:27 PM

You should call the amp makers toll free number if possible to make sure you won't violate your amp warranty if you hook that cab to it. I'd get a cab of either 4 or 8 ohms to use with it myself.

Twangbanger · January 11th, 2008, 01:30 PM

Depends on how speakers are wired. You'll have an impedance mismatch with the 16ohm cabinet. It won't hurt the amp, but the output power of the amp will be decreased. With a 8ohm internal speaker and a 16ohm added in parallel, you'll have a 6ohm speaker load. I'd put the selector switch on the 4ohm selection. It's not good to run an amp below it's output impedance. The best bet would be to get another 8ohm extension speaker, then you'd have 4ohms with them all hooked up together.
Good luck.

4 Strings · January 11th, 2008, 01:55 PM

An 8 and a 16 ohm speaker in parallell would give you 5,333 ohms in total, which should be just fine with the amp's impedance selector set to 4 ohms.
But just as Twangbanger sez, the best thing would be to get another 8 ohm speaker, since that would give you the 4 ohms which the amp "calls for".

Good luck!

Twangbanger · January 11th, 2008, 02:02 PM

My bad, I don't know why I thought the total was 6, I'm just lazy. I did the calculation, it's 5.3333333333333333333, haha!

tazzboy · January 11th, 2008, 02:04 PM

Seymour Duncan has an Ohms Cal http://www.duncanamps.com/technical/impedance.html

This is one that I used
http://colomar.com/Shavano/impedance_proc.php

chabby · January 11th, 2008, 02:08 PM

I don't get it. Why is the matching Epi VJ cab 16 ohms? Why isn't it 8 ohms like this new amp and my DRRI was? They are all 12" speakers why would Epi make it 16 ohms?

Twangbanger · January 11th, 2008, 02:15 PM

What amp do you have?
Is the Valve junior amp head unit designed for 16 ohms or it may have an output transformer with different load taps? If so, then that's why. Speakers come in all kinds of impedances. Champs have a 3.2ohm impedance and most 2 speaker fender amps are rated for 4ohm impedance. Just depends on the amp design specs. I noticed that the Epi extension cab only comes in a 16ohm version.
Here's the calculation for speakers in parallel.

Dacious · January 11th, 2008, 06:51 PM

Quote:

Originally Posted by chabby

I don't get it. Why is the matching Epi VJ cab 16 ohms? Why isn't it 8 ohms like this new amp and my DRRI was? They are all 12" speakers why would Epi make it 16 ohms?

Traditionally British amp makers used 16 ohm speakers (actually 15 ohms, but it's bugger-all difference). Most people with Marshall 4 x 12s would have 16 ohm celestions, and the most common impedance for those is 16 ohms (parallel-serial wiring) or 4 ohms ( all parallel). If they have 2 x 12s it is 8 ohms parallel.

So Marshall impedance selectors usually have 4, 8, 16 ohms settings.

I'd say when you plug the extension in with your amp you are converting the 16 ohm tap off the output tranny to the alternate 4 or 8ohm setting.

Then you have the option of a total 4 ohm load, which as the others point out covers an extension cab below 16 ohms; or 8 ohm which covers a 16 ohm cab plus the standard internal speaker.

If your internal speaker is 16 ohms, then your total load is 8 with a 16 ohm extension cab.

Marshall and PV also made single speaker 16 ohm cabs, and Vox used two 2 x 16 ohm cabs in their various AC30s for 8 ohms.

It's just the British vs American standard of 16 ohm s vs 8 ohm
speakers and the differing plethora of output impedances you get.

At least they gave you 4 or 8 ohms, which covers most options adequately.

chabby · January 11th, 2008, 08:34 PM

Still not sure if I should hook up the VJ cab for fun or not. ANd which to select the 4, or 8 ohm switch on the back of the amp. Again, the amps speaker is 8 ohms and the VJ cab is 16 ohms.

BoB/335 · January 11th, 2008, 09:13 PM

Someone suggested to call the manufacturer. After what I found in the Fender manuals, I would try to stay with the amp requirements.

studio1087 · January 11th, 2008, 10:45 PM

Does this help??

nick.s · January 12th, 2008, 02:20 AM

Quote:

Originally Posted by tazzboy

Seymour Duncan has an Ohms Cal http://www.duncanamps.com/technical/impedance.html

This is one that I used
http://colomar.com/Shavano/impedance_proc.php

great info tazzyboy! no more questions...!
thanks

BoB/335 · January 12th, 2008, 05:50 AM

Studio 1087

What a GREAT diagram!

January 11th, 2008, 12:45 PM	#1 (permalink)
chabby Tele-Afflicted Join Date: Jan 2004 Location: Seattle, WA Posts: 1,250	Confused about Ohms and speakers With regard to my new amps extension speaker jacks, there is one jack with a lever to select either 4 or 8 ohms. I have a epiphone Valve Junior Cabinet that reads 16 ohms on the back. Can I use that Epi cabinet as an extension speaker cab? If so, which do I select on the back of the new amp 4 or 8 ohms? It say the toal load must be 4 or 8 ohms so what load would the 8 ohm speaker in the amp and the 16 ohm speaker in the Epi cabinet put on it. I'm hoping it will equal either 4 or 8.

January 11th, 2008, 01:30 PM	#3 (permalink)
Twangbanger Tele-Holic Join Date: Mar 2003 Location: Marble Falls, TX Age: 27 Posts: 825 29 Photos	Depends on how speakers are wired. You'll have an impedance mismatch with the 16ohm cabinet. It won't hurt the amp, but the output power of the amp will be decreased. With a 8ohm internal speaker and a 16ohm added in parallel, you'll have a 6ohm speaker load. I'd put the selector switch on the 4ohm selection. It's not good to run an amp below it's output impedance. The best bet would be to get another 8ohm extension speaker, then you'd have 4ohms with them all hooked up together. Good luck. __________________ Play'n tele till I drop! *************** Bryan Hibler

January 11th, 2008, 02:02 PM	#5 (permalink)
Twangbanger Tele-Holic Join Date: Mar 2003 Location: Marble Falls, TX Age: 27 Posts: 825 29 Photos	My bad, I don't know why I thought the total was 6, I'm just lazy. I did the calculation, it's 5.3333333333333333333, haha! __________________ Play'n tele till I drop! *************** Bryan Hibler

January 11th, 2008, 02:04 PM	#6 (permalink)
tazzboy Friend of Leo's Join Date: May 2005 Location: Eugene, Oregon Age: 31 Posts: 2,680	Seymour Duncan has an Ohms Cal http://www.duncanamps.com/technical/impedance.html This is one that I used http://colomar.com/Shavano/impedance_proc.php __________________ tazzboy Guitar: 1982 Gibson Les Paul Standard AMP: 59 Bassman Reissue. EFFECTS: 2 Boss TR-2 Tremolo, Boss CE-2 Chorus, and Boss DM-3 Echo Delay.

January 11th, 2008, 02:15 PM	#8 (permalink)
Twangbanger Tele-Holic Join Date: Mar 2003 Location: Marble Falls, TX Age: 27 Posts: 825 29 Photos	What amp do you have? Is the Valve junior amp head unit designed for 16 ohms or it may have an output transformer with different load taps? If so, then that's why. Speakers come in all kinds of impedances. Champs have a 3.2ohm impedance and most 2 speaker fender amps are rated for 4ohm impedance. Just depends on the amp design specs. I noticed that the Epi extension cab only comes in a 16ohm version. Here's the calculation for speakers in parallel. __________________ Play'n tele till I drop! *************** Bryan Hibler

January 11th, 2008, 01:27 PM	#2 (permalink)
chet Poster Extraordinaire Join Date: Aug 2004 Location: The Jersey Shore Posts: 5,934	You should call the amp makers toll free number if possible to make sure you won't violate your amp warranty if you hook that cab to it. I'd get a cab of either 4 or 8 ohms to use with it myself.

January 11th, 2008, 01:55 PM	#4 (permalink)
4 Strings Tele-Meister Join Date: Jun 2007 Location: Gossip County Posts: 226	An 8 and a 16 ohm speaker in parallell would give you 5,333 ohms in total, which should be just fine with the amp's impedance selector set to 4 ohms. But just as Twangbanger sez, the best thing would be to get another 8 ohm speaker, since that would give you the 4 ohms which the amp "calls for". Good luck!

January 11th, 2008, 02:08 PM	#7 (permalink)
chabby Tele-Afflicted Join Date: Jan 2004 Location: Seattle, WA Posts: 1,250	I don't get it. Why is the matching Epi VJ cab 16 ohms? Why isn't it 8 ohms like this new amp and my DRRI was? They are all 12" speakers why would Epi make it 16 ohms?

January 11th, 2008, 08:34 PM	#10 (permalink)
chabby Tele-Afflicted Join Date: Jan 2004 Location: Seattle, WA Posts: 1,250	Still not sure if I should hook up the VJ cab for fun or not. ANd which to select the 4, or 8 ohm switch on the back of the amp. Again, the amps speaker is 8 ohms and the VJ cab is 16 ohms.

January 11th, 2008, 09:13 PM	#11 (permalink)
BoB/335 Tele-Meister Join Date: Aug 2003 Location: Long Island Posts: 473	Someone suggested to call the manufacturer. After what I found in the Fender manuals, I would try to stay with the amp requirements. __________________ BoB/335

January 11th, 2008, 10:45 PM	#12 (permalink)
studio1087 Friend of Leo's Join Date: May 2003 Location: Near Milwaukee Age: 44 Posts: 3,462 36 Photos	Does this help?? __________________ JLG Carry On

January 12th, 2008, 05:50 AM	#14 (permalink)
BoB/335 Tele-Meister Join Date: Aug 2003 Location: Long Island Posts: 473	Studio 1087 What a GREAT diagram! __________________ BoB/335