#1
so i really dont get it. for example if i have a 1x12 with a 4/8/16 ohm switch, and i want to add a 2x12 cab, what ohms would i use. would i just use the cab? or could i use all 3 12 inch speakers?
#2
1. It depends on the ohmage of the cab.
2. I don't know if you have a head or a combo, but with a combo you can only use all 3 12" speakers if your amp supports EXTENSION.

EXTENSION is adding a cab while the original speaker plays as well.

EXTERNAL is only running the speakers in the cab.
"Experience is not what happens to you. It is what you do with what happens to you." - Aldous Huxley
#3
well, its a bugera v22. it has 2 plugs for a speaker (one is in use by the stock speaker) and then a 4/8/16 ohn switch.

the speaker/setup is running 8 ohms now.

so if i go to a 2x12 cab and run all 3 speakers, how many ohms (if i get the same 8 ohm speakers or sometthing)?
#4
Three 8 ohm speakers in parallel will give you 2.7 ohms - don't do it.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
well what speakers would i need to buy?

how do you get 2.7? what math is involved?
#6
The external jack should have it's minimum ohm labeled. You don't have to do the math with the internal speaker. You want to match the amps ohm to the speaker as close as possible but you never want the speaker ohms to be less than the amps.

Here's the math... but just buy a cab that matches whatever ohm is labeled on the external jack...

"Speakers can be connected to each other in two methods: parallel and series. If the speakers are connected in a series, the impedance's are added to each other. For example, two 8-ohm speakers in a series have a total impedance of 16 ohms. In cases where speakers of the same impedance are connected in a parallel, the total is the impedance of one speaker divided by how many speakers there are. For parallel connections of speakers with differing impedance levels, the total impedance is computed by multiplying the impedance of the speakers. The product is then divided by the sum of the speakers' impedance. "

Read more: Speaker Ohms Explained | eHow.com http://www.ehow.com/about_5241127_speaker-ohms-explained.html#ixzz0sSKwWW9Y
Last edited by 667 at Jul 1, 2010,
#7
ok well imp retty sure its 8 ohms.

can i run 3 speakers? (stock speaker plus a 2x12?) couldnt i run a 2x12 cab with 4 ohms speakers, run in series, and then the 8 ohm stock speaker?

wouldnt that give 16 ohms?

and what about amp output? instead of 22 at 8 ohms thats 10.5 at 16 ohms right?

does that mean less power to each speaker or less power ofmy amp overall? i bought a 22 watt amp, i dont want to turn it inot 10 watts?!?!

am i getting this right?
#8
Quote by ikey_
ok well imp retty sure its 8 ohms.

can i run 3 speakers? (stock speaker plus a 2x12?) couldnt i run a 2x12 cab with 4 ohms speakers, run in series, and then the 8 ohm stock speaker?

wouldnt that give 16 ohms?

and what about amp output? instead of 22 at 8 ohms thats 10.5 at 16 ohms right?

does that mean less power to each speaker or less power ofmy amp overall? i bought a 22 watt amp, i dont want to turn it inot 10 watts?!?!

am i getting this right?


You're just reading into it too much. If you were wiring it up yourself from scratch, then you worry about all the math stuff.

Whatever is marked on your external jack is what you need to go with irrigardless of what it's running on the inside (unless it's an ancient amp). So if the external jack says 8, then you can plug an 8 or 16 ohm cab into it. The combo will drive the internal speaker along with the external(s). Some amps have multiple external jacks for different ohmage cabs and wiring schemes - other's have a switch. If it only has one external jack and no switch, then the minimum ohm is listed and you go with that for the external cab.

When you buy a cab with multiple speaker, you don't have to do math either. The ohm of the cab will be listed on the back next to the jack - and you don't have to worry about what's inside and how it's wired and what ohm each speaker is rated for.

When you have a miss-match (16 ohm cab into 8 ohm amp), you just lose a little bit of your max volume.. but I'm sure your not diming the volume anyway..
Last edited by 667 at Jul 1, 2010,
#9
ok so matching ohms = same volume

more ohms = less volume

so....les ohms (4hm cab into 8ohm speaker, useing the 4ohm switch setting) = higher volume?

i read somewhere changing ohms can change sound...particularly bass response. is that right?
Last edited by ikey_ at Jul 2, 2010,
#10
No. A cab with a lower impedance rating than your amp's output will cause flyback voltage that will destroy the OT.
E-peen:
Rhodes Gemini
Fryette Ultra Lead
Peavey 6505
THD Flexi 50

Gibson R0 Prototype
EBMM JP13 Rosewood
Fender CS Mary Kaye

WTLT

(512) Audio Engineering - Custom Pedal Builds, Mods and Repairs
#11
woops! typo. it was 0. i meant 4 ohms. if i put a 4 ohm cabinet and then switch my amp to the 4ohm setting, what effect does that have on sound?
#12
Quote by ikey_
ok so matching ohms = same volume

more ohms = less volume

so....les ohms (4hm cab into 8ohm speaker, useing the 4ohm switch setting) = higher volume?

i read somewhere changing ohms can change sound...particularly bass response. is that right?



In a sense, yes matching = more volume. When you match, the amp and speakers are running at peak efficiency.

I had to figure this stuff out too a little while ago.. here it is in layman's terms.

Ohm's are a resistance rating. The higher the number the more resistance is applied to the current going through the cable. If the cabs resistance less than the amps, then the cab will pull more current out of the amp than it can safely provide - and you end up blowing the transformer or something.

There is no such thing as 0 ohm... that would be no resistance whatsoever and that's
impossible... I think.
Last edited by 667 at Jul 2, 2010,
#13
yes i know. i edited it, type. i meant 4.

my amp has an phm switch. it can go 4, 8, or 16. standard is 8 stock.

so, if i had a cab that was 4 ohms and i put teh amp switch on 4 ohms....what does that do? match? because regualr is 8. does moving the switch make it match?

also, just in general does a 4 ohm amp, a 8 ohm amp and a 16 ohm amp (same type). so basically does resistance affect sound?
#14
Quote by ikey_
so, if i had a cab that was 4 ohms and i put teh amp switch on 4 ohms....what does that do? match? because regualr is 8. does moving the switch make it match?



You wont hurt anything. When you have a mismatch (only cab ohm higher of course), the system isn't operating at its peak efficiency - less current, less volume. When you match, you get the optimum flow of current to the speaker that the amp is capable of.
#15
Quote by 667
You wont hurt anything. When you have a mismatch (only cab ohm higher of course), the system isn't operating at its peak efficiency - less current, less volume. When you match, you get the optimum flow of current to the speaker that the amp is capable of.

If the mismatch is large enough, bad stuff happens regardless.
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#16
Quote by 667
In a sense, yes matching = more volume. When you match, the amp and speakers are running at peak efficiency.

I had to figure this stuff out too a little while ago.. here it is in layman's terms.

Ohm's are a resistance rating. The higher the number the more resistance is applied to the current going through the cable. If the cabs resistance less than the amps, then the cab will pull more current out of the amp than it can safely provide - and you end up blowing the transformer or something.


this man knows what he's talking about...

things are easy when using one speaker: find a cabinet with matching or higher ohmage. however, if you more ohms on the cab, the volume is gonna drop.

when connecting more than one speaker, it's either gonna be series or parallel. connecting in series (each speaker after the other one) means adding up ohms, which creates big ohmages, which in turn means little volume. therefor most amp to cab connections are parallel (each speaker is connected to the amp). you then needed to use this little formula to know the total impedance:

1 / ((1/ohm speaker #1) + (1/ohm speaker #2) + (1/ohm speaker #3) + ... )

for example, connecting a 4, 8 and 16 ohm cabinet in parallel means you get a total impedance of 1 / (1/4 + 1/8 + 1/16) = 1 / (0,25 + 0,125 + 0,0625) = 1 / 0,4375 = 2,29 ohm.

EDIT: obviously, if you use two 8 ohm speakers, the formule becomes 1 / (1/8 + 1/8) = 1 / 0,25 = 4 which is the same as (ohm per speaker) / (number of speakers) - so better use that formule if all your speakers have the same impedance.


that's about everything I know about it in a nutshell... I like maths and I have to deal with this kind of stuff every summer again
Quote by tubetime86
Most people don't give a shit about tone... We are the exception, not the rule.




I probably am a bit more rule than exception though
Last edited by adriaanwouters at Jul 2, 2010,
#17
Quote by Kanthras
If the mismatch is large enough, bad stuff happens regardless.



Yup. Good point. I sould have added within reason. If you go crazy and start stringing speakers and cabs together in series, bad stuff will happen.
#18
Quote by 667
Yup. Good point. I sould have added within reason. If you go crazy and start stringing speakers and cabs together in series, bad stuff will happen.

Yeah, but the problem is you never really know where the limit of your equipment is until it's too late. :\
Gear:
- Bugera 333
- VJ & VJ cab
- Jackson JS30
- TS9

Bugera Users Militia. We are horrible people. With a sprinkler fetish.
~ BUM: For all things extinguishing

Rackmount Tube Amp Project <<< Updates!
#19
Quote by Kanthras
Yeah, but the problem is you never really know where the limit of your equipment is until it's too late. :\


Agreed,.. when you're building a cab or two - or working on something not spec'd out. He's covered as long as he knows what he's dealing with and follows the rules.
#20
ok. but again, my amp can change between 4/8 and 16ohms. there is a switch.

so if i had an option to pick a setting, is there an advantage to using 4 ohms? is there an advantage to using 8 ohms? 16ohms?

if god could build a setup, what ohms would it be?