# 4ohms and 8ohm question



## LaRSin (Nov 27, 2006)

My amp is say's 200 watts at 4 ohms Can I use my extension cab which is (100 watt)1x12 at 8 ohms without hurting either one??

http://guitarscanada.com/Board/showthread.php?t=25408


----------



## Wild Bill (May 3, 2006)

LaRSin said:


> My amp is say's 200 watts at 4 ohms Can I use my extension cab which is (100 watt)1x12 at 8 ohms without hurting either one??
> 
> http://guitarscanada.com/Board/showthread.php?t=25408


You didn't tell us anything about what kind of amp! It makes a BIG difference!

First of all, your amp's 200 watt @ 4 ohms rating means that it can deliver up to 200 watts into a 4 ohm load. If it is a solid state amp (transistors) it will deliver somewhat less as a maximum into an 8 ohm load and even less into a 16 ohm load.

A tube amp is different. It should deliver a maximum of 200 watts into 4,8 or 16 ohms, as long as the settings are the same. So if it has an 8 ohm output and you plug in an 8 ohm cabinet, you will still get a maximum of 200 watts.

The rating of a speaker cab means the maximum it can take without blowing up! So if your amp is cranked and puts more than 100 watts into the speaker cab it will likely get hot and eventually blow. The mismatch of an 8 ohm cab and the 4 ohm 200 watt rating doesn't help you much, as it's not easy to predict exactly how much less the amp will deliver into 8 ohms as 4 ohm. It will likely still be more than 100watts, which is the max rating of yor 1-12 cab.

"Do ya feel lucky, punk? Well, do ya?" ---Clint Eastwood.

:food-smiley-004:


----------



## LaRSin (Nov 27, 2006)

Wild Bill said:


> You didn't tell us anything about what kind of amp! It makes a BIG difference!


It's in the link
But here it is .. Old solid state...
*1970's Traynor Group 3 VC Amplifier*

I just got this given to me tonight and wanted to know if you guy's had any info on it, All I could find on google was it's 120 watts,

It's is working ,, the volume knob crackles a little when turned and the reverb doesn't seem to work (unless it needs the foot switch), The amp work's great when I hooked up my GT-8 ,

Also my cab is 8 ohms (Crate GT112SL 1x12 Guitar Cabinet) and the amp says 4 ohms , will this hurt either one if I use it that way ??


----------



## LaRSin (Nov 27, 2006)

this is the only think I find on google:

*1975*

Work had progressed slowly on the grant-funded research Jack initiated in 1971. Even though the project
involved guitar amps which are inherantly far from technology-prone, Yorkville needed to tackle that issue
successfully while keeping government grant inspectors happy about the level of “Innovative Technology”. The
government said, “No tubes in the design”. No problem - the lab used MOSFETs, new solid-state devices which
were alleged to perform like tubes. They said, “No passive tone control circuits.” Again, no problem - the lab
designed active tone circuits including the semi-parametric type found on recording mixers.
Dirk Vandersleen, despite interruptions to design several products, had managed to work on the project’s
electronic designs from time to time and in the Spring of 1975, it looked like he was through. Engineer George
Jung had come up with chassis/case designs inspired somewhat by the Mono Block in that they were all
aluminum but less massive, and the government engineers were very pleased at how “innovative” everything
was. Even the top and bottom plate fasteners were far-fetched. Instead if screws, 2-part plastic hammer-in pegs
were used which required two screwdrivers to pry out (repairmen would not be amused).
The remaining details to be worked out were cosmetics and a name for the line. Four people including Jack Long
were directly involved either overseeing or designing the products (Pete Traynor was not among them) and a
whole group of people had been involved as advisors, so it was decided that they should be called the Group
Series.
There were six heads, five cabinets and a twin-twelve combo. Everything was divided into power groups - Group
One was fifty watts with green control panels, Group Two was 100 Watts with blue control panels and *Group
Three was 120 Watts with yellow control panels*. As mentioned before, the amps featured active tone controls. No
guitar amps then on the market had this feature - few if any do, even to this day; guitar amps historically feature
passive tone controls. Consequently, no-one had ever plugged into an amp that worked like these. And, just to
make the experience more memorable, some of these controls were semi-parametric.
“Semi-parametric”? Yes. All the amps in Group One and Two had a mid control associated with a “shift” knob and
a switch to designate the range of frequencies in which the shift knob operated. For those familiar with recording
mixers, “shift” was simply another word for “sweep”. For the unannointed, these are features which alter the
center frequency of an active tone control. For example, the midrange control on a regular guitar amp tends to be
very roughly centerd around 500Hz. In an active EQ circuit such as this, the center frequency is (a) more defined,
(b) able to make a peak as well as a notch in the frequency response (passive midrange controls can only make a
notch) and (c) capable of being swept or “shifted” across the audio band making very serious changes in the
sound.
But that wasn’t all. When you set such a midrange control up or down, then “shift” it while someone is playing
through the amp, you get a sound effect. Boost the mid then shift it and it sounds like a wah-wah, cut it and the
sound is a little like a phaser. Of course you can’t twist a shift knob and play too so, on the Group Two VC guitar
head (VC standing for voltage-controlled filter which is how the shift circuit worked in all these amps), a “shift
pedal” jack was installed. This would work with any volume pedal as long as the potentiometer was 100K linear.
Now you could just plug in a volume pedal, turn the mid up or down, set the range switch to low (300Hz to
1200Hz), mid (700Hz to 2500Hz) or high (1200Hz to 5000Hz), then play and work the pedal to shift. Fun, but
confusing.
Then there was the tremolo. This wasn’t the ordinary “pull-pull” type where it repeatedly reduces the gain then
lets it go back up to normal, this was a “push-pull” tremolo with the gain going as far above normal as below
normal. Why such a thing? So that the tremolo could operate the voltage-controlled “shift” function (egad). Indeed,
there was a switch marked “Auto-Shift/Tremolo” which let you run the shift effect on automatic via the tremolo
oscillator. Then you could preset everything and switch it on or off with the tremolo footswitch. Innovative, but
confusing.
Note: for people who have a Group 2VC or 3VC and have trouble getting the auto shift to work, experiment with
different shift control settings. The shift control has an effect on this automatic function. A resistor inside might
also need changing. Have a technician check it out.


----------



## greco (Jul 15, 2007)

I tend to always want to avoid impedance mismatch along with speaker ratings that are too low (and I play at low volumes with tube amps). 

I like to sleep well at night.

What is the maximum power rating for your 1 x 12? Usually, AFAIK, these ratings are usually *a bit *on the conservative side...but 200 watts is one h*ll of a lot of power

Do you like to run your amp loud? ...I mean VERY loud!
You might want to avoid turning it up...until you have more information Re: the power rating for the speaker.

Maybe I'm wrong here...just hate to see you blow your speaker (as Wild Bill has already indicated)

Cheers

Dave


----------



## Big_Daddy (Apr 2, 2009)

From Shavano Music Online:

All speakers have a rated "impedance," which is not quite the same thing as electrical "resistance" although they are allied concepts like, say, velocity and acceleration. There are discussions, charts, and even a little calculator on this site that will tell you what the "impedance" of a given combination of speakers, wired in a certain way, will be. For our purposes, let's just think of a single speaker hooked to a single amp. The speaker's voice coil presents a certain electrical resistance to the amplifier, measured in ohms, because it has a coil of fairly thin wire (the voice coil) that current passes through, like trying to pump the contents of a swimming pool through a piece of aquarium hose - the physical limitations introduce resistance to free movement of electrons. Then the magnetic fields created by the current interact with the fixed magnet structure and move the cone or diaphragm around, which also takes some effort (in the form of physical resistance, from the cone mass, its "surround" or suspension and the resistance of the air it's trying to move). The actual "impedance" a speaker presents to the amplifier depends on both of these things and varies with frequency. The "nominal" impedance of a speaker is not supposed to dip more than 20% over the covered frequency range - that is, an 8-ohm speaker probably doesn't present less than 6.4 ohms at any point, although it may rise to many times that at other points. If you measure the electrical resistance of an "8 ohm" speaker's voice coil with an ohmmeter, you'll probably get a result of six-point-something. 

Impedance is important mostly because amplifiers expect to be pushing speakers within a given impedance range, for electrical reasons beyond the scope of this discussion. *If they "see" greater impedance, they simply put out less power. If they "see" impedance that's too low, they can try to put out more power than they are designed for, which heats a lot of expensive amp parts past their capabilities and can burn them up. *

Whether a power amplifier (or the power-output section of an integrated or "combo" amplifier) can handle a low-impedance load of 4 ohms, or even 2 ohms, is generally a function of the ruggedness of its design and resistance to overheating. Amps that will handle low-impedance loads at high wattage levels are almost always fan-cooled and weigh as much as your average Volkswagen. If the amp manufacturer is reputable, they will publish ratings that tell you the minimum safe speaker-impedance load, and the amp's wattage output into various loads at and above that figure. In selecting an amp in the first place, you want "RMS" ratings, which are a true indication of power output, and not "peak" or "PMPO" or "transient" ratings, which for some manufacturers are just a handy way of lying to you. Amp and speaker makers catering to the DJ market are known for this, touting a low-power design as "1000 watts" because it can reach that level at a certain frequency, for a millisecond, on a very cold Tuesday. They are more honest than the car-stereo ratings, but only by a little bit. A true "RMS" rating tells you what the amp can do on a warm day in Dallas, over the span of a four-hour gig, and over the entire range of frequencies. 

So, let's say you have an amp rated to deliver a true 200 watts RMS at 8 ohms. If you drive an 8-ohm speaker rated at 20 watts with this amp, and turn it up gradually, it will get louder and louder. Then at some point it will not get much louder and the sound will become progressively more distorted. Eventually it will stop working altogether, although the burned-out speaker may emit a wisp of smoke (you can smell this when it happens). You have deformed and/or melted the voice coil from the buildup of heat within the speaker. Your speaker is now magically transformed into a doorstop.

Now let's take the inverse, an amp rated at 20 watts RMS, and a speaker rated at 200 watts RMS. Doing the same destructive testing, the speaker gets louder and louder, and then again starts to distort. But this time it's not the cone excursion, or the buildup of heat in the voice coil, that's causing the distortion. Instead, it's bad stuff happening in the output stage of the amplifier, and it's a tossup whether your speaker gives up first, from trying to reproduce the "clipped" or horribly distorted sound, or whether your amplifier simply experiences a meltdown. In the amp-speaker mismatch I've just described, I'd look for the fatal wisp of smoke from the amp. Now your amp is the doorstop.

At low volumes, either sort of amp-speaker mismatch is OK, because you're operating within the capabilities of the weakest link. It's when you crank things up that you want to be sure the amp and speaker are a reasonable match for each other. It's OK, probably even desirable, for your amp to be capable of greater output than your speaker can handle, because that helps forestall amp clipping and overheating in what is almost always the more expensive component of the two. You just won't be able to set the amp at full throttle without risking your speaker(s). The overcapacity of the amp in this situation is sometimes called "headroom," but then so are a lot of other completely unrelated electro-acoustic relationships, so forget I said that. It's also OK for your speakers to be able to handle greater power than your amp can put out, assuming a proper impedance match, but again don't expect to run your amp wide open without risking damage to its internal organs, or at least distorted sound. Since you're not thinking about amp-speaker matching in the middle of a gig when you decide that the proper execution of a particular song demands that it be painfully loud, I'd advise designing a little safety into the system by making sure the amp can handle the speakers and vice-versa.


_The bold text refers to your concern. Hope this helps.

"Older legends say that tube amplifiers can drive lower impedances than their rating demands. So a tube amp with a label saying "8-ohm" may drive 4 and 8 ohms. You can go down but not up. Don't try 16 ohms. And never run a tube amplifier without speakers attached."

bd_


----------



## greco (Jul 15, 2007)

Big_Daddy said:


> .........
> *At low volumes, either sort of amp-speaker mismatch is OK, because you're operating within the capabilities of the weakest link. It's when you crank things up that you want to be sure the amp and speaker are a reasonable match for each other. *It's OK, probably even desirable, for your amp to be capable of greater output than your speaker can handle, because that helps forestall amp clipping and overheating in what is almost always the more expensive component of the two. You just won't be able to set the amp at full throttle without risking your speaker(s). The overcapacity of the amp in this situation is sometimes called "headroom," but then so are a lot of other completely unrelated electro-acoustic relationships, so forget I said that. It's also OK for your speakers to be able to handle greater power than your amp can put out, assuming a proper impedance match, but again don't expect to run your amp wide open without risking damage to its internal organs, or at least distorted sound. Since you're not thinking about amp-speaker matching in the middle of a gig when you decide that the proper execution of a particular song demands that it be painfully loud, I'd advise designing a little safety into the system by making sure the amp can handle the speakers and vice-versa.


The above (portion) was my thinking also...however, written in more detail and clarity. 
*Thanks Big_Daddy (for the entire post)*

Save yourself the agony of worry...find yourself a new speaker with the proper specs...you got the amp at the best price possible...correct? ("given to me")

Cheers

Dave


----------



## LaRSin (Nov 27, 2006)

just a thought , do you think it could 120 watts into 8 ohms ??

The history on them does mention 120 watts..

Grasping at straws here :sport-smiley-002:


----------



## Wild Bill (May 3, 2006)

LaRSin said:


> just a thought , do you think it could 120 watts into 8 ohms ??
> 
> The history on them does mention 120 watts..
> 
> Grasping at straws here :sport-smiley-002:


Let's put it more simply, LaRSin. 

You have an amp which can put out way more power than your speaker cab is rated.

You can use that speaker cab and keep the volume control down. It will probably be ok.

However, if ever you give in to temptation and crank up that volume control you will probably blow your speaker cabinet up!

Putting 200 watts of loud power into something that is rated for only half of that is not likely to work.

It's up to you!

:food-smiley-004:


----------



## GTmaker (Apr 24, 2006)

seems like the right thread for this question...

I never hear about a speaker's wattage (power handling) as it pertains to the total ohms it is connected to.

let me explain.
1 speaker rated for 45 watts and is 16 ohms..
The assumption here is that it can handle 45 watts of power.

Lets take 2 of these speakers and wire them up in paralel.
The total ohms now is 8.

Question...are the 2 speakers still only handling 45 watts max.?

any input is good.


----------



## Big_Daddy (Apr 2, 2009)

GTmaker said:


> seems like the right thread for this question...
> 
> I never hear about a speaker's wattage (power handling) as it pertains to the total ohms it is connected to.
> 
> ...


I believe it depends on the power output of the amplifier. Each speaker would receive half of the amplifier's 8-ohm power. If you used a 100-watt amp with an 8-ohm speaker out, each speaker would receive 50 watts of power at peak volume.


----------



## greco (Jul 15, 2007)

GTmaker said:


> seems like the right thread for this question...
> 
> I never hear about a speaker's wattage (power handling) as it pertains to the total ohms it is connected to.
> 
> ...


This is an interesting question...bump to the top for some more responses.

Cheers

Dave


----------



## Wild Bill (May 3, 2006)

GTmaker said:


> seems like the right thread for this question...
> 
> I never hear about a speaker's wattage (power handling) as it pertains to the total ohms it is connected to.
> 
> ...


First, forget about the ohms. If a speaker is rated at 45 watts maximum then that's the most power you can safely drive into it. Drive it harder and you run the risk of blowing it up.

Now, a speaker can be rated at 45 watts. It can be a 4, 8 or 16 ohm speaker. It doesn't matter what ohms it is. It still is rated for a maximum of 45 watts.

Put 2 speakers together, both being the same ohms. It can be (2) 4 ohm, (2) 8 ohm or (2) 423.997 ohms. It doesn't matter. Put them in series or put them in parallel. Two speakers of equal ohms will share the power equally.

If one speaker can handle 45 watts then two speakers of the same type together can handle a maximum of 90 watts.

Hope this makes it clear.

:food-smiley-004:


----------



## greco (Jul 15, 2007)

Wild Bill said:


> If one speaker can handle 45 watts then two speakers of the same type together can handle a maximum of 90 watts.
> 
> Hope this makes it clear.
> 
> :food-smiley-004:


This was going to be my response (honestly...LOL)
...I just wasn't 100% sure.

Cheers

Dave


----------



## Big_Daddy (Apr 2, 2009)

That is essentially what I was saying (I think). :smile:


----------



## Vintage_Groove (Mar 4, 2008)

I ended up picking up a Bass amp that is rated 200w @ 4 ohms. Later I picked up 2 used Bass cabinets, a 2x10 rated 400w @ 4 ohms, and a 1x18 rated 400w @ 8 ohms. 

Problem was I can't run both cabs at a nice volume thru the amp. So what I did was get a pure power amp rated for 2, 4 and 8 ohms on 2 separate channels. So now I run the Bass amp into the pure amp which powers both cabinets separately. It works great.


----------



## Jim DaddyO (Mar 20, 2009)

This is all from "what I heard/understand" so if there are errors please set me straight.

-Tube amps are more forgiving to impedance mismatches while transistor amps only like what they are rated for.

-You can put lower wattage speakers with your amp, just don't turn it up or you risk blowing the speakers.

-Add up the power rating of similar speakers for the power handling rating (ex. a 4x10 cab with 25 watt speakers will handle a 100 watt head)

-If you use hugely over rated speakers (100 watt speakers and a 15 watt amp) on a transistor amp and crank it full out, you risk the amp going into DC feedback and blowing the amp (really foggy on this one)

Am I correct?


----------



## Wild Bill (May 3, 2006)

Jim DaddyO said:


> This is all from "what I heard/understand" so if there are errors please set me straight.
> 
> -Tube amps are more forgiving to impedance mismatches while transistor amps only like what they are rated for.
> 
> ...


All except the past point!

It's true that if you crank up a small transistor amp THAT IS POORLY DESIGNED it will distort and generate clipped waves. Clipped waves will have a higher average power out than nice sine waves.

If you have speakers that are only a bit higher rated than the maximum rating of that cheapo transistor amp it's possible that you can blow them.

However, there is no way in hell that a supply capable of only 15 watts can blow a device that is rated for 100 watts! So having a 15 watt crapola amp blow 100 watt speakers is just stretching things WAY too far!

This idea has been around so long that it is almost an urban myth. It started back when we first started seeing transistor amps. Some cheapo manufacturers cut things too fine with the ratings of their speakers. What's more, many of those amps would blow up easily anyway. When they did the circuit would allow the full DC power from the power supply to flow through the speakers, blowing them. 

Salesmen at hifi stores needed a line of BS to handle angry customers so they started misapplying the idea of excessive power spikes from an amp driven into clipping as the reason the speakers blew. In effect, they made the customer feel it was HIS fault! At that point the customer usually slunk away and the store was off the hook.

I should point out too that in the hundreds of years that this old, old man has been around in electronics I've NEVER actually seen speakers blown up because of using too small an amp and driving it into clipping! Hifi stores still spread this idea 'cuz it sells bigger amps!

:food-smiley-004:


----------



## Rugburn (Jan 14, 2009)

When Fender unveiled their "Zodiac" series apparantly *ALL* the models they brought to the trade show died on their first day. Something like eight in total. Eventually leading the sales people to state that they were "show" models and couldn't be played.


----------



## GTmaker (Apr 24, 2006)

first of all, thanks to all that responded to my question....

on another but related note....

my Fender Bassman LTD has 4 10" speakers ( we all know that)
I believe these speakers are rated at 25 watts each.
My simple math tell me that these speakers as a group should handle 100 watts.

Question.
Why would Fender match these speakers with a 45 watt head?

Personaly, I believe that speakers should allways have plenty of head room above the rated amplifier but thats just me.

more light is needed on this subject.


----------



## Wild Bill (May 3, 2006)

GTmaker said:


> first of all, thanks to all that responded to my question....
> 
> on another but related note....
> 
> ...


Well, you have to understand, when you make guitar speakers it can actually be cheaper to use a standard 25 watt speaker than to make a custom one rated at 12.5 watts. The materials involved may result in a speaker that will handle at least 25 watts anyway!

A speaker's power rating is not a simple thing. You have a voice coil made of small gauge wire, suspended in a magnetic field and fastened to a cone. The gauge of the wire can only handle so much current. The wiring in your walls uses 14 ga. wire and is rated for 15 amps. Voice coil wire might be rated for only an amp or two. 

This might be derated somewhat, since it doesn't blow quickly like a fuse. What happens is that the wire heats up. The style of the speaker influences ventilation, which affects how fast that heat is dissipated. The mechanical stress of working against the magnet and in actually moving the cone adds a bit of heat. Enough heat and the wire melts or blows.

The style of music is also a factor. A lot of dynamic range and soft passages following loud ones allows the voice coil wire to get rid of some of that heat.

So when someone makes a speaker they have a great deal of leeway in how they set the rating. Companies like Eminence or Weber will pump power into a speaker model until they actually blow it! They will abuse the poor thing terribly, trying to get a conservative idea of how much power the typical player can put through that speaker. With these guys, you can safely put a 100 watt speaker with a 100 watt amp and not worry if the amp has spare power beyond its published ratings.

A speaker made by Kung Fooey Looey Off Shore Speaker Emporium might not have the same conservative power rating.

It's important when thinking about such things to not get too anal retentive. Someone without much technical background can be rather smart in their thinking and come up with something absolutely loopy. This is because technical things have technical factors. You need to maybe open a book and get a grasp on some of the basics. Your mind can extrapolate complicated reasoning from what are initially vague ideas. It will sound logical but be completely wrong, since you didn't know enough in the first place.

Long ago I was a construction inspector and continually ran into government inspectors waving rule books that they didn't understand. They would be making decisions based more on the english grammar of the rules than the original engineering intent.

There are balconies in Hamilton that to this day I refuse to walk on!

I also had a spell as a cable tv installer. Since we ran our main lines on Bell telephone poles they had the right to inspect our work. Many of their rules were simply stupid! For instance, the rules called for the cable wire to be grounded at the house. We had often put a copper strap around an outside water faucet for a garden hose. One day some Bell inspector banned the practice. The rule book said that any such water pipe must be one that had a continuous flow of water through it. This was to ensure that no one grounded to a scrap piece of pipe that perhaps was left over from an old plumbing setup and wasn't connected to anything any longer. Bell's new head inspector read this to mean that since most garden hose faucets had a shut off valve in the basement if the valve was shut there would no longer be water flowing to the faucet outside! So we had to run our ground wire into the basement and put our ground strap on the pipe BEFORE the cutoff valve!

Even a layman would know that the electrical ground is through the metal of the pipe and not the water. Whether the shut off valve was cranked open or closed had SFA to do with the electrons running to ground!

What's even sadder is that electrically it is good practice to make ground wires as short as possible. To satisfy this Bell Telephone English major/electrical inspector meant longer ground wires.

A good friend of mind once remarked way back in the early 1980's something that I've never forgotten. He said "As a society things keep getting more and more complicated, yet society itself keeps getting less capable of handling it!"

Geez, all those atom bombs, space shots and not enough people in church on Sunday! Where's it all gonna end?

:food-smiley-004:


----------



## Big_Daddy (Apr 2, 2009)

HaHa! Great post!


----------



## Rugburn (Jan 14, 2009)

GTmaker said:


> first of all, thanks to all that responded to my question....
> 
> on another but related note....
> 
> ...


The speakers in the Bassman are reissues of the Jensen P10R. Vintage speakers of this size generally didn't handle more than 30 watts. In an effort to deliver clean tones at higher volumes, Fender used four 10 inch speakers. Vintage style speakers distort easily compared to modern ones. This configuration ensured that speaker distortion would be at a minimum. 

Shawn


----------



## GTmaker (Apr 24, 2006)

"Geez, all those atom bombs, space shots and not enough people in church on Sunday! Where's it all gonna end?"

A tiny microscopic virus that we have no cure for.
I am convinced thats how it will all end for us.


Thanks again for those great posts Wild Bill. They are worth the price of admission.


----------



## bzrkrage (Mar 20, 2011)

GTmaker said:


> A tiny microscopic virus that we have no cure for.
> I am convinced thats how it will all end for us.


When did you edit this? 2009? Oh mighty Prophet!!!


----------

