Ohm Rating

Chondropython

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I'm looking at cabinets and was trying to figure out how the ohm loads work...

I see that most speakers available are either 8 or 16 ohm. I'm thinking of a 2x12 cabinet, so if I run 2 speakers rated at 16ohms, would that be an 8 ohm load?

Does the ohm rating have an effect on sound?
 

bufbills

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In parallel. Series 32ohms. I cant hear a difference.
 

BrianGT

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I'm looking at cabinets and was trying to figure out how the ohm loads work...

I see that most speakers available are either 8 or 16 ohm. I'm thinking of a 2x12 cabinet, so if I run 2 speakers rated at 16ohms, would that be an 8 ohm load?

Does the ohm rating have an effect on sound?

If you wired them in parallel it would be a 8 ohm load.........if you string them together in series it would be 32 ohm.
 

Chondropython

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So how are some of the 4x12 Marshall cabs that I see available rated at 16 ohms?
 

BrianGT

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So how are some of the 4x12 Marshall cabs that I see available rated at 16 ohms?

Some of their cabs are wired series/parallel to give two different ohmages available depending if you use it in stereo or mono....
Also not all 4x12 cabs use 16 ohm speakers..

There is a sticky at the top of this page that will answer all your questions.
 

bufbills

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Lots of info here. Do a little reading so your questions can be more specific to particular cabs. You will get much better answers. There are different speakers in different cabs. Additionally, there are different build materials, varying in quality.
 

Chondropython

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I am considering a Sourmash 2x12 slant cab that I will use with my Marshall Class 5 head. I would load it with 25W greenbacks.

The class 5 has 8 and 16 ohm speaker outputs... I just thought it was wierd that a 2x12 would have an 8 ohm load when the Marshall 1960AX has 4 of the same speakers and is 16 ohm.

Does Sourmash typically provide all of the jacks / wiring required to install speakers? Also, what about the screws that attach the speakers?

These are probably dumb questions, but I've never used anything but combos, so this stuff is all new to me.
 

Chondropython

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I've looked at the sticky, and now I see where the parallel vs. series wiring changes the ohm load... does series vs. parallel have any difference on the sound? Why would you always just use series to keep the load down?
 

rocknhorse1

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Sourmash provides the mounting screws and installs the "T" nuts used to thread the mounting screws in (they don't screw into the wood).
He will put a jack on, but be specific to what kind you want, otherwise it will just be a single input. He does not wire the cab, and you will likely need to buy wire as well (radio shack).
 

eaglewolf

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So how are some of the 4x12 Marshall cabs that I see available rated at 16 ohms?

Depends on how they choose to wire it and what the rating of the speakers are. I would expect them to use four identical speakers.

Four 4 ohm speakers in series would be 16 ohms. Wired in parallel those same four 4 ohm speakers would be 1 ohm (definitely not recommended for most applications unless the amplifier is designed for that load.)

If you use four 16 ohm speakers, you could wire two pairs in parallel (8 ohms each pair) and then wire the two pairs in series for a total of 16 ohms. You could also wire two pairs in series (32 ohms each pair) and then wire the two pairs in parallel with each other for a total of 16 ohms. Electrically speaking though, I think that is saying the same thing.

If you wired the same 16 ohm speakers all in parallel, you would have a 4 ohm load.

In my Sourmash 2X12, I ordered two 16 ohm Scumback speakers and wired them in parallel for an 8 ohm load.

Confused yet? (Damn engineers! :D ) It is really just about how resistances add up in a circuit. The math is simple if you use identical resistances. It should be noted that with speakers we are really talking about impedance rather than resistance, and that actually varies over the frequency range that is fed to the speaker. But for practical purposes in a guitar amp, that is irrelavant. I checked my 2X12 with a meter and it wasn't exactly 8 ohms, but was close enough that I don't worry about it.

David
 

Chondropython

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Is there any logic behind not having a standard?

If your chosen amp head could run at 8 or 16, would you run two 16 ohm speakers in parallel at 8ohms, or two 8 ohm speakers in series at 16 ohms?
 

Case24

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Is there any logic behind not having a standard?

If your chosen amp head could run at 8 or 16, would you run two 16 ohm speakers in parallel at 8ohms, or two 8 ohm speakers in series at 16 ohms?

It depends on what kind of feel you want. Speakers wired in parellel have more dampening effect on each other and when wired in series they tend to be a bit looser and raw. Not that my stone ears can tell much of a difference mind you. It's a bit like the difference between open back and closed back cabs.
 

hipofutura

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Confused yet? (Damn engineers! :D ) It is really just about how resistances add up in a circuit. The math is simple if you use identical resistances. It should be noted that with speakers we are really talking about impedance rather than resistance, and that actually varies over the frequency range that is fed to the speaker. David

You make an excellent point, David!

Since I have nothing constructive to contribute to this thread, I'll just add to the confusion. I have 16 ohm speakers that have a 7 ohm DCR (normal for these speakers). Very spooky!
 

eaglewolf

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Is there any logic behind not having a standard?

If your chosen amp head could run at 8 or 16, would you run two 16 ohm speakers in parallel at 8ohms, or two 8 ohm speakers in series at 16 ohms?

You could look at it the way I did. Speakers became available at a good price that were 16 ohms each. I didn't want a 32 ohm cabinet, so I wired them in parallel for an 8 ohm load. Since the amp I was building the cab for had 4, 8, and 16 ohm outputs, it worked fine for me. Adding another 8 ohm cabinet would allow me to have either a 16 ohm setup (wiring the 2 cabs in series) or a 4 ohm setup (wiring them in parallel.) I kind of like 8 ohm speakers for some reason, so if I was buying new I would probably have bought the same thing. However, if the used speakers that I found had been 8 ohm speakers, then I would have a 16 ohm cabinet as I would have wired them in series. The nice thing about a higher impedance cabinet is that you stand less of a chance of damaging your transformers by overloading them if you plug into the wrong jack.

As for a standard, different amps have different outputs making a standard difficult. By letting the users choose, you get a more options of what you put together. That said, most guitar amps I've looked at have 4 ohm, 8 ohm, 16 ohm, or some combination of those outputs. So in a way, that is the standard. Whether you hook up your speakers correctly or not is an altogether different matter!

David
 

Chondropython

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Thanks, guys... this has been very educational.

Next stupid question... is there a rule of thumb for sizing you cabinet wattage against the head's wattage? In the short-term, this cabinet will be used with a Class 5, but I plan to buy a 50watt plexi at some point in the not too distant future. I'm debating whether to get this Sourmash 2x12, or just pony up for the 1960AX I really want... Given the low wattage of the class 5, both cabs will be way more watts.... I could go ahead and get the 1960AX now, but would the C5 sound better through a lower wattage cabinet?
 

JakeM

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The quality of a sourmash cab will FAR surpass the quality of a marshall. With the marshall you will be pushing twice as much air as the 212 but I personally love the look and sound of a low 212 setup. Easy and compact but can still sound HUGE.

Jake
 

eaglewolf

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Thanks, guys... this has been very educational.

Next stupid question... is there a rule of thumb for sizing you cabinet wattage against the head's wattage? In the short-term, this cabinet will be used with a Class 5, but I plan to buy a 50watt plexi at some point in the not too distant future. I'm debating whether to get this Sourmash 2x12, or just pony up for the 1960AX I really want... Given the low wattage of the class 5, both cabs will be way more watts.... I could go ahead and get the 1960AX now, but would the C5 sound better through a lower wattage cabinet?

Which cabinet will sound better is a matter of personal opinion, but most here will tell you that a custom built 2X12 (or 4X12 if you prefer) will sound better than the Marshall 1960AX. The currently used Celestion speakers don't get a lot of respect as there are much better speakers available (Scumback, WGS, Weber, etc.) I had an opportunity to buy a 1960 cabinet for about the same as I paid for my 2X12, and it was strongly recommended that I go with the Scumback equipped Sourmash 2X12 cab. I didn't really want a 4X12, but the price was right. I think I'm happier with the choice I made.

There are a couple of ways to go on this. You could just forget about the Class 5 and what is best for it and go with the cab for the Plexi. The C5 will likely sound best with a cab designed for its power rating, but it won't sound bad with something rated higher. The other option is get something that meets your needs now and worry about a cab for the Plexi when you get around to buying one. Often our plans don't work out quite the way we thought they would, or our desires change over time.

As for the rule of thumb of cabinet power vs. speaker rating, the advice normally given for a tube amp is that the speakers should be rated at approximately double the amp output rating or higher. The output ratings of tube amps is typically the clean rating, and most of us drive our amps into overdrive which is putting out much more power than the rated output. So for a 50W Plexi, you would be looking at a 2X12 that has a couple of 50-65W speakers, depending on what the manufacturer you are looking at offers.

In my case, I'm using two 30W speakers for a 35W amp. That's a little on the low side, but I'm also not pushing my amp to its limits at the moment so I should be okay with this setup. I think if I get to the point that I am pushing it I might add a second cabinet to double the rating of the speakers. Note that the output wattage of the amp is split evenly among the speakers if you are using identical impedance on all or your speakers (that's the ohm rating we were discussing earlier, NOT the wattage rating.)

Hope this helps.

David
 

Chondropython

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I see... I actually have a Marshall 1933 1x12 cab laying around... I believe that it has the stock GT12-75 speaker in it. Perhaps I'd better off replacing that speaker with something of lower wattage for use with the C5, and then just ordering a 4x12 cab with the plexi in mind.

I was going to try to use the C5 as a practice amp with my band, but was concerned about it not being loud enough, hence the idea of getting a larger cab for it.

Is there a particular speaker of the ones you mentioned above (i'm not familar with any of them other than I've read the name on MLP before) that have the oldschool greenback vibe to them?
 

eaglewolf

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Honestly, I'm not that familiar with the Greenback sound. However, all of the manufacturers mentioned make a clone of that speaker.

I was just listening to some clips of the WGS Reaper and Green Beret that sounded quite good. The Green Beret is WGS' version of the Greenback according to the video. Consider the Reaper if you want more bottom and top end and the ability to cut through the mix. (I'm parroting what the video said, but it sounded right from the clip.) WGS has got to be one of the great values in speakers by the way.

Check out the video on the http://www.mylespaul.com/forums/squawk-box/149656-corona-speaker-search.html thread in the Squawkbox. Scumback and Weber have versions of that speaker as well.

There are others much more qualified to answer your questions that will probably add their thoughts.

David
 

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