Converting 16 ohm Cab to 4 ohms power or sound quality loss????

[andyJB]

I have a new Marshal 425A 4X12 cab with 16 ohm Celestian Greenbacks. My Mesa Amp (Express 5:25) only has 3 outputs. 1 x 8 ohm and 2 x 4 ohms.

Obviously (mathamatically) I cannot turn my amp into an 8 ohm box but I can link all 16 ohm speakers in Parallel to make it run at 4 ohms.

What I want to know is will running the box in Parallel at 4 ohms effect my power output of the speakers (currently 100 watts combined) and will it have an effect on the tone (sound quality).

Will a Mesa 5:25 at 4 ohms run a 4 x 12 4 ohms well?

 

[Victory Pete]

Your power rating will be the same, 100 watts. The tone of the cab could change. Apparently it will even change if you rewired it but kept the 16 ohms. I found this out a while ago. There are 2 ways to wire a Marshall cab with 4 16 ohm speakers to get 16 ohm total. 2 speakers in series in parallel with 2 speakers in series, that is how most cabs are. You can also have 2 parallel speakers in series with 2 speakers in parallel. I am not sure what your new tone will be, it has something to do with the damping. I think speakers all in series will have more tighter response, whereas the speakers in parallel will be a little looser response.
Victory Pete

 

[Outlaws]

Your power rating will be the same, 100 watts. The tone of the cab could change. Apparently it will even change if you rewired it but kept the 16 ohms. I found this out a while ago. There are 2 ways to wire a Marshall cab with 4 16 ohm speakers to get 16 ohm total. 2 speakers in series in parallel with 2 speakers in series, that is how most cabs are. You can also have 2 parallel speakers in series with 2 speakers in parallel. I am not sure what your new tone will be, it has something to do with the damping. I think speakers all in series will have more tighter response, whereas the speakers in parallel will be a little looser response.
Victory Pete

I seriously hope you meant this....
2 speakers in series, with another set in series, parallel to the first set.

2 speakers in parallel, a series speaker on each of those.

Because that is the exact same thing.

There is only one way to get 16ohms out of a 412 cab loaded with 16ohm speakers.

 

[ggunn]

I seriously hope you meant this....
So, 2 speakers in series, with another set in series, parallel to the first set?

Or, 2 speakers in parallel, a series speaker on each of those?

Because that is the exact same thing.

There is only one way to get 16ohms out of a 412 cab loaded with 16ohm speakers.

Well, a series-parallel hookup is different topologically from a parallel-series circuit. They are indeed equivalent, however, in terms of overall impedance and the way the power is shared among the speakers.

 

[ranjam]

Oh, oh! This is going to be one of those 'Just because you can't hear grass grow doesn't mean I can't' pissing contests, isn't it?

 

[andyJB]

Oh, oh! This is going to be one of those 'Just because you can't hear grass grow doesn't mean I can't' pissing contests, isn't it?

I dont think the question should be too dificult to answer. Either it will have an effect on sound (tone) or it will not. Its a pretty black and white question that someone with some technical knowledge of speakers should be able to answer.

 

[andyJB]

Your power rating will be the same, 100 watts. The tone of the cab could change. Apparently it will even change if you rewired it but kept the 16 ohms. I found this out a while ago. There are 2 ways to wire a Marshall cab with 4 16 ohm speakers to get 16 ohm total. 2 speakers in series in parallel with 2 speakers in series, that is how most cabs are. You can also have 2 parallel speakers in series with 2 speakers in parallel. I am not sure what your new tone will be, it has something to do with the damping. I think speakers all in series will have more tighter response, whereas the speakers in parallel will be a little looser response.
Victory Pete

Thanks for the answer but I do not want to run it in 16 ohms, I want to run it in 4 ohms.

 

[Harvey Gerst]

Lemme try to explain it:

Think of each 16 Ohm speaker as a light bulb that draws 25 Watts. If you hook up two in parallel and put it across the amp's 4 Ohm output, it'll draw 50 watts - 25 watts to each speaker. 4 speakers in parallel will draw the full 100 watts since the load is now the same as the amp - 4 Ohms. Each speaker will pull 25 watts from the available 100 watts.

As a bit of enlightenment, let's also look at the two ways of hooking up 4x12, 16 Ohm speakers to a 16 Ohm output:

The choices are Series/Parallel or Parallel/Series. If you put two 16 Ohm speakers in Series, you get 32 Ohms. You'll get about 1/2 the output of the amp into that load (about 50 watts). Put another bank of two 16 Ohm speakers (also wired in series) in parallel with the first bank, and that get the other 50 watts - 25 watts per speaker, total.

If you put two 16 Ohm speakers in parallel, you get 8 Ohms. That will increase the output of the amp into that load, but the amp won't like it.. Put another bank of two 16 Ohm speakers (also wired in parallel) in series with the first bank, and that will raise the total to 16 Ohms. Back to our 25 watts per speaker total.

Is there a difference in the sound between a 4 Ohm load and a 16 Ohm load? Yes, the damping at the amplifier's transformer will be changed. That subject is too vast for a small discussion thread here. That's a BIG can of worms.

 

[Victory Pete]

Thanks for the answer but I do not want to run it in 16 ohms, I want to run it in 4 ohms.

Yes I know, And you can. I think you already know how to wire it that way. And your tone will probably change. It will even change if you rewired it for the same 16 ohm imedence. I was pointing out how there is more than one way to wire 4 speakers for the same impedance. I hope this helps.
VP

 

[andyJB]

Lemme try to explain it:

Think of each 16 Ohm speaker as a light bulb that draws 25 Watts. If you hook up two in parallel and put it across the amp's 4 Ohm output, it'll draw 50 watts - 25 watts to each speaker. 4 speakers in parallel will draw the full 100 watts since the load is now the same as the amp - 4 Ohms. Each speaker will pull 25 watts from the available 100 watts.

As a bit of enlightenment, let's also look at the two ways of hooking up 4x12, 16 Ohm speakers to a 16 Ohm output:

The choices are Series/Parallel or Parallel/Series. If you put two 16 Ohm speakers in Series, you get 32 Ohms. You'll get about 1/2 the output of the amp into that load (about 50 watts). Put another bank of two 16 Ohm speakers (also wired in series) in parallel with the first bank, and that get the other 50 watts - 25 watts per speaker, total.

If you put two 16 Ohm speakers in parallel, you get 8 Ohms. That will increase the output of the amp into that load, but the amp won't like it.. Put another bank of two 16 Ohm speakers (also wired in parallel) in series with the first bank, and that will raise the total to 16 Ohms. Back to our 25 watts per speaker total.

Is there a difference in the sound between a 4 Ohm load and a 16 Ohm load? Yes, the damping at the amplifier's transformer will be changed. That subject is too vast for a small discussion thread here. That's a BIG can of worms.

Thanks Harvey, most of that information is basic electronics which I actually understand quite well. I didnt communicate my question as well as I could have (or some peoples interperetation of my question is different to what I asked (my fault)) so here goes again.

I will rewire my Cab so it runs at 4 ohms. By wiring up all four 16 ohm speakers in parallel I can turn the 4X12 cab into a 4 ohm cabinet. This is a pretty easy modification that pretty much anyone with a pair of wire cutters and a bit of extra cable can do in about 15 minutes.

This will make my newly rewired 4 ohm cabinet match the 4 ohm output of the Mesa amp (which only has a 4 or 8 ohm output jack).

OK so I will have a 4 ohm output from the amp going into a 4 ohm speaker cabinet (which is 4 x 16 ohm speakers wired in paralell) basic elecronics.

Now here is the question again to all. "What I am trying to establish is if I do the above will there be a difference in sound (ie TONE) between a 4 X12 (16 ohm speakers wired in Parallel to make 4 ohms) and a 4X12 (16 ohm speakers wired in Series Parallel to make 16 ohm) ?????????

What is the actual difference in Tone between these 2 options (A4x12 wired at 16 ohms and a 4x12 wired at 4 ohms)????? Is one fat and loud and one soft and skinny etc... I am trying to establish the difference in plain english that I can understand. It cant be that hard people.

Has anyone actually done this before.

 

[ocnor]

I will rewire my Cab so it runs at 4 ohms. By wiring up all four 16 ohm speakers in parallel I can turn the 4X12 cab into a 4 ohm cabinet. This is a pretty easy modification that pretty much anyone with a pair of wire cutters and a bit of extra cable can do in about 15 minutes.

Go ahead and wire it up and see if you like it. What do you have to lose but a half hour of your time. You've already spent more time here trying to explain it than it would have taken to just rewire it. That's the only way to establish whether you will notice a difference or not.

 

[ggunn]

What is the actual difference in Tone between these 2 options (A4x12 wired at 16 ohms and a 4x12 wired at 4 ohms)????? Is one fat and loud and one soft and skinny etc... I am trying to establish the difference in plain english that I can understand. It cant be that hard people.

Oh, OK; I can answer this one. The answer is: You might hear a difference and you might not. It has as much to do with your amp's design as it does the speakers, and if it makes a difference you can hear, you might like it and you might not.

 

[Harvey Gerst]

Now here is the question again to all. "What I am trying to establish is if I do the above will there be a difference in sound (ie TONE) between a 4 X12 (16 ohm speakers wired in Parallel to make 4 ohms) and a 4X12 (16 ohm speakers wired in Series Parallel to make 16 ohm) ?????????

What is the actual difference in Tone between these 2 options (A4x12 wired at 16 ohms and a 4x12 wired at 4 ohms)????? Is one fat and loud and one soft and skinny etc... I am trying to establish the difference in plain English that I can understand. It cant be that hard people.

Putting a 16 Ohm load on your Mesa amp (on the 8 Ohm tap) will reduce the output of the speakers. The damping factor will go up a bit and the sound will probably be a little tighter, but thinner. Using the 4 Ohm tap on the Mesa to power a 16 Ohm load is NOT a good idea.

Putting a 4 Ohm load on your Mesa amp will give you maximum output, and you should hear a slightly rounder and fuller sound.

 

[ranjam]

What I was almost jokingly referring to was the Gerald Weber syndrome where he can hear a difference in a 4 x 12" cabinet with all 8-ohm speakers, and using the 8-ohm tap on the amplifier, if you wire the cabinet in series-parallel or parallel-series . But then again, he hears a difference in a single speaker amplifier when you reverse the phase of the speaker wiring. Apparently, a 'forward-playing' amplifier sounds different. But mismatching the OPT tap to the load is as old as the hills. You change the damping, the reflected impedance, and slightly alter the frequency response. With a good amplifier design and good tubes, I'd say try it and decide what you like. But with some Marshalls, and Sovtek tubes, it's a perfect storm for a free light show. I've rewired my own 16-ohm cabinets down to 4-ohms many times, since say a JCM800 had no 16-ohm output tap. The cabinet, the amplifier, and me myself have lived long and fruitful lives.

 

[MajorTom]

Going to 4 ohms - I personally don't think it should make more than a subtle difference at best, as far as what the cab sounds like. With a differenct head, it is going to sound a lot different anyway. It is perfectly "kosher", and should sound fine. The main thing is that you make sure all 4 speakers are in -phase, that the center conductor of the jack goes to the left speaker lug on all 4 (or right lug, it doesn't matter), and the shield conductor goes to the other lug.

At the amp - when you set the impedance lower, like to 4 ohms from 8, what happens is that some extra windings in the output transformer are engaged, to compensate for the lower speaker impedance. It isn't a "compromise" or anything, just a scheme to match the impedance of the amp to the speaker. Yes, an extra few windings on the output tranny will introduce more inductance, but of course, conversely, there will be less inductance in the speaker load.

Speaker wattage - a speaker's wattage is a rating of how much wattage it can handle from a heat dissipation standpoint. The amount of heat generated is proportional to output from the amp. It is not a rating of how much power a speaker will "draw", or at what point it will break up, or other things you sometimes read on the net. Whether wired as a 16 ohm cab or a 4 ohm, their ability to dissipate heat is the same. Your amps' output will be the same at 4 or 8 with the rated load.

 

[ggunn]

But then again, he hears a difference in a single speaker amplifier when you reverse the phase of the speaker wiring. Apparently, a 'forward-playing' amplifier sounds different.

Color me skeptical. What does he do with an amp like lots of Fenders where the normal channel is reverse polarity from the vibrato channel? He and Eric Johnson would have a lot to talk about...

 

[andyJB]

Thanks to all of you guys for your answers. The last 4 responses nailed it and gave me the info that I wanted.

Best Regards from Australia. Andy

 

[MajorTom]

Color me skeptical. What does he do with an amp like lots of Fenders where the normal channel is reverse polarity from the vibrato channel? He and Eric Johnson would have a lot to talk about...

Yes, what is "correct" phase anyway? Each preamp tube stage reverses phase, so a 3 stage preamp is reversed, a 2 or 4 is not. Reverb channels on BF Fenders, older Marshalls, '59 Bassmans... just 3 examples of amps that reversed the phase of the signal coming out of the guitar. No wonder they don't sound right.

I have also read that some pedals reverse phase. Modern speakers all seem to be marked the same way in regard to phase; i.e. if you hook up dissimilar speakers with regard to the "phase dot" they are in phase with each other Older ones (read "vintage") were not so standardized; some brands would be opposite with regard to the "phase dot".

Maybe some guys can hear the difference in signal phase, maybe I could if someone taught me what I was listening for, or maybe its just a bunch of hooey... One thing I always keep in mind when reading about that kind of stuff - In medical research, something like 50% of people will respond positively to the treatment of real medical conditions with sugar pills.

 

[Harvey Gerst]

"Speaker wattage" is not a rating of how much power a speaker will "draw".

No, but it's sometimes convenient to think in those terms when calculating the load on the amplifier when using various impedance speakers together on one amplifier. Like what happens when you hook a 16 Ohm speaker and an 8 Ohm speaker in parallel.

 

[Harvey Gerst]

Maybe some guys can hear the difference in signal phase, maybe I could if someone taught me what I was listening for.

Simple: one way, your sound "blows"; the other way, it "sucks".