16 ohm to 8 ohm quad box conversion

[desbo]

Hi all. Is it possible to rewire my 4 x 16 ohm quad box speaker cab (16 ohm series/parallel) to get 8 ohm load? Or are my alternatives only 4 (parallel/parallel) or 16 ohm?

[CaptDon]

Sadly 4 ohms is the only option other than 16 ohms or a crazy 64 ohms.

[desbo]

Thanks. You've confirmed my suspicions. I am getting a new amp which has 4 and 8 ohm output only. I think I will be better off reverting to 16 ohm and reduce risk of blowing things up. I believe the mismatch does affect the tone but it is subtle, according to Youtube.

[radiolistener]

You can use 1:4 impedance ratio transformer to match 16Ω speakers with 4Ω amplifier output.
1:4 impedance ratio transformer is 1:2 voltage ratio (or 1:2 turns ratio).

[CaptDon]

Read again R.L. He can rewire it to 4 ohms. That isn't what he wants. He wants 8 ohms. A different impedance ratio transformer would get the 8 ohms but not worth the hassle and severely effects tone.

[MrAl]

Hello,

If the amplifier is not too expensive you can get a second one, then do two sets of 16 ohms in parallel.
Drive both amplifiers with the same signal.

[radiolistener]

Read again R.L. He can rewire it to 4 ohms. That isn't what he wants. He wants 8 ohms.

using transformer is more easy solution than modifying speakers from 16 Ω to 4 Ω.

A different impedance ratio transformer would get the 8 ohms but not worth the hassle and severely effects tone.

The main issue with transformer is their size/weight. Since it should work with audio frequencies from 20 Hz, it will be hard to implement flat response at so low frequency. Such transformer will needs core with high magnetic permeability.

In order to avoid distortions due to core saturation at high power you can use more massive transformer core.

But anyway, I think implementing such low frequency transformer will be more easy than modifying speakers...


Transformers for speakers were very popular solution for old school tube power amplifiers, because tube amplifier has pretty high output impedance and transformers was used to match it with low impedance speakers.

[desbo]

I just had another idea. Would it be possible to install a switch that changed the wiring from series parallel (16 ohm) to parallel/parallel (4 ohm)? My new amp will do either 4 or 8 ohms. I could run on 4 ohm for the new amp but have the flexibility to switch back to 16 ohm which was the factory spec and which is safe to go with any amp.

[MrAl]

I just had another idea. Would it be possible to install a switch that changed the wiring from series parallel (16 ohm) to parallel/parallel (4 ohm)? My new amp will do either 4 or 8 ohms. I could run on 4 ohm for the new amp but have the flexibility to switch back to 16 ohm which was the factory spec and which is safe to go with any amp.

Hi,

Yes it is possible to switch from 16 to 4 Ohms with one switch or more than one switch using your speakers.

Since you mentioned that, using the theory of averaging, you could also get 13.6 Ohms.
To do this, you would RAPIDLY switch between 4 Ohms and 16 Ohms.  20 percent of the time you use 4 Ohms (all in parallel) and the other 80 precent of the time you use 16 Ohms (two parallel strings of two in series).  13.6 Ohms is closer to 8 Ohms.  The power would be shared equally among all four speakers but would not reach full power even with the volume turned all the way up.
If you did 50 percent for each set you would get 10 Ohms, but then the power would not be shared equally.
If you did 33.3 percent for 4 Ohms and 66.7 percent for 16 Ohms you'd get 8 Ohms, but then the power would not be shared equally among all of the 4 speakers that way either.
If the power is not shared equally you cannot use full volume.
The switching frequency would have to be something like 100kHz or greater.  Of course this would have to be tested.  This assumes that the amplifier is like most audio amplifiers that are basically voltage amplifiers.

[CaptDon]

Let's keep it practical here. He has an external cabinet 4 Speakers each of 16 ohms. 4 X 12" being common as are 4 X 10". No switching averaging 80%/20% or whatever idea is practical and his keyboard/guitar amplifier head would look at that crazy cludge and just go nuts. Totally impractical for a gig amp on stage. Also, a transformer that works at stage volume and can sound good passing the heavily distorted guitar waveshapes without showing coloring of the sound or looking like a dead short during the flat-topped portions of the waveshape also won't be found and if you could it would be heavy and just another burden of weight to lug around to the next gig. Remember a speaker during flat topping still shows a great deal of resistance, about 80% of the marked impedance in fact. Not so with transformers in that power range, probably under 1/2 ohm max. As for modding the speakers....a very easy chore. The typical wiring is either 2 X 16 in parallel giving 8 ohms, in series with an identical pair giving 16 ohms total OR all 4 X 16 ohm speakers in parallel giving 4 ohms. Incredibly easy to change the wiring since in 99% of the cases the speakers are connected with spade lug wiring and the only difference between the 16 ohm and 4 ohm cabinet when they left the factory was which way the wires were connected. They DID NOT use different part number wiring harnesses, they simply connected the harness (mostly 15" long wires with female spades on each end) differently. The end user can mod the cabinet in under 1/2 hour at zero cost and zero weight gain......but, sady, your choice is 16 ohms or 4 ohms UNLESS you buy 4X 8 ohm speakers Which many people do after blowing up the 16 ohm originals.

[MrAl]

Let's keep it practical here. He has an external cabinet 4 Speakers each of 16 ohms. 4 X 12" being common as are 4 X 10". No switching averaging 80%/20% or whatever idea is practical and his keyboard/guitar amplifier head would look at that crazy cludge and just go nuts. Totally impractical for a gig amp on stage. Also, a transformer that works at stage volume and can sound good passing the heavily distorted guitar waveshapes without showing coloring of the sound or looking like a dead short during the flat-topped portions of the waveshape also won't be found and if you could it would be heavy and just another burden of weight to lug around to the next gig. Remember a speaker during flat topping still shows a great deal of resistance, about 80% of the marked impedance in fact. Not so with transformers in that power range, probably under 1/2 ohm max. As for modding the speakers....a very easy chore. The typical wiring is either 2 X 16 in parallel giving 8 ohms, in series with an identical pair giving 16 ohms total OR all 4 X 16 ohm speakers in parallel giving 4 ohms. Incredibly easy to change the wiring since in 99% of the cases the speakers are connected with spade lug wiring and the only difference between the 16 ohm and 4 ohm cabinet when they left the factory was which way the wires were connected. They DID NOT use different part number wiring harnesses, they simply connected the harness (mostly 15" long wires with female spades on each end) differently. The end user can mod the cabinet in under 1/2 hour at zero cost and zero weight gain......but, sady, your choice is 16 ohms or 4 ohms UNLESS you buy 4X 8 ohm speakers Which many people do after blowing up the 16 ohm originals.

Hello there,

From your reply it sounds like you have never done an averaging analysis.  If you think it is not practical, then you must be rejecting one of the most modern designs for an audio amplifier which is the class D type amplifier.  I am not exactly sure why you reject that, maybe you just don't like switching circuits because they sound too complicated, but really there is a lot of theory in this area.

Just for a basic idea, if you had a 10 Ohm resistor and you switched it on and off with a 50 percent duty cycle, the circuit driving that resistor would see a resistance of 20 Ohms on average.  If you change the duty cycle to 33.3 percent, it would look like a 30 Ohm resistor.
That's just a brief look into this but of course there is a little more to it than that.  The driver has to be able to work with a switched resistance.  That means it must be able to handle that 10 Ohm resistor for whatever percent of the time it has to be 'on'.  Because the main load is not 'on' all the time that means this would come with a loss of power which can be significant or not depending on the application.

There are other solutions too though that are much simpler, but with a loss of power.
For example, four 16 Ohm resistors in parallel also in series with a 4 Ohm fixed resistor.  This makes the total resistance 8 Ohm although there will be a power loss of 50 percent which may or may not make a difference.
For two sets of two in series also in parallel with each other, the total resistance is 16 Ohms, and using a 16 Ohm fixed resistor in parallel with that set brings the total resistance seen by the driver to 8 Ohms.  Again though we have a power loss of 50 percent.

The solutions above come up when the user is limited to what they have and what they can get.  Obviously if they can get an 8 Ohm speaker that handles the whole power we wouldn't be here.  When limited to what we have on hand though, we have to improvise.
If none of the other solutions are acceptable then that's just the way it goes.  If also the 4 Ohm or 16 Ohm simpler solution is not acceptable then buy something that is acceptable.

[gbaddeley]

Is your new amp using tubes or solid state? For best efficiency and sound, a tube amp should be loaded with the correct impedance, not higher or lower. Worst case is that mismatch will damage the output tubes or transformer (over voltage or over current). In your case, parallel all the 16 ohm drivers (in phase!) and use the 4 ohm output.

[David Aurora]

Good lord, there is some absolute dumb fuck advice going on in this thread.

First things first, no go on the 8 ohms as you've gathered by now... sort of.

If you look at a standard Marshall cab you'll see you can connect it a bunch of different ways- 4 ohms mono, 16 ohms mono or 8 ohms stereo. It's done through a combination of a physical switch and some switching contacts on the connectors (also a common failure point, but that's another discussion...).

So yeah, with a little thinking and some switches you can run all options, just as long as you accept that the 8 ohm option would essentially work like two 2x12 cabs rather than a 4x12.

Second- if the amp says 4 or 8 ohm only, just wire the cab for 4 ohms. I cannot tell you how many amps I've repaired because someone ran the wrong load expecting a "subtle tone change". If it's a tube amp and you run it into 2 or 4 times the impedance you're gonna break stuff, and even if it's a solid state amp that's more forgiving of that you won't be getting optimum results.

[desbo]

Thanks David for getting my question. from my research, i had come to the conclusion that the most important thing is to ensure the speaker cab has a higher ohm rating than the amp. there may be a resistance mismatch, but it won't hurt the amp. running a high ohm setting into a lower rated cab will hurt the amp. is this still a valid conclusion. FYI, I'm getting a Mesa 5/25 which is 4/8 ohm output. my marshall quad is 16ohm. i have no concern running 8 ohm into 16 cab, but i wanted to avoid the mismatch and possible impact on tone. I could run the amp 4 ohm into 4 ohm cab, but I was just a bit worried that in future its a higher risk of damage as noone would expect a quad at 4 ohm. I would appreciate your thoughts.

[David Aurora]

Thanks David for getting my question. from my research, i had come to the conclusion that the most important thing is to ensure the speaker cab has a higher ohm rating than the amp. there may be a resistance mismatch, but it won't hurt the amp. running a high ohm setting into a lower rated cab will hurt the amp. is this still a valid conclusion. FYI, I'm getting a Mesa 5/25 which is 4/8 ohm output. my marshall quad is 16ohm. i have no concern running 8 ohm into 16 cab, but i wanted to avoid the mismatch and possible impact on tone. I could run the amp 4 ohm into 4 ohm cab, but I was just a bit worried that in future its a higher risk of damage as noone would expect a quad at 4 ohm. I would appreciate your thoughts.

Your conclusion is dead wrong sorry mate. You SHOULD be concerned running an 8 ohm amp into a 16 ohm cab. The ratings aren't printed there for the hell of it, they're there for important reasons.

If you're running a tube amp, your options are basically match impedance or regret not matching impedance. Your idea to run an 8 ohm output from a tube amp into a 16 ohm cab may as well be seeing how far you can run your diesel engine on petrol 

[themadhippy]

I'm getting a Mesa 5/25

are you also getting someone to carry it for you? every mesa ive come across has been surprisingly heavy for the size of the thing.

but I was just a bit worried that in future its a higher risk of damage as noone would expect a quad at 4 ohm.

Not so unusual and if you worried put a big label on the back of the cab with "4 ohms stupid"

[CaptDon]

Yes Mr. Al, I have been designing and repairing Class D amps since the first days of the Peavey DECA 424 and DECA 700. I was one of the first people to service those in the Central Pennsylvania area outside of the dealers sending the amps back to Peavey for repair. I was well enough known to the sound guys using the early 700's prior to the release of the improved DECA 724 that they brought their amps to me 'in warranty' since I was faster than a round trip to the factory. I am the GURU of repairing the switch mode power supplies found in the Carver CBA-1000, PM-1250 and PM-2.0T series. I even wrote a separate service manual for the power supply section. How will you apply your solution to the original poster who wants to gig today not a year from now. Will this switching circuit be home built, bought of the shelf, does it even exist? How will he install it and at what cost? Also as for impedance mis-match of an 8 ohm output tube amplifier driving a 16 ohm load, when the amplifier is lightly loaded the voltage swing on the plates becomes unusually high which can lead to arcing in the tubes or the output transformer which can be fatal to the tubes or transformer. Also, depending on how the screen grids of the output tubes are connected there can be damage to the grids if the plate voltage swings very low and the screen grids are more positively charged than the plates. The screens will draw heavy current and be destroyed quickly.

[ejeffrey]

Thanks David for getting my question. from my research, i had come to the conclusion that the most important thing is to ensure the speaker cab has a higher ohm rating than the amp. there may be a resistance mismatch, but it won't hurt the amp.

This is correct for solid state amplifiers but not necessarily tube amps.  In the latter case with no load it's possible the output transformer will saturate and / or the output voltage will rise too high.

[desbo]

Hi David, The Mesa manual includes the following sketch. This indicates that 8ohm into 16 ohm is a safe mismatch. In any case, I think I will go with 4 ohm on the cabinet and 4 ohm on the amp and put a big 4 OHMS ONLY STOOPID! sticker on the back. One final thing, if i put my multi meter across the socket, it should read 4 ohms right. Not being stupid, just a bit paranoid now.

[MrAl]

Yes Mr. Al, I have been designing and repairing Class D amps since the first days of the Peavey DECA 424 and DECA 700. I was one of the first people to service those in the Central Pennsylvania area outside of the dealers sending the amps back to Peavey for repair. I was well enough known to the sound guys using the early 700's prior to the release of the improved DECA 724 that they brought their amps to me 'in warranty' since I was faster than a round trip to the factory. I am the GURU of repairing the switch mode power supplies found in the Carver CBA-1000, PM-1250 and PM-2.0T series. I even wrote a separate service manual for the power supply section. How will you apply your solution to the original poster who wants to gig today not a year from now. Will this switching circuit be home built, bought of the shelf, does it even exist? How will he install it and at what cost? Also as for impedance mis-match of an 8 ohm output tube amplifier driving a 16 ohm load, when the amplifier is lightly loaded the voltage swing on the plates becomes unusually high which can lead to arcing in the tubes or the output transformer which can be fatal to the tubes or transformer. Also, depending on how the screen grids of the output tubes are connected there can be damage to the grids if the plate voltage swings very low and the screen grids are more positively charged than the plates. The screens will draw heavy current and be destroyed quickly.

Hello again,

Oh that's great.  It sounds then like you were not knocking the idea on the basis of raw theory, but on the practicality of such a thing.
That does make a lot of sense if he's in a hurry, and I did not really intend to design anything for anybody right now too busy with other things these days.
However, I see in another post that he may actually have a 4 Ohm output on the amplifer ?  If that's true then we all wasted our time.

[radiolistener]

If his amplifier support 4Ω and 8Ω output, most of all it can work with 16Ω load, but it will lead to lower power output and can significantly affect amplifier performance (SNR, THD, IMD, etc).

[CaptDon]

Desbo, be aware that a 16 ohm speaker will have a D.C. resistance of typically 9 to 13 ohms, therefore when you wire them all in parallel it will look more like 2.5 to 3 ohms D.C. resistance which is actually a nominal value for a single 4 ohm speaker. Cheers mate. Looks like you are making progress.

[David Aurora]

Hi David, The Mesa manual includes the following sketch. This indicates that 8ohm into 16 ohm is a safe mismatch. In any case, I think I will go with 4 ohm on the cabinet and 4 ohm on the amp and put a big 4 OHMS ONLY STOOPID! sticker on the back. One final thing, if i put my multi meter across the socket, it should read 4 ohms right. Not being stupid, just a bit paranoid now.

Mesa also claim you don't need to bias their amplifiers. All fun and games until shit starts red-plating.

I've spent the bulk of the last 10 years fixing tube amps for people who believed things they read on the internet. Take your chances if you want, it's your money, but again- impedance specs aren't random suggestions, they're based on how electronics actually work. Want it to work right? Match it. Want it to sort of work and maybe blow shit up? Don't match it. Simple.

[themadhippy]

surprised no ones mentioned the obvious solution that any rock guitarist  would see straight away,add  another quad cab.

[MrAl]

Desbo, be aware that a 16 ohm speaker will have a D.C. resistance of typically 9 to 13 ohms, therefore when you wire them all in parallel it will look more like 2.5 to 3 ohms D.C. resistance which is actually a nominal value for a single 4 ohm speaker. Cheers mate. Looks like you are making progress.

Hello again,

I do not know if you remember the old, old, old, OLD, speakers.  They had no permanent magnet.  Instead, they had an extra winding that was made for applying a DC current. That winding and the core metal would act as the permanent magnet.  I have not seen one like that in many years now.

[CaptDon]

Last of those electro-dynamic speakers I dealt with were on a 1930's vintage floor model radio. 2 X 12" and both had open magnetic field coils. I replaced them with a pair of 12" speakers from a modern Lowery organ that was killed by lightning and used an inductor to take the place of the field coils. The radio played in a corner of a local restaurant and brought me a lot of customers when the owner told them who fixed his radio. That thing probably sounded better than new!! People loved the old 6U5 magic eye tube and I had installed a nice bright new one.

[desbo]

Hi David

Just for the record, I found that you can get a Marshall jack plate that will switch between 4 & 16 ohm.

In any case, I have gone to 4 ohm and sounds just fine. Cheers.

[David Aurora]

Hi David

Just for the record, I found that you can get a Marshall jack plate that will switch between 4 & 16 ohm.

In any case, I have gone to 4 ohm and sounds just fine. Cheers.

Yep, and 8 when used as stereo like I mentioned earlier