Four 8 ohm speakers, need some design help

[Michael Smith]

I have (4) 12" 8 ohm speakers in my closet, pulled from various amps over the years. One Jensen, one Oxford and 2 Eminence. I will post a photo tomorrow. My idea is to build a 4 x 12 cabinet that is able to operate at 8 ohms for all 4 speakers or at 4 ohms for each pair of 8 ohms speakers (left and right or top and bottom). I know how to wire the 4 speakers in series-parallel for an 8 ohm load, but have come up with several ideas on how to get 2 speakers isolated for an 8 ohm load. I will draw out a decent schematic and convert it to a pdf, but before I do that, I am hoping someone will chime in and give me some ideas.

 

[elpico]

In theory there should be some loss of bass when you disconnect two speakers, as they'll move opposite of the driven ones and cancel them out a little, but it's probably nothing a tweak of the bass knob can't correct. If you can arrange the switching such that the non-driven speakers are shorted rather than open that may help them resist moving somewhat. It may make little difference in the end though.

 

[Peegoo]

@Michael Smith

A design option to overcome the 'detuned' aspect of inactive speakers in the same airspace as active ones would be to build an internal vertical baffle that makes the 4x12 cab two independent 2x12 cabs, siamese twin style.

For series/parallel options, look here. There are diagrams...

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

...

 

[Michael Smith]

In theory there should be some loss of bass when you disconnect two speakers, as they'll move opposite of the driven ones and cancel them out a little, but it's probably nothing a tweak of the bass knob can't correct. If you can arrange the switching such that the non-driven speakers are shorted rather than open that may help them resist moving somewhat. It may make little difference in the end though.

The cabinet I plan to build will be semi-open back, so I don't know if that will somewhat solve the issue of the non-connected speakers canceling out the bass response of the connected ones.

 

[Michael Smith]

@Michael Smith

A design option to overcome the 'detuned' aspect of inactive speakers in the same airspace as active ones would be to build an internal vertical baffle that makes the 4x12 cab two independent 2x12 cabs, siamese twin style.

For series/parallel options, look here. There are diagrams...

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

...

Ya, I could put a baffle to separate the 2 pairs of speakers, but I plan for the cabinet to be semi open back. I have looked at that plug and play jack plate before, but I don't think it will handle my plan to use four 8 ohm speakers.

 

[Michael Smith]

Here is my motley crew of 12" speakers I plan to use. The Jensen came out of my Deluxe Reverb. The square magnet Utah is from my Super Twin Reverb. The Carvin (Eminence) was in my Carvin Vintage 16 (which now has a 10" speaker), and the Fender (Eminence) was purchased over 20 years ago, probably for something I never built. I'm not sure how to pair the speakers. Except for the Jensen, the others are rated at 100 watts (or greater in the case of the Utah

.

 

[Wally]

The efficiency of each speaker is of some concern, imho, when mixing speakers this way.
You might like one of these…

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

 

[elpico]

The cabinet I plan to build will be semi-open back, so I don't know if that will somewhat solve the issue of the non-connected speakers canceling out the bass response of the connected ones.

It would still happen but it's probably fine. If you build it and you like the sound, then there's no problem.

 

[Michael Smith]

The efficiency of each speaker is of some concern, imho, when mixing speakers this way.
You might like one of these…

https://www.tubesandmore.com/products/jack-plate-plug-and-play-mono-stereo

I'm sure the efficiency of the speakers are different, and also the wattages, so I'll have to bear that in mind. These speakers have just been gathering dust, so I thought I would put them to use.

I did look at the plug and play device when it was brought up in another thread earlier this year. It appears to be for a 2 speaker setup, rather than 4.

 

[Michael Smith]

Here is a drawing of my proposed speaker wiring. The connections drawn in red are a normal series/parallel scheme, providing 8 ohms when all four 8 ohm speakers are in use. The connections drawn in blue are to use either the left two speakers or the right two speakers in parallel, for 4 ohms. The 2 switches either make or break the connections for the 4 speaker series wiring and the 2 speaker parallel wiring.

Hmm, my version of Adobe wouldn't let me covert the pdf to a jpeg or other format, so hopefully clicking on the attachment will open it in another tab. Someone let me know if that's not the case.

Edit: I just took a screen shot and edited it in Paint, so hopefully this works.

 

[schmee]

Ya, I could put a baffle to separate the 2 pairs of speakers, but I plan for the cabinet to be semi open back. I have looked at that plug and play jack plate before, but I don't think it will handle my plan to use four 8 ohm speakers.

I would not worry about unconnected speakers causing issues. Especially in an open back.
You wiring ideas are doable with a jack plate. One jack for the series parallel, when unplugged it breaks the pairing etc. I may have a diagram. No switches needed.

You may consider buying a pawn shop 4 x 12 cab to modify. They are out there dirt cheap. My neighbor has one for sale on CL for probably 6 months for $50. It even has 4 speakers in it! he bought it on a whim a few years ago for the same price!

 

[Swirling Snow]

Don't worry, be happy, this is one of those "It can't go wrong" projects.

My only caution is avoid a "stereo" switch. If someone throws it with two amps connected, sparks will fly.

 

[elpico]

Don't think you need three jacks. Can use one and just short across the speaker pair you want to turn off with the switch.

 

[Michael Smith]

Don't think you need three jacks. Can use one and just short across the speaker pair you want to turn off with the switch.

I designed it so I could use either pair of the 2 speakers in parallel (4 ohm) mode, thus 2 separate 4 ohm jacks. If the speakers were all the same model, I wouldn't need the ability to select which pair to use. The reason I have a dedicated jack for the series/parallel (8 ohm) wiring is for ease of remembering how things are supposed to be configured. Anytime an amp is plugged into the 8 ohm jack, the two switches must be in the 8 ohm position, and the opposite anytime an amp is plugged into either of the 4 ohm jacks.

There probably is a simpler way to do what I want it to accomplish.

 

[Michael Smith]

I would not worry about unconnected speakers causing issues. Especially in an open back.
You wiring ideas are doable with a jack plate. One jack for the series parallel, when unplugged it breaks the pairing etc. I may have a diagram. No switches needed.

You may consider buying a pawn shop 4 x 12 cab to modify. They are out there dirt cheap. My neighbor has one for sale on CL for probably 6 months for $50. It even has 4 speakers in it! he bought it on a whim a few years ago for the same price!

I may try a few pawn shops in my area. That's not a bad idea. However I do like the woodworking aspect of a project like this. I built a table saw fingerjointing jig a couple of years ago when I built my 4 x 10 cabinet. I used pine boards and even with 4 Weber 10A125 speakers, it weighs just shy of 30 pounds. The 4 x 12 will be considerably heavier, due to some of the large magnet speakers I have.

 

[Wally]

I did look at the plug and play device when it was brought up in another thread earlier this year. It appears to be for a 2 speaker setup, rather than 4.

Michael, that Jack plate is made for a 4 speaker cab. It is marked for use with 16 ohm speakers. In series parallel, 4x16 ohms yields the 16 ohm mono. In parallel, 4x16 ohms yields a 4 ohm load. In the ‘stereo’ mode, this plate yields 2x16 ohms in parallel to it an 8 ohm load from each of those two jacks.
With four 8 ohm speakers, each of those loads would be half of the labeled impedances….8 ohm mono, 2 ohm mojo, and two 4 ohm jacks.

 

[----RIP----]

I have (4) 12" 8 ohm speakers in my closet, pulled from various amps over the years. One Jensen, one Oxford and 2 Eminence. I will post a photo tomorrow. My idea is to build a 4 x 12 cabinet that is able to operate at 8 ohms for all 4 speakers or at 4 ohms for each pair of 8 ohms speakers (left and right or top and bottom). I know how to wire the 4 speakers in series-parallel for an 8 ohm load, but have come up with several ideas on how to get 2 speakers isolated for an 8 ohm load. I will draw out a decent schematic and convert it to a pdf, but before I do that, I am hoping someone will chime in and give me some ideas.

Why not wire each pair of 8 ohms in parallel to give 4 ohms each like you want? Then for all four at 8 ohms, put the two 4 ohm pairs in series. So, for all four speakers at 8 ohms, you would do parallel-series instead of series-parallel.

 

[Wally]

Know that parallel/series is rarely used due two aspects. With 16 ohm speakers, a failure of one speaker takes out the series pair leaving the other series pair in operation. This results in an impedance twice that of a single speaker…..32 ohms when running 16 ohm speakers. This would not be advisable. With 8 ohm speakers such as Michael is using, that load would be 16 ohms. These two speakers are also put under great stress due to having to carry the load that four speakers were carrying. That as spect may or not be a concern
depending on how hard one is pushing them.
The series/parallel mode suffers a ‘hard’ failure if one speaker goes out…..the cab stops making sound snd one should immediately shut the amp off.

 

[telemnemonics]

Why specifically do you feel the best cab to build holds four speakers?
You can hardly give away a 4x10 or 4x12 cab these days.
Build two 2x10 cabs!
Or one 2x10 cab.

If one is sitting because you didn’t like it in an amp, why even choose it now?

As commented on, they may not match well and it will not sound good if running two live with the other two as passive radiators.
So the cab needs a divider and needs switching with proper labeling and warning to all who approach to not fiddle with or bump the switch.

A nice thing about stereo is separating the two amps.
Same cab is not better in any way unless you have a very small van and good roadies with their own transportation.

Sell the speakers individually and buy one or two small cabs with better speakers.

 

[Michael Smith]

Michael, that Jack plate is made for a 4 speaker cab. It is marked for use with 16 ohm speakers. In series parallel, 4x16 ohms yields the 16 ohm mono. In parallel, 4x16 ohms yields a 4 ohm load. In the ‘stereo’ mode, this plate yields 2x16 ohms in parallel to it an 8 ohm load from each of those two jacks.
With four 8 ohm speakers, each of those loads would be half of the labeled impedances….8 ohm mono, 2 ohm mojo, and two 4 ohm jacks.

Thanks Wally, I'll have to take a fresh look at that jack plate.