Speaker box wiring impedance

Thread Starter

robismod

Joined Sep 22, 2015
100
I have a 4x12 instrument speaker cabinet that I’m splitting up as 2-12s on top, and 2 on the bottom. I want to be able to use as a 2 speaker cab sometimes, as well as 4 sometimes.
All speakers are 16ohm. Right now I have them wired positive to positive, negative to negative, and same to an input jack. This gives me an 8ohm load on each set of speakers. My plan is to wire in a DPST Switch to be able to engage all 4 when needed. If I just switch in one set to the other using the same pos to neg etc. scheme what will it do to my ohm load? I can’t seem to wrap my mind around it...
Thanks
 

dendad

Joined Feb 20, 2016
3,006
Resistors in series add. Those in parallel divide.
for example.
In this case, what is the lowest impedance your amplifier can drive?
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Resistors in series add. Those in parallel divide.
for example.
In this case, what is the lowest impedance your amplifier can drive?
I can’t make the video play on my phone but will look on YouTube.
As far as the amplifier, I’m not sure yet—I have a couple of combo amps that I will disconnect the speakers from them to use this cabinet. Trying to find their outputs now...
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Resistors in series add. Those in parallel divide.
for example.
In this case, what is the lowest impedance your amplifier can drive?
One amp is a stereo unit and is rated at 8ohms per channel...other Peavy unit is a single 12 amp...still digging ...
 

dendad

Joined Feb 20, 2016
3,006
That video may be a bit confusing. It is just the one I found. Not having looked at it all the way, I noticed he does waffle a bit.

You can run 2 16ohm speaker boxes in parallel to give you 8ohms, but if you were to put all 4 in parallel, it would be 4 ohms. Not wise.
But if you are just running one or two per channel, that should be ok.
Some amps have "A" and "B" speaker selection switches so it is just built in.
This should work ok.
Speakers.jpg
 

Thread Starter

robismod

Joined Sep 22, 2015
100
That video may be a bit confusing. It is just the one I found. Not having looked at it all the way, I noticed he does waffle a bit.

You can run 2 16ohm speaker boxes in parallel to give you 8ohms, but if you were to put all 4 in parallel, it would be 4 ohms. Not wise.
But if you are just running one or two per channel, that should be ok.
Some amps have "A" and "B" speaker selection switches so it is just built in.
This should work ok.
View attachment 189383
Thanks for that info and drawing...I think it might have just hit me that all I’m doing technically is connecting “two 12in speaker cabinets” together, or adding an extension cabinet to the main one. In this case I’m just putting all the speakers in the same box...haha...
The upper two speakers are wired from input jack positive to the positives on the two speakers. The negative from the jack is wired to the negatives of the speakers. The bottom speakers are from the switch I put in and feed the speakers in the same way as above. The switch is then connected to the input jack beside it. The bottom speakers are not connected until the switch is thrown. I hope that is right...haha...
So, don’t I have an 8ohm load on each set by themselves? Does that change when I engage both sets?
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Thanks for that info and drawing...I think it might have just hit me that all I’m doing technically is connecting “two 12in speaker cabinets” together, or adding an extension cabinet to the main one. In this case I’m just putting all the speakers in the same box...haha...
The upper two speakers are wired from input jack positive to the positives on the two speakers. The negative from the jack is wired to the negatives of the speakers. The bottom speakers are from the switch I put in and feed the speakers in the same way as above. The switch is then connected to the input jack beside it. The bottom speakers are not connected until the switch is thrown. I hope that is right...haha...
So, don’t I have an 8ohm load on each set by themselves? Does that change when I engage both sets?
Oops! Did I end up wiring each set in parallel?
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Yikes! I believe I see what you were telling me above—by combining the two sets the way I have, I’ll drop down to 4 ohms, yes? And not good...ouch...
 

liquidair

Joined Oct 1, 2009
112
There's nothing inherently wrong with dropping to 4 ohms unless your amp's impedance doesn't have a selector or isn't a 4 ohm output. The parallel wiring will sound tighter than series or series parallel as the amp sees both/all speakers in parallel.
 

Thread Starter

robismod

Joined Sep 22, 2015
100
There's nothing inherently wrong with dropping to 4 ohms unless your amp's impedance doesn't have a selector or isn't a 4 ohm output. The parallel wiring will sound tighter than series or series parallel as the amp sees both/all speakers in parallel.
The units I’ll be using I believe are 8ohm...
 

MrSoftware

Joined Oct 29, 2013
1,564
Instead of wiring the speakers together inside the cabinet, why not just wire each speaker separately to the outside of the cabinet. 4 lugs per cabinet, 2 for each speaker. This will give you maximum flexibility, and less worry about a switch failing.
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Instead of wiring the speakers together inside the cabinet, why not just wire each speaker separately to the outside of the cabinet. 4 lugs per cabinet, 2 for each speaker. This will give you maximum flexibility, and less worry about a switch failing.
Hmmmm...this is a top angled cabinet with 2-12in speakers on top and the flat-facing bottom has two. I want to be able to just use the top 2 at times so I can hear more directly and that way the bottom 2 don’t blow straight out off stage and peel the audience’s hair off...LOL...and then depending on how it works, I might find times where I want to use the full cabinet. The toggle switch is heavy-duty so I don’t anticipate ever having an issue inside the cabinet...BUT as much as I’m digging I’m just not seeing anything out there on how anyone else does it. They probably do it right—just get specific cabinets for the specific job...haha
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Oh, and the input jack and the switch are mounted in a flush plate on the back panel...
 

Thread Starter

robismod

Joined Sep 22, 2015
100
Dang my mind is a terrible thing...LoL
What if...is it feasible to have the cabinet wired up normally in series/parallel, 16 ohm load, and then flip a switch to break the signal to the two bottom speakers?? Would that change the load ohms?
 

dendad

Joined Feb 20, 2016
3,006
However you wire them up, the ohms will change.
If you go series/parallel, you could have the switch just short out the unwanted speakers, but the remaining ones will increase in volume.
 

Thread Starter

robismod

Joined Sep 22, 2015
100
However you wire them up, the ohms will change.
If you go series/parallel, you could have the switch just short out the unwanted speakers, but the remaining ones will increase in volume.
Ah ha! So the shorting method could work—would leaving the wiring intact yet broken with a switch change the ohm load to a bad level?
 
The speaker enclosure is designed for the spec's of the speaker in it. If you have 2 speakers in one enclosure then it will produce different sounding bass if it has 4 speakers in it and if it has 4 speakers in one enclosure then it will produce different sounding bass if it has only 2 of the speakers working.

I think an enclosure with 4 speakers but with only two of the speakers working will produce almost no bass because the speakers that are not working will seem like large holes in the enclosure.
 
Top