Speaker Wiring Implications
For bass, you are better off if your woofers are in parallel with each other. The reason is simple - woofers have a low note resonant frequency where the impedance shoots up real high.
This graph shows a speaker not mounted
in a cabinet (free-air) starting at 10 Hz
When you put bass speakers in series, the resonant note impedance is additive, and you end up with dead notes in the deep bass. If you wire them in parallel, since each speaker will have a slightly different resonant peak, and the effect will be substantially less pronounced.
Using the sample woofer from above (8 ohm woofer), you will have one to 3 notes that are at or near an 80 ohm impedance if the speakers are wired in series. The same speaker wired in parallel could have exactly the same notes drop out, but one speakers resonant notes tend to overlap the other speakers non-resonant notes slightly, so while the the same notes are not a powerful, they are still there.
What this says is:
In a bass cabinet with 4 speakers, if you want a 4 ohm load, you are better off using 4 16 ohm speakers in parallel. Using 4 ohm speakers is a marginal choice for bass because to get 4 ohms as a cabinet load, you need to wire in Series/Parallel, and that gets you the high additive resonant peak of 2 speakers - while its fine for guitar (since it does not have low notes like bass), its not a great solution for anything with deep bass needs.
Subwoofers with multiple speakers or cabinets should never be wired in series (connections to an amplifier).
Your speakers are what ever impedance they are, you can't change them. Its your amp that will have problems with lower impedances, not your speakers.
So, if you have a power amp that can drive down to 2 ohms, you can put 2 4 ohm cabinets on it in parallel and it will be fine. If the power amp can only drive down to 4 ohms, then you are limited to a single 4 ohm cabinet (or 2 4ohm cabinets in series - giving you an 8 ohm load).
Every time you run something in series, you drop the power to the devices.
An amp that outputs 1000 watts at 2 ohms will output 500 watts at 4 ohms and 250 watts at 8 ohms. So increasing the impedance really cuts your power to the speakers. At the same time, 2 4 ohm speakers in series become an 8 ohm load, in which each evenly splits what ever power is available between them.
So lets say you have 1 4 ohm speaker with an amp that outputs 500 watts at 4 ohms. That single speaker will see 500 watts. if you now add another 4 ohm speaker in series, you have done 2 things - reduced the power output of the amp by 50% (because you switched from a 4 ohm load to an 8 ohm load), leaving you 250 watts of power, but its spread evenly between the 2 woofers - each are now seeing 125 watts per speaker. Essentially, you have reduced the power that each of the speakers see by 75%. In the case of deep bass, now you also added to the resonant note boost, so you are likely to end up with a pronounced dead note in your cabinet.
Putting things in series allows you to use lower power speakers (because the wattage to them gets cut substantially), but with less power to them, they will not be as loud as speakers wired in parallel when they see less power to them..
What I do
Everything is a compromise.
In my 4X speaker cabinets, I tend to only use 16 ohm speakers - it gives me the most options. I often build cabinets with switches to allow me to switch between 2 different impedances.
NOTE: Many Marshall 4X12's use all 16 ohm speakers.
Questions? Comments? .
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