Speaker wiring and extension cab question?

[Creeper]

Many combos such as the Fender Rumble 500 will have two power ratings I.e:

500 Watts @ 4 ohms (with External Speaker), 350 Watts @ 8 ohms (Internal)

i wondered how this is achieved, I “think” it would be by having the two internal speakers as 4ohm wired in series, which gives you the 8ohm load when operating the combo by itself, then once an 8ohm extension cab is connected it effectively becomes two 8ohm cabs in parallel which run at 4ohms.

Is this correct and will most combos have there speakers wired in series if there is the ability to add an extension cab??

 

[James Nada]

Yes.

Either that, or the two internal speakers are 16 ohms each and wired in parallel.

 

[Creeper]

1 hour ago, James Nada said:

Yes.

Either that, or the two internal speakers are 16 ohms each and wired in parallel.

 

Thanks, would there be a preferred way to do this, or do manufactures do it differently,  would two 4 ohm speakers in serial or 16ohm in parallel make any difference to the performance or sound??

[James Nada]

9 hours ago, Creeper said:

Thanks, would there be a preferred way to do this, or do manufactures do it differently,  would two 4 ohm speakers in serial or 16ohm in parallel make any difference to the performance or sound??

I'm no expert, but I be surprised if there was any difference in performance or sound. 

I expect manufacturers choose 4 or 16 ohms depending on which is cheapest, which itself will probably be determined by the most commonly used in their other products or which the speaker manufacturer sells most of.  The only way to be sure is to take your combo apart and see what the label says.

[Adethefade]

Adding cabs is usually going to produce improved results. When amplifying low frequencies you need as much amplifier power as you can possibly achieve; once a bass sound is loud and clean, you're off to a flying start. As well as increasing amplifier power by reducing the impedance presented to the amp, adding another cab introduces another sound source which adds SPL, it'll be a different sound because it's probably a different cab, and when speaker enclosures are coupled (stacked or side-by-side) they tend to enhance each other's performance. 

In short, massive power and loads of cabs!

[Matt P]

i wouldn't expect there to be a difference in performance or sound but the choice of series or parallel speakers in a 2 speaker cab is sometimes down to what happens if one of the speakers fails, it they are parallel then the amp is suddenly seeing a 16 ohm load, if they are in series then the amp is suddenly seeing no load at all (which is usually very serious for amps with valve power sections0

 

the amp manufacturer will decide which outcome is the least disastrous and go for that (if they're engineering it properly)

 

Matt