Speaker impedence question

[Little Ricky]

I'm looking to ad an extension speaker to a combo that has 2x8ohm speakers in parallel (4ohm). Looking at the illustration I take it that the top setup will yield a 6 ohm load and the bottom a 12 ohm load. Does this sound right or am I completely off the mark. Thanks

[phatt]

Top one;
Consider the top 2 speakers as one 4 Ohm driver.
Any extra speaker across the terminals (as you have drawn) will yield less than the lowest Z which in this case puts it under 4 Ohms and a Bad idea. 8|
The Bottom is the same circuit, except the lower driver is out of phase.

Sadly There is no quick fix for these issues except to start again with different driver Zs that add up to the required load.
Phil.

[phatt]

You can do mismatching like this.
Total load here is 8 Ohms.
Phil.

[J M Fahey]

True enough.
That said, I'd love to know *which* "a combo" is.
*Some* amps (notably old Peaveys) were overbuilt, had 4 TO3 metallic transistors where just 2 would have been used by anybody else, and tolerated 2 ohm loads.
In *that* case, adding a single 8 ohm external speaker might be well tolerated .
But in cut throat pricing modern amps, forget it, too tightly specified.

[Little Ricky]

Thanks guys.  2 16ohm drivers it'll have to be. then the extension will bring it back down to 4 ohm when used.

The combo is one of my many Vox Pathfinder projects. This one with a TDA2040  so it can run the 4 ohm load. It's been running happily for 8-10 hours of gig time at 4ohm,even so  there is NO way I'd want to push that.

This amp has become like luggage, I can't get rid of it, it keeps coming home . "Can I get an amp just like the one you put together for.....?",  Done. " Can it be louder?" Done. " Can it be cleaner?"

Can somebody please shoot me?

[Little Ricky]

Thanks phatt, I'll give the series wiring a shot as well. Without the ext cab it it might not have enough  output.  I'm getting asked to deliver too much from a 15w ss amp.

That being said I'm working on another Pathfinder and taking J M Fahey's idea of adding a separate power amp to the cabinet.  This is a friend I'm working with and I really want to make him happy. Which is tough because we started with the wrong amp.

[Roly]

Thanks guys.  2 16ohm drivers it'll have to be. then the extension will bring it back down to 4 ohm when used.

The combo is one of my many Vox Pathfinder projects. This one with a TDA2040  so it can run the 4 ohm load. It's been running happily for 8-10 hours of gig time at 4ohm,even so  there is NO way I'd want to push that.

This amp has become like luggage, I can't get rid of it, it keeps coming home . "Can I get an amp just like the one you put together for.....?",  Done. " Can it be louder?" Done. " Can it be cleaner?"

Can somebody please shoot me?

BANG!  {your wish is my command  8| }.

By "luggage" you don't happen to mean the Diskworld luggage...

"The Luggage had been describes as half suitcase, half homicidal maniac"


{this guy actually built a radio controlled one}

Now I could tolerate an amp that got itself out of the truck and set itself up on stage (even if it was prone to biting the occasional drunken punter ... hummm. now that I come to think of it...  :dbtu: ).