Impedance

[Ken]

I want to use some extention speakers on one of my boxes, a Sharp that has 4 ohm mains. These mains are disconected automatically when the extentions are plugged in.
I'm wondering how to stop the mains from being disconected (a switch perhaps? ) and whether or not I can run 4 ohm extentions simultaineously. If my memory serves me correct (it's been a few years) Z, or impedance, is adds up in series but subtracts in parallel. I should be able to run them all at the same time in parallel without loading the amp, right?
I checked online and this seems right, but I'm more interested in hands on experience with boomers. Anyone have any ideas?
Any help would be grealy appreciated.
Thanks,
Ken

 

[Superduper]

Ken,

Running an extra set of 4 ohm speakers in parallel will drop the impedance to 2 ohms. There are a few amps that can run stable at 2 ohms but that is the exeption, rather than the rule. More than likely, a 2 ohm load will overload your amp and potentially blow it out. Don't do it.

If you really want to run 4 speakers, then run 2 pairs of external 8 ohm speakers in parallel. This will maintain your 4 ohm total load.

 

[Ken]

Thanks, I am in the process of further study and you have tweeked my curiosity even more. I found a real good link at s2g and this is going to be pretty complicated.
The Sharp box I wanted to match w/ Sharp speakers is a little confusing. Each 4 ohm main is wired in series to a 4 ohm tweeter. Yet on the case, the extention speaker outlets specifically says to add 4 ohm speakers, which cut out the mains and tweeters.
I have also got a resister and capacitor attached to each main & tweeter. I'm going to wade through my resources 'cause I suspect they act as a filter on some frequencys, plus add Xl &Xc to the circuit.

Don't worry, I aint gonna turn the switch until I figure this out on paper. Looks like I gotta get out a resister color code sheet and find a value on the electrolytics.
I still gotta find out how to keep the mains on when I plug in the extentions. I know the headphones also cut out the speakers, but that's just a simple ring-tip-switch. Oh, well, I haven't done this for years.

Just a little rusty, I guess. Baby steps...

 

[Superduper]

I don't believe the woofers are wired in series with 4 ohm tweeters. That must be a mistake. If you recheck, I think you'll find that they are wired in parallel with the tweeters running through a bipolar high pass capacitor.

The reason why the case says to use 4 ohm external speakers is to maintain a 4 ohm load. That is also the reason why the internal speakers are bypassed when external speakers are connected. If you're wondering why they cut out, it's because the jack itself acts like a switch.

If you really want to have the internal speakers on at the same time as the external speakers, then I highly recommend that they are wired in series and not in parallel. I really think introducing a 2 ohm load can potentially blow out your amp. That's because a 2 ohm load will allow your amp to pass approx twice as much power as with a 4 ohm load, for which it was probably not designed for. However, if you like to learn through experience and want to tinker or try it out, then be my guest. Your next post might be entitled "how come my boombox has no sound?" or "my boombox started smoking"

 

[Ken]

Don't worry. When it comes to a precious boomer, I definately will take your years of experience to heart..

No arcing & sparking on this end. Everything gets done on paper first. I'll keep you posted.