speaker impedance

[jimmy]

hi all

how would i go about wiring two 8 ohm speakers together to get a total impedance of 8 ohms? is this even possible?

cheers
Jim

[Ge_Whiz]

No, not possible. You have two choices: speakers in series (careful to link one +ve to the next speaker's -ve), 16 ohms; or speakers in parallel (+ve to +ve, -ve to -ve), 4 ohms.

[jimmy]

oh  :?

heres the deal: i tore apart my solid state amp to snag the speakers for my tube amp, and also for installation of a new half decent preamp. my tube amp (firefly) is rated for 8 ohms.

what do i do?

cheers
Jim

[RDV]

Use one speaker.

RDV

[jimmy]

:!:  i cant belive i didnt think of that.

what would happen if i used 4 ohms anyway? is it bad for the amp?

cheers
Jim

[sir_modulus]

one tube amps: YES. You could end up damaging almost everything in the amp(OT, Tubes, PT) and this is if the impedence is higher OR lower. On a SS amp, you'll basically only damage the output trans. with lower impedence (eg. using 4ohm load on an 8ohm P.Amp)

[Lonestarjohnny]

Most basic PA amps are Rated down to 2 ohm's, in other words it's O.K. to run the S/S amp at Max. output,
A tube amp though is another bird of a different color,
You take the tube amp that's rated for 8 ohm's and run it on 2 ohm's and very shortly there after you will have problem's, bad problem's on some amps,
You can get away with running the 8 ohm amp on 16 ohm's with no problem, but you want get maximum output so, the best situation is if your amp call's for a 4 ohm load, use a 4 ohm load, your amp will be a lot better off for it and so will you, it cost money to go see the amp repairman !
JD

[jimmy]

alrighty then. thanks for the help and info!

cheers
Jim

[jimmy]

what if...

i wired some 1ohm resistors in there somewhere.  the speakers are currently running in series, so if i stick a total of 8 ohms of resistance in parallel will this lower the impedance and make everything ok?

just an idea...
Jim

[Joe Davisson]

This is probably wrong in practice, but could a capacitor's reactance be used to fix the total impedance?

The reactance (at 1khz) of a 10uF cap comes in at around 16 ohms. So would putting that in parallel with the speakers (connected in series to get 16-ohms) would reduce the total reactance to around 8-ohms?

Of course it would muffle the sound, but just wondering if that's even right...

-Joe

[Lonestarjohnny]

Joe, that was done a lot back in the 40's and 50's, some company's saved money by doing just that, and yes you do have to be selective on what you put in bacause it will filter.
also, Jimmy, go to the Altec speaker site and look at the transformer's they added to the speaker to get the ohmage they wanted the speaker to operate at.
JD

[Tubebass]

Hey Jimmy!
 IMO, a little amp like the Firefly shouldn't have a problem with either 4 or 16 ohms. Try it with one speaker, with two in parallel and with two in series and see what sounds best. Just make sure to power the amp down or put it on standby when changing connections-tube amps don't like open circuits on the output. Shorting the output for a brief time is usually ok.

[jimmy]

thanks for the info guys!

ran the firefly through 16 ohms... sounds incredible. ive fitted some switching jacks to the speaker cab i created so i can now run 8 or 16 ohms anyway. thanks again!

cheers
Jim