1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Adding a second input to a speaker cabinet

Discussion in 'Amp Central Station' started by chrisdb, Jan 23, 2021.

  1. chrisdb

    chrisdb TDPRI Member

    Age:
    66
    Posts:
    24
    Joined:
    Nov 20, 2012
    Location:
    philadelphia
    I have a vintage Acoustic 104 amp with a 6x10 4 ohm speaker cabinet. I am thinking of adding a second wiring harness and input jack to put 2 parallel strings of 3spekars in series to obtain 8 ohm impedance. The idea is to make uIt available for an 8 ohm amp head and still be able to go back to the original amp head using the existing input.
    I can't see a reason why this shouldn't work but maybe I'm missing something ?
     
  2. strat a various

    strat a various Friend of Leo's

    Posts:
    4,116
    Joined:
    May 9, 2008
    Location:
    Texas
    Isn't the cabinet a 104 and the amp a 150? Anyway,I had an Acoustic 150 amp (that optionally matched a 104 6x10 cab).

    As long as you don't go under the recommended impedance. I presume that's a 4 ohm cab, right? If so, don't go under 4 ohms.

    Anything higher is fine, I used my 150 with an 8 ohm cab often.
     
  3. chrisdb

    chrisdb TDPRI Member

    Age:
    66
    Posts:
    24
    Joined:
    Nov 20, 2012
    Location:
    philadelphia
    You are absolutely correct-it's a 150 head and a 104 speaker cabinet. I never opened it up so I am presuming that it is six 24 Ohm speakers wired in series.
    If I understand you correctly you are using your 150 head into an 8 ohm cabinet. My aim is to make it possible to use an 8 ohm amp into the 6x10 cabinet...perhaps wiring the individual speakers back to a central location where they could be switched from 6 in series to two "3 in series" wired parallel.
    I agree totally that a 4 ohm output into an 8 ohm cabinet shouldn't be a problem. Going the other way, say an 8 Ohm amp into a 4 Ohm cabinet might be asking for trouble.
    Thanks for your input, and it's very cool to hear from another person who still plays these great old amps from back in the day when solid state wasn't a synonym for piece of cr*p
     
  4. strat a various

    strat a various Friend of Leo's

    Posts:
    4,116
    Joined:
    May 9, 2008
    Location:
    Texas
    I'm not sure if I'm remembering the impedance of that cab. I think 4 ohms, but I'd test it if I were you.

    Also, I read the speakers in those cabs were 24 ohm speakers. I'm not certain that's right either. If it were mine, I'd measure each speaker separately, just to be sure.

    Here is a link to an impedance calculator if that would be handy:

    https://www.stereofactor.com/speaker-impedance-calculator/
     
  5. chrisdb

    chrisdb TDPRI Member

    Age:
    66
    Posts:
    24
    Joined:
    Nov 20, 2012
    Location:
    philadelphia
    yes.. a 4 Ohm cabinet. My guess is six 24 Ohm speakers are wired in series and together is a 4 Ohm load to the amp.
    thanks so much for your advice and the calculator link too.I'll be checking that out for sure
     
  6. Burning Fingers

    Burning Fingers Tele-Meister

    Age:
    67
    Posts:
    110
    Joined:
    Mar 6, 2019
    Location:
    Australia
    Um...It seems there is some confusion about parallel and series wiring.

    For the cab impedance to be 4 ohms it means the speakers are wired in parallel not in series.

    If they were wired in series the cab impedance would be 24*6 = 144 ohms !

    The suggested method of connecting in parallel, 2 strings of 3 * 24 ohm speakers that are in series would give you 36 ohms....not 8 ohms.

    3 speakers each of 24 ohms in parallel gives you 8 ohms and if you put those in series with another 3 24 ohm speakers in parallel you get 16 ohms.

    When speakers are in series you ADD the impedance of all the speakers.

    When speakers of equal impedance are in parallel you simply divide the impedance of one speaker by the number of speakers...that's how your 6 24 ohm speakers in parallel equal a total impedance of 4 ohms...24 divided by 6.

    Unfortunately you won't be getting 8 ohms total impedance using 6 * 24 ohm speakers regardless of how you wire them.
     
    dan40 likes this.
  7. Dukex

    Dukex Tele-Afflicted

    Posts:
    1,101
    Joined:
    Nov 8, 2012
    Location:
    SoCal
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.