Audio Speaker loads,  4 ohms or even lower - Page 1
Forum section: electronics / beginners

author: RJSV
author_rank: Super Contributor
timestamp: December 16, 2024, 06:19:25 pm
content: With newer audio power amps, how bad is it, to run into a lower impedance (speaker) load ?Older tube powered amps often run into 4 speakers, whose total gets down to 2 ohms, or even less.So, especially with digital everything these days, how bad is it, to impose such loads ?A Fender Super Reverb model, along with aux speaker box, would be something down around @ OHM, or even less....but that set-up runs on vac. tubes.

author: TimFox
author_rank: Super Contributor
timestamp: December 16, 2024, 06:48:22 pm
content: Vacuum-tube amplifiers normally ran with output transformers, often with multiple secondary taps for 4, 8, and 16 ohms.If you have multiple speakers on one output, you can run them in series or series-parallel for a higher load impedance on the amplifier output.On "hi-fi" amplifiers, I have never seen a 2 ohm output tap: I'm not familiar with instrument amplifiers.On solid-state switching amplifiers, the specification is for maximum voltage and maximum current: check the manual.

author: themadhippy
author_rank: Super Contributor
timestamp: December 16, 2024, 07:14:58 pm
content: some high power amps will happily play with 2 ohms,lab gruppen for example.but go too low and the speaker cables start becoming more of the load

author: RJSV
author_rank: Super Contributor
timestamp: December 16, 2024, 10:38:16 pm
content: Thanks folks:I know the typical older Fender guitar amps would drive 4 speakers, each at 8 ohms, so that parallel shows as 2 ohms. But often that amp was used with supplement speaker boxes, like from the 'Bassman' product line, so the total parallel situation would be close to '1' ohm !I'm also with similar question applied to (my) recent purchase of electronics containing birthday cards, as that application can be surprising when driving sound through a ten inch low end woofer.(Sorry, lol; THAT commercial product has no specification sheet,...at least not easily available.)

author: Analog Kid
author_rank: Super Contributor
timestamp: December 16, 2024, 10:42:49 pm
content: Quote from: RJSV on December 16, 2024, 10:38:16 pmI thought©® that those 4 speakers would be wired in series-parallel so the total impedance was still 8 ohms.

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2024, 10:52:39 pm
content: Quote from: Analog Kid on December 16, 2024, 10:42:49 pmSeries is generally not a good idea, since it reduces the damping factor. It might not be so bad, if the speakers are all in the same cabinet, so their cones are mechanically coupled, but still not great.

author: CaptDon
author_rank: Super Contributor
timestamp: December 16, 2024, 11:34:32 pm
content: You may be surprised how some of the guitar amps and speakers are wired. 4 X 8 ohms can still be 8 ohms. 2 in series = 16 ohms, then parallel that with a second series pair and you have 8 ohms. Some of the guitar amps have a very unusual 'auxilliary' speaker jack wired to put the aux cabinet in series with the internal speakers, there are 2 X 8ohms in parallel = 4 ohms in the cabinet and then you plug in an external 4 ohm cabinet and due to the sneaky aux jack wiring the amp will see 8 ohms not 2. Nearly all good quality power amps sense final stage transistor emitter current or MOSFET source current and will 'fold back' or current limit saving the amp from damage. As for the statement about damping, isn't damping the ratio of speaker impedance to amplifier 'apparent' output impedance? So does a single 8 ohm speaker see a different damping factor than a pair of 4 ohm speakers in series or how about a pair of 16 ohm speakers in parallel? In today's solid state very powerful amplifiers that use no output transformer we generally assume any impedance up to and including an open circuit that is 'greater than' the amp's minimum specified output impedance will be fine. Going lower can lead to damage and LESS not more actual measured power at the load. Amplifiers with output transformers should not be working into higher than rated impedances. Maximum power transfer will occur at the rated impedance.

author: RJSV
author_rank: Super Contributor
timestamp: December 17, 2024, 02:34:25 am
content: Ah, thanks. So, I could NOT assume that ANY type output could drive ANY speaker type...Might not damage a special gift card, toy piano, etc. but still possible to damage due to excess current.Low cost of a toy might still allow for experimentation, on limited budgets.Yes, though, I'm sure...the 4 speakers in my amp had a central connection soldering piece having TWO connection points, going to two wires over to the amp chassis jack.A TOY output, by the way, drives my DUAL brand 10 inch bass driver quite well, at moderate volume, (just not boomy at low end).

author: CaptDon
author_rank: Super Contributor
timestamp: December 17, 2024, 03:23:34 am
content: 4 X 16 ohms = 4ohms was very very common in 4 X 12" guitar cabinets. You still see many 16 ohm 12" guitar speakers on Ebay. My Peavey classic 100 series with 2 X 8 ohm 12" in the combo cabinet puts anything plugged into the AUX speaker connector in series with the internal speakers. So when plugging in an external 4 ohms the amp actually sees and 8 ohm load.

author: RJSV
author_rank: Super Contributor
timestamp: December 17, 2024, 09:46:26 am
content: Wow, I think you are right, as I've been assuming the 10 inch Fender speakers are 8 ohms.I can also see how an AUX jack could switch, between ground in the simple case, while placing any extra speaker in series.Thanks.