Adding 2wire speakers to a 4wire system
January 16, 2006 1:59 PM   Subscribe

hifi-lter: I want to add an extra pair of speakers to my Panasonic (sa-pm25) hi-fi. But each of the existing speakers have 4 wires (2x 2pairs).

On the back of the hi-fi, each of the pairs have a (+) and (-) connector. I've only ever seen speakers with 2 wires before. So, can I add a normal pair of speakers with just 2 wires to this hi-fi? If not, do I need special speakers, or some kind of convertor?

If it helps, the manual is here:
posted by blacksky to Technology (9 answers total)
Putting aside the 4-wire issue for a moment, you shouldn't really be connecting speakers in parallel. If you must do it, you should calculate the cumulative resistance of the speakers with the Resistors in Parallel formula (you could do it in series too, of course) and make sure that it is within spec on the amplifier. (It isn't a big deal to run an amp out of spec if you are very careful about it - never turn the volume up very much, make sure it doesn't get hot, etc. - but it isn't a good idea for a permanent setup).

As for the 4-wire connection, this is either biamping or biwiring. Very likely biamping actually, which means you can't easily connect extra speakers...
posted by Chuckles at 2:49 PM on January 16, 2006

It is very strange that this type of product would use biamping...

One theory: It is possible that the lower frequency driver is driven with a Class-D amplifier switching just over 20kHz, and the tweeter is driven by a more traditional amplifier. The low switching frequency wouldn't do a good job on high frequency sounds, but high frequency sounds are easier to reproduce, so the advantage of Class-D operation are less important. Hence combining two different types of amplifier might make sense...
posted by Chuckles at 2:57 PM on January 16, 2006

the spec in the manual implies it's got two amplifiers with more power at low frequencies. i think you're right.
posted by andrew cooke at 5:32 PM on January 16, 2006

Yep, it is right there in black and white... -1 for reading comprehension, I guess.

It is pretty surprising to see it in a consumer product, but the more I think about it the more I can see that the economics probably do work... Eliminating the speaker cross-overs is a good savings. The savings from amplifier efficiency improvements is minor at this low power level, but then the cost of the added wires and terminals is pretty minor too.
posted by Chuckles at 5:55 PM on January 16, 2006

You could add different speakers by connecting them only to the high side, but it won't sound great (unless the main speakers are nearby and you still get bass from them). Otherwise you're kind of screwed.
posted by cillit bang at 7:27 PM on January 16, 2006

Response by poster: Thanks for the info. As you probably guessed, I'm a complete hifi illiterate. So this is probably a stupid question: Would it not be possible to connect the output from the 2 amps, and let the crossover in the new speakers sort it out?
posted by blacksky at 3:30 AM on January 17, 2006

the trouble with that is you're also connecting the output from one amplifier back into the output from the other. that just feels bad to me, but thinking about exactly why i'm not 100% sure.

i think it's because amplifiers (especially cheap ones, and especially especially the kind that is driving the bass) use feedback to reduce distortion. that may sound contradictory, but what they do is compare the output against what they're given as the input, and make constant changes to ensure that the output is a faithful (but amplified) copy of the input.

hopefully you can see from that, that if you add extra signal to the output (by connecting the output of another transformer) you're going to confuse things. each amplifier is going to try correcting itself because it sees the output from the other. i have no idea what will happen, but i can't imagine it would be pleasant.
posted by andrew cooke at 4:07 AM on January 17, 2006

transfomer -> amplifier
posted by andrew cooke at 4:40 AM on January 17, 2006

andrew cooke's explanation is good.... He is describing a process by which the amplifier would become unstable and be driven into oscillation, which will more than likely cause one of the transistors/FETs to overheat and fail - think of early computer controlled fighter planes that crashed due to pilot-induced oscillation.

Parallel audio amplifiers isn't out of the question entirely, although it is very unusual for many good reasons. In this case Panasonic would have done it to save money, if they could (and if it saved money...).
posted by Chuckles at 7:46 AM on January 17, 2006

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