connecting hi-fi speakers, ohms impedance etc

[Jbravo]

I hope this is the right forum, I figured it was the right place to find the people with the relevant expertise anyway

I have a hi-fi amplifier and stereo speakers, all was working fine

I bought a subwoofer and the amp has a switch to power a second pair of speakers so I connected it to one channel which worked fine. Seeing as the (mono) subwoofer only had one pair of wires and the amp had outputs for stereo speakers, I then wired the subwoofer in such a way that it was connected to both L and R outputs simultaneously, which presumably makes it louder and also ensures both channels get the added low frequencies reproduced by the subwoofer.

Anyhow, I turned it up and it sounded great for 10 seconds or so then silence and the amp no longer works

To be fair this doesn't really surprise me as I don't really understand speaker ratings (ohms, impedance etc) but I do know it's important to consider these things to prevent such damage happening - doh

anywayyyyyyyy, can anyone explain to me how I should go about connecting a mono subwoofer to a stereo amp and how to be sure it won't cause any damage next time? Any advice is greatly appreciated

[GaryG]

I don't think it's the speaker impedance that killed your amp but rather wiring both outputs together. You effectively shorted the two channels directly together which could cause all sorts of problems. If the amp had short circuit protection it may have survived but... <shrugs>.

There are ways of bridging two power amps to drive a single speaker but you have to invert one input signal and generally not something you do with a regular hifi amp. I'd advise getting an amp with a dedicated sub out (maybe a home cinema one?), an amp with a preamp out that can be connected to an active sub or a sub that has high level inputs which can take the speaker outs from your amp.

Maybe something like the WhatHiFi forum would have people who could recommended specific models.

Have fun!

[Jbravo]

thanks Gary, I've since learned it was a pretty silly thing to do and asking for trouble. I've since ordered a cheap 3 channel amp with dedicated Sub output. At least the experience was educational

[GaryG]

what doesn't kill you etc etc etc...

[Jbravo]

what doesn't kill you etc etc etc...

aye!

[Jim Y]

How did you wire across both channels?
If you wired across both + terminals only, then you wouldn't get much bass as this way you only get what's different between L & R which isn't the Bass as this is usually mixed equal to L & R.
If you connected to both L & R and bonded both channels together - you probably blow the amp fuses.

If the amp has bridged (BTL) outputs...

Wiring between L + and R - only ( or R+ and L-), could possibly work! That would give what is only common between L&R which includes the Bass. This often works in cars because BTL output is common there. If it isn't BTL it's the same as you first tried because either - terminal is ground.

[Jbravo]

thanks Jim, yeah I must have shorted out those stereo outputs. I'm hoping it's just a fuse which can be easily replaced :/