sub with out an amp
16 May 2005, 09:09 AM
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sub with out an amp
i have just been bought subwoofer (sony xplod 12" 1200watt)
and i have no amp because im skint i was wondering if i could run it of my head unit untill i have the funds to get an amp
and i have no amp because im skint i was wondering if i could run it of my head unit untill i have the funds to get an amp
16 May 2005, 12:32 PM
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hmmm, if it was me, i would disconnet the rear speakers, and bridge both left and right +'s together, and both left and right -'s together, with audio cable and and put it into the sub. otherwise you are going to strain 1 rear channel. if you see what i mean
16 May 2005, 12:33 PM
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You can't bridge a head unit's internal channels. Messing about trying to do that will at best put the head unit into protection, and at worst wipe out the amp in the head unit.
You can run a sub off head units, and someone on talkaudio got a surprising amount of output out of one. Have a search over there for more info.
You can run a sub off head units, and someone on talkaudio got a surprising amount of output out of one. Have a search over there for more info.
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16 May 2005, 12:43 PM
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really?, i did this on an old Sony a couple of years back and it worked a treat for prolly 6 months before i bought an amp and did it the conventional way.
im genuinly interested, in what way would it damage it?
Si
im genuinly interested, in what way would it damage it?
Si
17 May 2005, 09:20 AM
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Should be fine plugging it into one speaker output. Ideally you'd only have the bass frequencies going to the sub, however given the power rating of the sub (apparently lots) and the head unit (not too much) it won't cause problems.
Go for it!
Go for it!
17 May 2005, 09:45 AM
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By bridging, I assume you mean using the positive of one and the negative of the other output, or something like that?
You're commoning up outputs that were never meant to be commoned up... Having seen a head unit amp instantly destroyed by someone trying to wire both sets of outputs across one speaker, I'd imagine that it will not do the amp any good at all, however it does depend on the sort of amp used in the h/u.
Warning: I could be wrong from this point in
.
Bridging an amp normally means that one channel receives an inverted signal to amplify.
A 2 channel amp has L and R inputs and outputs. If you elect to bridge, then you might need to configure the amp using a config switch, and might use + of left as positive, and + of right as negative - it'll depend on the amp's config. What's happening is that internally the right channel is being fed an inverted image of the left channel, hence the amplitude of the overall signal will be double what a single channel will produce. The grounds of the channels will be commoned up internally IIRC...
I'm surprised that bridging produced anything! What unit was it, and how did you wire it up.
As ru' says, use 1 set of outputs. If you want to filter the frequencies, use a coil (inductor) of appropriate value in series with the sub - most car audio shops will sell these. "In series" means wiring it so all the signal goes through the coil, so wire one end of the coil to the amp + output, and the other end to the speaker + input.
BTW, I ran my first sub without any filtration and it sounded acceptable - subs have a steep-ish natural rolloff, and if the sub is in a boot you won't hear much high frequency anyhow...
You're commoning up outputs that were never meant to be commoned up... Having seen a head unit amp instantly destroyed by someone trying to wire both sets of outputs across one speaker, I'd imagine that it will not do the amp any good at all, however it does depend on the sort of amp used in the h/u.
Warning: I could be wrong from this point in
.Bridging an amp normally means that one channel receives an inverted signal to amplify.
A 2 channel amp has L and R inputs and outputs. If you elect to bridge, then you might need to configure the amp using a config switch, and might use + of left as positive, and + of right as negative - it'll depend on the amp's config. What's happening is that internally the right channel is being fed an inverted image of the left channel, hence the amplitude of the overall signal will be double what a single channel will produce. The grounds of the channels will be commoned up internally IIRC...
I'm surprised that bridging produced anything! What unit was it, and how did you wire it up.
As ru' says, use 1 set of outputs. If you want to filter the frequencies, use a coil (inductor) of appropriate value in series with the sub - most car audio shops will sell these. "In series" means wiring it so all the signal goes through the coil, so wire one end of the coil to the amp + output, and the other end to the speaker + input.
BTW, I ran my first sub without any filtration and it sounded acceptable - subs have a steep-ish natural rolloff, and if the sub is in a boot you won't hear much high frequency anyhow...
17 May 2005, 09:56 AM
#12
A 2 channel amp to power you sub can be bought very cheaply, from about £20. You will also need a wiring kit but that isnt that much either. Ebay will be good for second hand offers.
I wouldnt bother running it off your headunit, it will not have enough power to make it sound very good and you will need to block off the high frequencys using a filter to stop the chance of damaging the sub.
I wouldnt bother running it off your headunit, it will not have enough power to make it sound very good and you will need to block off the high frequencys using a filter to stop the chance of damaging the sub.
17 May 2005, 10:33 AM
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Originally Posted by chiark
By bridging, I assume you mean using the positive of one and the negative of the other output, or something like that?
You're commoning up outputs that were never meant to be commoned up... Having seen a head unit amp instantly destroyed by someone trying to wire both sets of outputs across one speaker, I'd imagine that it will not do the amp any good at all, however it does depend on the sort of amp used in the h/u.
Warning: I could be wrong from this point in .
Bridging an amp normally means that one channel receives an inverted signal to amplify.
A 2 channel amp has L and R inputs and outputs. If you elect to bridge, then you might need to configure the amp using a config switch, and might use + of left as positive, and + of right as negative - it'll depend on the amp's config. What's happening is that internally the right channel is being fed an inverted image of the left channel, hence the amplitude of the overall signal will be double what a single channel will produce. The grounds of the channels will be commoned up internally IIRC...
I'm surprised that bridging produced anything! What unit was it, and how did you wire it up.
As ru' says, use 1 set of outputs. If you want to filter the frequencies, use a coil (inductor) of appropriate value in series with the sub - most car audio shops will sell these. "In series" means wiring it so all the signal goes through the coil, so wire one end of the coil to the amp + output, and the other end to the speaker + input.
BTW, I ran my first sub without any filtration and it sounded acceptable - subs have a steep-ish natural rolloff, and if the sub is in a boot you won't hear much high frequency anyhow...
You're commoning up outputs that were never meant to be commoned up... Having seen a head unit amp instantly destroyed by someone trying to wire both sets of outputs across one speaker, I'd imagine that it will not do the amp any good at all, however it does depend on the sort of amp used in the h/u.
Warning: I could be wrong from this point in
.Bridging an amp normally means that one channel receives an inverted signal to amplify.
A 2 channel amp has L and R inputs and outputs. If you elect to bridge, then you might need to configure the amp using a config switch, and might use + of left as positive, and + of right as negative - it'll depend on the amp's config. What's happening is that internally the right channel is being fed an inverted image of the left channel, hence the amplitude of the overall signal will be double what a single channel will produce. The grounds of the channels will be commoned up internally IIRC...
I'm surprised that bridging produced anything! What unit was it, and how did you wire it up.
As ru' says, use 1 set of outputs. If you want to filter the frequencies, use a coil (inductor) of appropriate value in series with the sub - most car audio shops will sell these. "In series" means wiring it so all the signal goes through the coil, so wire one end of the coil to the amp + output, and the other end to the speaker + input.
BTW, I ran my first sub without any filtration and it sounded acceptable - subs have a steep-ish natural rolloff, and if the sub is in a boot you won't hear much high frequency anyhow...
Its still in my wifes 306 so i dont know the actual model as shes out at the mo.
Simon.
17 May 2005, 05:51 PM
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That's just the config that knocked out a mate's head unit. Something is ringing vague bells in my head about common grounds, etc... I'll have a google 
But if it's working, and still working, that's good. The amp isn't bridged in that config tho.
But if it's working, and still working, that's good. The amp isn't bridged in that config tho.
17 May 2005, 11:45 PM
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Nick - I guess what you're thinking of re: common grounds is that some head units have all the speaker -ve's grounded (or very low impedance connection to ground). Therefore, connecting e.g. right rear +ve to left rear -ve to "bridge" the amp will effectively short out the left rear amp and blow something up.
As for connecting both +ves and both -ves together (which as you state, isn't bridging) - well that depends on the amp. If you have a "very stereo" signal, you could end up with the rear left output stage fighting the rear right output stage to create a different instantaneous output voltage, potentially blowing one or the other. Depends on the configuration of the amps, output impedances etc - IIRC some output stages are a lot more tolerant of being backdriven than others.
I'd expect you'll find that there will be little or no benefit in "parallelling" the two outputs. It potentially gives you roughly half the output impedance and therefore maintains output voltage better when flowing a lot of current through a fairly low impedance sub. However, I'd guess that in most car head units the limiting factor on absolute power is either total current through the unit or total heat dissipation in the head unit rather than output impedance of the amp stage.
As for connecting both +ves and both -ves together (which as you state, isn't bridging) - well that depends on the amp. If you have a "very stereo" signal, you could end up with the rear left output stage fighting the rear right output stage to create a different instantaneous output voltage, potentially blowing one or the other. Depends on the configuration of the amps, output impedances etc - IIRC some output stages are a lot more tolerant of being backdriven than others.
I'd expect you'll find that there will be little or no benefit in "parallelling" the two outputs. It potentially gives you roughly half the output impedance and therefore maintains output voltage better when flowing a lot of current through a fairly low impedance sub. However, I'd guess that in most car head units the limiting factor on absolute power is either total current through the unit or total heat dissipation in the head unit rather than output impedance of the amp stage.
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