exaisle Posted February 2, 2009 Share Posted February 2, 2009 Moderation: One of the topic in the sound forum dealt with 2 and 4 core speaker cables - it then went off topic by considering the implications of commoning systems, and the theory of why it would or wouldn't work. We've moved this out of sound into general tech chat as although it relates to sound, a wider readership could find this interesting. All the posts on this subject have been moved into this new topicoriginal topic here The only real problem, and it's quite small really, is when you make the cables up, you put one end on and the four cables are in the correct lay to make a neat connection. At the other end they are in the wrong order, meaning you have to have a little more exposed and they need to cross inside the plug. To do it properly you need to heatshrink the end, otherwise, the sheath tends to pop out of the grip, putting stress on the terminals. Nope. All you do is pull the sheath (outer jacket) back an inch or two, cut the conductors an inch shorter, terminate, push the sheath back toward the connector, and tighten the strain relief. My cables are going on 7 years old, and I've never had a sheath back out. I'm inviting a flood of wrath here....just wondering if it's feasible to wire three banks of speakers with one four-core cable? Say +1 to tops, -1 to mids and +2 to bins, using -2 as a common/neutral? After all, it's AC we're talking about here......isnt it? Not that Ive done that. I just use 4 core connectors on my rig to ensure I dont connect it the wrong way around...so my tops are +1/-1 and the bins are +2/-2 (and I use two x two-core cables each side). E Link to comment Share on other sites More sharing options...
jonathanhill Posted February 3, 2009 Share Posted February 3, 2009 Far as I know you can't do that. Amplifier outputs are DC, not ac. Effectively you would common the negative side of the amplifiers together which would most likely blow the drivers. The safe way would be to use 8 pole speakons with 1+/1- as HF, 2+/2- as LF and 3+/3- as sub. Think I am right, but I am more lamps than noise... Link to comment Share on other sites More sharing options...
Simon Lewis Posted February 3, 2009 Share Posted February 3, 2009 Amplifier outputs are DC, not ac. ......Think I am right, but I am more lamps than noise... Certainly not!!! If the amp produced DC at a high output power, the loudspeaker would shoot as far forward as the suspension would allow, then the coil would catch fire. I'm inviting a flood of wrath here....just wondering if it's feasible to wire three banks of speakers with one four-core cable? Say +1 to tops, -1 to mids and +2 to bins, using -2 as a common/neutral? After all, it's AC we're talking about here......isnt it? No, you cannot do this, since the amp outputs cannot be connected*. Keep each pair of wires from the amp terminals separate. To do what you want, use 8 core cable and an NL8 connector. Simon * well you can - but the amp might not work afterwards... Link to comment Share on other sites More sharing options...
jonathanhill Posted February 3, 2009 Share Posted February 3, 2009 Amplifier outputs are DC, not ac. ......Think I am right, but I am more lamps than noise... Certainly not!!! If the amp produced DC at a high output power, the loudspeaker would shoot as far forward as the suspension would allow, then the coil would catch fire. As far as I recall, from a simple class-A amplifier, the rails are 12VDC and ground and it is the switching nature of the transistor that allows higher currents to flow between emitter and collector with respect to the signal on the base. Fairly sure this is the same for the class-B amps, they just use a push-pull transistor pair, with one device taking the positive cycle and the other taking the negative cycle. Cannot remember what a class-C does, I just know that it is unsuitable for audio as weird things happen to the output waveform - they use it for radar. Link to comment Share on other sites More sharing options...
Chris Beesley Posted February 3, 2009 Share Posted February 3, 2009 The output of any audio amplifier MUST be AC to enable the speaker to move back and forth creating the sound waves.... as Simon said earlier a DC signal would simply hold the speaker cone in one, static point burning out the voice coil in a very short space of time. Link to comment Share on other sites More sharing options...
jonathanhill Posted February 3, 2009 Share Posted February 3, 2009 The power supply of an amplifier takes an ac supply and then rectifies it to a positive DC supply and a negative DC supply. These rail supplies are then switched by the output devices with reference to the signal input to create the output. Effectively the output of the amplifier is a pseudo ac signal that is actually derived from a +ve and -ve DC supply, albeit a continuously variable voltage with both +ve and -ve cycles with reference to ground. That is the point I was trying to make, rather clumsily. Link to comment Share on other sites More sharing options...
sleah Posted February 3, 2009 Share Posted February 3, 2009 The power supply of an amplifier takes an ac supply and then rectifies it to a positive DC supply and a negative DC supply. These rail supplies are then switched by the output devices with reference to the signal input to create the output. Effectively the output of the amplifier is a pseudo ac signal that is actually derived from a +ve and -ve DC supply, albeit a continuously variable voltage with both +ve and -ve cycles with reference to ground. That is the point I was trying to make, rather clumsily. You got there in the end!You could also say the output varies from being almost DC, i.e. very very low sub bass, to almost +ve and -ve at the sametime, i.e. very very high note. :) Unless the reader fully understands AC, DC, frequencies and waveforms, not to mention PSU's, it's probably safer to stick to saying an audio signal is AC! Link to comment Share on other sites More sharing options...
jonathanhill Posted February 3, 2009 Share Posted February 3, 2009 Unless the reader fully understands AC, DC, frequencies and waveforms, not to mention PSU's, it's probably safer to stick to saying an audio signal is AC! This s a technical forum though... Link to comment Share on other sites More sharing options...
Rob_Beech Posted February 3, 2009 Share Posted February 3, 2009 But given the nature of the OP (2 years ago may I add). A question on this level would expect answers on this level,] Eg, the OP asked a rather low level question about speaker cables and wiring. Asking a question on this level would not expect to go into advanced details about amplifier types and the way they work. No disrespect to the OP or anyone else. It is a technical forum, but we have users that are just starting out in the industry, those that have been in it a while, and those people in the industry that have forgotten more than most of us know (Simon as an example......not saying that Simon is forgetful.) Rob Link to comment Share on other sites More sharing options...
Simon Lewis Posted February 3, 2009 Share Posted February 3, 2009 That is the point I was trying to make, rather clumsily. the key thing is that the output transistors allow current from the supply rails to flow in such a way as to provide an amplified version of the input signal. If there wasn't a fairly close correlation between the two (apart from amplitude) then the result would be distortion. Link to comment Share on other sites More sharing options...
J Pearce Posted February 3, 2009 Share Posted February 3, 2009 The other issue with commoning returns (if it were possible in the first place) is that one 2.5mm conductor carries the return current of all three circuits, and would probably overheat that core or limit the system. Link to comment Share on other sites More sharing options...
exaisle Posted February 4, 2009 Author Share Posted February 4, 2009 Thanks to all for your responses.... The output of a power amplifier is designed to cause a coil to move backwards and forwards (which moves air). Isnt that remarkably similar to any AC motor? OK, the layout of the coils and magnets are different, the frequency varies, etc etc but the basics are the same. So...can I connect the neutral from three AC motors together? Anybody ever come across 3-phase? Is it fair of me to compare this concept with an unbalanced 3-phase circuit? As regards overheating, the current carried by the neutral wire is the same as that carried by the live, but the voltage is lower, so I would argue that overheating as mentioned by J Pearce in an earlier post shouldnt arise. (The old Bulgin lighting connectors had four live but only two neutral wires). So....to return to my original question.....why can't the "neutral" side of three power amps be connected? I'm not proposing to try it any time soon but I'd like to know the "why" rather than "it just can't". E. Link to comment Share on other sites More sharing options...
Rob_Beech Posted February 4, 2009 Share Posted February 4, 2009 No entirely. My knowledge is more limited to putting lots and lots of boxes in the right place and making them sound ok. We can use 1 neutral for 3 phase mains supplies where we have unbalanced loads as the 3 phases are 120 degrees out of phase therefore the maximum current can be from 0 to the maximum current of the Live, say 32A, the cable should be rated for this, and if the Lives are, then the N is too. So, if we lined up the phases we could potentially send much higher currents down the Neutral. Link to comment Share on other sites More sharing options...
paulears Posted February 4, 2009 Share Posted February 4, 2009 Moderation: One of the topic in the sound forum dealt with 2 and 4 core speaker cables - it then went off topic by considering the implications of commoning systems, and the theory of why it would or wouldn't work. We've moved this out of sound into general tech chat as although it relates to sound, a wider readership could find this interesting. All the posts on this subject have been moved into this new topicoriginal topic here Link to comment Share on other sites More sharing options...
jonathanhill Posted February 4, 2009 Share Posted February 4, 2009 So...can I connect the neutral from three AC motors together? Anybody ever come across 3-phase? Is it fair of me to compare this concept with an unbalanced 3-phase circuit? Generally three phase motors (certainly those wired in delta formation) do not require a neutral. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.