pilgrim Posted January 27, 2009 Share Posted January 27, 2009 Quick question – if you link - two passive monitors together (via a speaker lead) both monitors 300w - 8ohms – powered by one side of a power amp say 750w – 8ohms - what sort of power would they draw from the amp – 600w or less. I am guessing that it would be less – but is there a per cent less or does it change with power and ohms. Any one got any ideas Link to comment Share on other sites More sharing options...
Shez Posted January 27, 2009 Share Posted January 27, 2009 300 + 300 = 600. OK, so it's not exactly that simple, but it's near enough. The amp would need to be capable of supplying that in to a four ohm load, and the speakers would have to be well enough matched to share the power equally, but 600W is pretty much where it is. Link to comment Share on other sites More sharing options...
Sound In Gloucestershire Posted January 27, 2009 Share Posted January 27, 2009 if the amp is 750w at 8ohms, check what wattage it is at 4 ohms, id guess its about 1,000w at 4ohms, but could be higher! Therefore you could be putting 500w into each monitor.... Link to comment Share on other sites More sharing options...
RaymondTerrific Posted January 27, 2009 Share Posted January 27, 2009 Therefore you could be putting 500w into each monitor.... That is ok though because you don't use all the power from an amplifier all the time. It's better for your amplifier to be capable of producing more power than your speakers' power rating so that it can handle transients without clipping. The power rating on your speakers is the maximum average power so they can easily handle peaks above that without being destroyed. Regularly send square waves to them though and they'll soon need replacing. Link to comment Share on other sites More sharing options...
Rexeltw Posted January 28, 2009 Share Posted January 28, 2009 It's better for your amplifier to be capable of producing more power than your speakers' power rating so that it can handle transients without clipping. The power rating on your speakers is the maximum average power so they can easily handle peaks above that without being destroyed. Regularly send square waves to them though and they'll soon need replacing. True but if you have an unplanned transient (heaven forbid!) then you are just a bit more likely to pop the voicecoil out of the magnet running overpowered. Should be fine though, we normally spec touring systems with at least 20% excess power in the drive racks just to cover things. Just don't wire up a MC2 E80 into a PS8 and expect it to run flat out forever... Link to comment Share on other sites More sharing options...
dknoise Posted January 28, 2009 Share Posted January 28, 2009 Quick question – if you link - two passive monitors together (via a speaker lead) both monitors 300w - 8ohms – powered by one side of a power amp say 750w – 8ohms - what sort of power would they draw from the amp – 600w or less. I am guessing that it would be less – but is there a per cent less or does it change with power and ohms. Any one got any ideas If both wedges are rated at 300w rms @ 8 ohms, If you connect them in parallel they will take an amp rated 1200W @ 4ohms Link to comment Share on other sites More sharing options...
Rob_Beech Posted January 28, 2009 Share Posted January 28, 2009 just to cover things. Just don't wire up a MC2 E80 into a PS8 and expect it to run flat out forever... Another new model? or did you mean 90? Either way, good advice A concurrent post has been automatically merged from this point on. If both wedges are rated at 300w rms @ 8 ohms, If you connect them in parallel they will take an amp rated 1200W @ 4ohms But not continuously. But then again what is RMS, how do we link the RMS handling of a speaker to the RMS output of an amplifier nowadays? Neither have any standards to work to so we rarely know exactly what a speaker will handle both short term and long term, nor so we know what all amplifiers output both short term and long term. Link to comment Share on other sites More sharing options...
dknoise Posted January 28, 2009 Share Posted January 28, 2009 just to cover things. Just don't wire up a MC2 E80 into a PS8 and expect it to run flat out forever... Another new model? or did you mean 90? Either way, good advice A concurrent post has been automatically merged from this point on. If both wedges are rated at 300w rms @ 8 ohms, If you connect them in parallel they will take an amp rated 1200W @ 4ohms But not continuously. But then again what is RMS, how do we link the RMS handling of a speaker to the RMS output of an amplifier nowadays? Neither have any standards to work to so we rarely know exactly what a speaker will handle both short term and long term, nor so we know what all amplifiers output both short term and long term. with program material, with a reasonable crest factor, in the real world. Link to comment Share on other sites More sharing options...
drsound Posted January 28, 2009 Share Posted January 28, 2009 Size is unimportant (according to my missus anyway boom boom). You can safely run a 100w compression driver all day long from a Macro 5002 as long as you control the maximum voltage - transients causing physical damage - and overall energy going into the coil leading to heating effects causing melting, fire and red faces. There is a skill to this involving knowing what you're doing though. It's really quite common to bi-amp wedges from two channels of an amp meaning that the HF channel has the same potential output power as the LF side despite the driver only being rated at perhaps 10% of the power. Equally you can destroy a "1000w" speaker driver with a 100w amp if you try hard enough. Give it a go, it's very amusing. Link to comment Share on other sites More sharing options...
pilgrim Posted January 28, 2009 Author Share Posted January 28, 2009 thanks ALL- this is starting to make sense. what would be the best suited amp 'power rating wise' - if I have a 500w 15inch sub at 8ohms - linked via speaker lead to a mid/top combo of 2 x 300w 12inch at 8 ohms with 2 compression drivers 45w each @ 8ohms. also does anybody know if they still make the eminence T - 0812 compression driver 8ohms - around 45w 'but not 100% sure' - or anything that could do the same job - long shot this one - but any help would be great. Link to comment Share on other sites More sharing options...
ChazHS Posted January 28, 2009 Share Posted January 28, 2009 thanks ALL- this is starting to make sense. what would be the best suited amp 'power rating wise' - if I have a 500w 15inch sub at 8ohms - linked via speaker lead to a mid/top combo of 2 x 300w 12inch at 8 ohms with 2 compression drivers 45w each @ 8ohms. also does anybody know if they still make the eminence T - 0812 compression driver 8ohms - around 45w 'but not 100% sure' - or anything that could do the same job - long shot this one - but any help would be great. Using the inbuilt crossover? I wouldn't reccomend it, the amplifier won't like driving two seperate power of speaker, it dosen't know to give one 500W and the other 450W or whatever it may use. I'd only ever daisy chain speakers of the same power. Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 28, 2009 Share Posted January 28, 2009 Just don't wire up a MC2 E80 into a PS8 and expect it to run flat out forever... No, I'd put a PS8 TD controller between and allow it to sense voice coil temperature, dynamics and diaphragm displacement ;-) Link to comment Share on other sites More sharing options...
ChazHS Posted January 28, 2009 Share Posted January 28, 2009 Just don't wire up a MC2 E80 into a PS8 and expect it to run flat out forever... No, I'd put a PS8 TD controller between and allow it to sense voice coil temperature, dynamics and diaphragm displacement ;-) Out of interest, how does it know the temperature? The resistance in the lines? Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 28, 2009 Share Posted January 28, 2009 Out of interest, how does it know the temperature? The resistance in the lines? The controller has sense leads connected to the amplifier terminals. This signal is processed in such a way to model the cone displacement and the voice coil temperature. The inbuilt VCAs can then adjust the signal to the amplifier in order to protect the loudspeaker. There's also a much faster acting peak limiter to protect against peak voltages. Measuring actual voice coil temperature isn't too easy, but there are some methods where the voice coil becomes the "unknown resistor" in a Wheatstone Bridge arrangement, with a large value capacitor allowing the dc component to be measured whilst still putting a high level ac signal through. I think there's a circuit diagram in Dickinson's loudspeaker Design book. Simon Link to comment Share on other sites More sharing options...
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