The Boogie Man Posted September 21, 2006 Share Posted September 21, 2006 Hi all, Could someone just clear up a point? Does an amplifier with a stated, say 500 watts rms, on full volume, recieving a 0db test signal, produce that wattage. And if so does the the same amp recieving a dynamic signal that has peaks and troughs of say -5 to +5dbs produce 500 watts at the peak of the signal or is it being forced to produce more as the signal passes 0db? Secondly the ratings for speakers. if rated at 250 rms, 500 program and 1000 peak, should a speaker be matched to the amp based on the program wattage of 500 or the 250 rms? I'm just wondering if there is a peak power output for an amp should it be matched to the peak power output of a speaker? cheers Baz Link to comment Share on other sites More sharing options...
dbuckley Posted September 22, 2006 Share Posted September 22, 2006 Oh man, can of worms. There is a normal assumption that an amp rated at 500W RMS will produce 500W RMS continuously when fed with a test signal (often 1KHz sine). The amp will produce more power, but not continuously. How much more is down to (1) the capacity of the power supply to deliver more power short term , (2) the amplifier itself to remain linear and thus not clip, (3) the ability to dissapate heat before overheating Speakers are best rated using the AES power measurement, which is how much bandwidth limited pink noise they can handle for two hours. Its normally more than the RMS and less than the peak. Peak is determined by mechanical constraints, basicall how far the cone moves before it bumps into stops or destroys the supports. AES is determined by thermal effects, how hot the voice coils can get before melting. My take on this is that your amp should exceed the speakers peak handling by a bit, so the amp can cleanly deliver more than the speakers program power on peaks, so no clipping, but you should ensure the average drive should be within the AES rating. This normally happens with music; watching the LEDs on the desk if the peaks get the 0db going the average will be at least 6dB lower. However if you can deliver peak power at 0dB and then run full bandwidth pink noise at 0dB you will have meltdown. Being sure of not melting speakers can be a problem if you run hard. Some speakers that have clever controllers (Celestion SR, Nexo) measure the power a speaker is being given, and turn the audio down if there is risk of thermal damage. If you're going to push, its always a good idea to have limiters on the crossover, to prevent excessive drive. Link to comment Share on other sites More sharing options...
saturnx21 Posted September 22, 2006 Share Posted September 22, 2006 Hi all Hope I'm not stating the obvious but when matching speakers to amps it must be remembered that the amp will only out put it's maximum at it's lowest stable ohm'age so if you have a 500w amp at 2ohms bridged and you put two 250w speakers @ 4ohms to it you will only get around 125 watts in to each speaker! but to the best knowledge you carn't buy 2 ohm speakers so I would recommend finding an amp that will produce 500 watts in to each channal @ 4 ohms, as you should rate your amp to the peak rating of your speakers. Hope that helps! (and makes sense its bin a long day!!!) Link to comment Share on other sites More sharing options...
Pete Posted September 22, 2006 Share Posted September 22, 2006 Hope I'm not stating the obvious but when matching speakers to amps it must be remembered that the amp will only out put it's maximum at it's lowest stable ohm'age so if you have a 500w amp at 2ohms bridged and you put two 250w speakers @ 4ohms to it you will only get around 125 watts in to each speaker! but to the best knowledge you carn't buy 2 ohm speakers so I would recommend finding an amp that will produce 500 watts in to each channal @ 4 ohms, as you should rate your amp to the peak rating of your speakers. Exscuse my early morning post,but making it a single 500w ( at 2 ohm channel) would quite happily drive to 250w (4 ohm) speakers because theyre connected in series so youd get a 500w 2 ohm load! Link to comment Share on other sites More sharing options...
dbuckley Posted September 22, 2006 Share Posted September 22, 2006 ... 250w (4 ohm) speakers because theyre connected in series so youd get a 500w 2 ohm load!Connected in what exactly? 2:<anything>am posts are prone to trouble... Link to comment Share on other sites More sharing options...
The Boogie Man Posted September 22, 2006 Author Share Posted September 22, 2006 Hi all, dbuckley, cheers for that, so in essence then the program wattage ( aes? ) is the one to roughly go by. Then keep an eye on the type of meterial being put through the system. ie an amp producing 650 rms 4ohm would be well suited to a speaker with a 300 watt rms, 600 watt program? Personaly my type of music is handy in that my voice and guitar don't use a great range, and I compress and gate both signals pre-mixer then gate compress and limit to 0db post mixer. So the final signal to the amps still has a certain amount of dynamics ( I'm not quite as monotone as a test signal, I hope). cheersbaz Link to comment Share on other sites More sharing options...
jayselway Posted September 23, 2006 Share Posted September 23, 2006 ... 250w (4 ohm) speakers because theyre connected in series so youd get a 500w 2 ohm load!I was wondering about this when I read the post in the early hours of this morning, but knowing what my 3am posts can be like, I didn't chance a 5:30am one! Link to comment Share on other sites More sharing options...
Tomo Posted September 23, 2006 Share Posted September 23, 2006 Impedance matching is about power transfer. Maximum power transfer happens when the impedance of the load is equal to the impendance of the supply. If your amp says "500W at 8Ohms", that means that if you connect an 8 Ohm load to it (usually a speaker) it will dump 500W of power into the load. It will also dissipate 500W within its driving transistors, which will get warm. If you connect a 16Ohm load, then the increased impedance will limit current, and you'll get roughly half the power output.As the current has been reduced, the amps dissipate less internally and stay cooler. If you connect a 4 Ohm load, then the speakers will actually get roughly 2/3 power because a greater percentage of the power available will be dissipated within the amps - so the amps will get hotter as well. By fitting transformers, you can match impedances to get maximum output power. You can also match impedances by connecing up speakers in series and/or parallel: If you connect two 8 Ohm speakers in series, they look like a 16 Ohm speaker.If you connect two 8 Ohm speakers in parallel, they look like a 4 Ohm speaker. Link to comment Share on other sites More sharing options...
dbuckley Posted September 23, 2006 Share Posted September 23, 2006 ie an amp producing 650 rms 4ohm would be well suited to a speaker with a 300 watt rms, 600 watt program?As long as the speaker is 4 ohm, and you act responsibly, then yep, thats a reasonable match, certainly one I'd be happy with. Link to comment Share on other sites More sharing options...
Rob_Beech Posted September 24, 2006 Share Posted September 24, 2006 If you connect a 4 Ohm load, then the speakers will actually get roughly 2/3 power because a greater percentage of the power available will be dissipated within the amps - so the amps will get hotter as well. This all depends on the amplifier. it is commonly around this point. However some switch mode amplifiers are capable of almost 2x the power. My powersoft Digam 7000's give around 1800watts per channel at 4ohms, and 3500 watts per channel at 2ohms. On the other side of things, I have known amps that will only give about 20% extra output at 2ohms than 4ohms. Rob Link to comment Share on other sites More sharing options...
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