How much power do I REALLY need (revised)
Notice: this is a long detailed reply, if you wish to "get to the gist" of this, skip to the end of the post.. (last 3 paragraphs) I am a speaker re-coner, and amp/electronic repair type as well, I build speakers, and most of what I use is proprietary, I have a live sound company, rental business, and DJ/KJ businesses. I moderate the dbx forum. I have found that in this audio business, "The more you learn, the less you know"..
For a complete discussion of this type we need to understand a few things. one is what the speaker will be expected to do... there we want to know if were going to be doing live sound, or playback of heavily compressed CD/MP3 type music.
The former, Live sound, requires more power (more dynamics) and there your 2-4 times the rated power comes in. The 4 times factor is headroom and is only ever recommended for instantaneous peaks measured in microseconds/ milliseconds duration. You have to understand that typical rock music has a duty cycle of 1/5 -1/3 duty meaning that amp is only working 1/5th of the time, during regular reproduction cycles.
The other amount of time the amp is "resting". Point of fact: NO amplifier made can do 100% duty cycle. PERIOD
Note here that most amps are current rated @ 1/5th power, that is to say that Crown rates the Xti 4000 @ 10.5 amps. This is the 1/5th power rating. That same amp can draw in excess of 20 amps the closer you get to the amps maximum output power. This would be closer to the 1/3 duty cycle.
Playback of pre-recorded (read heavily compressed) music is a totally different animal. This is why we predicate any discussion about amp power ratings by talking about duty cycle. Compression is a process where the AVERAGE loudness is increased. This has been a scheme to lure listeners in by having the LOUDEST radio station on the dial, get more attention with more average loudness... more IN YOU FACE ... if you will.
Here were going to take a look at speakers and how they work. Speakers are basically resistors (a coil of wire with a given DC resistance) and they resist the current flow, and dissipate that power in the form of heat. So the power that amp generates goes though the coil of wire and is dissipated in the form of heat. The coil of wire (voice coil) however, moves through the gap and dissipates the heat by the pumping motion of the speaker cone which creates air flow through the gap (the gap is the space between the magnet former, and the voice coil).
Speaker power ratings: Most quality speakers come with 3 ratings,
1. RMS: this value, this is derived from a pink noise signal (all frequency sound with a known crest factor) applied to the speaker 24 hours a day 7 days a week .. basically it could take that amount of power indefinitely...
2. Program: as mentioned above average music played @ 1/5 duty cycle
3. Peak: instantaneous peaks for milliseconds of duration maximum
So, in pre recorded music the heavy compression scheme increases the duty cycle, the amp doesn't get to rest as much. The speaker, also sees an increased temperature at the voice coil. This would also be true if you heavily compressed your live sound, or if you are re-enforcing death metal or other similar genre of music with high BPM.
Back to pre recorded music.. the power factor here is typically the PROGRAM rating, that means your generally SAFE using the program power rating, but you CANNOT DAMAGE YOUR SPEAKERS with RMS rated program material. Even if it's heavily clipped. As was pointed out earlier in the discussion, if clipped sound blew speakers, then guitar players would be in a major hurt bag...
There is a few more aspects of this issue, but lets conclude this by saying IF you exhaust the power amps power supply, clip light on too much of the time, OR too much AVERAGE power/duty cycle, you WILL cause additional heat buildup in the voice coils that the motion/airflow cannot sufficiently cool.
As Jerry pointed out you can also apply too much power in instantaneous fashion and slam the voice coil against the mechanical stops (back plate of the magnet structure) and/or tear the surround, or spider with too much excrusion (overpowering).
In summary, When your looking for an amp you need to look at the application your trying to use the speakers for. If it's important to get the MOST out of what you have, in live sound, you need to look in the 2-4 times the rated power, closer to the 4 times for subwoofer duty. Here gain structure, and knowing the clip point of your amps is EXTREMELY important. If you want a modicum of safety get the program rating, and make double damn sure you don't clip the amps!
Pre-recorded (heavily compressed ) material requires a different strategy...if you ABSOLUTELY must preserve the speakers (not ever blow anything) stick with the RMS speaker rating. The down side of this is, you won't get the most out of your system, and in order to get more loudness you need to add more speakers. Note here that for each additional speaker that is close coupled (placed together) there is a 3dB gain (free power). The same holds true (except for HF horns) boundaries (walls, floors, ceilings), a 3dB gain for each boundary.
If you looking to get the best performance with a modicum of safety with pre-recoreded music choose an amp that has the program rated power capability, and NO CLIPPING of the amps! There is a LOT more to this issue , like speaker cables(type, gauge, and conductor type and orientation) connectors, back electromotive force, that determine how much of the amplifiers power actually gets to the speakers.
For a complete discussion of this type we need to understand a few things. one is what the speaker will be expected to do... there we want to know if were going to be doing live sound, or playback of heavily compressed CD/MP3 type music.
The former, Live sound, requires more power (more dynamics) and there your 2-4 times the rated power comes in. The 4 times factor is headroom and is only ever recommended for instantaneous peaks measured in microseconds/ milliseconds duration. You have to understand that typical rock music has a duty cycle of 1/5 -1/3 duty meaning that amp is only working 1/5th of the time, during regular reproduction cycles.
The other amount of time the amp is "resting". Point of fact: NO amplifier made can do 100% duty cycle. PERIOD
Note here that most amps are current rated @ 1/5th power, that is to say that Crown rates the Xti 4000 @ 10.5 amps. This is the 1/5th power rating. That same amp can draw in excess of 20 amps the closer you get to the amps maximum output power. This would be closer to the 1/3 duty cycle.
Playback of pre-recorded (read heavily compressed) music is a totally different animal. This is why we predicate any discussion about amp power ratings by talking about duty cycle. Compression is a process where the AVERAGE loudness is increased. This has been a scheme to lure listeners in by having the LOUDEST radio station on the dial, get more attention with more average loudness... more IN YOU FACE ... if you will.
Here were going to take a look at speakers and how they work. Speakers are basically resistors (a coil of wire with a given DC resistance) and they resist the current flow, and dissipate that power in the form of heat. So the power that amp generates goes though the coil of wire and is dissipated in the form of heat. The coil of wire (voice coil) however, moves through the gap and dissipates the heat by the pumping motion of the speaker cone which creates air flow through the gap (the gap is the space between the magnet former, and the voice coil).
Speaker power ratings: Most quality speakers come with 3 ratings,
1. RMS: this value, this is derived from a pink noise signal (all frequency sound with a known crest factor) applied to the speaker 24 hours a day 7 days a week .. basically it could take that amount of power indefinitely...
2. Program: as mentioned above average music played @ 1/5 duty cycle
3. Peak: instantaneous peaks for milliseconds of duration maximum
So, in pre recorded music the heavy compression scheme increases the duty cycle, the amp doesn't get to rest as much. The speaker, also sees an increased temperature at the voice coil. This would also be true if you heavily compressed your live sound, or if you are re-enforcing death metal or other similar genre of music with high BPM.
Back to pre recorded music.. the power factor here is typically the PROGRAM rating, that means your generally SAFE using the program power rating, but you CANNOT DAMAGE YOUR SPEAKERS with RMS rated program material. Even if it's heavily clipped. As was pointed out earlier in the discussion, if clipped sound blew speakers, then guitar players would be in a major hurt bag...
There is a few more aspects of this issue, but lets conclude this by saying IF you exhaust the power amps power supply, clip light on too much of the time, OR too much AVERAGE power/duty cycle, you WILL cause additional heat buildup in the voice coils that the motion/airflow cannot sufficiently cool.
As Jerry pointed out you can also apply too much power in instantaneous fashion and slam the voice coil against the mechanical stops (back plate of the magnet structure) and/or tear the surround, or spider with too much excrusion (overpowering).
In summary, When your looking for an amp you need to look at the application your trying to use the speakers for. If it's important to get the MOST out of what you have, in live sound, you need to look in the 2-4 times the rated power, closer to the 4 times for subwoofer duty. Here gain structure, and knowing the clip point of your amps is EXTREMELY important. If you want a modicum of safety get the program rating, and make double damn sure you don't clip the amps!
Pre-recorded (heavily compressed ) material requires a different strategy...if you ABSOLUTELY must preserve the speakers (not ever blow anything) stick with the RMS speaker rating. The down side of this is, you won't get the most out of your system, and in order to get more loudness you need to add more speakers. Note here that for each additional speaker that is close coupled (placed together) there is a 3dB gain (free power). The same holds true (except for HF horns) boundaries (walls, floors, ceilings), a 3dB gain for each boundary.
If you looking to get the best performance with a modicum of safety with pre-recoreded music choose an amp that has the program rated power capability, and NO CLIPPING of the amps! There is a LOT more to this issue , like speaker cables(type, gauge, and conductor type and orientation) connectors, back electromotive force, that determine how much of the amplifiers power actually gets to the speakers.
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