Clipping, Power and Voice Coil Damage
02-04-2009, 05:28 PM
#31
50 Watt CAFz'r
Join Date: Jun 2007
Posts: 109
Damaging Woofers:
When a woofer is driven with a high powered amplifier to high levels, there will be a significant amount of current flowing through the voice coil. Since the voice coil has resistance, there is a voltage drop across the speaker's voice coil (which the amplifier appreciates greatly :-). This means that there may be a great amount of power being dissipated (in the form of heat) in the voice coil. When a speaker is driven with lots of clean power, the cone moves a great deal (in proportion to the output voltage from the amplifier). For speakers with vented pole pieces (or other types of venting), this movement forces a lot of air to flow in the magnetic gap (area where the voice coil rides). When the woofer moves out of the basket, the chamber that's under the dust cap and around the voice coil expands (increases in volume) which pulls cool air into the magnetic gap. When the woofer moves the other direction, the chamber size is reduced and the hot air is forced out of the vent in the pole piece. This air flow cools the voice coil. If a relatively low powered amplifier is driven into clipping (to a full square wave for a lot of people), a relatively large portion of the time, the voltage delivered to the voice coil no longer resembles a sine wave as it would with an unclipped signal. While the amplifier's output is clipped, the voice coil is not being motivated to move as far as it should for the power that's being delivered to it and therefore is likely not being cooled sufficiently (since the speaker is driven by a linear motor, the voltage applied to the voice coil determines how far the voice coil moves from its point of rest). ... Remember that during the clipped portion of the waveform current is still flowing through the voice coil. Since the displacement of the voice coil (and therefore the airflow around the voice coil) is no longer proportional to the heat being generated, the voice coil can overheat. This excess heat may cause the voice coil former to be physically distorted and/or melt the insulation off of the voice coil wire and/or cause the adhesives to fail (especially if the speaker is rated to handle no more than the power that the amp can produce cleanly). If your speakers are rated (honestly) to handle the maximum 'clean' power that your amplifier can produce, slight clipping isn't generally a problem. Severe clipping is more likely to cause a problem.
When a woofer is driven with a high powered amplifier to high levels, there will be a significant amount of current flowing through the voice coil. Since the voice coil has resistance, there is a voltage drop across the speaker's voice coil (which the amplifier appreciates greatly :-). This means that there may be a great amount of power being dissipated (in the form of heat) in the voice coil. When a speaker is driven with lots of clean power, the cone moves a great deal (in proportion to the output voltage from the amplifier). For speakers with vented pole pieces (or other types of venting), this movement forces a lot of air to flow in the magnetic gap (area where the voice coil rides). When the woofer moves out of the basket, the chamber that's under the dust cap and around the voice coil expands (increases in volume) which pulls cool air into the magnetic gap. When the woofer moves the other direction, the chamber size is reduced and the hot air is forced out of the vent in the pole piece. This air flow cools the voice coil. If a relatively low powered amplifier is driven into clipping (to a full square wave for a lot of people), a relatively large portion of the time, the voltage delivered to the voice coil no longer resembles a sine wave as it would with an unclipped signal. While the amplifier's output is clipped, the voice coil is not being motivated to move as far as it should for the power that's being delivered to it and therefore is likely not being cooled sufficiently (since the speaker is driven by a linear motor, the voltage applied to the voice coil determines how far the voice coil moves from its point of rest). ... Remember that during the clipped portion of the waveform current is still flowing through the voice coil. Since the displacement of the voice coil (and therefore the airflow around the voice coil) is no longer proportional to the heat being generated, the voice coil can overheat. This excess heat may cause the voice coil former to be physically distorted and/or melt the insulation off of the voice coil wire and/or cause the adhesives to fail (especially if the speaker is rated to handle no more than the power that the amp can produce cleanly). If your speakers are rated (honestly) to handle the maximum 'clean' power that your amplifier can produce, slight clipping isn't generally a problem. Severe clipping is more likely to cause a problem.
02-04-2009, 06:20 PM
#32
Sorry Ryannow.. BCAE is a pretty good site for learning the basics but it's pretty mickey mouse; and hardley material I'd reference..
The fact is that even if you send square wave to a speaker the cone is still going to move in a sinusoidal fasion... First consider that 67% of any additional power gained by clipping the signal is going to be at the fundamental.. The rest of the power will be in odd order harmonics which are sinewaves superimposed on top of the fundamental. The higher the harmonic the less energy is present and at some point the inductance of the driver will start to filter out these higher frequencies too..
The bottom line is that a clipped wave will not cause a speaker's cone to 'hang' as you are trying to suggest..
I'd also add that as far as I am concearned I think that many people worry too much about clipping damaging thier speakers/subs.. if it sounds distorted turn it down.. and frankley if a bit of distortion is going to send your drivers over the edge then it was probably going to happen sooner or later anyway..
The fact is that even if you send square wave to a speaker the cone is still going to move in a sinusoidal fasion... First consider that 67% of any additional power gained by clipping the signal is going to be at the fundamental.. The rest of the power will be in odd order harmonics which are sinewaves superimposed on top of the fundamental. The higher the harmonic the less energy is present and at some point the inductance of the driver will start to filter out these higher frequencies too..
The bottom line is that a clipped wave will not cause a speaker's cone to 'hang' as you are trying to suggest..
I'd also add that as far as I am concearned I think that many people worry too much about clipping damaging thier speakers/subs.. if it sounds distorted turn it down.. and frankley if a bit of distortion is going to send your drivers over the edge then it was probably going to happen sooner or later anyway..
Last edited by Haunz; 02-04-2009 at 06:22 PM.
02-04-2009, 07:21 PM
#33
50 Watt CAFz'r
Join Date: Jun 2007
Posts: 109
hey, its deffinately a lot better than wikipedia. i'm not trying to suggest the speaker is going to hang. the signal does tho. i'm just trying to say that a clipped signal will cause the speaker to build up excess heat. and that's where damage can come from.
02-04-2009, 11:40 PM
#34
The signal really doesn't hang either.. and what is interesting is that there are two types of clipping modes an amplifier can go through.. but, the main point I like to drive home is that your average amp cannot produce more then about 30% it's rated output at nominal load without an ungodly amount of distortion...
If 30% more power is going to cause your speakers to blow then listening for 2x as long as normal will also spell certain death.. point being the drivers are quite likely not going to last..
If 30% more power is going to cause your speakers to blow then listening for 2x as long as normal will also spell certain death.. point being the drivers are quite likely not going to last..
02-05-2009, 10:47 PM
#35
50 Watt CAFz'r
Join Date: May 2007
Posts: 384
How about this one then? I'm not very good at explaining stuff but this one is very straigh forward.
http://www.mobileelectronics.com.au/forums/lofiversion/index.php/t77525.html
02-06-2009, 04:52 PM
#36
500 Watt CAFz'r
Thread Starter
Join Date: Jan 2008
Posts: 537
Sorry Ryannow.. BCAE is a pretty good site for learning the basics but it's pretty mickey mouse; and hardley material I'd reference..
The fact is that even if you send square wave to a speaker the cone is still going to move in a sinusoidal fasion... First consider that 67% of any additional power gained by clipping the signal is going to be at the fundamental.. The rest of the power will be in odd order harmonics which are sinewaves superimposed on top of the fundamental. The higher the harmonic the less energy is present and at some point the inductance of the driver will start to filter out these higher frequencies too..
The bottom line is that a clipped wave will not cause a speaker's cone to 'hang' as you are trying to suggest..
I'd also add that as far as I am concearned I think that many people worry too much about clipping damaging thier speakers/subs.. if it sounds distorted turn it down.. and frankley if a bit of distortion is going to send your drivers over the edge then it was probably going to happen sooner or later anyway..
The fact is that even if you send square wave to a speaker the cone is still going to move in a sinusoidal fasion... First consider that 67% of any additional power gained by clipping the signal is going to be at the fundamental.. The rest of the power will be in odd order harmonics which are sinewaves superimposed on top of the fundamental. The higher the harmonic the less energy is present and at some point the inductance of the driver will start to filter out these higher frequencies too..
The bottom line is that a clipped wave will not cause a speaker's cone to 'hang' as you are trying to suggest..
I'd also add that as far as I am concearned I think that many people worry too much about clipping damaging thier speakers/subs.. if it sounds distorted turn it down.. and frankley if a bit of distortion is going to send your drivers over the edge then it was probably going to happen sooner or later anyway..
02-06-2009, 04:55 PM
#37
500 Watt CAFz'r
Thread Starter
Join Date: Jan 2008
Posts: 537
answer me this: how does presenting an arbitrary driver that is rated for and can handle100wrms with a clipped signal of 30w justify overpowering it? that doesn't even make sense. at the point where the signal is clipped, there is still a large amount power moving through the voice coil, but little to no cone movement. if the cone was moving in the normal sine wave motion at this point (ie. with a better amp), it would be able to withstand the power, but since it has halted at this point, the heat cannot be given off.
02-06-2009, 05:01 PM
#38
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Join Date: Jan 2008
Posts: 537
On a side note, did you ever measure the power you drove your speakers with or were you relying on amplifier power ratings to determine it?
02-06-2009, 05:02 PM
#39
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Posts: 537
02-06-2009, 05:08 PM
#40
Heating comes from the power dissipation. It is possible to drive more power into a speaker than it's rated handling, but the average power dissipation mustn't be exceeded. In other words it must be given time to cool between beats, explosions or whatever.
On a side note, did you ever measure the power you drove your speakers with or were you relying on amplifier power ratings to determine it?
On a side note, did you ever measure the power you drove your speakers with or were you relying on amplifier power ratings to determine it?
Nick
