too little power on your subs?

[dave_Edwards 1]

As you have probably heard, some people say that too little power can blow speakers. Well... How can I say this... BS!!!!

Too little power will only cause the maximum output level to be low. Abuse and the defective 'wing nut' (an idiot) connected to the volume control blow speakers with low powered amplifiers. If driving a speaker with low power would cause them to fail, speakers would fail every time you lower the volume on the head unit. I will try to explain what happens when speakers are driven with clipped signals but remember... you get what you pay for.

Note:

This page deals mainly with speaker damage that involves thermal damage of the voice coil. Speakers can also be damaged mechanically by driving it beyond what the suspension can handle. Mechanical damage is generally caused by driving the speaker with too much power but it can also be done when a speaker is in a ported enclosure and is driven with frequencies below the port tuning frequency. Most of the damage I've seen has been thermal damage to the voice coil.

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). At points a, b, d, e, f and h the voltage is changing causing the voice coil to move in the gap and therefore pull in fresh cool air. At points c and g, the voice coil may still be moving a little due to momentum but may not be moving enough to cool properly. 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.

Severe Clipping (square wave):

It always amazes me when I hear some idiot driving down the road and the audio is clearly distorted (is that possible . Many people drive their amplifiers into what could be called a square wave output .

This means that the power is double but the cooling of the voice coil will not increase in proportion with the power increase (since the voice coil isn't moving as much as it needs to be for the given power dissipation). This will lead to the voice coil overheating. If we compared the output of a 100 watt amp (the one that's clipping) to a 200 watt amp, the 200 watt amplifier would be able to push the speaker as much as 40% farther than the 100 watt amp (depending on the frequency of the signal). This extra travel (in each direction from its point of rest) would result in added airflow around the voice coil.

The RMS voltage of a pure sine wave is equal to the peak voltage multiplied by 0.707. The RMS voltage of a pure square wave it equal to the peak voltage. For 2 waveforms with equal amplitude the RMS voltage of the square wave is 1.414 times the voltage of the sine wave. If we use the example of the 100 watt amp which can produce a sine wave of 20 volts RMS, we can see that the output power at hard clipping is double the power it can produce cleanly.

Clean Signal Calculations:

P = E^2/R

P = 20^2/4 (4 ohm speaker)

P = 400/4

P = 100 watts RMS

Square Wave Signal Calculations:

P = E^2/R

P = 28.28^2/4 (the RMS voltage is 1.414 times the RMS voltage of the sine wave)

P = 800/4

P = 200 watts RMS

Note:

If your speakers are capable of handling significantly more than your amplifier can produce, driving them with a clipped signal will not likely hurt them.

If the speakers can handle 3 or 4 times the power that your amplifier can produce, there's virtually no way to damage your speakers (no matter how clipped the signal is).

If your speakers are rated for the same power handling as your amplifier is capable of producing cleanly, driving them with a clipped signal for extended periods of time may cause speaker damage and/or premature failure.

If your speakers are rated for the same power handling as your amplifier is capable of producing cleanly, driving them with a square wave signal for extended periods of time will likely cause speaker damage.

[TeamXSSChris 0]

Did this all come from the same book? Just wondering.

[Guest Guest]

Did this all come from the same book? Just wondering.

it came from my note pad---and some came from the "Basic Car Audio Knowlege" section of Perry Babin's page---very knowlegable man.

[ss454 0]

Actually I read somewhere that if a sub is pushed with extrememly too little power, say 50wrms on a subs that takes 1200rms then the cooling of the sub will not some into play because it will never move the cone and could eventually burn the coil. You would have to play it for a long time I am sure.

[Guest Guest]

Actually I read somewhere that if a sub is pushed with extrememly too little power, say 50wrms on a subs that takes 1200rms then the cooling of the sub will not some into play because it will never move the cone and could eventually burn the coil. You would have to play it for a long time I am sure.

that is like saying that a Viper HAS to be ran at full throttle all the time----will it "burn out" just cruising around?

[Aaron Clinton 2,372]

not trying to hijack, but hey guest person, join the site man we would like to have ya

[dave_Edwards 1]

not trying to hijack, but hey guest person, join the site man we would like to have ya

sorry---it was me Dave---i forgot to log-in-------DUH!

[Guest Guest]

Well an engine does not perform like a sub. It has cooling in place if the motor is idleing where as a sub requires the cone to move for cooling to come into play.

[dave_Edwards 1]

Well an engine does not perform like a sub. It has cooling in place if the motor is idleing where as a sub requires the cone to move for cooling to come into play.

that is true---but when power is applied to a subwoofer-- the voice coils are not heated as much as they are when more power is applied to them.

[wizeguy4 0]

Not that it is any of my business and even though I agree wholeheartedly with what is written. The owner of the site that the above is copied from would rather if the information was linked back to the original site rather than be copied from it. I think it is very valuable information but this is his request

[dave_Edwards 1]

Not that it is any of my business and even though I agree wholeheartedly with what is written. The owner of the site that the above is copied from would rather if the information was linked back to the original site rather than be copied from it. I think it is very valuable information but this is his request

it is from the basic car audio knowlege site made by Perry Babin--I have purchased the CD(better than the site IMO)

but if you want to dig through all of it be my guest

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

[foolioGrimz 0]

Not that it is any of my business and even though I agree wholeheartedly with what is written. The owner of the site that the above is copied from would rather if the information was linked back to the original site rather than be copied from it. I think it is very valuable information but this is his request

it is from the basic car audio knowlege site made by Perry Babin--I have purchased the CD(better than the site IMO)

but if you want to dig through all of it be my guest

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

its the cut and paste man back in action! :boxin:

lol, JK

[Alanharthun 0]

I've seen it happen, especially with cheaper amps. Some of them start giving crazy voltages when pushed too far. Couple that with a speaker not moving the way it was designed to move. You could run into serious cooling issues.

[Tirefryr 1,742]

Dude, look at the dates on the threads.

[EPerez 236]

Dude, look at the dates on the threads.

I think this is the longest span of time that someone has dug up for a post..

[SpeakerBoy 64]

Lol damn.

[pmureika 31]

I know alot of subs that sound good at half the rated power.lol

Edited November 7, 2013 by pmureika

[Quentin Jarrell 671]

I run mine on 1/10 rated every day when I turn my volume knob in the head unit down.