is it bad to underpower a sub i have a 120w RMS alpine amp and im looking at getting a cheap 12 inch sony xplode sub i found one 800w pmpo and 250 rms would it damage the sub hooking it up to that amp with the gain right up please help me people

underpowering a sub will not damage it, the only problem is that underpowering might not get the sub moving enough for good bass repoduction. I would read into watts pmpo at all, rms is the best indicator but still isnt totally accurate, 120W RMS should be enough to power most subs without a problem except for high powered subs. That match would be fine I think

the 800watts is prolly Max not PMPO

underpowering a sub will not damage it, the only problem is that underpowering might not get the sub moving enough for good bass repoduction.

Underpowering the sub can easily damage it if the person running the stereo doesn't realise the amplifier is beginning to struggle. Below is a tech article I wrote last year with the help of my trusty 'Basic Car Audio Electronics' book by my side. You're welcome to read it all if you could be stuffed. :):)

Okay, there is a long reply and a short, the short is; No, it won't harm your speakers if your sensible with the volume knob.

The long answer is this; In most systems when you hears the speakers ‘distorting’ it’s not the speaker that is struggling, it’ the amp. Speakers are quite simple devices, all they do is reproduce the sound given to them regardless of what that sound may be.

When you ask an amp to do it’s job, it takes a relatively small sound wave and amplifies it before sending that bigger signal to the speakers. If you ask it to do more than it’s capable of (by turning the volume up full blast), it still tries to do what you have asked, but the new amplified sound wave becomes rough and sketchy due to the amp having to clip the top and bottom of the musical wave in order to produce the amplitude you have asked it for.

Imagine for a second a weight lifter. He is on the bench doing bench presses. With 100 pounds his movement will be nice and smooth and he’ll be almost faultless in his technique. Now you throw on another 300 pounds. He may still just be able to do it, but his arms and legs shake, his breathing becomes irregular and it looks woeful to watch.

You amp does the same, it still attempts to do what you have asked of it, but it sounds dreadful and you get that ‘distortion’ everyone talks about. And here lies the biggest problem – most people assume the speakers are dying, so they go and get a SMALLER amp and as you can imagine from reading above, the problem is just amplified (sorry, couldn’t resist throwing that pun in! :p ). Anyway, it gets worse. The resulting nasty wave is then transferred straight to the speaker which tends to knock the speaker itself around a fair bit. It also causes the speaker voice coil to heat up significantly as the stays are full power for longer periods during the sound wave during clipping.

Now don’t get me wrong, you can fry your speakers with too much power, but there are only two main ways to destroy a speaker. One is thermal (where the voice coil and/or the former melts because of too much current flowing through it) and overdriving (where the voice coil and former hit the bump plate on the bottom or tear the surround and/or spider(s) and pop the cone out the top).

Usually the volume is somewhat louder than one would be comfortable with before failure occurs.

The more technical minded explanation on clipping is this; 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. 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.

http://www.fastfoursforumscarclub.com/temp/amp_clipping.jpg

Then there is severe clipping (aka square wave). It always amazes me when I hear some idiot driving down the road and the audio is clearly distorted (you know what I mean). Many people drive their amplifiers into what could be called a square wave output (white line below). When an amplifier is pushed that hard, it is actually possible to drive the speaker with twice as much power as the amplifier can cleanly produce into the speaker. As you can see below, the yellow sine wave is the maximum 'clean' output that the amp can produce. When an amplifier is pushed way too hard, the signal will eventually look like the white line. The effective voltage of the white line is ~1.414 x the yellow line. This means the the total power driven into the speaker by the clipped (square wave) signal is double the power delivered by the 'clean' signal (yellow line). 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.

http://www.fastfoursforumscarclub.com/temp/amp_extreme_clipping.jpg

Note: 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 (as shown above), 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.

Fwoarrrr :shock: , no thats an explination!!!!

I always setup my amps so that at maximum clear volume from the HU, the gain is still within the unclipped range, that way you never push it to hard as your ears start bleeding before you reach the limit lol

It takes a long time to get through though... :(

It takes a long time to get through though... :(

has anyone got the older model sony sub if you go to www.sony.com.au and go to car entertainment and then clck on subwoofers and then click on the 12 inch sub that has a max price of 199 does anyone have this one and what amp have they got it connected to cause that the one i want unless i can find one with less power tomorrow at jb

Fwoarrrr :shock: , no thats an explination!!!!

I always setup my amps so that at maximum clear volume from the HU, the gain is still within the unclipped range, that way you never push it to hard as your ears start bleeding before you reach the limit lol

A amp on 1/4 gain and a HU on 1/2 output is the same as a amp on half gain and the HU on 1/4


Depending on the quality of the parts its best to use both at a low level. Too high on either and it can hit the rails of an amp (either the amp in the HU or the AMP itself) low level outputs (RCA's) dont have this problem as much as a cheap HU which is amped from the speaker outs

low level outputs (RCA's) dont have this problem as much as a cheap HU which is amped from the speaker outs

Yeah I'm running RCAs to the amp...isn't everyone? :redface: ...I'd never do it anyother way, While my components arn't top of the range or anything they arn't too bad???

SONY HU
Cadence AMP
Cadence SUB

i ended up getting the 800 watt sony sub for 79 buks i think its a discontinued line got it from wow sight and sound and i pluged it into my 120w amp and it sounded **** so i went out and brought a 2x200w boss amp with the cooling fan in it for 129 on special i was gonna buy the 222w sony amp for 119 but the guy said the boss one would give me better sound put it in before luved it

I have never used boss, but I know of a few people who have used them and don't like them at all, they said it's all low end stuff????

I have never used boss, but I know of a few people who have used them and don't like them at all, they said it's all low end stuff????

well yeah its low emd stuff but im a low end kind of guy when i start have probs which will probably be next week knowing boss then i will complain

well yeah its low emd stuff but im a low end kind of guy when i start have probs which will probably be next week knowing boss then i will complain

heheheh lol ahhh I know how you feel, not having an unlimited ammount of money to spend on a car :cry: