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Discussion Starter #1
Hi, I've just bought an Alpine MRP M500 (500W rms @2ohm, 300W rms @4ohm) and I've got a couple of questions about setting it up that aren't answered in the manual.
Firstly, at the moment I'll be using it to power 2 subs, each of which are 4ohm and only rated for 150W rms. Is it sensible to wire them in series to the outputs, reducing the power going to each speaker by showing the amp an 8 ohm load? or is the amp not or very low output at 8 ohm? Alternatively, would it be better to wire them in parallel, showing the amp a 2 ohm load and sending 250W rms to each speaker? (running the risk of blowing the speakers if I turn the volume too high)
Secondly, I'm going to replace these 2 subs pretty soon with 1 alpine type r 12" and dont know whether it is more sensible to get the dual 2 ohm voice coil model, wire the coils in series, showing the amp a 4 ohm load which would give the speaker the 300W rms at which it is rater, or would it be better to get the dual 4 ohm voice coil model, wire the coils in parallel to show the amp a 2 ohm load which would give the speaker 500W rms, again running the risk of blowing the speaker if I turn the volume too high?
I suppose at least if I bought the dual 2 ohm I would then be able to possibly at a later date buy another of the same, wire them both as 4 ohm, then wire them in parallel to the amp showing it 2ohm and giving each speaker 250W rms.
 

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I would run the subs you have right now in parallel....If the amp is tuned correctly I would think those subs will be just fine....When you do buy your alpine type r sub those are rated at 500w rms so get a dual 4ohm sub and also wire it in parallel
 

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well what are the subs that you have now that is important to make an educated desicion
 

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Discussion Starter #5
they're some crap old kenwood ones, KFC W300S I think, they dont make them anymore, but theyre 150W rms
 

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Discussion Starter #6
just in case anyone is interested, I emailed Alpine tech support and got a really helpful reply from them.
"Hi, the amp is designed for an optimum load of two ohms, so connect your
subs in parallel...... when you purchase the new sub get the dual 4 ohm
so again you can achieve to two ohm load...

Its actually easier to blow a sub with an amp that is too small,
underpowering will heat the coil much faster ,, non distorted clean power
will not blow up a sub, it may make it reach its mechanical movement limits
but that is not as damaging as distortion....you can always turn it down a
tad

Regards

Alpine Electronics of UK Ltd."

I never realised that distortion was more likely to damage subs than overpowering them.
 

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just saying to little power is wrong as its not the power level but people turning the gain to high and causin clipping. but yes distortion and cone flex is some of the worse things for speakers

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 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.

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). 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.
 

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Discussion Starter #8
That was a great explanation, thanks, I'm a physics graduate so its nice to have a full explanation I can understand rather than just being told "clipping damages your speakers". To be honest, I cant see it being an issue with me since I's rather have quiet music than clipping since I cant think of anything that sounds worse than clipping, but thanks for the explanation. Much appreciated and +rep
 
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