Choosing your amp

[Jhonno]

How do you choose an amp power rating, say your speakers were rated to 90w RMS.. what Wattage would you be looking for your amp to put out?

[johnono]

i was wondering this aswell,

what if the amp is more powerfull than the speakers can handle, would i rip them up?

and what happens to the power im not using?

neadless to say , i dont know sh*t about ice

[320Touring]

most amps have an 'input gain' adjuster on them, so you can effectively 'turn down' the amplifier effect.

Generally, i'd run a large power amp, but running at a lower level (this keeps the tempertures of the amp down-so it doesnt blow)

Had twin 12" subs (200w rms) run by a 2x 400w amp. therefore each channel had 2x the peak power of the speakers.

90w rms i'd be running at least a 2x 200w amp

[johnono]

top man!

[320Touring]

no bother johnono!its in apology for the Norway comment

Another tip is USE A REALLY THICK WIRE for the power supply lead, and fit an inline fuse at the battery end, and at the amp-better safe than sorry.

You can also 'bridge' amps, so can buy a 4x200w amp, and by wiring it right, end up with 2x channels outputting 350-400w each.

johnono try stripping down the whole airbox assembly and washing it down-check any breather pipes and see if theyre blocked

[johnono]

Geezaa!!

iԚ´m cool with the whole norway thing( ), i forgot about that totally dude

nice again for the amp adv.

and with the air box, i had the afm still conected, but the airbox looked clean enough, i think it was collecting in the afm, so that may be a project ( when iԚ´m a little more confident with it all )

nice one

[placey]

clipping is what blows speakers - clipping is when an amplifier cannot deliver a clean peak signal (because it's run out of power) so it delivers a the best it can - a sustained distorted current - which speakers can't handle. think of it like this - if you move your hand through a big flame you can take the heat - but hold your hand in a medium flame for 2 seconds and it will burn. therefore a small power amplifier will more easily blow speakers than a large power amplifier.

a pretty reliable method of assessing the power of an amp is to read the ratings of the fuses that are mounted somewhere on its case. then use ohms law and take into account a 50% efficiency. e.g. 2 20amp fuses gives 40 amps, 14.4 volt supply (from a healthy alternator) gives 576 but as amplifiers are generally about 50% efficeient (they make heat too) you can get about 280 watts peak from it. half this and add a bit for your rms value - about 150 watts rms. simple.

paul

[amit325i]

RMS is ratio 0.707 of peak, needless to say don't forget speaker sensitivity, less than 90db will require more rms to use it!

[BaggedE30]

[quote="placey"]clipping is what blows speakers - clipping is when an amplifier cannot deliver a clean peak signal (because it's run out of power) so it delivers a the best it can - a sustained distorted current - which speakers can't handle"

its not the clipping part that speakers cant handle, when clipping your squaring off the top of the sine wave turning the usual AC current used to drive speakers into a partially DC current, during this DC phase the speaker is not moving back or forth but still has a large current going through it..if clipping at very low power the voice coil will still be able to dissipate the heat its only at higher power levels where it really matters

"think of it like this - if you move your hand through a big flame you can take the heat - but hold your hand in a medium flame for 2 seconds and it will burn. therefore a small power amplifier will more easily blow speakers than a large power amplifier."

um no...thats like saying that by turning the volume down on the head unit you are more likely to blow speakers..if i had a "500Wrms" subwoofer with a 400wrms amp running clipped chances are id blow it if i had a 1000Wrms amp running clean power you wouldnt

[placey]

bagged

not sure how you've interpreted my words and disagreed with them then explained perfectly exactly what i was saying!?

it's the 'sustained distorted current' that kills speakers - forcing them out to full excursion and trying to keep them there.

ok the hand analogy may not be perfect but i was trying to say that a small current sustained is more likely to cause damage than a bery brief large current. i don't get how you went from that to turning down the volume on a head unit is more likely to blow speakers??

we haven't really answered the original question - what power for 90watt rated speakers. i'd say any sized amp will do a job - just set the gain sensibly to avoid distortion.

paul

[fowler]

well this is one for the ones who know ohms law acording to this i would have to a roughly a 100watt rms per chanel for a four speaker system
so four speakers at 4 ohms each totalling a 16 ohm load over a four channel amp
thus equalling 4 ohms per channel
so ocording that amps are only 50% efficient dependent on what class they are thats another whole ketlle of fish
so you would ideally like to push your speakers had rather that your amps because speakers are cheaper to replace
so i would suggest using a four channel 600 w like directed's 550/4 which means that it would be rouglly just over 100watts per channel so as this amp is 75% efficient youwould run the amp at roughly half gain so that the speakers coulkd be run in the turn it up to about 80% to really give the speakers a good pounding.
when ever fitting new speaker give them time to settle before caining them this is why most speakers DIE !!!

[johnono]

changed my mind

[Adam318i]

Hahaha, i know they make it so complicated.

I bet you just wanted an answer like, use a 200w amp.

Oh well

[johnono]

y get me

[320Touring]

johnono- just buy a 4x100w amp and and dont turn it up too much!

assuming you're not running more than 2 subs, a set of 6x9s etc then that should be more than adequate.

Everything these guys are saying is correct, but not really too much of a consideration for a basic ICE install

good luck

[johnono]

yea, iԚ´ve got it all in hand.

2 sets of compontnts, 130w each for allround

[BaggedE30]

[quote="fowler"]well this is one for the ones who know ohms law acording to this i would have to a roughly a 100watt rms per chanel for a four speaker system
so four speakers at 4 ohms each totalling a 16 ohm load over a four channel amp thus equalling 4 ohms per channel "

lol wot you couldve just said 4ohms per channel haha 16ohms over 4 channels lol never heard that one before and why do you have to know ohms law to state that

"so ocording that amps are only 50% efficient dependent on what class they are thats another whole ketlle of fish
so you would ideally like to push your speakers had rather that your amps because speakers are cheaper to replace"

lol not necessarily

"so i would suggest using a four channel 600 w like directed's 550/4 which means that it would be rouglly just over 100watts per channel so as this amp is 75% efficient youwould run the amp at roughly half gain so that the speakers coulkd be run in the turn it up to about 80% to really give the speakers a good pounding.
when ever fitting new speaker give them time to settle before caining them this is why most speakers DIE !!!"

lol as the amp is 75% efficient youve got to run the amp at half gain? haha...ok
and it isnt necessary to "run speakers in" despite peoples popular belief

[Jhonno]

you should let them warm up when cold tho as the rubber isnt as flexible!