Getting confused

[Mot]

gonna be buyin a sub an amp soon n im gettin confused with the ohms bollocks....

i'm gonna buy an alpine type r sub, u can get these in 4 ohm and 2 ohm

in this (http://caraudiosecurity.com/catalog/product_info.php+cPath+3_96_164+products_id+1028) deal the amp only pushes a sufficient amount of power at 2 ohms but the sub that comes with the deal is 4 ohms, does it matter and do i just sound stupid?

ta ppl, Mot

[Lloydy]

think of ohms as matching 2ohm out amp into matched 2 ohm in sub.

Match the impedance to get max power transfer. if u dont the full capabilty of the amp will not reach the sub and some will get reflected back reducing the sound and eventualy burning out ur amp or sub trust me i found out the hard way.

The easy way to explain it is think in water terms
u got two water pipes. if u join a 2 inch pipe to one the sme size the water flows freely (ie max power transfer)
if u join a 2 inch pie to a half inch pipe u get a blockage as such and there fore the water dont flow freely and puts preasure in the line .

is that good enough.

tell i bin doin this electronics bollox at college for 5 years ay.:)

[ste]

yeah, like lod sed! spoken like a text book! LOL!

[HAC]

Simple really. Assume that the amp provides a constant voltage swing (hypothetically call it 20rms for now)

Power = voltage squared divided by impedance.

V-squared = 400

Hence, at 8 ohm, power = 50W
at 4 ohm, power = 100Watts RMS.
Or at 2 ohm, power = 200 RMS
1 ohm gives 400 RMS.

Problem arrises that the transistors in the amp need to be capable of matching these huge current swings (power is current squared multiplied by impedence)
So at 1 ohm and 400watts, current = 20amps...pretty big all things considered.

Now things get silly. Say your amp has a voltage swing for 20V but only a current capability of 15A.
8 ohm, 50Watts (V=20 I=2.5)
4 ohm, 100Watts (V=20 I=5)
2 ohm, 200watts (V=20 I=10)
1 ohm, 225watts....not 400. (V=15 I=15)
It all goes horrid.

And then the amp's internal resistance becomes larger than the load on the output, causing more power to be lost through heat in the amp than the thing is pumping into you subs (or main speakers if you're as crazy with sound as myslelf). This can cause amp-meltdown and hence, the manufacturers don't like giving you a guaranttee on doing very low impedances.

Summary: (this thing looks like a lab report already...wonder if i can hand it in to one of my lecturers...if you're out there Mr Stansbridge, perhaps you could mark my exam paper up a bit :-) )

If your amp is desgned to run at 2 ohm and the restricting factor is the voltage swing, putting 4 ohm speakers on it will give you only half the power. If it's current that the limiting factor at 2 ohm, you'll get power out of your 4 ohm speakers a lot closer to the value the amp quotes for 2 ohms.

In my personal experience (stickin a scope on the end of my amps cos uni work is boring without a little spice) it's the current that usually limits amps that run to 2 ohm. An amp I have does 200watts into 4 ohms and only 300 into 2 ohms, not 400.

Good luck...and get some mamoth-thick wiring when working into small impednaces.

[DeanDTurb]

you dont have to get low guae wire for low impedence ratings, go by the fuse rating on the amp

[HAC]

You don't need lower guage wire to the amp from the battery for lower impedances, but you do from the amp to the speaker as lower impedances use higher current and lower voltage to produce the same power as higher impedances.