Hi,
a car stereo salesman told me that I if use an amp at 2 ohms vs 4 ohms, I will lose SQ because it play louder. I tend to disagree : if the amp is high-quality and can handle the load, and the sub(s) can handle the power, I don't see why SQ would suffer. What do you think?

Denis

 

That's why he's a salesman

I can't imagine how the SQ would be affected by the voice coil impedance (ie the ohms seen by the amp). I'm sure someone with a better understanding of electrical components could explain why. Common sense says they wouldn't sell 2 ohm subs if 4 ohms sounded better.

 

Dont 2 ohm subs put down more power?

 

not exactly, most amps put out more power when your subs are wired to a lower impedence

 

All an ohm is is a rating of resistance. the higher quality the amp is, the more power it can have run through it with out being damaged. 2ohm will sound the same as 4ohm SQ-wise. and a 2ohm sub will sound the same as a 4ohm sub when they are given the same power. the only difference is that it takes twice as much power to run the 4ohm sub as it does the 2ohm sub. the only downside to using a lower impedance is that your amp will heat up more at 2ohm(there is twice the power going through it so that should be obvious). that salesman is full of it don't listen to him.

 

The old thing that was touted, back in about the '80's was amp damping factor. As the subs impedance halves, so does the amps damping factor and therefore it's control of the subs. But then came along some engineers who actually measured these things and they found out that 99.9% of amps that measure their damping factor don't measure it properly. They also discovered that the amp has to be pretty cheap to have a damping factor bad enough to be audibly worse than another otherwise the same amp.

If your amps greatest stable output is into a 2 ohm load, then try to get that load at the amp terminals. The heat an amp produces is pretty difficult to calculate. Generally speaking an amp is least efficient at about 1/3 power and below. And most efficient at the highest output level. Heat is the "result" of the amps inefficiency and an amp is generally hottest when runnning in the least efficient mode. But that is a double edged sword since at the least efficient point it is also ouputting the least power.

So basically don't worry about it. If the amp is rated to be able to play at the nominal impedance of your speakers, go for it.

 

Most amps have higher THD at lower impedance levels. Also, impedance is measured in ohms and is a measurement of AC resistance . . .

 

I am going to buy at Solo Baric L7 12" at 2 omh and have it powered by a RF amp 1001bd that puts out 1000rms watts at 2 omh.

 

Impedance can be measured with AC or DC current going through a circuit and essentially the resistance to electron flow through a circuit. Your power wires, DC, have a resistance to the flow of electrons. Your speaker wires and voice coil, AC, have resistance to the flow of electrons. Nominal impedance is "in name only", basically the average value over the normal operating frequency. There are large variances in impedance of a moving coil speaker. This affects frequency response and is a result of the factors that determine the frequency response. At resonance, Fs, the impedance peaks typically at a point 2 - 40 times the nominal value. At that frequency the speaker needs the least electrical power to move so despite the significant increase in resistance the speaker will move more air.

The true definitions are:
DC impedance - Essentially ohms law, Current = Voltage / Resistance, R = E / I, R = resistance, E = voltage, I = current.

AC impedance - resistance is a function of frequency and is the "ratio of the harmonic excitation of a system to its response (in consistent units), both of which are complex quantities, and both of whose arguments increase linearly with time at the same rate. The term applies to linear systems only and the terms and definitions relating to impedance apply to sinusoidal conditions only." ISO, International Standards Organization. Taken from The Audio Dictionary, Glenn D. White.