Bi-amping or buy a subwoofer?

No. If the impedance of both drive units is equal (which it should be at 8 ohms), then by the equation for power, (V x V) / R, then the power is dependant on the voltage that the amplifier can generate across its terminals. A 120W amplifier can generate 1.414 times larger voltage across its terminals than a 60W amplifier can.

Now, the only issue with this is that the impedance seen at various frequencies is not constant, and will have dips and peaks. For the amplifier to cope with this it needs to have enough ability to supply the current demanded for any impedance seen when a voltage within the limits of the amplifier is required. Biamping helps give this additional current ability, and since impedance dips are most often seen in the bass region, it is best to have the more powerful amplifier drive the bass because it will have more current capability.

However, the likelihood in domestic listening of getting anywhere near 60W output power is extremely low.

 

Isaac, Informative posts. Thanks

I remember reading somewhere (TNT ?) that LF carries higher current and therefore benefit from larger dia cable. Anything in this?

 

As I said, impedance dips are usually seen in the bass region.

Because Power also is equal to I x I x R (where I is current), you can see that for a given power, if you decrease R then I must increase. Because of the relationship P = V x I, if I increases then V decreases for a given P, but V is not usually the problem.

So, simply put, where the impedance R drops, I must increase to maintain power level P.

The amount of current that goes to each driver depends on the source material. If you have a track of only a bass guitar then not much is going to go to the tweeter. Similarly, if you have a solid 100Hz sine wave then almost all of the current will go to the bass driver and very little to the tweeter (as you'd be looking so far down the harmonics that very little power would be carried). A solid 10kHz sine wave would put a lot of current to the tweeter, and little to none to bass driver. Not exactly common situations.

So it depends on crossover design (and frequencies), speaker design, and source material. I would imagine that in most situations with most source material with most speakers more current does go to the bass driver.

 

Thanks Isaac
In my bi-wired setup LF cable dia is twice as that for HF

Skin effect comes into it as well I suppose!

 

Thanks for the detail Isaac, it's appreciated.

cheers,
Rob.

 

Skin effect isn't significant at audio frequencies.

 

Defenetely the most versatile choice, and my favourite...

 

There's a second hand MDP500 for sale over at avforums if you are after one.

Matt.

 

Thanks Matt.
The prices here in Sweden seems to be quite a bit lower. I want the G6 version so I'd have to upgrade as well.

/Michael