Real world biwiring results & recent upgrades - hifi fever still rising

[TrevC]

"Maybe one of you intelligent people can answer a question I have regarding impedance.

What happens to impedance if you are biamping? Say you've got 2, 2 channel amps, one amp per speaker? One channel doing highs and the other doing lows. The speaker is rated at 4ohms nominal. Would the amp still see the nominal or would it be halved? What if you had mono amps driving low and highs separately? I imagine in this instance the amp would see a difference?"

Presumably you aren't going active with electronic crossovers so If, say, you are only connecting to the bass the amplifier will see exactly the same impedance at bass frequencies as it would have done without biamping. Above that the impedance will rise. There are no power or performance gains with such a set up, you are just wasting an amplifier, because the amplifier is still producing output at all frequencies but they aren't being used.

 

[davedotco]

Just to add that in a passive bi-amp setup as described, both amplifiers are delivering a full range signal.

Ie the HF amplifier is producing a full range signal, so even though the crossover may be 3000hz, it is still producing the volts to drive at, say, 100hz, in fact the output voltage will be the same on both HF and LF amplifiers at all frequencies.

What the crossover does to the HF amplifier is to progressively increase the impedance as seen by the power amplifier so that below the crossover, at bass frequences, say 100hz, the impedence is very high indeed, so there is minimal current flow.

As we know, power is voltage x current, so the power delivered at 100hz is extreemly low.

The other issues Vlad mentioned, impedance variations and the like are common to all passive loudspeakers, however wired.

 

[Anderson]

Thanks for the input gents.

Something that I would be tempted to do in the future would be to convert a set of speakers to active using something like a Behringer Ultradrive Pro and a couple of pro amps. I'm just scared that I would end up ruining my speakers or in all probability not getting a significant audioable benefit. If nothing else I think it would be a fun project.

 

[Vladimir]

Maybe one of you intelligent people can answer a question I have regarding impedance.

Those might be busy at the moment so I'll give it a go.

What happens to impedance if you are biamping? Say you've got 2, 2 channel amps, one amp per speaker? One channel doing highs and the other doing lows. The speaker is rated at 4ohms nominal. Would the amp still see the nominal or would it be halved? What if you had mono amps driving low and highs separately? I imagine in this instance the amp would see a difference?

Each speaker driver has it's own average and nominal impedance, which are not that usefull to know for choosing an adequate amplifier. Average is just statistical number and nominal is arbitrarily chosen by the manufacturer as a buyer rough orientation for choosing amplifiers. Much more usefull are minimum and maximum measured impedance at a certain frequency.
With bi-amping each amplifier will see a different impedance load as frequency varies. The amplifier assigned to the woofers will work more than the one on the midrange and high frequencies.

Example: If a pair of speakers dip to 2 ohms at 80Hz, those are a very difficult load, unlike speakers who dip to 2 ohms at 8000Hz. This is simply because lower frequencies suck more power from the amp. low frequency, big waves, big drivers, more mass to move etc. etc. more work for the amp.

When you biamp with 2 stereo power amplifiers, you split the frequency range at the speaker crossover point and this means more work for one of the amps assigned to the woofers. If the impedance in the LF is well behaved (above 4ohms and no nasty phase shifts) and the one in the MF/HF is going crazy, you have nothing to worry about since the MF/HF amplifier will not break a sweat in that frequency range, regardless of impedance and phase shifts. However, if the impedance in the LF drops to nasty 2 ohms and has 60 degree phase shifts, that amplifier pushing the woofer section will have a very difficult time. Best solution is to have a smaller stereo amp for the MF/HF and bigger stereo power amp for the LF.

When you amplify with 2 monoaural power amps, you basically connect them as they are one stereo amplifier split into 3 boxes (preamp, L mono amp, R mono amp). The benefit is better channel separation and doubling on power section PSU with additional separate PSU for the preamp.

When you amplify with 4 monoaural power amps, you have the most 'ideal' situation where every monoaural amp drives one of the channels frequency halves. You can buy 4 amps, out of which 2 very powerfull and ignorant of speaker load and 2 for the MF/HF not that powerfull, simply spend the extra money in the LF where it matters.

 

[Vladimir]

Get cheap second hand tweeters and woofers for car audio to experiment with.

Considering you are biamping, you can freely mix driver impedances.

Example: 8 ohms for the highs and 4 ohms for the lows. This is OK since you are using separate amplifiers and one will work with 8 ohms load and the other with 4 ohms.

Mixing 8 ohm drivers and 4 ohm drivers on a single amplifier in parallel is a bad idea since the impedance drops under 3 ohms when combined.