Biwiring question

This is possibly a silly question to the experts , but when you have a 2way speaker thats rated at 8 ohms , and then biwire using two sets of amp speaker posts rather than the one set ....will the speaker rating alter?.Im asking because according to my pm7200 manual you should only use speakers rated at 16 ohms when using both sets of speaker outputs.So does that mean that when i biwire , the tweeter and woofer should be 16 ohms each to satisfy the amps requirements properly?.I know that biwiring cannot be proved scientifically to provide any advantages ,but would still like to know the answer to my question
tia
ellisonwales

 

no matter how many cables you run to the speakers the amp still sees the same impediance.

16ohms is an easier load on an amp then 8ohms. Hence when you use 2 pairs of speakers, each pair needs to be an easier load as the amp is doing twice as much work.

 

Thanks for reply Chris, though im not sure i understand the answer.Does that mean that most tweeter/woofer 2 way speakers of 8 ohms are wired in parallel and therefore 16 ohms?
tia
ellisonwales

 

Hi

Typically in a modern two way the bass will be 4ohm and the tweeter 8ohm, the whole signal is divided into two parts high and low via an x- over, so hence the bi-wire is possible, the amp would in this case see nominal average that would depend on the signal it was being given i.e. it's frequency and also the value of the combined X-over and driver values, so for example a signal broken down might look like this full bandwidth 20-20,000 Hz , bass 20-3.5khz and tweeter 3.5-20khz they the bass and the tweeter act as one if you see what I mean, just doing there own thing as it where, that's why the rating on a loudspeaker is nominal, so in a bi-wire the cable that takes only the tweeter information does not have to handle the heaver bass currents and vice versa.

Stuart

 

To try to answer your question ellison.

You can in theory connect as many pairs of loudspeakers to your pm7200 as you want (although I wouldn't recommend it as eventually the available power will be spread to thinly and you won't hear anything!).

However for every additional pair of loudspeakers you connect you must ensure the nominal impedance seen by the amplifier is not less than 8 ohms (in the case of the pm7200). Do a quick search for calculating values of resistance in parallel and series – it's basic stuff.

The second question. If a loudspeaker comprises two drive units (woofer and tweeter) both of a nominal 8 ohm rating and wired in parallel the nominal impedance seen by the amplifier would be 4 ohms. A 'difficult' load which would draw significant current.

To compensate for this a 4 ohm resistor would be wired in series to give a total of 8 ohms – as part of the crossover and usually in series with the tweeter to match drive unit sensitivities.

In short bi-wiring does not alter, in any significant way, the impedance seen by the amplifier.

 

But it's pretty pointless, unless you are in the business of selling cable, buy better wire and use wire jumpers instead of brass things tha come with speakers, TBH any old wire is preferable to brass jumpers.

 

Thank you all for explaining to me.It is clearer now.As for the biwiring...well i have the cable spare so why not.I know theres a school of thought that says different types of single wire make no difference either as long as its a decent diameter to start with.It could be the placebo effect but im pretty sure that some cable talk 2.5mm cable i have seems to give a more trebly effect than another brand of 2.5 mm though.
Thanks again
ellisonwales

 

Well said.