Impedance matching ????

[cblinko]

I am building my own speakers into the walls of my home. I am using 2 61/2 woofers and a tweeter for each output of the home theater set up. I also have a powered subwoofer and a manufactured center channel speaker. I understand the crossovers but I don't know exactly how to maintain 8 ohms of impedance when using 3 speakers. Do I add resistors to equal 8 ohms with the speakers in parallel ? How does this work

[dthomas]

Re: Impedance matching ????

I am building my own speakers into the walls of my home. I am using 2 61/2 woofers and a tweeter for each output of the home theater set up. I also have a powered subwoofer and a manufactured center channel speaker. I understand the crossovers but I don't know exactly how to maintain 8 ohms of impedance when using 3 speakers. Do I add resistors to equal 8 ohms with the speakers in parallel ? How does this work

If you are going to use 2 woofers and you want an 8 ohm load then you need to series two 4 ohm woofers or parallel 2 16 ohms woofers. Not many 16 ohm woofers available though but two 4 ohm woofers wired in series is not a bad option.

If your woofers are 8 ohms then in their passband they will either be 4 ohms (parallel-wired) or 16 ohms (series-wired). Not really any way around it. Adding resistors is not a real good idea as this will alter the parameters (Q) of the woofers and if you expect to drive them with much power you will need very large power resistors to dissipate the heat.

4 ohm loads are not too big of a deal for most decent amplifiers. Helps if you post what kind of drivers you are using.

Dave

[Wolf]

Re: Impedance matching ????

I am building my own speakers into the walls of my home. I am using 2 61/2 woofers and a tweeter for each output of the home theater set up. I also have a powered subwoofer and a manufactured center channel speaker. I understand the crossovers but I don't know exactly how to maintain 8 ohms of impedance when using 3 speakers. Do I add resistors to equal 8 ohms with the speakers in parallel ? How does this work

With a xover connected to the drivers, the individual frequency ranges are independently filtered for each driver's best ranges. As a driver and it's xover electrically approach the xover frequency, the impedance rises to an almost infinite value when done correctly. The rise in impedance is also the cause for reduced output in the range the driver is not to operate. Since the woofer will have a rising impedance with increasing frequency, and the tweeter will have increasing impedance with decreasing frequency, the net impedance will be the nominal level and drivers will not be in parallel with each other. This was one factor when I was starting as a speaker hobbyist that the books didn't make plainly. You don't need extra resistors to make the impedance appropriate in cases like this.
Later,
Wolf