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RE: A and B speaker use.

98.23.53.6

In Reply to: RE: A and B speaker use. posted by DRam on October 28, 2015 at 08:57:04

Speaker impedance varies with frequency, and some speaker have deep but narrow impedance dips at certain frequencies, usually around the resonance frequency. Others far less so.

Can you find impedance curves for your speakers? I think you would be OK with two 8-ohm pairs if they are a true 8-ohms and without significant dips that fall below 4 ohms. It would also be nice if the lowest dips for each pair occurred at quite different frequencies.

Playing two pairs loudly also results in more potential problems.

Another option would to be put a 4-ohm resistor in series on each side for one of the pairs, but that will cause that pair to play lower and may mess up stuff like the receiver damping factor.

Modern surround sound systems are designed to handle 3+ pairs of speakers at once, and do not seem to be prone to blowing up, tho I did trip the breakers on my 6.1 Pioneer playing the "Master and Commander" DVD fairly loudly. Fortunately, the unit reset and there was no permanent damage. It was the cannon fire that did it I'm sure as it happened during a ship gun battle. Has not happened again.Just when I said to myself "this is quite realistic" the receiver went quiet.

Follow Ups:

RE: A and B speaker use. - Crazy Dave 08:13:06 10/30/15 (0)
Adcom had a nice speaker switch box called a GFS-3 that had impedance protection of some kind. You probably can get one used for a song.

Dave
A and B speaker use. - DRam 20:36:53 10/29/15 (2)
A search for impedance curves for the Polk Monitors came up blank. The Marantz speakers have had the tweeters and woofers replaced with Parts Express items long ago, no charts for them.

The Marantz are rated as 8 ohms, the Polk Monitors are "compatible with 8 ohm outputs", whatever that means.

Would 2 ohm resistors on each set of speakers work? That way it would seem the output loss would be balanced and still raise the impedance to a safe level.
- RE: A and B speaker use. - DavidLD 05:22:11 10/30/15 (1)
  Probably, but the speaker builders hang out on the tech board on the parts express site. Maybe post your dilemma on that board and see what suggestions they might have. I still think you would be fine if both pairs of speakers were true 8-ohms. Speaker systems with a nominal rated impedance of higher than 8-ohms are rare indeed, and if Denon had really not wanted you to run two pair of 8-ohm speakers at once, they would have set up the switching differently.
  
  The board you need to pose your question on is here.
  http://techtalk.parts-express.com/forumdisplay.php?2-Tech-Talk-Forum
  
  just cut and paste to that board. They deal with impedance issues regularly, as the nominal impedance is crucial in DIY designs.
  - RE: A and B speaker use. - DRam 08:31:13 10/30/15 (0)
    Thanks. I have registered and will pursue things there.

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