Running 8 ohm A and 6 ohm B channel.

[Unicorncob]

I have a few new receivers that I purchased recently.
Hitachi SR-903 series E
Marantz 4230
Pioneer SX-838

I’m wondering about powering mixed ohm speakers. I have a set of ELAC B6 speakers DB61-BK and a pair of Boston Acoustic T830 towers. The ELAC’s are 6 ohm, the Boston’s are 8 ohm. I know very little about vintage gear but love the sound! The last thing I want to do is fry one of my receivers. Joined this forum to start learning a bit more about what I have and what the do’s and don’ts are when it comes to amperage ohms and what kind of gear can power what speakers. This is my first post so forgive me if it’s in the wrong section. Thanks!

 

[Steven Tate]

If I'm not mistaken, Marantz receivers run the A and B speaker terminals in parallel. Running 8+6 ohm speakers in parallel will give you an impedance below 4 ohms. I personally wouldn't do it - especially on vintage equipment that might not be running at peak performance. Hopefully someone else will chime in to verify.

 

[whoaru99]

It makes 3.4 ohms nominal if they are in parallel. A lot of gear specs say 4 ohms minimum. The safe bet is to follow the recommendations.

Personally, though, I think there is not much risk at normal playback level.

If the gear is poorly ventilated or used for crankfests probably better to stick with (or above) the specified minimum too.

 

[charles 1973]

If "The last thing I want to do is fry one of my receivers" then follow the advice on the back of most receivers and amps and only use 1 pair of speakers at a time if any of them are under 8 ohms, Or 2 pair of 8+ ohm speakers. My Onkyo AVR has protection for overheating and will shut down (and has), hopefully before it fries. Perhaps vintage receivers do to, Then again perhaps not. You might get away with running a 8 ohm and 6 ohm pair at moderate volume if the receiver is well ventilated, Like whoara99 suggests. It should also be clean inside. But it would still be a crap shoot.

You could though in a 2 ohm resistor in line with the 6 ohm speaker to get the 8 ohms. That's what those speaker switches do with protection on, and they seem to work well for casual listening.

 

[Unicorncob]

If I'm not mistaken, Marantz receivers run the A and B speaker terminals in parallel. Running 8+6 ohm speakers in parallel will give you an impedance below 4 ohms. I personally wouldn't do it - especially on vintage equipment that might not be running at peak performance. Hopefully someone else will chime in to verify.

Thank you. I’m only just learning exactly how ohms work.

 

[Steven Tate]

In general, for speakers in series, add the impedance numbers. For two speakers in parallel, if they are the same impedance, just half the impedance of one of them. Two 8 ohm speakers in parallel are the equivalent of 4 ohms. #Whoaru99 is correct. The actual formula for calculating resistance of 8 ohms plus 6 ohms in parallel results in 3.4 ohms. Impedance isn’t exactly resistance, but treating nominal impedance like resistance for ballpark calculations is adequate.

 

[smokey2255]

If "The last thing I want to do is fry one of my receivers" then follow the advice on the back of most receivers and amps and only use 1 pair of speakers at a time if any of them are under 8 ohms, Or 2 pair of 8+ ohm speakers. My Onkyo AVR has protection for overheating and will shut down (and has), hopefully before it fries. Perhaps vintage receivers do to, Then again perhaps not. You might get away with running a 8 ohm and 6 ohm pair at moderate volume if the receiver is well ventilated, Like whoara99 suggests. It should also be clean inside. But it would still be a crap shoot.

You could though in a 2 ohm resistor in line with the 6 ohm speaker to get the 8 ohms. That's what those speaker switches do with protection on, and they seem to work well for casual listening.

What would the extra resistor do to the sound from the speakers? Would changing the resistance change the sound?

 

[quaddriver]

ill level with you, if you open up a lot of speakers, you will find a 2-10 ohm 5-10 watter inline with the tweeter....

 

[whoaru99]

Indeed, but generally for a different purpose than the case here.

 

[whoaru99]

What would the extra resistor do to the sound from the speakers? Would changing the resistance change the sound?

A series resistor in this case simply wastes power.

In the case of a 2 ohm resistor in series with 6 ohm, at a level of 20W power, the resistor would be wasting about 5 of the 20 watts, or pick a number and consider 25% wasted.

If running multiple pair of speakers is your prerogative then you'll be better served in the long run by getting an amp rated for, say, 2 ohm loads. Or, if you have pre outs available, a second amp (having gain/level controls) for the additional pair of speakers.

 

[Steven Tate]

I did this once when I had. Pair of 8 ohm speakers and a pair of 4 ohm that I wanted to run at the same time. I used two 2 ohm cement resistors in series on each 4 ohm to be able to dissipate the power. But the use was for strictly background music in two rooms. Volume was probably at 10%. I just wouldn’t do this for primary listening at medium to high volumes.

 

[quaddriver]

right,

Indeed, but generally for a different purpose than the case here.

but do you REALLY think speaker manufacturers invented some sort of new partlyobtanium to make a tiny bookshelf speaker handle 100+ watts?

I tell people, take off the grilles, turn out the lights and crank it at night. tell me if on each bass crack there is a flash or glow from the bass reflex port...fuse lights. the same things that lit the dials of many a marantz are also wired in series to burn off enough power to ensure the speaker driver lives.

things, aint always as they appear!

 

[whoaru99]

right,

but do you REALLY think speaker manufacturers invented some sort of new partlyobtanium to make a tiny bookshelf speaker handle 100+ watts?

...

Can you clarify what you are asking (or insinuating)?

 

[quaddriver]

come to my L-pad and I will explain! ;-)