Speaker wiring

[apsoul]

Hi there, I am currently setting up a makeshift sound system in my garage. Nearly all parts have been 'donated' thus the hodge-podge mess i'm working with.

I was wondering if it would be possible to set up 3 sets of speakers a series-parallel circuit connecting to the 'b' channel of my receiver. the speakers are rated at 6, 8, and 16 ohms. if my calculations are correct, a series-parallel setup would result in 7.46 ohms total resistance. (6 and 8 ohm speakers in series, parallel to 16 ohm speakers)

I know too low of an impedance rated speakers will overheat a solid state amp, but if my amp is rated at 8 ohms, would 7.46 ohms worth of resistance do damage? Would I just need to make sure that i had a small fan blowing on the amp's internal components to remove excess heat?

Thanks for any help

 

[Oreo]

Hi there, I am currently setting up a makeshift sound system in my garage. Nearly all parts have been 'donated' thus the hodge-podge mess i'm working with.

I was wondering if it would be possible to set up 3 sets of speakers a series-parallel circuit connecting to the 'b' channel of my receiver. the speakers are rated at 6, 8, and 16 ohms. if my calculations are correct, a series-parallel setup would result in 7.46 ohms total resistance. (6 and 8 ohm speakers in series, parallel to 16 ohm speakers)

I know too low of an impedance rated speakers will overheat a solid state amp, but if my amp is rated at 8 ohms, would 7.46 ohms worth of resistance do damage? Would I just need to make sure that i had a small fan blowing on the amp's internal components to remove excess heat?

Thanks for any help

I'm not to good with the electrical side of things, so i can't really give you a proper answer with any certainty. But what i do know is if it's a good amp they are often underspec'd, and will drive more than they often state.

So that leads me to the question of, what amp is it ?

 

[ReikokuKo]

I am very curious about this set up. Please post back what happens.
(I would just run it and monitor it, I imagine a fuse would blow if that set up doesn't work.)

 

[apsoul]

Well it's a Panasonic RA-6500 receiver. All audio originates from my computer in 5.1 config. Setup is as follows

From PC:
Fronts: Philips spa7210-17 computer speakers (40w 3/4" tweeter, 3" driver)
Sides: Output to Panasonic RA-6500
Cen/Sub: disabled

From Panasonic RA-6500:
B Channel: Panasonic CS-R590 Floor (8ohm 150w 3-way approx 10", 5", 1 3/4")
A Channel: Panasonic Thrusters SB 360 Shelf (8 ohm 7w 6 1/2" duo-cone, 6 1/2" Passive Radiator @ 40Hz)

computer is against front wall with pc speakers on desk. CS-R590's in front corners on shelf 5ft off floor, SB 360's in rear corners 3ft off ground

I would like to replace the current A channel setup from Receiver to:
Aiwa SX NS115 speakers (6 ohm, came with 90's aiwa 3cd stereo) and the Panasonic sb-360's(8 ohm) in a series circuit parallel to the small panasonic satellites (16ohm).



Also, a major question that is more valuable to me than any others that i've had is if i run the theoretical 7.46ohms setup out of said amp rated at 8 ohms, would the only concern i should have is excess heat?? The same if i ran 6ohm speakers from the amp?

Thanks again.

 

[strollin]

How did you come up with 7.46 ohms? 6+8=14, 14+16=30/2=15 ohms. What formula did you use? The impedance of speakers in series are added together, impedance of speakers in parallel are halved.

Technically, resistance isn't the correct term. If you used a multimeter to measure the resistance at the speaker terminals, you wouldn't see 8 ohms or anything close. Impedance is the actual figure we want and it's not a fixed value but varies with the frequency. An 8 ohm speaker's impedance may vary between 4 and 50 ohms depending on the frequency.

 

[apsoul]

The setup should be

6 Ohm and 8 Ohm speakers in series = 14 Ohms
run that series parallel to the 16 Ohm speakers.

/* Strollin, in your post, I'm assuming that when you stated "14+16=30/2=15ohms" that you were figuring the setup as i just described, however in parallel you don't add the ohms and then divide by 2, its a bit more complex when using different impedances. If speakers are of same impedance you just take ohms and divide by number of speaker sets. et al 2 sets of 8 ohm speakers would be total of 4ohms impedance. */

To figure total impedance with speaker sets of different impedance, you have to figure volts and amps into the formula. Now the impedance of any speaker will be the same regardless of the volts going to the speaker, so we will make things simple and just figure a constant 1 volt going to each speaker. the formula would be:
1v/16ohms + 1v/14ohms = .1339 amps drawn from the receiver.
1v/.1339amps = 7.468 ohms.

 

[apsoul]

edit: @ReikokuKo: I would just give it a test run without confirmation and keep an eye on things. However, this setup is in my garage and it's the old wiring that i'm not sure how much i trust. I just want to make sure the only thing I need to worry about is heat, because I could easily set up a 200mm computer fan powered by my computer blowing down on the internal receiver components. I also have a bunch of leftover heat sinks that I could use to further assist cooling.

was supposed to be an edit, sorry for the double post

 

[Apokalipse]

How did you come up with 7.46 ohms? 6+8=14, 14+16=30/2=15 ohms. What formula did you use? The impedance of speakers in series are added together, impedance of speakers in parallel are halved.

Parallel resistance is calculated with 1/Rt = 1/R1 + 1/R2 + .... 1/Rn

Rt = total resistance
R1, R2 ... Rn = parallel resistors

Technically, resistance isn't the correct term. If you used a multimeter to measure the resistance at the speaker terminals, you wouldn't see 8 ohms or anything close. Impedance is the actual figure we want and it's not a fixed value but varies with the frequency. An 8 ohm speaker's impedance may vary between 4 and 50 ohms depending on the frequency.

The rated resistance is the average. It's not incorrect, it just isn't the whole picture.

Anyway, I'd imagine that speakers with higher resistance wouldn't hurt the amp. It just means it won't be as loud, and possibly become distorted.

 

[strollin]

...
/* Strollin, in your post, I'm assuming that when you stated "14+16=30/2=15ohms" that you were figuring the setup as i just described, however in parallel you don't add the ohms and then divide by 2, its a bit more complex when using different impedances. If speakers are of same impedance you just take ohms and divide by number of speaker sets. et al 2 sets of 8 ohm speakers would be total of 4ohms impedance. */

Of course you're right. I don't know what the heck I was thinking when I posted that. Sorry. I plead temporary insanity.

 

[apsoul]

@Apokalipse: I am questioning about running speakers with a total resistance less than what the amp is rated for. If my theoretical setup came out to be something like 8.5ohms then i would have immediately set it up as solid state amps can handle extra impedance without damage, albeit with some lessening of the sound quality. From what i understand too low of a resistance in solid state amps causes the excess current to be turned into heat via the ?voltage regulators? of the amp. Therefore, if I hooked up my speakers as stated above, the extra .009amps per volt would be absorbed by the amp and turned into heat.

1v/7.468ohms=.1339amps; 1v/8ohms=.125amps
.1339amps-.125amps= .0089 extra amps per volt

My apologies for being so meticulous, or nit-picky if you prefer, with my questions/answers but I can't afford to damage this amp for a couple reasons:
1. It is the only audio source I have for my parties, movies, and games. (other than my computer speakers which just don't cut it when there's 20+ people hanging around)
2. I don't have the money to get another if I do fry it.
3. It is my fathers, he likes old stuff, and i can't even find documentation online about this receiver, never mind a replacement.

As always, thanks for the help/feedback

Edit: Ok, so going with the "Resistance rating of the amp/speakers is just the average, and that it varies with frequency. What frequencies create higher resistance? Is this frequency to resistance ratio linear? I'm asking this because the speakers that i'm trying to run with total impedance of 7.468ohms are not full range. With that thought, then what happens when the amp sends out a frequency that the speakers can not produce? Would that result in higher resistance, or none at all? This idea also makes me think that if resistance is lower near the frequency range that my speakers can not produce, (and the amp is rated to handle full range speakers at 8ohms) then the amp should not encounter any resistances that it is not rated for.

sidenote: I think i'm getting to deep into this.