using resistors when designing speakers (1 Viewer)

[Brian Dobbs]

Hi all. I have two 4 ohm speakers that I am going to use for one channel of a stereo receiver. I was going to align them in series to create 8 ohms, because of the 8 ohm output of the receiver. But then I thought, can't I just add a 4 ohm resistor to each speaker to create 8 ohms, and then I could use a speaker for each channnel?
I just want to know which idea is better:
-aligning the speakers in series
or
-using 4 ohm resistors for each
Thanks

 

[Saurav]

Wouldn't you get more sound output if you used two speakers?

 

[Peter Johnson]

2 speakers on 1 channel? Why not just use 1?
Connecting speakers in series is generally a bad idea, as they interfere with each other.
Putting a resistor is series, is also not really an option.
1. The resistor will dissipate power
2. You will shift the crossover point and/or effect the FR of the speaker.
3. Damping factor will be effected..
And the list goes on..
Basically..if it was me, I would run the speakers normally, just be VERY careful. All amps will usually run a 4 ohm load, but run out of current quickly. So, be careful.

 

[Tor Arne]

You should read a book on the subject of speaker design.
Regards,
TAH

 

[Brian Dobbs]

How could the speakers interfere with each other? The ONLY speakers I am using are just 12" woofers, so I'm only producing bass notes with this setup. I have four 12" speakers. Each are 4 ohms. My receiver requires an 8 ohm speaker. That's why I was going to hook the speakers up in series. What's the problem with that?
Also, there are no crossovers in this setup. I just want to know if I can run 4 different resistors to four different speakers on 4 different channels. My receiver has A and/or B switching.
I would like to read a book on speaker design, but I thought it would be a good idea to come here first and get a quick answer.

 

[ThomasW]

Not a good idea 1/2 the power will go into the resistor

 

[Brian Dobbs]

Would you care to elaborate? Why will half the power go to the resistor. I don't understand.

 

[Kevin P]

A resistor wastes power, as current flowing through it is converted into heat instead of sound. A 4 ohm speaker with a resistor won't play as loud as a 8 ohm speaker. Also, resistance and impedance are two different things, so adding a 4 ohm resistor to a 4 ohm driver doesn't create an 8 ohm driver.
I don't know if such a device exists, but if someone makes a 8 ohm to 4 ohm transformer, that would probably work pretty well too. Otherwise, you should either just use one woofer and don't turn it up too loud and risk overloading your amp, or connect the two woofers in series. It's not perfect, but it'll work.
If you're building a subwoofer, perhaps it'll be better to use a separate amp that can handle the 4 ohm load, rather than a receiver.
KJP

 

[Brian Dobbs]

Thank you for a great response!

 

[Neil Weinstock]

I'm trying to understand why connecting the two drivers in series is not the obvious and only answer. Assuming they are identical drivers, this is standard practice in car audio, and from what I can tell in DIY home sub making as well. You create a series/parallel network of identical drivers to create the desired impedance, in this case 8 ohms.
Oh, and having the two drivers in series will be more efficient than just the one with the volume turned down, so you'll get more output.
What am I missing?

 

[Cees Alons]

Brian,
(1) It's not advisable to put a resistor in series with the driver, for the reason given above (losing power in the resistor). Furthermore, the resistor has to be a very heavy one (or it may melt).
Also, the resistor would be a purely-Ohm resistor and would adversely influence the frequency response (normally some irregularities of the driver response are reversed by it's resistance to the current-driven amplifier). It could even be better then, to simply connect the 4 Ohm speaker to the 8 Ohm channel (to be done with some caution, but not as desastrous as some people think )
(2) You can indeed connect two speaker in parallel or in series. Parallel would halve the resistance, in series would double it.
Because the speakers are completely equal (well.. as good as it can be..), there's not much disadvantage to that. But you have to make sure you connect "in phase". This goes like this: wire from amplifier goes to + (or red) connection on speaker 1; wire from - (or blue) connection on speaker 1 goes to + (or red) connection on speaker 2; wire from - (or blue) connection of speaker 2 goes to amplifier. You will understand that the + and - or red and blue could be marked differently. If the connections aren't marked you could use the battery method, but I'm not going to explain that now .
Good luck,
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[Edited last by Cees Alons on August 24, 2001 at 08:11 AM]

 

[Brian Dobbs]

Thank you Neil and Cees for such great answers. I totally couldn't agree with you guys more.