Creating a 6ohm load with 8ohm speakers? (1 Viewer)

[Stephen Hopkins]

I'm wondering if it would be feasible to use resistors to create a 6 ohm load on a capable receiver using 8ohm speakers, to squeeze that extra bit of power out.

I got this idea when looking at the stats of a receiver i'm thinking about buying that had a 35 watt jump from 8ohm to 6ohm.

I know a 35watt increase would only translate to about 1db of extra volume, and wouldn't make that much of a difference, and would also raise the THD, so it might not be to any advantage at all, even though the 6ohm THD of the receiver in question is still only .7%, which is less than the 1% 8ohm THD of my current receiver. I'm really asking this to see if my meager understanding of some basic electronic theory is correct.

If so, what resistors would you use to do it? and would you simply solder them to one end of your speaker wire?

Thanks

 

[Chris Brown]

I think it would be counter-productive as you would be routing some of the current through the resister instead of the speaker.

 

[John Kotches]

Chris,

Right. Not to mention that the impedance of the majority of speakers is nowhere near a flat line.

Stephen,

A 1dB change in volume is a barely perceptible increase. 3dB (an easily noticable difference) requires twice the power.

For our ears to perceive a doubling of loudness requires 10dB of change, which requires 10x the power.

Regards,

 

[Stephen Hopkins]

As i mentioned, i know it wouldn't be a large difference and i know it might be counterproductive, as i stated in my original post. I was asking from more of a theoretical standpount, like in terms of electriconics theory.

Thanks

 

[Dustin B]

Steven, I think one of John's comments requires a little more explanation. Your typical speaker rated at an 8ohm nominal impedance will actually have an impedance range from 4-6ohms up to 30ohms+ depending on the frequency being played.

I also think (not 100% sure on this) adding a resistor in the path will muck with the crossover.

 

[John Garcia]

Not to mention that, while you are getting the "extra" power, you are also working the receiver harder to get it. Nothing is free.

 

[BrianWoerndle]

I don't even know if that is possible. Lets start with some definitions. Impedance is a measure of resistance through an electrical current measured in ohms. The machanics of the speaker is what causes the resistance. Some sounds are easier to produce, therefore have lower resistance, while some are harder. Some speakers are designed to have a lower resistance (4 ohm speakers), but most mass market speakers are designed with an 8 ohm nominal load. Nominal is a key word. That means that it is an average of 8 ohms. At times it will be much more, and much less, but will usually run at about 8 ohms. So, adding a resistor in the middle will lower the resistance between the receiver and resistor, but the speaker will still pull on the resistor as it needs.
Once you understand that, it is easy to see how that translates into power. The less resistance the speaker, the hader it can pull power from an amp. Think about a tug of war, when yoh have less people resisting you on the other side, you can pull harder. So the less resistance a speaker has, the harder the amp has to work to feed the speaker with power. If an amp works too hard it will cause too much heat to built and eventually damage the amp.
So there is basically nothing you can do to change the power except get a new amp. A resistor might be able to lower the impedance a little, but there are too many other things that will overshadow the difference.

 

[Saurav]

If so, what resistors would you use to do it? and would you simply solder them to one end of your speaker wire?

Again, on purely theoretical grounds - if you're trying to bring the impedance down, you'll need to add a resistor in parallel, so it would go across the terminals. Soldering it in-line with one wire will add it in series, which will raise the impedance. What kind of resistor - the value depends on what you want the combined impedance to be. The power rating should be high enough so that it doesn't start smoking when you turn up the volume. I believe that resistors used in speaker crossovers are usually rated for around 10W, maybe higher. Most resistors used inside electronic components are rated for 0.25W or 0.5W, so if you hooked up one of these, it would self-destruct instantly when you turned the amp on.

 

[Stephen Hopkins]

The last 2 posts are the kind of answers i was looking for.
So essientially, it would be pulling more power from the amp, but the speakers wouldn't receive any of this power because it would be disapated by the resistor?
Thanks

 

[Saurav]

So essientially, it would be pulling more power from the amp, but the speakers wouldn't receive any of this power because it would be disapated by the resistor?

Exactly.

 

[jeff lam]

Sound quality would most likely be degraded as well unless you use top quality components. All in all, it's not worth it.

 

[Chris PC]

Unless you re-designed the actual speakers, you would get less sound and at lower quality, and not an improvement.