Yes, really.
Those resistors are "minimally inductive" not non-inductive.
At audio frequencies the tiny amount of inductance has basically zero noticeable effect... but there is always some inductance.
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An Impedance-reducing Resistor?
- Thread starter domjohnson
- Start date
Yes, really.
Those resistors are "minimally inductive" not non-inductive.
At audio frequencies the tiny amount of inductance has basically zero noticeable effect... but there is always some inductance.
- Aug 21, 2008
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- Owner, SGD Music Products
Sure it does when we are dealing with inductive reactance, such as a pickup or speaker coil. Try taking an AC resistance reading on a guitar pickup at different frequencies.
The inductive reactance of an inductor increases as the frequency across it increases therefore inductive reactance is proportional to frequency ( XL α ) as the back emf generated in the inductor is equal to its inductance multiplied by the rate of change of current in the inductor. Also as the frequency increases the current flowing through the inductor also reduces in value.
Those are inductors. Not resistors.
I was referring to resistors.
And yes, I know resistors have an inductive value but it is so small at audio frequencies that it can be ignored.
v= L* di/dt
You stated that resistance changes with frequency in your origional post.
Not you are calling it inductive reactance.
Not the same.
- Aug 21, 2008
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- Owner, SGD Music Products
I was referring to speakers. That's what this post was about. Coils are inductors.
Being pedantic for the sake of it doesn't solve any problems. It turns into a pissing match.
If you are going to make sweeping statements and then pick nits afterwards when someone disagrees it is usually a good idea to stay with the same nits.
YMMV....
FWIW In my day job as an electrical engineer being pedantic means I can deliver reliable, accurate solutions to whatever problem is handed to me by the bossman.
This ensures a reliable source of employment.
Perhaps winding wire around pickups is not so exacting. Not sure.
- Aug 21, 2008
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- Owner, SGD Music Products
Come over to the pickup makers forum and talk to the two scientist that post there. We discuss AC resistance all the time as it relates to coils.
The bottom line is a fixed resistor across the output of an amplifier does not behave like a speaker.
And look up the word pedantic.
A bit testy are we today?
Who pissed in your post toasties?
You stated "resistance" changes with frequency.
No, it doesn't.
Pedantic:
Knowing the difference between the word "resistance" and the term " inductive reactance" and when to use them.
done...
- Aug 21, 2008
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- Owner, SGD Music Products
My cat died Saturday. Sorry if I'm a grouch.
I said AC resistance increases with frequency. That's when we are dealing with an inductor. And I was referring to the speaker coil.
My point was that it is different from a fixed resistance.
I started off saying that resistance is different from impedance. If you are plotting the impedance curve of something like a speaker, you do it over a range of frequencies. The impedance of a speaker is not a constant. It's actual impedance changes with frequency. That won't happen with a fixed resistor. The DC resistance you read on a speaker is the nominal impedance.
If you guys have something to say to each other that is not related to the OP's question, why not just PM each other.
All this unnecissary reading (pissing) wastes my time.
Back to the original question, If I understand correctly, I beleive the issue is you have an amp and cab, would like more volume, but have limited transport space, and the amp is capaable of more output power at a lower impedance.
It is typically not possible to reconfigure the existing drivers from say 8 ohms to 4 ohms without replacing them.
The second option is to replace the amp with one that can deliver the maximum rated power of the speaker cab at the cabs current impedance.
All this unnecissary reading (pissing) wastes my time.
Back to the original question, If I understand correctly, I beleive the issue is you have an amp and cab, would like more volume, but have limited transport space, and the amp is capaable of more output power at a lower impedance.
It is typically not possible to reconfigure the existing drivers from say 8 ohms to 4 ohms without replacing them.
The second option is to replace the amp with one that can deliver the maximum rated power of the speaker cab at the cabs current impedance.
Adding a resistor over the other output of the amp will give you a handly pocket warmer if you're on a cold stage, that's about it.....
(no, don't do that either)
(no, don't do that either)
Not looking to start any arguments, just want to point out the highlighted is the DCR of the speaker and not the nominal impedance factored from the impedance curve.
These transformers can be used to half the impedance that the amp is driving, and for SS amps may increase the power by close to a factor of two. But as others have stated this will result in a SPL increase of only about 3db, which is not all that useful.
The other use for the transformer is to use it the other way around, and double the impedance experienced by the amp. You might ask "why would you do that?" Suppose you had a cabinet configuration that was 2 ohms and your amp can't drive such a low impedance load? The transformer would let you increase the load to 4 ohms so it was safe to use with the amp. But there is so much great gear out there you should be able to configure a rig without such a device...
OP: What you really need to be doing is thinking in terms of how many db of SPL you need. Then you can holistically look at the power output of various amps into different loads, taking their sensitivity into account. This will enable you to compute the maximum SPL from any given configuration, and then you can choose something that works for you. I guess it boils down to knowing your needs before you buy.
Cheers,
Jim
Passinwind
I know nothing.
- Dec 3, 2003
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- Designer/Toaster Tech @ Passinwind Electronics
It's probably most useful for guys with big tube amps and big cabs that are not matched to those amps. I used to get queries about that scenario fairly often when I still was in the repair business.
You would still be putting the same amount of power into the cabinet (assuming your amp puts out double the watts at 4ohm vs 8ohm). You would double the output power of the amp. Why would you want to do this? The only reason I could see even close to logical would be to try and overdrive the output tubes on a tube power section. They do sell stuff like that where you would be getting an adjustable matching device. I think this idea is silly. That being said, you might like the sound produced by the result...
@domjhonson, any speaker always has an impedance and a resistance. If you have noticed before, all speakers come with a power rating. Some are 800W, some are much higher or much lesser than that. You can always add more resistance in it if you intend on using it with bigger amps so that it can allow more current to pass through without blowing up. Bigger and better speakers normally have a very high power rating that is much higher resistance values so that can cater the challenge of bigger input. You can just try that and keep us posted with your results.
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Mr. Foxen
Commercial User
Don't think it makes any sort of sense. Especially not making sense to post it in a dead thread.
