If you have an amp which wants an 8 ohm load, what would happen if you put a 4 ohm resistor between it and a 4 ohm speaker? Would it sound the same, or would it be attenuated?
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More questions about impedance
- Thread starter stradivarius151
- Start date
First of all you'd have to find a resistor that handles the same power as your speaker. Otherwise you'll need a fire extinguisher. And a new amp.
First you'll need to find a non inductive 4 ohm resistor that can handle the power from your amp. If it isn't non-inductive, then your damping factor will go to crap. Then you'll need to hook it up in series with your cab.
If what I said makes no sense to you, then don't bother with this experiment. You'll probably blow up your amp. Actually, don't do it even if you understand what I'm on about. It's still too risky.
Edit: what amp do you have?
If what I said makes no sense to you, then don't bother with this experiment. You'll probably blow up your amp. Actually, don't do it even if you understand what I'm on about. It's still too risky.
Edit: what amp do you have?
Not an experiment, just a question. Assuming a 4 ohm resistor as you described above, what would happen?
Would heat be dissipated from the resistor?
Would heat be dissipated from the resistor?
Yes. Half of the power of the amp would be dissipated from the resistor as heat.
What everyone else said.
If you have the proper resistor, technically it would work. But it really is a self defeating proposition.
A resistor that can handle a lot of power, be that low in resistance and be non-inductive would be very pricey. So much so that the money is better spent putting it towards another cab, that would actually increase your loudness, rather than sucking off half the power and using your amp as a space heater.
Right. I'm a diy person, I've built guitars and do all my own setup/repairs. I'm looking to get into the amp world, and I've got a few off-the-wall ideas I'm looking to try just to see how they'd work. I'm focused here on attenuation, without impinging on tone, for the good ol' apartment volume problem.
Why couldn't a suitable voltage divider, that sent some to speaker, and some to ground, work?
What about a really tiny amp? Do more powerful cabs put out more sound for a given amp?
Would your standard tiny carbon resistor melt by generating the kind of heat that it would coming from a power amp?
There is probably something in the sticky, or there should be as this gets asked about every other month.
"You cannot turn a 4 ohm speaker into an 8 ohm one with a resistor. It's impedence is 4 ohms and that's that. Amp outputs are rated with 'impedence' specifications, not 'resistance' specifications. Impedence is not the same as resistance."
"You cannot turn a 4 ohm speaker into an 8 ohm one with a resistor. It's impedence is 4 ohms and that's that. Amp outputs are rated with 'impedence' specifications, not 'resistance' specifications. Impedence is not the same as resistance."
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It would work. Commercial "power soaks" have been around for a long time.
A tiny amp is one way to do it as long as it has the sound you want. Not sure if there are any that tiny though.
More efficient cabs are louder than less efficient cabs for a given amp.
Yes. For large attenution, the L-pad would have to dissipate the full power of the amp.
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Voltage divider? For all of the same reasons that the series resistor is not a good practical way to handle this.
Get a little practice amp. That's the only really wise thing you've said. Use it. Turn it down or use headphones. Or get an Amplug. Tone considerations went out the window when you started talking about that series resistance nonsense.
No, the resistor would not melt. It would burn. Or it may just go "pop" like a fuse, and let the smoke out in one swell foop.
Kind of changed your tune from "not an experiment, just askin" to what sounds to me like you do want to try this.
Not to be harsh, but based on the questions you are asking, I don't think you are ready to get into the amp world. Not like this. IMHO, you need to do some serious boning up on basic electronics theory. After you have a grasp of resistance, voltage, current, and power at D.C. you then move on to A.C. electronics theory. That's where you learn about inductance, impedance and the reactances. Then start spending some quality library time reading about how audio amplifiers and speakers work.
Grasshopper... as quickly as you can, recite ohms law.
That is it right there. Resistance is a simple DC parameter. Impedance takes into account capacitive and inductive reactance in addition to simple resistance.
Capacitive reactance = 1 / 2 Pi f C
Inductive reactance = 2 Pi f L
Since f (frequency) to the speaker changes as you play so do the reactance values.
An attenuator will work but you have to use an attenuator that is rated the handle the output power of the amp, otherwise you will just smoke the attenuator. Amps are typically rated from tens to hundreds of Watts. Those little leaded carbon resistors are most commonly rated at a quarter of a Watt although you can get them up to about two Watts which is still way short of what you need to build an attenuator for a common bass amp. Some of the tonal characteristics of an amp/cab combination come from how the two interact with each other. Putting an attenuator between the two will change that interaction which might have a good, bad, or neutral effect on the tone that you perceive. If you want to build an attenuator you need to use resistors rated to handle your amps power level, not tiny carbon resistors. They typically have metal or ceramic bodies and while they are inductive, most commonly, they will not be inductive enough to cause issues at audio frequencies. If you are building an attenuator for the output of your Amateur Radio transmitter, then you have to worry about resistor inductance.
A small amp is what most of us use for practice at home. A cab that can handle 500 W may be louder or softer than a cab rated at 30 W when both are driven from a 10 W amp. The factor that determines how loud a cab will be when driven by some power level within its power rating is its efficiency. An efficient cab will be louder than an inefficient cab. But in the end both a small amp and your stage amp have volume controls. Using a small amp will prevent you from producing a wall shaking volume level if you accidentally play a few bars with the volume cranked but for the most part it seems that you could do what you want to do by simply turning down the volume.
In spite of what has been said here resistance is part of the impedance of a cab and it is in fact the most important part because part of resistance of the cab determines the part of the amplifier power that actually gets turned into sound. Impedance is complex in the mathematical sense. It is comprised of a real part, the resistance, and an imaginary part, the reactance. The reactance can be either positive (inductive) or negative (capacitive) but the resistance is always positive (for a cab anyway, there are exceptions for other types of circuits). The resistance of a typical resistor does not vary much with frequency but the resistance of a speaker cab may vary significantly over frequency so the DC resistance you measure with a meter will not tell the whole story of how the cab will work when driven by a bass guitar signal. The reactance of anything varies with frequency and quite commonly changes from inductive to capacitive, and potentially back and forth many times, as the frequency varies. Part of the cab's resistance represents the ability of the cab to turn electrical power into audible sound output power and part of it represents losses in the cab. The ratio of the two determines the cab's efficiency.
You don't solve this problem with a resistor or a voltage divider, you would use an impedance transformer.
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Better to configure your rig so you don't have this issue in the first place.
As long as that 4 ohm resistor is in the form of a second (and hopefully similarly spec'd) speaker, it should work great!
That's a nice transformer and less expensive than I imagined it would be.
Still, at $185 US) or $267 USD including a box with connectors, you could buy a bass cab, or at least be well on your way to buying one depending on how $$ of a cab you want.