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Speaker Impedance

 

New member
Username: Leomorales

Post Number: 1
Registered: Oct-04
I would like to know if there is anything I can do to either increase or decrease the impedance of a speaker, I am planning to assemble an amplifier, which specifies that i do not use speaker with impedance below 4 ohms and the other that i do not use speaker with impedance greater that 4 ohms. Please help me. Thank you.
 

Silver Member
Username: Fryguy

Nova Scotia Canada

Post Number: 247
Registered: Jun-04
You can always use a speaker load greater then the minimum rated load! Just never go lower then 4 ohm load or it over loads the amp.
 

J. Vigne
Unregistered guest


Actually what it does is underload the amp. With an impedance that is under the minimum you risk damage because the amp is literally not seeing enough of a load. It is difficult to overload an amp by having too much impedance and going with a higher impedance is always the safer bet. It is difficult to imagine an amp that says nothing higher than 4 Ohms. Are you sure you read that correctly. Even most speakers rated at 4 Ohms will have portions of the frequency response that are higher that 4 Ohms. And they will also have impedance that falls below 4 Ohms and most amps will have trouble with that load if it is too predominant.



 

J. Vigne
Unregistered guest


And to answer your question - you can put a load resistor in series with your speaker. That will raise the impedance. But it is better to simply buy a speaker that matches the load your amplifier wants to see as opposed to changing what you haven't got.



 

Silver Member
Username: Fryguy

Nova Scotia Canada

Post Number: 251
Registered: Jun-04
The difference between Resistance and Impedance:

Resistance: Measurement unit the Ohm
Impedance: Measurement unit the Ohm

Basic Differences:
Resistance: Resistance to the flow of DC current.
Impedance: Resistance to the flow of AC current (Though not always a true AC current)

Details, Explanations and Examples:

Impedance depends on the characteristics of the load (like inductance and capacitance) with an AC current (or close to AC current like a pulsed DC, Square wave, etc).
The two characteristics are inductive reactance and capacitive reactance.

Inductive reactance passes low frequencies and capacitive reactance passes high frequencies. This is why they have a big role in the effective resistance in an AC circuit.

This is why a tweeter will burn out with bass because for a tweeter to have the same load at its operating frequency its inductance is different. If the frequency is lowered its resistance decreases, so it can decrease to well under 1 ohm at around 100 Hz!
This is why a capacitor is placed in series because a capacitor passes high frequencies and filters out the bass. An inductor for a subwoofer does the opposite. This is the principle for the operation of a passive (crossover) filter. Because of the frequency splitting to different drivers the amp may have three (or more) speakers but the amp will always have the apparent load of only one speaker (Only works with a proper crossover that splits the different frequencies between the drivers, the standard rules of paralleling don't apply with a crossover in a 2-3-4 way system).

How is Resistance/Impedance affected by hooking in series or parallel?

For a series load, just sum the total of each resistance/impedance of the loads

For parallel loads it gets complicated. See the attached pictures for the formulas.



 

Silver Member
Username: Fryguy

Nova Scotia Canada

Post Number: 252
Registered: Jun-04
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Silver Member
Username: Fryguy

Nova Scotia Canada

Post Number: 253
Registered: Jun-04
My article and many more topics can be found at http://fryguy.ca/Forum/viewtopic.php?p=37#37
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