What is impedance???

[cozneffect]

What is impedance and how does it effect the performance of the spks. Also, if a receiver meant for spks. having 6 ohms impedance is connected to spks. having 8 ohms impedance, what would happen?

Out of Denon AVR2105 and HK AVR335, which is the better receiver and in what ways??

Thanks.

 

[Buckeyefan 1]

What is impedance and how does it effect the performance of the spks. Also, if a receiver meant for spks. having 6 ohms impedance is connected to spks. having 8 ohms impedance, what would happen?

Out of Denon AVR2105 and HK AVR335, which is the better receiver and in what ways??

Thanks.

Impedance means resistance. The lower the impedance, the less resistance. 4 and 6 ohm speakers require very solid amplifiers and large heat sinks to avoid overheating (if driven hard).

Both are decent mid level receivers, but IMO the AVR335 is the better of the two. The AVR2805 would be a better competitor to the 335. Check out the weight of that HK compared to the Denons.

 

[DaveOCP]

8-6 ohm loads are generally the standard spec for receivers. When an amp "sees" a lower resistance, it produces more power. How much more depends on the design of the amp. The best can double their output at 4ohms compared to 8ohms. Most power amps can handle 4ohm loads without a problem, but thats usually asking too much for a receiver.

Digital amps because they normally run so cool can usually dish out some serious power with very low resistance. For example, the Sunfire 600~two which is normally 600W per channel @ 8ohms can dish out short peaks of 4000W per channel with a 1ohm load.

 

[Rip Van Woofer]

Running an amp into a low impedance load is kind of like running your car engine at full throttle in neutral: it generates lots of power but will ultimately overheat and self-destruct.

Keep in mind that zero resistance/impedance is a short circuit. Just about every electronic device needs to operate into a load with some resistance or it goes poof (or bang!). So the lower the impedance the closer you get to a short. Never a good thing!

Bottom line: do not use speakers below the rated impedance of your amp or receiver. You will trip its protection circuits and/or shorten its life.

FWIW, strictly speaking, impedance (Z) applies to alternating current, and is more complex than DC resistance (R) even though both are stated in ohms. Audio signals are of course AC.

 

[Steve Ganahl]

I have a Yamaha RX-V657 Receiver, which can be set for either 4 or 8 Ohm resistance.
I have Canton LE 103 speakers, "nominally rated 4 to 8 Ohms"
What would be the benefit of setting the impedance to 4 Ohms? It sound like all that would happen is the receiver would run hotter.

 

[DaveOCP]

Actually, Anthem's Statement P5 power amp is capable of survivng a short. One genius reviewer shorted a channel with a fork, and the amp was able to reproduce and amplify the fork's natural resonance. It didnt sound so good, but it worked.

Steve, there would most likely be no change. No speaker stays at the same resistance level throught the entire 20hz-20khz range. Some "8ohms nominal" speakers can dip below 3ohms at certain frequencies. Provided your Yamaha is working fine at the 8ohms position, I would leave it.

 

[mulester7]

http://www.audiovideo101.com/dictionary/default.asp


Impedance

The resistance to the flow of an electric current in a circuit measured in ohms. Impedance is what restrains the flow an electric current making it more difficult for the current to move through a circuit.

Impedance is similar to a dam in a river. If the river is a circuit (to be a true circuit the river would need to run in a complete circle) then the water is the electric current. The water flows freely when there are no obstructions to resist the flow. The dam in the river resists the flow of water. By fully opening the dam there is no resistance. The further closed the dam becomes, the more difficult it is for the water to flow. A dam of 1 ohm would have very little resistance (although a dam’s resistance to water is not measured in ohms, impedance is and so ohms will be used for this example). As the dam’s resistance to the water’s flow, it’s impedance, increases to 2 ohms it becomes more difficult for the water to flow. Similarly, as the dam’s impedance grows to 4 ohms and then 8 ohms and beyond it becomes more and more difficult for the water to flow. In an electric current, low impedance lets more current flow.

A well designed amplifier with a strong power supply will double the amount of power in watts that it sends to a speaker with each halving of impedance. For instance, an amplifier might send 100 watts to a speaker with an 8-ohm impedance. When the impedance is halved to 4 ohms that amplifier would send out 200 watts of power. In the real world, few amplifiers are actually able to double their power output as impedance halves due to limitations on their power supply and design. Additionally, few amplifiers are able to put out power for any significant length of time with impedances of 3 ohms or less (the amplifier must be able to supply huge amounts of power as the impedance decreases below 4 ohms – in fact, many receivers cannot operate below 6 or even 8 ohms).

When shopping for speakers, you will see figures stating the nominal impedance of a speaker (most speakers have a nominal impedance of between 4 and 8 ohms). This is the speaker’s average resistance to the flow of current through the circuit going from the amplifier into the speaker and back to the amplifier. However, this figure is only the average impedance rating across all frequencies into which the speaker produces output. In reality, the impedance may drop at some points to 2 or 3 ohms and may reach 40, 50 or even 60 ohms at other frequencies. For this reason, it is beneficial to have a strong amplifier able to produce large amounts of power down into small impedance loads.

Generally, receivers should be mated with speakers having a nominal impedance of 8 ohms or so while separate amplifiers may be used with speakers with nominal impedances of 4 ohms or so. A speaker with an 8 ohm nominal impedance will not generally have as low a minimum impedance as a speaker with a lower nominal impedance such as a 4 ohm speaker.

The most important impedance rating to be aware of is that used with speakers. You may also see impedance ratings for speaker wire and other types of wire. In most cases thicker, heavier gauge wire (such as 10 or 12 gauge) will have a lower impedance and allow more current to flow through. In essence, lower impedance means lower resistance allowing more power to pass through while higher impedance restricts power thus restricting the amount of current able to flow in a circuit.

 

[Steve Ganahl]

Two newbie questions:
1: If the speaker lists its impedance at "4 to 8" Ohms, should I treat it as a 4 or an 8 Ohm speaker.
2: If 4 Ohm speakers require more powere, why would anyone choose one over an 8 Ohm speaker? Is there a difference in sound quality or performance?

 

[mtrycrafts]

What is impedance and how does it effect the performance of the spks. Also, if a receiver meant for spks. having 6 ohms impedance is connected to spks. having 8 ohms impedance, what would happen?

Out of Denon AVR2105 and HK AVR335, which is the better receiver and in what ways??

Thanks.

Impedance is resistance in alternating current circuits. In a DC circuit, you have resistance, no impedance.

6 ohms is not much different from 8 ohms and your amp should drive it well.

Don't forget though, that impedance of a speaker varies with frequency.

 

[mtrycrafts]

Two newbie questions:
1: If the speaker lists its impedance at "4 to 8" Ohms, should I treat it as a 4 or an 8 Ohm speaker.

You may want to look for a 'nominal' impedance rating for that speaker. Call the company. All speakers have impedance variations as it is frequency dependent and is not a flat impedance but can vary from around 4 ohms, at times lower, to as high as 20 ohms at some frequencies. That is why you should find out its nominal impedance.


2: If 4 Ohm speakers require more powere, why would anyone choose one over an 8 Ohm speaker? Is there a difference in sound quality or performance?

Sound quality is independent of impedance.

 

[j_garcia]

Usually when a speaker lists 4 to 8 Ohms, it most likely means 4 Ohms min and 8 Ohms max, so I would consider it an 8 Ohm nominal speaker. As mtrycrafts mentioned, impedance varies depending on the frequency reproduced.

 

[DaveOCP]

Compared to headphones, differences in loudspeaker impedance are pretty insignificant. Headphones can differ by hundreds or even thousands of ohms. The AKG K1000s in particular are brutal. 120ohms and a sensitivity of just 74db/mW. They need about 5-10W from a power amp in order to be driven properly.

 

[j_garcia]

Compared to headphones, differences in loudspeaker impedance are pretty insignificant.

I would have to disagree with that. When talking about normal speakers, lower impedance speakers are clearly tougher to drive and the difference between a tough to drive 4 Ohm speaker and an easy to drive 8 Ohm of similar sensitivity speaker can be very significant. I went from Paradigm Monitor 5s, which are a dual midbass design (2.5 way) and a similar sensitivity (.5dB difference) to my current dual midbass (Di'Appolito) 4 Ohm speakers and the difference in the amount of current the new speakers required was quite a bit more.

 

[WmAx]

Compared to headphones, differences in loudspeaker impedance are pretty insignificant. Headphones can differ by hundreds or even thousands of ohms. The AKG K1000s in particular are brutal. 120ohms and a sensitivity of just 74db/mW. They need about 5-10W from a power amp in order to be driven properly.

The load impedance is of far less importance when it is high in relation to the output impedance of the amplifier. But in the case of very high load impedances with low efficiency such as the headphone you specified, current ability is not an issue, but voltage amplitude is an important consideration that may tend to be overlooked. Also, at the sensitivity you specified for the K1000, only about 1 watt is required to produce a SPL of 104 dB. Less is sufficient for the majority of music. 5 watts is a high ball estimate that would only be required in the very rare circumstances of extremely dynamic, worst case scenario music samples. However, as I have mentioned voltage consideration, realize that this K1000 would require about 11VRMS to produce 1 watt into 120 ohm load impedance. So, the vast majority of battery powered headphone amplifiers, for example, would not be sufficient, as to produce 11 VRMS would require a DC power supply[battery] that is about 31.2 VDC. In the case of extremely dynamic music that would require the 5 watt input, most AC powered headphone amplifiers would not be sufficient in this extreme case due to the voltage limits. Voltage limits of some headphone amplilfiers is probably the reason for AKG recommending a small speaker amplifier. However, if I remember correctly, the AKG K1000 only has a 1 watt max. power input rating. You would not want to actually drive the headphone to a SPL that it would need 5 watts.

-Chris

 

[PENG]

Just to add to what has already been mentioned, impedance may be represented mathematically as a complex number. It can have any combinations, or all of the following 3 components:

1. Resistance - it does not change with frequency, aside from skin effect, that makes it slightly higher at very high frequencies. Hence people sometimes refer to it as D.C. resistance, as it is relatively unaffected by the frequency of the current passing through it.

2. Inductive reactance - it value increases with frequency.

3. Capacitive reactance - it value decreases with frequency, that's why it offers high resistance to low frequency signals and blocks d.c. (frequency=0). It offers very low resistance to high frequency signals.

A typical loudspeaker circuit is a complex load that likely has all 3 components that interact with the amplifier.

Apparently, some receivers provide a 4 ohm selector that simply lower the d.c. rail voltage to limit the output power. In that particular case, you actually get less power output in the 4 ohm position.