Impedance & Sensitivity of a Speaker, & Damping Factor

[Big Daddy]

Sherlock Ohms.jpg


IMPEDANCE

Definition
Impedance is the electrical characteristic of a speaker that restricts or impedes the flow of power. It is an attempt to quantify the difficulty a receiver or amplifier will have in driving a speaker. The standard of measurement for resistance and impedance is Ohm. The symbol for Ohm is the Greek letter omega (Ω). One ohm is the resistance between two points of a conductor that requires one volt of potential to produce one ampere of current across its terminals. In the process, one watt of energy is converted into heat.

What Is the Difference Between Resistance and Impedance?
Resistance is a concept used for DC (direct current) whereas impedance is used for the AC (alternating current).

Resistance
Resistance is caused by collision of electrons and ions in the conductor and convert part of the electrical energy to heat. In other words, resistance is the opposition to electric current. Different materials have different resistances. Pure resistance does not change with frequency. The DC resistance of a conductor can be computed by the following formula:

R = ρ . ( L / A)

where:

R = DC resistance
L = Length of the conductor in meters
A = Cross-sectional area in square meters
ρ (Greek Rho) = Electrical resistivity of the material in Ohm per meter.

Resistivity of the Best Conductors (Ohm per Meter)
Silver: 1.6 x 10^-8
Copper: 1.7 x 10^-8
Gold: 2.4 x 10^-8
Aluminum or Aluminium: 2.7 x 10^-8

Impedance
AC current, however, oscillates as a sine wave so the sign is always changing. This means that other factors such as inductance and capacitance must be considered. Inductance is the magnetic field that is created when current flows through an object. Capacitance is the ability of an object to hold an electrical charge. Therefore, impedance is a more general form of resistance that also includes some kind of reaction. Because of inductance and capacitance, this opposition to current varies with frequency. Capacitance increases as frequency decreases. Inductance increases as frequency increases. Because of this frequency dependence, impedance cannot be measured with a multimeter like DC resistance.

Impedance = Resistance + Reactance
Reactance = Inductance + Capacitance

Nominal Versus Minimum Impedance
Speakers like all suspending objects have a resonant frequency (denoted by Fs) at which they will vibrate most freely. At this frequency, the voice coil is vibrating with the maximum amplitude and velocity.

A loudspeaker’s impedance varies widely with frequency. Nominal impedance is a representative number that approximates the average impedance. As the signal frequency changes, there will be two impedance peaks at low frequencies. The higher of the two peaks corresponds to the driver and enclosure (cabinet) resonance frequencies. The lower of the two peaks corresponds to the combination of vent and enclosure resonance frequencies. Sealed enclosures do not have a vent and thus will exhibit only the speaker/cabinet resonance frequency peak. There will also be impedance drops. These are nearly always caused by the crossover networks, and can create a significant load problem for the receiver/amplifier.

The following diagram exhibits the impedance vs. frequency of an 8 ohm (nominal) speaker. Note that the highest point at resonance is 17.5 ohms in this example, while the minimum impedance is around 5 ohms.

Diagram Created by Big Daddy

At resonance frequency, the speaker is very resistive and creates no problem. The minimum impedance is normally the problem. The loudspeaker in the above diagram was listed as an 8 ohm speaker. You will note that the impedance value is below 8 ohms for all frequencies between 100 to 3,500Hz. The amplifier will see less than 6 ohms between 130 and 1,000Hz. What is important to note is that the actual load at a particular frequency represented to the amplifier is dependent on the impedance at that frequency.

Problem With Low Impedance Speakers
Impedance restricts the flow of power from your receiver or amplifier. People may erroneously conclude that less impedance would be better. The truth is a low impedance load puts a lot of stress on a receiver or amplifier by asking it to supply more current than receiver/amplifier is capable of producing. This is similar to a water pipe and a water pump. Increasing the pipe diameter (lowering the impedance) increases the water flow (current) but causes the water pump (amplifier) to work harder to maintain the desired amount of water pressure (voltage).

A loudspeaker's impedance works against the current flow from the receiver/amplifier. The current flow from the receiver/amplifier actually performs the work by causing the voice coil attached to the paper cone of the speaker to move back and forth in the created magnetic field. This causes the loudspeaker's cone to start the air molecules bumping in to each other to produce sound. The more current that flows, the greater the cone's movement and the louder the sound that is produced.

In the phenomenon described above, the loudspeaker takes the electrical current from the receiver/amplifier and transforms it into acoustical energy. However, the loudspeaker loses some of that energy in the form of heat. The higher the loudspeaker's impedance, the less current flow from the receiver/amplifier. The lower the loudspeaker's impedance, the more current will flow from the receiver/amplifier.

The receiver/amplifier produces energy in the form of both voltage and current. Voltage, like pressure, represents the potential to create power to do work. Power is produced when there is current flow. The more power, the more work that can be done. The amount of work that can be done is also dependent on how much resistance the loudspeaker creates against the current flow.

If we know the value of the load resistance, we can derive the current flow by measuring the voltage. The receiver/amplifier acts for the most part as a voltage source. If there is a source voltage of 20 volts and if the loudspeaker has an impedance of 8 ohms, then the power delivered by the receiver/amplifier can be calculated from Ohm’s law:

P = V . I, and since I = V / R, P = V^2 / R

Where:

P = Power in Watts
V = Voltage in Volts
I = Current in Amperes
R = Resistance or Impedance in Ohms (Ω)

P = V^2 / R = (20) . (20) / 8 = 50 Watts

If the same 20 volts source voltage is applied to a 4 ohm loudspeaker, then the power delivered by the receiver/amplifier will be:

P = V^2 / R = (20) . (20) / 4 = 100 Watts

As the impedance drops, the demand for current to be delivered by the amplifier increases. So, if you change from an 8 Ohm speaker to a 4 Ohm speaker, the current doubles when the voltage is held constant. Therefore, if you choose a low impedance speaker (4 Ohms nominal), make sure that your receiver/amplifier can supply the current that will be necessary to drive the speaker at high listening levels.

The biggest problem with using mid-level receivers and low impedance speakers is the inadequacy of the power supply. Using a 4 Ω loudspeaker on a receiver/amplifier rated 6 Ω or greater could lead to overheating and amplifier failure. Most receivers cannot handle 4 Ω speakers. If you have 4 Ω speakers, you should use a separate amplifier to drive them. Also use thicker wires (lower gauge number) for low impedance speakers. Some higher-end receivers have bigger and better power supply units and can handle low impedance speakers better. However, it is a good idea to keep the volume low and make sure there is proper ventillation.

http://www.audioholics.com/education...r-or-amplifier

Some Receivers have an impedance selector switch. The manufacturer puts them there for UL/CSA approvals as well as easing consumer concerns about driving low impedance loads. These switches step down voltage feed to the power sections which will limit dynamics and overall fidelity. Keep the switch set for 8 ohms regardless of the impedance of your speakers and ensure proper ventilation of the Receiver.

There is more information on Impedance Switch in POST #13.


Impedance Matching

See POST #114


Connecting Multiple Speakers to a Single Power Source

Series Loudspeakers: When loudspeakers are wired in series, the impedance to current flow increases and less power is developed.

This connection would give a final impedance of 8 ohms.

If several speakers are connected to a power source in series, the formula to calulate the net impedance can be found by using the following formula:

Net Impedance = R1 + R2 + R3 + ...

Parallel Loudspeakers: When loudspeakers are wired in parallel, the opposition to current flow from the amplifier is decreased and more power is produced.

This connection would give a final impedance of 2 ohms.

When working with loudspeakers, it is a good idea not to mix speakers with different impedances in the same enclosures because they will not be able to perform at the same power levels and therefore will not be able to reinforce one another.

If we only deal with loudspeakers of similar impedances, then the rules to calculate equivalent impedances are simplified. In series loudspeakers, take the like impedance of one loudspeaker and multiply it by the number of loudspeakers. Four 8 ohm speakers connected in series will have an impedance of 8 x 4 = 32 Ω.

In parallel loudspeakers, take the like impedance of the speakers wired in parallel and divide it by the number of loudspeakers. For example, four 8 Ω loudspeakers connected to an amplifier in parallel will present an impedance of 8 / 4 = 2 Ω.

To calculate the net impedance when two speakers are attached in parallel to the same power source, we can use the following formula:

Net Impedance = Product of the Speaker Impedances ÷ Sum of the Impedances

For example, if two 8 Ω speakers are connected together, you would divide 64 by 16 or

(8 * 8) / (8 + 8) = 64 / 16 = 4 Ω

If several speakers are connected to a power source in parallel, the formula to calulate the net resistance can be found by using the following formula:

Net Impedance = 1 / (1/R1 + 1/R2 + 1/R3 + ...)

Series/Parallel Connection: In the following diagram, the net impedance of the top two speakers connected in series is 8 ohms. The net impedance of the bottom two speakers connected in series is also 8 ohms. Two series of 8 ohms each that connected in parallel will yield a net impedance of 4 ohms.

This connection would give a final impedance of 4 ohms.

Connecting Three Speakers or other Combinations:

See POST #120.


The following calculator calculates the net impedance of series/parallel speakers:

Subwoofer Enclosure Calculators, Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators

MEASUREMENT OF SPEAKER SENSITIVITY

Sensitivity is calculated by measuring the sound pressure level at one meter, with 1 watt of input power, at 1KHz (1,000Hz) or pink noise. This may be important because it requires twice the power to increase the volume of a speaker by 3dB. Horn loaded enclosures such as Klipsch are used to manufacture very sensitive loudspeakers. A funnel is placed in front of the speaker, acting as an acoustic amplifier, thus improving the efficiency and the directivity of the speaker. However, sensitive speakers do not necessarily produce better sound.

Many companies use voltage to measure sensitivity. Here again, 2.83 volts are inputted and measured at 1 meter.

Note that from Ohm's Law, P = V^2 / R. Therefore, 2.83 volts into an 8 ohm load is equal to 1 watt, P = (2.83)^2 / 8 = 1 Watt.

A speaker's efficiency in transforming power into sound is to a certain extend determined by the impedance of a speaker, 2.83 volts becomes 1.5 watts at 6 ohms and 2 watts at 4 ohms, a 3dB increase.

When you are dealing with sensitivity, do not confuse the cabinet size with driver size. The size of the cabinet will affect the sensitivity. Generally, bookshelf speakers are more inefficient than larger floor standing speakers. What this really means is that smaller bookshelf speakers need more power to play as loud as their bigger brothers.

Larger driver cone size helps the low frequency extension of the driver, but not necessarily its sensitivity. Some very small full-range drivers such as the Fostex 4" drivers have sensitivity over 100dBs. This is also true about some super tweeters. Although they are very small, their sensitivity is around 106dBs.

Something else that you should be aware off is that manufacturers do not use the same standards when they measure sensitivity. Speaker sensitivity is usually specified in dBs with 1 watt input measured with a microphone placed one meter from the speaker and on the speaker axis between the tweeter and midrange. Some manufacturers use a single frequency, often 1,000Hz, to measure sensitivity. If the speaker has a peak or dip at that frequency, the results will be a little misleading. Measurements at NRC are normally done with a range of frequencies between 300Hz and 3,000Hz.

Also, for an 8-ohm speaker, 1 watt input is equivant to 2.83 volts. Do you measure a 4 ohm speaker at 1 watt (1.42 volts) or at 2.83 volts (2 watts)? If you use 2.83 volts on a 4-ohm speaker, the result will be 3dBs higher. Some marketers may prefer that.

8_Ohm Speaker.jpg 4_Ohm Speaker.jpg

Hoffman's Iron Law
When designing a loudspeaker, it is not possible to combine high sensitivity with compact enclosure size and adequate low frequency response. You can only choose two of the three parameters. For example, if you decide to build a small speaker with extended low frequency response, you must accept low sensitivity. This rule is sometimes called Hoffman's Iron Law, named after J. Anthony Hoffman (the "H" in KLH). This rule is a mathematical formula and was originally formulated in early 1960's and later refined by Thiele & Small (TS parameters), whose work now forms the basis of loudspeaker/subwoofer design.

Hoffman's Law states that the efficiency of a loudspeaker (woofer system) is directly proportional to its cabinet volume and the cube of its low frequency cutoff. This implies that if you want to lower the low frequency extension of the speaker by a factor of 2 from 60Hz to 30Hz and keep the same cabinet size, you will have to accept much lower sensitivity. In order to maintain the same level of efficiency, you must increase the cabinet volume by 2^3 = 8 times. In other words, if you want to lower the cutoff frequency of a loudspeaker and maintain the same the level of output, you need an extremely larger cabinet.

To summarize, low-frequency extension, cabinet size, and efficiency form the three key factors in speaker design. To increase any of them, you have to give up something from the other two. Of the three parameters, cabinet size is the most sensitive. That is why it is always recommended that you select the largest cabinet that you can live with. Since most people may not have the room to accomodate large speakers or cannot afford powerful amplifiers to achieve the desired loudness with inefficient speakers, that is another reason why subwoofers are becoming so popular. They have their own dedicated amplifiers and you can hide them almost anywhere.

If you want low frequency extension and are not willing to live with a very large speaker cabinet, the only other option besides a subwoofer is to use multiple drivers within the same cabinet. If you connect two identical woofers in parallel, the impedance will drop by half and you gain about 6dB in output (sensitivity). If you connect the two woofers in series, the impedance will double and there will be no increase in sensitivity.

As an example, if you are dealing with an 8-ohm driver that has a low sensitivity of 85dB and you want a very efficient speaker with over 90dB of sensitivity and 8-ohm impedance, you will need four identical 8-ohm drivers. You will have to connect each pair of drivers in series (impedance will rise to 16 ohms) and then connect the two sets of drivers in parallel. The net impedance will drop to 8 ohms and the sensitivity will increase over 90dB.

The procedure described in the previous paragraph is a common approach in dealing with sensitivity, but as they say, there is no free lunch and there are trade-offs. When you feed identical signals to these drivers, the frequencies from these drivers will interact somewhere in front of the speaker, resulting in comb filtering. As a result, some frequencies will be reinforced while others are attenuated and you will end up with peaks and valleys and a jagged frequency response.

Power Versus Sensitivity
It requires twice the power to increase the volume of a speaker by 3dB. The table below, for a speaker with sensitivity rating of 87dB, shows how much you need to increase power to get an additional 3dB increase in volume.

DAMPING FACTOR

Why Do We Need Damping?
Without any type of damping, when the signal to a loudspeaker stops, it keeps on vibrating due to inertia. This is called ringing or overhang. In other words, the speaker produces sound waves that are not part of the original signal. The frequency of the sound that the speaker produces with this movement will be at the resonant frequency of the moving system. As an example, suppose the incoming signal is a short and precise sound from a kick-drum. When the kick-drum signal stops, the speaker’s cone continues to vibrate back and forth in its suspension and the sharp sound from the kick drum turns into a boomy rhythm.

What is Damping?
Damping is the term used in reducing the sound produced by a loudspeaker’s moving diaphragm after the signal stops.

Types of Loudspeaker Damping
There are two types of loudspeaker damping: mechanical and electrical. The loudspeaker's suspension and its quality determine the amount of mechanical damping. Manufacturer’s try to use sophisticated techniques to improve the mechanical damping of their loudspeakers.

Electrical Damping Factor
Electrical damping is provided by the receiver/amplifier. Electrical damping is the ability of a receiver/amplifier to control a loudspeaker’s motion after the signal has stopped. The higher the damping factor, the better the receiver/amplifier will control the loudspeaker and help reduce overhang distortion.

How Does Electrical Damping Work?
When a loudspeaker’s cone vibrates in a magnetic field, it generates a signal like a microphone. This signal will have an opposite polarity and is called Electro Motive Force (EMF). It travels back through the speaker wire to the receiver/amplifier’s output and it is send back again to the speaker. Because of its opposite polarity, it will damp or impede the loudspeaker’s overhang. The smaller the receiver/amplifier's output impedance, the greater will be the effect of back EMF on the loudspeaker's motion.

As you can see, it is not the amplifier that controls the loudspeaker. The loudspeaker damps itself through the output circuitry of the receiver/amplifier. The lower the output impedance of the receiver/amplifier, the larger will be the effect of the back EMF on the loudspeaker’s overhang or ringing.

A Practical Experiment to Understand Back EMF
Take a woofer that is not connected to anything and put your ear next to the cone of the woofer. Now tap on it with your fingers. You will hear a low-pitched thump sound. Repeat the experiment, but this time short the speaker terminals with a pair of wires attached to the loudspeaker’s terminals. Because of back EMF, you should hear a much tighter thump sound.

Calculation of Damping Factor (DF)
The Electrical Damping Factor (DF) coefficient is determined by dividing the loudspeaker’s load impedance by the source impedance of the receiver/amplifier.

Electrical Damping Factor = Load Impedance / Source Impedance

A typical receiver/amplifier’s source impedance is 0.02 Ohms. If the load impedance of the loudspeaker is 8 ohms, then the damping factor can be calculated as follows:

DF = 8 / .02 = 400

If the loudspeaker’s impedance drops to 4 Ohms, the electrical damping factor will also drop:

DF = 4 / .02 = 200

The damping factor is the ability of the receiver/amplifier to control the loudspeaker’s load. The impedance of the load and the impedance of the output (source) affect the receiver/amplifier's ability to control its load.

High damping factor usually means that the bass response will be well defined and tight, whereas a low damping factor will result in a loose sounding bass. Tube amplifiers generally have lower damping factors compared to solid state amplifiers. This may contribute to their typically loose bass response, which may be very pleasant and many audiophiles describe as warm. Because the electrical damping is minimal, it is a good guarantee that you are hearing what the loudspeaker’s designer has created.

Size of the Loudspeaker’s Driver
Electrical damping becomes more important as the size of the loudspeaker’s driver becomes larger. Subwoofers have the most problems regarding damping. Their moving mass is quite high and their suspensions are relatively weak compared to their size. Because of this they have relatively weaker mechanical damping and therefore electrical damping becomes more important. In severe cases, if proper damping is not used, the moving mass of the subwoofer creates a one note bass. High frequency drivers have much lighter mass, stiffer suspensions, and stronger mechanical damping. As a result, electrical damping becomes relatively less important.

Effect of Speaker Wires
The electrical damping factor is also affected by the resistance of the speaker wires. Speaker wires like most electronic devices have resistance that oppose the flow of current. The thinner the wire and the longer the length of the wire, the larger will be the resistance of the speaker wire. Therefore, we need to slighly modify the electrical damping formula to account for the effect of speaker wires. The modified formula is as follows:

Damping Factor = Load Impedance / (Source Impedance + Cable Impedance)

Conclusion
Like most other specifications, damping factor by itself does not tell you that a receiver/amplifier is good. There is a lot more to designing a good receiver/amplifier besides output impedance and damping factor. A very high damping factor usually means that the receiver/amplifier has very low output impedance, and many people worry that because of high negative feedback, such a receiver/amplifier may distort the sound. It is widely accepted that the damping factor should be around 20 or higher. A damping factor below 20 does change the performance of the loudspeaker (for better or for worse, depending upon the speaker). But it is hard to prove that a damping factor of 300 is better than 20.

CONCLUDING REMARKS

With DC power sources, you only have to worry about the resistance of a conductor. Resistance is caused by collision of electrons and ions in a conductor and convert part of the electrical energy to heat. In other words, resistance is the opposition to electric current. Different materials have different resistances. Pure resistance does not change with frequency.

AC current, however, oscillates as a sine wave so the sign is always changing. This means that other factors such as inductance and capacitance must be considered. Inductance is the magnetic field that is created when current flows through an object. Capacitance is the ability of an object to hold an electrical charge.

With AC current, a cable is affected by three electrical properties: Resistance, Inductance, and Capacitance. Most cables are made out of copper. A few are made out of silver. Silver and copper have the lowest resistance and the highest conductivity out of all the metals. In addition, thickness of the wires (lower gauge number) reduces resistance.

You can find an explanation of Inductance and Capacitance in https://forum.blu-ray.com/audio-theo...er-cables.html thread.

REFERENCES AND ADDITIONAL INFORMATION

http://www.mcsquared.com/nsca98.htm
Home Toys Article - Speaker Impedance, Your Amplifier And You.
Impedance, and how it affects audio equipment
http://www.colomar.com/Shavano/spkr_wiring.html
Loudspeaker - Wikipedia, the free encyclopedia
http://www.installdr.com/TechDocs/999016.pdf
Series Parallel Speaker Impedance
http://www.hometheaterhifi.com/volume_1_1/v1n1spk.html
Speaker Impedance Explained - Ohms
http://www.hometheaterhifi.com/the-s...nsitivity.html
Pro Co Sound | On Stage with the Best
http://www.integratedaudio.com/help/sensitivity.pdf
GoodSound! "Features" -- Understanding Loudspeaker Sensitivity (2/2008)
http://www.diyaudio.com/forums/multi...ml#post1665512
http://www.soundstagenetwork.com/ind...d=16&Itemid=18
http://www.soundstagemagazine.com/me...udspeakers.htm
http://www.the-home-cinema-guide.com...nsitivity.html
Welcome to www.SoundStageAV.com
Mc Squared System Design Group, Inc. - Interpreting Loudspeaker Specs
Peavey.com :: Impedance in Audio Technology
http://web.media.mit.edu/~meyers/mcg...udspeakers.pdf
Untitled Document
Damping factor - Wikipedia, the free encyclopedia
Legendary Audio Classics: Damping Factor
Damping Factor: Effects On System Response — Reviews and News from Audioholics
Damping Factor with Calculator
Butler Audio
http://www.hometheaterhifi.com/the-s...ng-factor.html
http://www.roger-russell.com/wire/damptoole.htm
Missing Link in Speaker Operation
Study Hall, Professional Audio Resources - Pro Sound Web
What is the difference between resistance and impedance?
Electrical resistance - Engineering

[prerich]

Very Good Daddy! Many people are fooled by ohm ratings (the lower the better falsehood - I think they are confusing speaker wire gauge ) and the other falsehood of higher sensitivity speakers sound better ... no they are just louder. In truth my Snells are more open than my Heresy's, the Heresy's are just louder. Now when my upgrades are complete next year - my Snells will just as sensitive as my Heresy's, but they should produce a better sound - not because of the sensitivity increase but because of crossover design. The Heresy's are there because of convienence (height) not because they sound better, but they do sound good and different .

Don't let speaker specs be the end all in your choices - let your ears do the chosing (I think this is what you are communicating Daddy)

[JasonR]

I get more of a kick out of the power ratings. People put to much weight in it when choosing a receiver.

[JJ]

I reached that conclusion over the summer. There is more to sound than the numbers. And THAT'S what sensitivity is...ohhhh... Thanks, Big D.

[Sir Terrence]

Big Daddy, you have out done your self again. Shame on you for providing this accurate and in depth post...you should be beaten!

[Big Daddy]

Originally Posted by Sir Terrence

Big Daddy, you have out done your self again. Shame on you for providing this accurate and in depth post...you should be beaten!

There is more to come on Damping Factor. Instead of beating me, buy me the new Oppo Blu-ray/SACD/DVD-A player.

[Big Daddy]

Originally Posted by Silo5

I'm getting mixed messages about ohms and receivers. I have an Onkyo 805 and was looking at Martin Logan Preface (4 ohms nominal), Fresco i center (4 ohms minumum & 6 ohms nominal), and Vignette surrounds (6 ohms nominal). I contacted Onkyo and Martin Logan and asked each of them the same question: Would my 805 be able to handle the speakers I listed above? Here was Onkyo's reply:
"Thank You for contacting Onkyo USA Product Support.
If you set the receiver to 4 ohms then all speakers connected have to be 4 ohms as well. You can not mix and match impedances.
Onkyo Representative*".
Here was Martin Logan's reply:
"Thank you for your inquiry. You should be able to set your receiver at
4 ohms without having any concern for damaging your speakers. All of
our speakers require a high current so you should be fine. Please let
me know if you have any other questions.
Thank you,
Martin Logan Representative*
MartinLogan LTD".
Can anyone clear this up for me? Thanks in advance.
*Actual names were edited out, in case there are "legal issues" for using their names w/o permission

As a general rule, I do not recommend using a receiver with 4 ohm speakers. For example, Axiom will not sell you their top-of-the-line 4 ohm speakers, if you are using a receiver.

I always recommend a power amplifiers that can handle 4 ohm speakers. For example, I use my Denon receiver as a preamp and use separate power amps to drive all my speakers, including my two passive Hsu subwoofers. As far as mixing impedances are concerned, some of my speakers are 8 ohm, some are 6 ohm, and some are 4 ohm. In over 10 years of using these amps, I haven't had any problems.

As far as your Onkyo receiver is concerned, check the manual and see if it is rated for 4 ohm speakers. If the answer is yes, you should not have a problem in normal listening modes. Can you mix 4 ohm with 6 ohm? My answer is yes, unless Onkyo knows something that their receivers cannot handle it. I have never heard of such a thing.

Normally, when a receiver is not made to handle 4 ohm speakers and you turn the volume up, it may distort and overheat. Chances are that your receiver will get damaged before your speakers.

[Big Daddy]

Originally Posted by Silo5

According the the manual, it says:
4 ohms: Select if the impedance of any speaker is 4 ohms or more but less than 6.

6 ohms: Select if the impedance of all speakers are between 6 and 16 ohms.

On a side note, I've been looking at various brands of speakers since February. I finally find a decent set of speakers and now it comes down to this! All of the Martin Logan's that I looked at are rated either 4, 5, or 6 ohms, but are said to be compatible with each other.

Apparently the Onkyo receiver is made in such a way that it cannot handle mixed impedances. However, I don't forsee a problem as a speaker with a nominal impedance of 6 ohm can go way below 4 ohm or way above 6 ohm. Just to be on the safe side, try to use all 4 ohm or all 6 ohm speakers.

[Silo5]

Originally Posted by Big Daddy

Apparently the Onkyo receiver is made in such a way that it cannot handle mixed impedances. However, I don't forsee a problem as a speaker with a nominal impedance of 6 ohm can go way below 4 ohm or way above 6 ohm. Just to be on the safe side, try to use all 4 ohm or all 6 ohm speakers.

Alas! When I thought my search for speakers was over, it's actually just begun!

I do a lot of reading and research on this forum, but will occasionally post when I have questions. You are one of the few on here that I feel provide knowledgeable and helpful information. Thanks for your advice.

[welwynnick]

Excellent post, and a difficult subject explained very well, without using jargon.

One thing though, does anyone else have a problem with this bit?

Why Do We Need Damping?
Normally, when the signal to a loudspeaker stops, it keeps on vibrating due to inertia. This is called ringing or overhang. In other words, the speaker produces sound waves that are not part of the original signal. The frequency of the sound that the speaker produces with this movement will be at the resonant frequency of the moving system. As an example, suppose the incoming signal is a short and precise sound from a kick-drum. When the kick-drum signal stops, the speaker’s cone continues to vibrate back and forth in its suspension and the sharp sound from the kick drum turns into a boomy rhythm.

[Big Daddy]

Originally Posted by welwynnick

Excellent post, and a difficult subject explained very well, without using jargon.
One thing though, does anyone else have a problem with this bit?

Thank you for your words of support. I kind of understand your concern about that paragraph.That paragraph is the introduction to the next few paragraphs. By itself, it is taking it out of context. To avoid any confusion, I replaced the word "Normally" at the begining of the paragraph with the sentence, "Without any type of damping".

[jomari]

excellent posting kind sir!

to Mr. Silo5,

id highly recommend avoiding using 4 ohm speakers as mentioned by bigdaddy. 6 ohms is the limit id place on most recievers, and above of course.

long story short,
its going to stress your reciever, and might also damage your speakers in the long run. the reciever isnt built to handle 4 ohms, imo, like most of the higher end gears can.

[Big Daddy]

SHOULD WE USE THE IMPEDANCE SWITCH ON THE BACK OF THE RECEIVER?

http://www.audioholics.com/education...ector-switch-1

Let's examine some power measurements of receivers I measured in the past that featured impedance selector switches to deduce exactly what they are doing. The receivers range in price from $500 all the way up to $5,500.

Low Impedance (Z) Mode - is the receivers "low" setting that the manufacturer recommends using when you attach loudspeakers rated below 8-ohms. (This mode limits the output voltage, and therefore the maximum current any given speaker can demand of it).

High Impedance (Z) Mode - is the receivers "high" setting that the manufacturer recommends using when you attach loudspeakers rated at 6-ohms or higher. This is usually the default setting the receiver ships in, and the rating which the manufacturer optimizes his parts for, since they only have to advertise ONE power rating before the consumer will reach for his checkbook or credit card.

PLoss - Power Loss (%) determined by comparing the Low Z and High Z power numbers for each receiver using the following equation: (1 - LowZ / HighZ) * 100

ImpedanceSwitch.jpg

Note: All tests were conducted with one channel driven at 0.1% THD + N using a 1kHz test frequency except the 1% THD tests which were conducted by Sound & Vision Magazine.

As you can see in the tabulated data above, 5 of the 6 receivers exhibited significantly less output power when their switches were set in the "low impedance" mode for both 8 and 4-ohm loads. In fact the lowest priced Yamaha (RX-V661) and Onkyo (TK-NR5007) models exhibited the most power scaling in the low impedance mode (72% reduction, 60% reduction, respectively) The RX-V2700 power derating of the low impedance mode was interesting in that it maintained their specified 8-ohm output power rating of 140 watts into a 4-ohm load. I find it noteworthy that the Yamaha RX-Z11 power output did NOT change based on the impedance switch setting. It's obvious in this case that the designers of this receiver were confident no derating was needed to pass the regulatory testing. This isn't surprising giving the sheer size and expense of this engineering marvel, hence why they call it their flagship model!

What the "low impedance" setting accomplished (except for the Yamaha RX-Z11) was to step down the rail voltage fed to the amplifier by the secondary of the power transformer. The unfortunate side effect was clipping at a much lower power level as seen in the tabulated test results. The low switch setting appears to limit the maximum available current draw on the transformer to about 1/3rd (Onkyo TX-NR5007) as much as the high setting so that it would be able to play continuously (at a significantly reduced power level) during the UL/CSA certification testing while generating significantly less heat.

[jomari]

i dont think i can compete with big daddy with stickies.

id probably be banned if ever i made another one...

great thread big daddy, hopefully, we can re-route newcomers to these stickies.

better yet, have em search a bit.

[Big Daddy]

Originally Posted by jomari

i dont think i can compete with big daddy with stickies.
id probably be banned if ever i made another one...
great thread big daddy, hopefully, we can re-route newcomers to these stickies.
better yet, have em search a bit.

Thanks for the compliments. There is a thread for Home Theater Virgins that has listed most of these other threads with stickies.

[jomari]

quickly dashed over there. hopefully i can contribute as much as i can here as well...

[ozzman]

This has been a great read and thanks again for helping me through PM.
I feel a lot safer now with high volumes

I had 8ohms running in each channel even though my fronts are 6 ohms . All the rest of my speakers are 8 ohms (I'll will let you know that my reciever never ran hot so i never thought of it).

I had two choices:

(1)set to 8ohms (for speakers 8ohms or higher)

(2)when you set it to 6 ohms it automatically sets the fronts to 4ohms(for speakers 4ohms or higher)
and the rest 6 ohms (for speakers 6ohms or higher)

I had it set to #1 and with help with Bigdaddy i went to #2 And surprisingly to me there's no change in the sound (volume or power).

Bigdaddy told me it wouldn't effect the sound even before i listened for myself.

How does my reciever know to put 6ohms to my fronts and 8 ohms to the rest of my speakers?(Or does it) On #2 setting
Is this a feature that my reciever has ,Do most recievers do this?
Iam confused on how this works?

BigDaddys the man

[Big Daddy]

Originally Posted by ozzman

This has been a great read and thanks again for helping me through PM.
I feel a lot safer now with high volumes

I had 8ohms running in each channel even though my fronts are 6 ohms . All the rest of my speakers are 8 ohms (I'll will let you know that my reciever never ran hot so i never thought of it).

I had two choices:

(1)set to 8ohms (for speakers 8ohms or higher)

(2)when you set it to 6 ohms it automatically sets the fronts to 4ohms(for speakers 4ohms or higher)
and the rest 6 ohms (for speakers 6ohms or higher)

I had it set to #1 and with help with Bigdaddy i went to #2 And surprisingly to me there's no change in the sound (volume or power).

Bigdaddy told me it wouldn't effect the sound even before i listened for myself.

How does my reciever know to put 6ohms to my fronts and 8 ohms to the rest of my speakers?(Or does it) On #2 setting
Is this a feature that my reciever has ,Do most recievers do this?
Iam confused on how this works?
BigDaddys the man

I agree. Big Daddy is the man.
Anyway, your receiver doesn't know. When you set it to 6 ohm, it can handle speakers 6 and higher. If you set it to 8 ohm, it may not be able to handle 6 ohm speakers properly. As I said in the OP, impedance is not a constant thing. It varies quite a bit with frequency. As long as the impedance drops below the capability of your receiver for a short period of time, you are ok.

Each receiver is different. It all depends on the manufacturer. Most high-end amplifiers can handle 4 ohm and above easily. Some go down to 2 ohm. That is one reason I use my receiver as preamp and rely on external amplifiers to drive my speakers. Some of my speakers are 6 ohm and some are 4 ohm.

[ozzman]

Thanks Brother

[ozzman]

Tell me boys,because i really don't know.What this means to you with my reciever

http://www.audioholics.com/reviews/r...-configuration