I would like to know information about resistance (Ohms)
What is the difference between 2,4,6,8,12,16 ohms speakers and how would an amplifier handle them ?

THANKS

Home Toys - Impedence
Speaker Impedence
Wikipedia - Impedence
Wikipedia - Ohm's Law

Google and Wikipedia are your friends. You can also try the HydrogenAudio search function - this has been discussed many times. I hope you find what you are after.

Ask a simple question ...

you are really talking impedance not resistance since you are talking speakers and therefore have a reactive (Z or phase) part of the coil.
If you open up pretty much any speaker the normal construction is that you take copper wire and wind it around a magnet, when you send the audio signal from the amp to the speaker the coil of wire will deflect (move) in relation to the magnet and that it turn is what forces the speaker cone to move, which moves the air, which produces the audio.

So after all that - the wire you coil around the magnet will be of a certain length and will have accordingly a certain impedance, generally they make them 2, 4, 8 ohms.

Why do they do that - power! Your $50 cheap stereo would need a massive Amplifier if you attached it to a 2 ohm speaker, the $50 stereo would then need a $100 amplifier and then it would no longer be $50, so you attach 8 or 16 ohm speakers so that you don't need the power to drive it. BTW you might know ohms law P=IR (Power = Current * resistance), since to have a good party you need at least 500W of music, so you can get away with I= 62.5A with the 8 ohm speakers or I = 250A with 2 ohm speakers. PS - next time you see a little stereo offer 500W of power you can ask them about how much current it draws and then ask them why it doesn't draw 62A like it should!

Anyhow so there is the difference - an amp to deliver 62A is cheaper than a 250A. And so now why don't they build all speakers to 8, 16, etc ohms. 2 reasons, first to achive very low tones <50Hz you need speakers that can move a lot of air, to do that you need to provide it with a lot of power hense the reason most of the real subwoofers (15-50Hz) are 2ohm speakers. Second the sound quality is generally better since it has more power in the coil for faster responce and to drive the cone. But you can go to the other extreme is that a tweeter will have no audible difference between a 2 or 4 or 8 ohm speaker because the difference will be inaudible.

ANyways hopefully that will answer some of your questions

But what will I answer if they say "Because our stereo provides 62.5 volts to our 8 ohm speakers and power is equal to v^2/r, so 4000/8 = 500 watts?"

It's got to do with the length of the wire in the coil, the size of the coil and number of turns. In a complete speaker (not just a driver) the crossover has more effect on the impedence than the drivers themselves.


The limit on the power of most amplifier designs is the Safe Operating Area of the output devices (BJTs or MOSFETs generally). Output devices generally run up against their current limit before they run up against their voltage or power limits. Which means that many amps will be able to drive more power into 8 ohms than 4, for example.

It's a good point - but I fear your arithmetic is wrong. If my amplifier puts 500W into my speakers, it should draw more than 2.25A (or 4.5A in the USA) from the wall. The amplifier can source more current than it draws because it uses a transformer to step the voltage down. So when you buy an amplifier read the current draw value, multiply by your wall voltage (220-240 in Europe/Africa, 110 in USA) and compare the values. If the output is more than 75% of Wall Voltage*Current Input be very suspicious.


I think you are wrong about this. You could just as easily build a 32ohm sub that sounds exactly like a 2ohm sub. However, it would be much harder to drive - you would need four times the voltage and you would struggle to find output devices that can take that amount of voltage and still have the properties required for an amplifier.

Just a correction

Power = Current * Voltage

Voltage = Current * Resistance

Power = Current² * Resistance

1.What I have understood is that an amplifier would deliver more power to a 2Ω Speaker but eventually forcing the amplifier. On the other hand an amplifier would find it easier to deliver power to an 8Ω speaker.

Please correct me if i'm wrong !


2.What is 62A ? (hope isn't ampers)

3. What would be the first thing you would look in an amplifier ?
4. What would you buy a 16Ω speaker or a 2Ω one ?

5.I have been studying physics for a small period of time but still can't figure out the difference between resistance and impedance since both use R=V/I
Should I use resistance or impedance when talking on Ohms ?

P.S - I found your answers very useful but most of them are quite straight forward, therfore I missed out some things sorry for asking so many questions.

Lots of thanks

resistance is related to impedance, but is only really relevant in direct current.

Impedance varies with frequency, but for practical applications, the maths is the same.

this also means an amp designed for 8 ohm will sound different on 4 ohm or 16 ohm. i forget how to make this stuff ideal, but it probably doesn't matter much (my speakers are pretty flat-sounding at 6 ohm on an amp meant for 8 ohms).

Impedance (Z) is the magnitude of the complex sum R+jwL+1/(jwC) where j^2=-1, w=2*pi*Freq, L is Inductance, C is capacitance and R is resistance. The angle of this sum (equivalent to arctan([wL-1/wC]/R)) is called the phase angle and it's cosine the Power Factor (pf). For impedance Z, the Power delivered to a load (like a speaker) isn't just V*I, it's V*I*pf.

This article should clear up your issues:
Wikipedia - Impedance

What do you mean by this ?

Thanks

Can someone answer my other questions ?

Thanks

From what I have read I can say that Impedance and resistance are basically the same but you would find impedance only in ac and resistance in dc and since speakers are always ac the term impedance would be the appropriate one.

Am I right ?

BTW does an amplifier deliver ac only or dc aswell.

Right.

Sound signals have no energy in DC. A good amplifier should deliver no more than 50mV DC.

Ohm's Law is V = IR (or I = V/R or R = V/I). You're thinking of P = I^2R. Thus 500 = I^2*(8) gives a mere ~7.9 A.

@ rfarris - Sorry my mistake, it should be P=VI, in either case I was been a bit flippant about 62A since normal spearers for small stereos get a few volts and generally in the milliAmp range for current. So if they said that their stereo delivers 64V i would give them the same look as if they told me 64A. Anyways 500W is generously the combined sum of all speakers at their peak theroetical power, generally normal power output is RMS - and in general practice 10% of max (not RMS - just audio labeling ie 500W=50 real Watts).

@cabbagerat
- You forgot the crosssection of the wire which will also change the resistance and therefore the impedence.
- Actually (although I'm not a speaker designer but I do have an degree in electrical engineering) I don't think it would be possible to have a 32ohm speaker simulate a 2ohm, as you said the power needed would be enourmous and also don't forget that designing speakers you want to keep the phase similar, i think this would be hard to do for a 32ohm sub. I could be wrong but that is my assumption.

@Audio Vox
1) An Amp is designed to deliver X Watts - You will need more Watts to drive a 2Ohm speaker than a 8Ohm. An amp cannot deliver more power than its maximum (safe) limit, it is like plugging a lamp vs a fridge into the wall socket - the fridge will use more power than the lamp, likewise the 2ohm speaker will use more power than the 8, but you cannot get more power from your amp than what it can deliver.
2) Yes A=Amperes, it was a flippant calculation - that was also wrong as Mike Giacomelli and _io_ pointed out. Nevertheless 8A is a huge amount of power to a speaker - I doubt there exists a speaker that needs 8A.
3) First thing - how much money in your wallet - 100W car amp at Radio Shack for $30 or Mark Levinson reference Amp for $100 000 - hmmm choices
4) That really isn't a choice - a 2ohm will be a subwoofer in which case you will not find any (that i know of) subwoofers of 16ohms - but you are going to have to specify - are you trying to build some speakers or buy them? If you want to build then there are lots of science behind building - do a lot of reading and research if you are at this stage and want to build your own. If you want to buy then the choices are already made for you.
5) - seems to be answered



Resistance is the static or DC part of impedance, reactance is the dynamic or AC part. ie Impedance = Resistance +j Reactance. There is a lot of math around this and you can find a lot on the net about this. Impedance is the right term but it applies to a real part, resistance, which deals with the lenght of wire from the amp out to the speaker and back, PLUS the reactive part which is the 'imaginary' resistance which has to the resistance of the cable at different frequencies. You can really complicated since all wire has not only impedance but inductance (L) and Capacitance© and all of these are complex (real & imaginary parts). so if you want to keep it simple deal with just the resistance of 8ohms, impedance although slung around like everyone hip knows speakers have impedance, is in fact a complex number and would have to be given in the format Im=Res +jRea. So until some good salesperson gives you that as the impedance you can safely take the value (2,4,8ohms) as the resistance

Amps will always have an AC & DC part - you try to minimize the DC part.

1st Of ALL I would like to thankyou all for the great help.




Hold on why shouldn't a good salesperson give me the right impedance instead of using resistance ? (What difference would it do to me)

Some one said that a good amplifier delivers dc current ,but how come the speaker needs ac current in order to move the coil ?

And last thing the amplifier i'm targeting to is an NAD C352 having the following specifications



Therfore, from what I can see the amplifier would be capable of delivering good power to the speakers with 2 ohms.





Could you please simplify this, and tell me exactly what resistance and impedance have in common. The reason is because now i'm asking to myself why should I use the term resistance instead of impedance !

Thanks

Resistance ( R) is for DC, impedance (Z) is the same thing, but for AC, and it behaves in a more complex way.

For example in DC, U=RI, well, this is wrong in AC.
In AC, |U|=|Z|x|I|, with |Z| >= R.

But when does reactance and impedance collide in then.

Where "Z-bar" (with the bar on top) is the impedance, R the resistance, and "Rea-bar" the reactance.
In the previous formula, |Z| was the modulus of Z-bar, that is its amplitude.
Z-bar is the complete impedance, it features both the amplitude and the phase of the impedance.
By definition, R has no phase, because DC has no phase. Thus


PS : R does not depend on frequency, but Rea does. That's why the impedance Z depends on frequency.

Yeah ok.

But then if I talk about sound delivered from the amplifier to the speaker what term should I use resistance or impedance ? (in ohms)


Is there a link which you can give me to see a diagram that explains the energy transfered from the mains to the amplifier to the speaker ,stating the current type etc.

Thanks

This has sort of been explained already but I will try to clear it up. Say there is a resistor. If there is a constant voltage ACCROSS the resister and a constant current THROUGH it we are talking about direct current (DC). By ohms law, V/I = R, the resistance R is defined by this law. In ANY DC situation this is true ALL THE TIME. If we now have a resistor with a variable voltage ACCROSS it and with a variable current THROUGH it, we are talking about alternating current (AC). Since an IDEAL resistor has NO capacitance and NO inductance, the impedance of the resistor is still the same value as the resistance no matter what frequency we drive it with because V/I = Z and as it was already pointed out in this thread, Z = R + 1/jwC + jwL, where j = -1^.5 w = the frequency in radians (to convert w = 2*pi*f) C = the capacitance and L = the inductance. Since the resistor has no capacitance or inductance, both of the imaginary parts of the complex number go to zero (sort of). As you can see from the math, the imaginary part of the complex number "gets large" (goes to infinity) when the frequency is small (DC) or the capacitance is small (basically zero). Fortunately, in the real world, you can never have zero capacitance between two points in an electric circuit and the actual capacitance across a real world resistor (or system) acts in parallel with the resistor, not in series and thus can be ignored (this is a whole other topic but it is just how the math works out). Now instead of a resistor, we have a speaker. If we drive it with a sine wave with a given frequency and set amplitude, there will be a current that goes through the speaker. Now suppose we keep the same voltage but change the frequency. There will be a different amount of current flowing through the speaker because, V/Z = I, and Z as the equation shows above is frequency dependant. That is the difference between resistance and impedance. From the above equation, impedance also causes a phase shift, (the imaginary or j part of the equation) that pure resistance will not cause. The amount phase shift if also frequency dependant.

While I don't want to kill your curiousity most people have a hard time understanding the concept of the phase or imaginary part of a signal, and unless you are going to get into amp or speaker design there really is not much use knowing what the actual impedence of your speakers are since you really cannot change it.

I said a good salesperson because most salespeople know that impedance is the 'term' you use for speakers but most of them have no idea what impedance really is, most people just state that the speaker impedance is 8Ohms, and as I said impedance is a complex value and would have to be expressed in complex notation (R + jZ). since the reactance is frequency dependant you would really need to see a graph of the impedance to see a DC resistance of x ohms plus a varying reactace (in ohms) which depends on the frequency to give you the impedance.

And even knowing the actual impedance what does that tell you - not much unless you need to know it for some bizarre reason.

I don't think anyone said a good amp delivers DC current - a good amp minimizes the DC current.

You should read into the details about the actual power delivered, usually it is 240 RMS all channels combined, so if you are looking at a 5.1 amp you could be looking at 240/6 = 40W RMS each speaker which may or may not be the power you need.

There really is not an easy way to simply complex numbers - You have to be able to grasp the concept of complex numbers (real & imaginary numbers) before this complex values make sense.
If I sell you a speaker and I tell you it is 8ohm - then i am telling you than R=8, the Resistance is 8 ohm, the fact is that the speaker is really something 8 +j0.05 and that is the impedence, but because to sell stuff and make brand A sound better than brand B they try to use buzzword which are used but then taken out of context or not used properly (as in this case). Case in point is the example I used earlier about the rated watts they advertize for the stereos - everyone wants more watts for the same price so there are various ways of measuring power, Power (root-mean-square, peak, average), usually in audio you measure RMS (root mean square) for power but most labels display peak to peak power in order to give the maximum power value, the fact that you would really never achive this is not yet considered false advertizing. So the fact that salespeople say this speaker has an impedance of 8 ohms are actually saying (even though they probably don't know it) is that the resistance is 8 ohms and we don't know what the reactance is.

- both resistance & reactance are measured in ohms that is part of the condition of having a complex number is that the units will be the same. If you have only 1 number (ie 2, 4, 8 ohms) that will be resistance.


- What exactly are you trying to see? If you are looking for the reactance (imaginary parts) you wouldn't see that in a block diagram of an amp. also there are various amp designs. You seem to be searching for answers which I'm not sure you know why you want to know them.

Edit: TwoJ: It is incorrect to use the term power when talking about current. "...so you attach 8 or 16 ohm speakers so that you don't need the power to drive it." I do not know the specifics about power and efficiency for speakers with different impedances, but I think you meant to say that with a higher impedance, (8 or 16 ohm) you don't need as much current to drive the speaker. You would however, everything else equal, need more voltage to drive it and thus the same amount of power. This would not be true if speakers with lower impedances were more efficient with turning power into sound. While I do not know for sure, I suspect that the impedance of a speaker is not very related to the efficiency.

I was talking power, current voltage and resistance are related items, you cannot say reduce the current without saying reduce the power, and since amps & speakers are rated in watts (power) not amps, it is proper to say reduce/increase the power from an amp, or to a speaker.

I was about to post exactly the same thing.


No, not really. Yes current, voltage and resistance are related (by V=IR) but what you said above about power an speaker impedence is wrong. It takes just as much power to drive a 32ohm speaker as a 2ohm speaker (assuming similar efficiency, which is fair) but the 32ohm speaker will need more voltage across it and draw less current than the 2 ohm speaker.

A few things to (maybe?) help clear up some confusion:

Most amplifiers are designed to output a certain maximum voltage across the speaker terminals. The impedance of the speaker will determine how much electrical current will be needed from the amplifier in order to maintain that voltage. Less expensive amplifiers typically can not produce enough current to maintain that voltage into low impedances (like 4 ohms or less), so the amplifier will current limit (distort) or overheat depending on the design.

It is critical to note that speaker "impedance" is an average number. The typical speaker will have a fairly significant range of impedance over the audio frequency range - say from 4 ohms to 16 ohms or sometimes even a bigger range. This means that an 8 ohm speaker is approximately 8 ohms across the range, maybe exactly 8 ohms at only a few frequencies, and typically not 8 ohms for most frequencies. But on average it is about 8 ohms and that is a pretty good guideline.

So, if your amplifier can not produce a large amount of current and your speaker impedance is low, then you will get lower maximum voltage numbers out of the amplifier and thus lower power amounts depending on frequency.

The speaker amplifier interaction is made complicated by the frequencies present in the music - there may not be strong signals where the amplifier can't produce enough current so its not an audible issue. Another factor is that some amplifiers may not behave well into highly reactive impedances if they are marginally stable (could go into oscillation), so even a good average impedance can cause audible problems with certain amplifiers.

So, because of all of this complexity the speaker and amplifier manufacturers have come up with the speaker average impedance and the amplifier recommended minimum impedance concepts. Not specific at all, but this really is not that big of an issue. It really only affects maximum volume capability vs. frequency and the safety of the amplifier from damage in lower cost designs. I would just make sure you don't grossly mismatch the numbers and not worry too much about it.

What is a bigger factor on sound quality is the output impedance of the amplifier. If the amplifier has a high output impedance (say, > 0.5 ohms) it will interact with the impedance of the speaker and create an uneven frequency response that can be audible (might sound more pleasing, might not, but less accurate amplification for certain). However, this is typically not even an issue in a reasonably competent transistor amplifier design and usually is a minor issue with tube based designs.

If you are looking for guidance on buying an amplifier I would look at:
1) What type of speakers are you going to connect it to and what is their sensitivity? - this will determine how much voltage you need. Very sensitivie speakers need very little voltage (power). For example, some horn designs can play over 100dB with 1 watt, about 88dB / 1W is typical. Doubling amplifier power only adds 3dB to maximum sound level, so pick your power level based on speaker sensitivity, your taste in typical volume levels, desire for overkill, etc.
2) What is the speaker impedance? - this will determine how much current you need. Just general guideline - no need for calculations - do you need an amp that can maintain current delivery down to 2ohms, etc.
3) How much do you want to spend? You can spend a little or a fortune.
4) Check out other factors like frequency response, S/N ratio, distortion to make sure they are reasonable.
5) Check out any other features you care about (remote on/off control, styling, number of channels, etc.)
6) Shorten the list of amps, listen to them with your intended speakers, buy what you like and just enjoy listening.

If you are looking for guidance on buying an amplifier I would look at:

1) What type of speakers are you going to connect it to and what is their sensitivity? - this will determine how much voltage you need. Very sensitivie speakers need very little voltage (power). For example, some horn designs can play over 100dB with 1 watt, about 88dB / 1W is typical. Doubling amplifier power only adds 3dB to maximum sound level, so pick your power level based on speaker sensitivity, your taste in typical volume levels, desire for overkill, etc.

(Could you explain better this part and tell me why sensitivity is so important.)

2) What is the speaker impedance? - this will determine how much current you need. Just general guideline - no need for calculations - do you need an amp that can maintain current delivery down to 2ohms, etc.

Two 8ohms speakers and a 2ohm subwoofer

3) How much do you want to spend? You can spend a little or a fortune.

Not really a fortune but want do something which would suit me at its max.

4) Check out other factors like frequency response, S/N ratio, distortion to make sure they are reasonable.

Where can I check this ? Is it so important ?

5) Check out any other features you care about (remote on/off control, styling, number of channels, etc.)

Right now I am searching NAD's official web, they have a dedicated feature included on most amps called powerdrive.?

6) Shorten the list of amps, listen to them with your intended speakers, buy what you like and just enjoy listening.

NAD, Marantz, Denon ,Rotel, Linn ,Harman Kardon and a few others.
Any suggestions from your experience in Audio ??

Does IMPEDANCE effent sound quality

THANKS FOR ALL YOUR HELP !

Hey Audio Vox,
I'll try to answer these for you:



1) Sensitivity is so important because different speakers will play at significantly different volumes with the same input power. For example, a typical speaker will play 88dB with 1 watt of power, and +3dB louder for every 2x the power.
So 2W = 88dB + 3dB = 92dB
4W = 92dB + 3dB = 95dB
8W = 95dB + 3dB = 98dB
etc.

Another very efficient speaker may have a higher sensitivity of say 98dB with 1 watt of power. In this case, this speaker only needs 1 watt to play the same volume that the first speaker requires 8 watts to achieve. Note, the terms efficiency and sensitivity are typically used interchangeably and have little to do with sound quality, just volume level.

So, there are two points to be made:
a) With an efficient speaker you need less amplifier power to reach the same volume level, which can save a lot of money in amplifier expense.
b) You need to double the amplifier power rating before you achieve a minor audible increase in maximum volume. So, going from 50 watts to 100 watts will only get you +3dB more potential output which is relatively subtle (general rule of thumb is approximately +10dB sounds "twice as loud"), and going from 50 watts to 65 watts may not be audible at all, especially given other factors.

2) Is it a powered subwoofer? If so, the built in amplifier will handle the 2 ohms and you don't need to worry about it. If it is a passive subwoofer, then I am skeptical that its nominal rating is 2 ohms - that is really unusual. If it really is 2 ohms, then you need to know if it is in series or parallel with the satellites - if its in series then it adds to the satellite impedance which would give you 10 ohms which is not a problem typically, in parallel it will drop below 2 ohms which is not a good idea (stressful for almost any amplifier). Or if you'll drive it directly with an amplifier then you'll want a robust amplifier to drive 2 ohms and make sure the amplifier has a very low output impedance (see #6 below).

3) I guess "a fortune" is pretty relative. One person's "expensive $10,000 amp" is another person's "reasonable" choice.

4) Manufacturer web sites / specifications should have these. Typically this is not much of a problem as most amplifiers are pretty decent these days, but S/N ratios over 85dB relative to 1 watt are probably fine (lower ratings may make amplifier noise audible at the listening seat when no music is playing, the more efficient the speaker the louder the noise will be), the higher the better, distortion below 0.1% is probably not audible under most reasonable circumstances, the lower the better (all else being equal which is not typically the case), frequency response should be from 20Hz to 20,000 Hz +/- about 1 dB or less with a wider frequency range somewhat desireable from an overkill/safety margin standpoint. Output impedance would be good to know too (see below) but rarely specified as well as rated output power at lower impedances. An ideal voltage source (which an ideal amplifier would be) would double its power output at a given voltage every time the impedance drops in half, so the closer your amplifier can get to something like:
8 ohms = 100 watts
4 ohms = 200 watts
2 ohms = 400 watts
1 ohm = 800 watts
the higher the current delivery capability and the more robust the output stage/power supplies are. Remember, this is an ideal case and is really overkill in the real world. As long as the amplifier can increase power into lower impedances it usually indicatess a pretty strong circuit.

5) Not sure what "Powerdrive" is, sounds like a marketing lingo for some benefit claimed for their circuitry. Doesn't mean this feature doesn't do what it claims, just that it is hard to say what it does. Remember, there are tradeoffs to every design decision.

6) All good brands you mention. There are quite a lot of decent amplifier manufacturers out there, so anybody who has been in business for some time is probably making decent equipment. Depending on how high-end you want to get you could check out such brands as Krell, Boulder, Theta Digital, Mark Levinson. I used to use Adcom amps which worked great for me (I have active speakers now).

See my post about impedance and sound quality (pasted for convenience):

What is a bigger factor on sound quality is the potential interaction of speaker impedance with the output impedance of the amplifier. If the amplifier has a high output impedance (say, > 0.5 ohms) it will interact with the impedance of the speaker and create an uneven frequency response that can be audible (might sound more pleasing, might not, but less accurate amplification for certain). However, this is typically not even an issue in a reasonably competent transistor amplifier design and usually is a minor issue with tube based designs.

As far as speakers go, the frequency response, dispertion, dynamic range, distortion and acoustic interaction with the room will typically swamp the measured differences in amplification. Impedance is not something I would worry about too much - only to make sure I don't have a gross mismatch between speaker and amplifier.

What exactly did I say that is wrong?
Of course you can make the power equal for a 32ohm speaker the same as a 2ohm speaker if you change the voltage or current so that the 2 circuits are equivalent in power. However in reality does the voltage swing of a 32ohm speaker allow you to put a 2ohm speaker under the same power - most likely not. Most components (amps, speakers, electrical components) have their general operating range of what input and output voltage AND current they can handle, most often people just refer to this as the power of the device.

When you go buy a speaker it will be rated as X Watts, sure manufactures could list it as this speaker can handle up to x Amps, or x Volts, but they use Watts ie power. So when you increase the volume you increase the voltage AND current to the speaker, so you cannot just talk about current or voltage you talk about their combined effect which is power.

This statement does not really make sense. At least to me it doesn't. For amplifier there are two basic parts, the voltage amplifier (the preamp i.e. volume control) and the current amplifier (the actual amplifier). Yes they can be separate components and even cleverly engineered to be electrically close to each other, but any music system has both. The signal goes into the voltage amplifier first and it applies a gain which could either be positive or negative. This signal then passes on through the current amplifier which ideally passes along the exact same voltage levels as the voltage amplifier output, but it now “backs it up” with the required current to maintain that voltage over small impedances. With an ideal amp, if you had a 32 ohm speaker attached to it and then replaced it with a 2 ohm speaker, the 2 ohm speaker would have much more power delivered to it and sound much louder (if they have the same efficiency). It is impossible to apply the same voltage accross a 2 ohm speaker as a 32 ohm and drive it with the same amount of power. You need to turn down the gain of the voltage amplifier so that the voltage across the 2 ohm speaker is less.

Edit: It is also very possible for the current amplifier to act as a voltage controlled current source (although I don't know which is used in actual commercial designs) in which case the current would be the same for different impedances, with different voltages but my general point remains the same.

1. Its a car subwoofer, not active and has an impedance of 2ohms.

2. What do you mean by

How will I know ?

3. I would like to drive the subwoofer independly
2channels ---> 2 speakers of 8ohms
1 channel ----> 1 subwoofer of 2ohms


I have found my speakers specifications.

Frequency response: 55 - 20K Hz
Sensitivity: 89dB @ 1m/2.83V ms
Maximum output: 109 dB SPL

1. 55 - 20K Hz Whats this exactly ?
2. @ 1m/2.83V ms Why is it @1m/2.83v ms
3. Maximum output: 109 dB SPL ??? 109db ?

No, what "impedance" usually means is the modulus |Z| of the complex impedance Z-bar.
So when I say that a speaker has an 8 Ohm impedance, I mean that |Z| is around 8 Ohms, not necessarily R.
When impedance curves are published, they are always divided into amplitude (=modulus, |Z|) and phase, never into resistance and reactance.

So what would what would this |Z| be then ?

I was about say the same thing. Also, you can never say that the impedance of a speaker is simply 8+j0.05 or any single value. The impedance of a speaker is very dependant upon frequency. It might be 8+j0.05 at 1kHz but it will not be that same value everywhere between 20-20kHz. If a speaker was made to be such (unfortunately not possible...probably), it would be the first.

I guess we are splitting a thinner & thinner hair

As I said I am not an expert for audio and how they determine what 8Ohms is, be it resistance or modulus (root mean square) or some other value.

However I stand by my statement that just saying a speaker is 8ohms is not impedance (I'll accept that it is not resistance if it is the modulas). Impedance is a complex quanity and whether you wish to express it as x + jwY, or |Z|<(angle) you are not talking about a scaler quantity.

This is then a good example of something taken out of context if they are taking the modulas of the impedance and calling it impedance

@philly - yes you are right that the impedance would be frequency dependant, I was trying to be brief without getting too technical.

@Audio Vox - If you take the impedance of your speaker as 8 + j(4*w), and for argument sake say w=2(pi)f=1 then your impedance is 8 + j4 so the modulas or root-mean-square |Z| = SQR(8^2 + 4^2) = SQR (64+16) = Sqr(80) = 8.94 Ohms
This gives the value for the combined effect of the real & imaginary parts of the impedance.

Hmmm, interesting. So, you want to drive a 2ohm subwoofer directly, so you will need a pretty robust amplifier for that. What kind of amplifiers are you going to use - receiver for the speakers and a new amp for the subwoofer? I recommend you use a crossover to filter the bass out of the signal driving the speakers and to channel the bass to the subwoofer. If you use a receiver, most home theater receivers have this capability built in. If you are just using a stereo receiver or preamp/amp combo then it might get a bit more complicated. Because you'll drive them separately they will effectively be in another circuit and neither parallel or in series.

For your speaker specifications:
1) 55 - 20kHz is the frequency response. Basically means it will play bass down to 55Hz and all frequencies up to the generally accepted high frequency limit of human hearing at 20kHz. However, with no tolerance range or any other conditions specified this isn't too helpful (+/- 3 dB, etc.). 55Hz isn't very low, so if you like low bass then the subwoofer may help (don't know sub specifications). Speaker specifications are very complex - suggest another thread if you have more questions.
2) Sensitivity is typically defined as sound level for a given power input to the speaker measured at 1 meter in front of the speaker. 2.83V is 1 watt of power when applied across an 8 ohm load. So we would probably assume that the speaker is 8 ohms, otherwise the 2.83V will draw more than 1 watt if the impedance is lower, which means you will have to compensate for the difference and the 1 watt sensitivity is actually lower than the number given.

At any rate, your speaker is about average playing 89dB at 1 meter with 1 watt of input power.

3) Maximum output of 109dB SPL (SPL = sound pressure level) means it will play 109dB before it can't play any louder or play without damage or play without massive distortion. Without more specifications this isn't too helpful, but let's just say they can probably play pretty darned loud. 0 dB SPL is defined at an acoustic power level that is generally accepted to be approximately the limit of human hearing for soft sounds, so the speaker can play 109dB louder than the theoreticlly softest sound you can hear. 120dB is often cited as the threshold where sound begins to cause physical pain, so 109dB is pretty loud.

By the way, a dB is the abbreviation for "decibel" which is a logarathmic ratio, so all dB numbers specify an amplitude relative to another amplitude. As in "your speaker can play a maximum loudness of 109dB of sound pressure level (SPL) RELATIVE TO the threshold of human hearing." dB can be used to specify ratios in sound pressure, voltage, power, etc.

Hope all this helps.

I'm not exactly sure what you meant by this, but the way I think you mean it is wrong. I take it as, you stand by this statement:

but I could be misunderstanding.

In any case, to clarify, that statement is wrong.
Pio said it pretty well.



Between the audible range, the magnitude of the impedance should hover around 8 ohms for an 8 ohm speaker. It will not be 8 + j whatever. If it is, it’s probably a poorly speced speaker as it will always have a higher impedance than 8 ohms, at any frequency. It is easy to measure the real part of a speaker. Hook it up to a DC voltage source (a AA battery maybe) and measure the current (there are other methods, an ohm meter for one, but that’s cheating) . You will most likely find that 8 ohm speakers have a DC resistance around 4-6 ohms. The impedance would therefore be something like 5.2 + j whatever. Try it out.

55 - 20kHz is the frequency response. Basically means it will play bass down to 55Hz and all frequencies up to the generally accepted high frequency limit of human hearing at 20kHz. However, with no tolerance range or any other conditions specified this isn't too helpful (+/- 3 dB, etc.). 55Hz isn't very low, so if you like low bass then the subwoofer may help (don't know sub specifications)

Does this apply to bass only or treble aswell ?

The amplifier I'm interested too Is an NAD 372

Its feature list includes:

2 x 150W Minimum Continuous Power into 4/8 ohms
220W, 340W, 460W IHF Dynamic Power into 8, 4 and 2 ohms, respectively
PowerDrive™
High Current Holmgren™ Toroidal Power Transformer
Bridgeable to 400W Mono (8 ohms)
A/B Speaker outputs with remote switching
7 Line Inputs, including Two Tape In/Outs
Main-amp input & 2 pre-amp outputs
Bass and Treble Controls with Tone Defeat Switch
Relay Input Switching
All Discrete Circuitry
Gold plated RCA Connectors
Short signal path from input to output
NAD Soft Clipping™
Headphone socket
IEC Detachable Power Cable
12V Trigger Output
IR Input/Output
NAD SR-5 Full System Remote Control

WHAT ARE THE ONES HIGHLIGHTED IN RED EXACTLY ?
(because it states that 150*2 would be @ 4/8 ohms, and then it states other high power ratings which aren't very clear at least to me.)

Subwoofer specs:

http://www.onlinecarstereo.com/CarAudio/Pr...ProductID=14066

@philly - I was saying that I can accept that R is not 8ohms, if manufacturers use the modulas to indicate the value as Pio says.
What I was saying is that, the value Xohms, is no longer the impedance, because impedance is a complex value and not a scaler quantity, ie impedance would have to be in the form X +jY or |Z|<(angle) to be impedance, just to say that the impedance is |Z| would not be correct.

@Audio Vox - Not sure why they are in Red, i think maybe it is another form of putting an asterix (*) indicating that in the fine print they are somewhat exagerating. I think in this post a few people have mentioned that powe can be measured various ways. What I would take this as is the amp can deliver between 150 - 220W of power to the combined (stereo) speakers. So when you buy the speakers you have to make sure they can handle that POWER (not current or voltage).

This is not easy, and your method doesn't tell the value of R !
Imagine an 8 ohms tweeter with first order filter (one capacitor in serial). Say that the tweeter is a pure resistance R. The impedance is then R+1/jCw, with R=8 Ohms.
But when you apply DC, the resistance is infinite !

I have highlighted them just for the sake that someone could tell me what behind all this. This was also a reference
to a person that asked for my current amplifier + speakers specifications.

Yes, you are correct. We were talking about different situations however. I was talking about a pure driver with no filters (which I should have specified) only (which I do think this does work for). This probably was not good of me as most of the time you buy 2, 3, 4… way speaker systems with filters already in place in which case this method will not necessarily work as you pointed out. Please correct me if I am wrong about the driver only situation however.

Can someone help me with this :



Does this apply to bass only or treble aswell ?

The amplifier I'm interested too Is an NAD 372

Its feature list includes:

2 x 150W Minimum Continuous Power into 4/8 ohms
220W, 340W, 460W IHF Dynamic Power into 8, 4 and 2 ohms, respectively
PowerDrive™
High Current Holmgren™ Toroidal Power Transformer
Bridgeable to 400W Mono (8 ohms)
A/B Speaker outputs with remote switching
7 Line Inputs, including Two Tape In/Outs
Main-amp input & 2 pre-amp outputs
Bass and Treble Controls with Tone Defeat Switch
Relay Input Switching
All Discrete Circuitry
Gold plated RCA Connectors
Short signal path from input to output
NAD Soft Clipping™
Headphone socket
IEC Detachable Power Cable
12V Trigger Output
IR Input/Output
NAD SR-5 Full System Remote Control

WHAT ARE THE ONES HIGHLIGHTED IN RED EXACTLY ?
(because it states that 150*2 would be @ 4/8 ohms, and then it states other high power ratings which aren't very clear at least to me.)

Subwoofer specs:

http://www.onlinecarstereo.com/CarAudio/Pr...ProductID=14066

When you connect an ordinary stereo amplifier, you connect each speaker between a + and - terminal. You can also combine both amplifiers into one bigger one by tying the + of one channel and the - of the other together and connecting between the remaining + and - terminals.
Setting this up is very amplifier specific - read your user's manual before you do it.

That's the amount of power the amplifier can push into the specified loads. This isn't really useful without a specification of the amplfier distortion at those maxima. For example my (home build) amplfier can push 60W into an 8 ohm load at <0.1% THD (Total Harmonic Distortion) but almost 90W into the same load while clipping heavily (about 20% THD).

What they mean by Dynamic Power is that is the maximum power the amplifier can put into transients in the music. It cannot achieve this sort of power with continuous tones without cooking the output devices.

Interesting thing to advertise. With the general excellent quality of audio op amps these days (see TI's Burr Brown parts for example) having a few ICs in your amp isn't the mark of shame it used to be.

An attempt to process the signal to introduce even order (tube like) harmonic distortion instead of the harder sounding odd order harmonic distortion. This kind of thing is quite nice if implemented properly - it can reduce ugly sounding distortion on transients that drive the amplifier into clipping. On the other hand if you are running your amplifier into clipping as a matter of course you need a bigger amplifier (and probably new tweeters).

All Discrete Circuitry

Interesting thing to advertise. With the general excellent quality of audio op amps these days (see TI's Burr Brown parts for example) having a few ICs in your amp isn't the mark of shame it used to be.

Can you clearify this please.



THANKS VERY MUCH FOR YOUR PATIENCE !

I was just saying that, while "All Discrete Circuitry" sound impressive on advertising and spec sheets, it doesn't mean much in terms of sound quality, power or anything else.

Your personal suggestion ! on the amp ans speakers.

(For a small pub/bar)

Does this apply to bass only or treble aswell ?

2. I have red about the large variety of crossovers but can't figure out the difference and effect in sound there would be between a crossover of 1.5 kHz and a crossover of 10.80kHz can you help ?

Thanks