Everything you need to know about speaker impedance

hey this is Steve Guttenberg I and the audio fili act and I am here with Andrew Jones from elac and you're gonna help me out with in peace everybody asks me and asks you to explain the meaning of impedance and whether or not their receiver amplifier will work with a 4 ohm speaker an 8 ohm speaker clear the air take it over hand meaning of your beads think more difficult than understanding the meaning of life it seemed right ok so surprisingly or maybe not surprisingly to me anyway is there is an international standard for rating nominal impedance of loudspeaker and it's a very simple specification if you say the nominal impedance is let's say 8 ohms what we mean is the minimum pians shall not fall below 80% of the nominal impedance so in the case of an 8 ohm speaker 80% of that is 6 point 4 ohms the minimum should not drop below that over the defined frequency range of the speaker and the defined frequencies remain - the speaker is the minus 10 DB points so you got a frequency range and you've got a minimum level it should not drop below so 8 ohm so you can mean 6.4 ohms 6 ohm speaker means 4 point 8 and a forum speaker me means 3 point 2 very simple unfortunately a speaker isn't very simple so that's not really a very comprehensive understanding of what the impedance characteristic of the speaker is so let's go back to basics let's take a resistor we know from Ohm's law precisely how much current will flow if we apply a certain voltage to a certain resistance right regardless of frequency so we were to take a sweat sine wave for example sweep it from 20 Hertz to 20 kilohertz into an 8 ohm load the current will remain the same at all frequencies if we take a complex musical signal we can exactly predict how much current that each frequency band will flow because it's a resistance now it's gotten to a speaker it couldn't be further from a simple resistance it's almost never a resistance unless you do some extraordinary jiggling with the crossovers like the original CAF 104 to was a constant resistive impedance a Magna pan because of its technology is pretty much a constant resistance so you know what you're getting regular moving coil speakers or alleged statics are not simple impedance a closed box will have a resonant frequency where the impedance rises typically let's say 40 50 60 Hertz depending on the cutoff of the speaker it will then start with AA well it could go 30 or 40 ohms really oh yes elect static can go to hundreds of certain things is it all depends on the design of the driver then it'll fall to an in band minimum typically somewhere around 100 150 Hertz then they'll start rising because the voice girl has some inductance and the crossover components will almost always cause a rise in impedance at the crossover frequency he'll then drop back down again through the treble range until it starts rising at the - C range a vented box will have a double hump at the low frequencies say maybe at 30 Hertz and 60 Hertz with a minimum at the tuning frequency let's say 55 Hertz so it's just going boom boom right and if we're going to follow the convention that simply said the minimum of this 8 ohm speaker is 6.4 ohms then you look at all these homes it cannot go below 6.4 the minimum between the homes but it will by definition therefore be higher everywhere else and we don't even say how high that can be the original debut was 20 or 30 ohms in the treble region from memory don't quote me on that but very high so all we care about is the minimum unfortunately what does that mean in terms of what the amplifier is required to produce let's go back to that simple swept sine wave we sweep with a sine wave at some point the current draw will be much higher than everywhere else and that's where that minimum impedance is but with music when we've got a complex musical spectrum that's constantly changing it's very difficult to predict what the current flow is and that's what we care about with men and beans how much current does the Empire yes now because music most of the times fairly complex and the power is spread across the spectrum then in the freaky ranges where the impedance is high it's not demanding much current draw so most times on music the current demand isn't as high as we'd think when we rate it as a four ohm speaker for example and that's if we're following the convention if we're true if we're quoting it accurately but maybe you have tom toms and maybe the energy is concentrated right at the minimum of where the impedances so for the duration of those particular instruments you'll have a higher instantaneous current draw is that gonna be a problem probably not because again if you got music concentrated in a very narrow spectrum at that frequency it's almost never going to be taxing the amplifier to full output level you'd be deafening yourself if you did that so in practice impedance is not as much of an issue unless you're at the party and I've gotten to tell people don't turn the volume control up this high so sort of extreme situations of parties or plain speakers outside or something the reality is whether your receiver says 8 ohms or 6 ohms or four it doesn't really matter except in extreme circumstances you have what people are going to do oh yes so we have to absolve ourselves of any blame so that's why that is a standard but because it's such a complex issue the standard couldn't really follow all the potential complexities so it makes it easy and thereby we can't really predict what is going to happen so from a legal point of view we follow the standard and say the minimum value is follows the standard but we know it's only over a relatively narrow frequency range but you've always got this issue when you're designing but you can't have everything sorry I try as best as I can but you can't have everything just like with efficiency box size bandwidth you can no I I get that but it's everything comes down to choices so if you lower the impedance the apparent sensitivity increases so if I design it as an 8 ohm system where the sensitivity of let's say 84 if I'm a designer is a 4 ohm system its sensitivity is now 87 right because so sensitive tea is not efficiency I have not changed the efficiency I've changed the sensitivity why does that matter because an amplifier provides voltage control so you switch from a speaker of 87 DB sensitivity to 1 of 84 and you go that's quiet it's lost all its dynamics it's only because it's quieter the efficiencies are the same but it's quieter so it's a way of cheating to gain have an advantage on a switch over the old days of just switching from once we get to another right so ultimately you care about impedance you care about sensitivity and we want to be true to the one standard that there is but it doesn't easily give a concept of the normal operating conditions how much are you going to be taxing we amplifier and unless you're playing really loud most times especially these days with all the protection circuitry that's typically built into same receivers these days what's likely to happen is if it starts overheating because it's trying to produce too much power it will just stop yeah it'll turn off or protect in that sense or it'll have current limiting so that once it tries you try and draw too much current you'll say no no I'm not going to give you anymore it might sound distorted when it's doing that but it's basically protecting itself but as a speaker manufacturer i cannot rely on that so i have to say you know this one i'm mating as a foreign system which means it could for some range drop down to 3.2 but everyone else it's got to be higher than that and combined with the fact that sometimes as i'm designing it i find the minimum peden s-- dropped to 4 ohms what do I call that I could call it a 5 ohm system because 80% to 5 ohms is 4 ohms no one's going to understand I'm going to get even more questions while my amplifier manufacturers routed it into 8 ohms and 6 ohms what do I do with 5 ohms well it's like this you see and it gets back into that complicated conversation in a practical sense if you're a lot of people always say oh I don't play really music that lab it everyday guy situation should they be fretting should they look at that impedance back and say no I can't buy this not just yours I mean any speaker that's a rated 4 ohms is that a reason not to buy to give this so off-the-record on-the-record you shouldn't track too much given at least one cop out on that safe okay but you've honestly rated according to the international standard now not everybody does that or sometimes there's a kind of halfway where a tonne compatible we don't really know what that means some people will say at least let's say a tonne compatible minimum of such-and-such so at least you do know there what the minimum and it's not in that case it's not obviously trying to be dishonest it's trying to make the point that the standard is so simplified that it doesn't clearly represent what's going to happen in practice so trying to get sort of a halfway house between not cheating but trying to represent the case if it's mostly above 6 ohms you gonna be ok but it's I know but it is because there is no straightforward answer other than to say you know you're probably gonna be ok but I can't if someone calls in and says my amplifier is only expecting to 8 or 6 I'm not going to say that absolutely you can use my forum speaker because if anything goes wrong with the amplifier it's kind of on me sometimes what some amplifier manufacturers do they give a continuous power 8 ohms and 6 ohms let's say and maybe that's also what's quoted on the back panel it'll say a tome or six old rating but when you look at the manufacturer's specifications not some review of it where they've tested it thoroughly but the actual manufacturer specifications it will say burst power into eight six four and two ohms that implies to me they've run it in two speakers or loads as low as 2 ohms and it was able to give briefly you know musically inclined brief periods it was able to drive 2 ohms so that gives me the hope of saying under those circumstances if they've quoted burst power down into 2 ohms then he's probably gonna be even even more yeah because she can never be absolutely it's a freaking receiver they do there's a number of receivers from I think at least a mile and then on will do that burst power rating so that gives me more confidence to say you know you're gonna gonna be ok but what you'll find probably is if you then call them manufacturer of the receiver they will hedge their bets as well and say oh no no no no no don't use a speaker lower than 6 ohms because everybody is trying to make sure I did it to myself

Channel: Steve Guttenberg Audiophiliac

Views: 43,763

Rating: 4.9197993 out of 5

Keywords: Andrew Jones, speaker impedance, Audiophiles, Stereophile, The Absolute Sound, ELAC

Id: DNfpYncOQRc

Length: 14min 56sec (896 seconds)

Published: Thu Feb 22 2018