What does the acoustic impedance of 4-8 ohms mean? Subs Resistance: Simple Arithmetic

The issue of acoustic resistance has already been discussed many times, but still I decided to return to it, due to the lack of a single final opinion on this matter! So, most modern amplifiers (based on their description) are usually designed to work with acoustics with a resistance of 6 - 8 Ohms. (8 Ohms seems to be the standard). At the same time, a lot of acoustics (especially those from the 70s-90s) have a nominal value of 4 Ohms! It is clear that this is precisely the “nominal” value, and that, in fact, this is a dynamic value, but still...! It is “stupidly” clear from physics that as the load resistance decreases, the current increases proportionally and there is a risk of burning the amplifier. With all this, some manufacturers openly declare the ability of their amplifiers to work with acoustics with almost any impedance, and some, on the contrary, warn against using speakers with inappropriate impedance! There are a lot of devices where these conditions are not specified at all! And what to do in this case, and in general, what is the general trend in this regard?
I would like to understand once and for all:
1-Is it possible to safely connect low-impedance speakers to any amplifier (both a transistor and a lamp)?
2-it is absolutely forbidden (and compliance must always be strictly observed)?
3-or is it a “lottery”, and each individual case is a separate risk (or lack thereof)?
Let's discuss!
Everything here, in principle, is quite banal and simple - when selecting an amplifier for speakers, be guided primarily by Class One, and not by performance characteristics. Let me explain.
If you look at the circuit diagram of a budget and an expensive amplifier, then in principle there is no difference - complete parity... So what's the catch?
In details and “safety margin” - budget amplifiers are designed for average volume with the possibility of short-term peaks, therefore the power supply unit, especially the transformer, is actually less powerful than the sum of two channels + efficiency. Output transistors and radiators, respectively, are also designed for this operating mode. Any transistors, especially bipolar ones, have an innate weak point - the crystal area. This crystal is physically unable to quickly transfer heat to the radiator and under long-term heavy load it simply melts - breakdown!
In an expensive amplifier, everything is done with reserve - long-term maximum output power of both channels + efficiency + 25%. Also output transistors, radiators, wires, transformers, electrolytes... in short - EVERYTHING!
All amplifiers, I repeat - ALL modern amplifiers (tube and stone) are designed for ANY load. Another question is what is the sensitivity of the speakers and what is the class of the amplifier in a given room volume. The speaker resistance can drop to 3 ohms, but the sensitivity is 93dB - the current is not very high even for a budget amplifier. But if it’s 85dB, for the same speaker you need either a 4 times more powerful budget amplifier, or with the same power (initial for 93dB), but of a higher class (we’re not considering sound quality at the moment).
Here's the arithmetic...
Well, actually, the conclusion is again unfortunately ambiguous! Like - in theory, everything is possible, but in practice, who knows! Just relying only on the price and level of the manufacturer was a bit scary for me personally! For example, let’s say, not very expensive NAD, nevertheless, boldly indicates in the manuals for its amplifiers various power values with resistances from 8 to 2 ohms, thereby confirming the possibility of their devices operating with such a load. At the same time, for example, in the description for my Alchemist, which is clearly more expensive and of a higher level, there is only mention of an 8 Ohm load!
I would like to clarify one more point - the connection of sensitivity to this whole story is not entirely clear.
Since sensitivity is, say, not quite an “electrical” parameter, reflecting the degree of sound pressure created by a speaker at a certain distance, when 1 Watt of power is supplied, then what does the current have to do with it?
In my understanding, when this one Watt is applied to acoustics with different sensitivity, but the same impedance, only the sound pressure created by it will change, in other words, one will simply play quieter. Why do we talk about increasing current?
Another question about the lamp. There is often just a set of output connectors for different load resistances. I would like to understand the principles of this approach.
sensitivity, let’s say not quite an “electrical” parameter
Sensitivity is the efficiency of acoustics. The lower the efficiency, the more current is needed to create the same sound. pressure.
question about the lamp. There is often just a set of output connectors for different load resistances
The 4-8-16 Ohm outputs are essentially the equivalent of an autotransformer. The bottom line is that the lowest distortion and highest efficiency in the transmission line (electrical term) is when the output impedance of the amplifier and the input speaker are matched. Tube amplifiers have a significantly higher output impedance, which is why they have a sectioned output winding of the transformer.
By the way, some companies make one universal 6 Ohm output. But as practice shows, this is still a compromise and such amplifiers play better with a high-impedance load...
in the description for my Alchemist, which is clearly more expensive and of a higher level, there is only mention of an 8 Ohm load!
Yes, there are a lot of such companies - they indicate the optimal honest power. The load in reality is ALWAYS reactive and frequency-dependent, therefore the performance characteristics of NAD are deceit. They take an active resistor and measure it... this is for lovers of beautiful numbers and pictures.
Thanks for the clarification!
About sensitivity, it means we were talking about the same thing, but from different sides!
Everything is clear now with the tube output too.
Otherwise, it turns out that any experiments with connecting low-impedance acoustics are done at your own peril and risk!
It’s not clear then, since so many predominantly vintage acoustics have an impedance of 4 Ohms, were the amplifiers of that time originally designed for this? (I'm just not very familiar with these types of amplifiers)
so many mostly vintage acoustics have an impedance of 4 ohms, were the amplifiers of that time originally designed for this?
Certainly. It is not the low-impedance as such that is critical, but the sensitivity... Therefore, the amplifier is always selected according to the sensitivity of the speakers, the room and the genres, and everything else is for the gourmand of electronics engineers...
And what is the exact principle of selection? (and rather the opposite, if we select acoustics for an existing system) We simply proceed from the fact that the higher the sensitivity, the lower the risk of burning out? Or is it possible to approach the issue with some kind of calculations?
And what is the exact principle of selection? (And rather the other way around, if we select acoustics for an existing system) Simply We proceed from the fact that the higher the sensitivity, the lower the risk of burning? Or is it possible to approach the issue with some kind of calculations?
Click to expand...

Well, yes... But, first of all, we decide on the class of the amplifier and speakers - this is more important than all other parameters. And so -
Soooo, the further into the forest, the more questions!

I can’t seem to get my head around the table! :-(Let's say you are interested in a volume level of about 80dB (at a distance of 1m as I understand it), let's say an acoustic system with a sensitivity of 91-95db. From the table we get something on the order of 0.6 watts???
I also want to add a nuance about our hearing. We hear the volume increase in a logarithmic sequence. If you notice, in magazines when measuring distortion and power, the scale is uneven 0.1-1-10-100... So, the difference in hearing between 10 and 100 watts is only two times... This is by the way about what is better In total, a person hears in the range of 0.1-10 watts (and why this range is very popular in tube technology), and then loses sensitivity to volume...
Soooo, the further into the forest, the more questions!
What should be understood by the class of amplifier and acoustics?
I can’t seem to get my head around the table! :-(Let's say you are interested in a volume level of about 80dB (at a distance of 1m as I understand it), let's say an acoustic system with a sensitivity of 91-95db. From the table we get something on the order of 0.6 watts???
Click to expand...
Hmmm! Well then, can you (for me, an idiot) give an example of how to draw a conclusion from all this about which amplifier to choose!? And how to tie all this to the question of 4 Ohm acoustics.
To begin with - what kind of speaker? room... genres...
Well, as I already said, the question is rather about selecting acoustics for an existing amplifier. I’ll try to describe what I’m generally thinking about. I have a single-ended tube circuit, and recently I came up with the idea of assembling a separate circuit based on it, because... Although he plays soulfully with my Tannoy 638, he still does not control this acoustics as the transistor Alchemist does. Single-cycle craftsman, initially designed for 8 Ohm acoustics, approximate design power 5-6 W, one single pair of acoustic connectors. Accordingly, I decided to match the lamp with sensitive (most likely vintage) acoustics. Because There is simply no separate room for this tract; I am planning a somewhat strange option. This set should be located at my workplace (on the table near the computer) and will be listened to in close proximity to the acoustics. (although all this will still be located in a room with an area of about 40 square meters!) Thus, the acoustics are planned to be bookshelf and not too large.
Having started to study the offers on the secondary market, I was faced with the fact that a lot of such acoustics have a resistance of 4 or 6 Ohms! Well, that’s where the thoughts actually began...
Oh yes, genres... Well, here almost everything can be except heavy metal, although mostly jazz, jazz-rock...

Explain what the difference is between 2 Ohm, 4 Ohm, 1 Ohm... And like 2 coils of 4 Ohm or 3 coils of 2 Ohm... What the hell is the difference? what exactly and what does it affect? It is clear that if the resistance is small, then more power will be required...

I'll try to explain quickly and simply. Let's consider the Amplifier-Sub combination. The lower the resistance (Ohms) of the sub, the more power the amplifier will produce (Watts). In car audio, 4 ohm speakers are mostly used. Subwoofers also come with lower resistance, as well as with several coils of some ohms.
Example1: at Kicker S15L7 4 2 coils of 4 ohms. YOU can choose from 2 options: serial and parallel connection of coils.
At sequential connection, the total resistance will be 4+4= 8 ohm
At parallel: 1/(resist_total)=1/(1/4+1/4)=1/(1/2) = 2 Ohm. That is, the total resistance will be 2 ohm.
Example2: at Kicker S15L7 2 2 coils each 2 ohm.
At sequential connection, the total resistance will be 2+2=4Ohm
At parallel: 1/(resist_total)=1/(1/2+1/2)=1 Ohm. That is, the total resistance will be 1 ohm.
There can be more than 2 coils, as on the SPLX 15/4, where there are 4 coils of 1 Ohm each.
The amplifier produces more watts with less resistance. Modern monoblocks generally operate stably at loads up to 1 ohm. Some(for example RF, DD) can work with less resistance, but this is rare and price extreme.
Example: Amplifier PowerAcoustik A3000DB according to the passport:
RMS@4ohm:1100W
RMS@2ohm:1800W
RMS@1ohm:2300W
The naked eye can see that an amplifier at 1 ohm is almost 2 times more powerful than at 4. That is, the price of a watt @ 1 ohm is 2 times less than at 2 ohms, which is certainly a big plus, since we live in a world of limited money. But they say that the sound becomes less quality with less resistance. I haven’t checked it myself, so I won’t confirm. Although it seems to me that 120DB obtained from an 8 Ohm speaker and from a 1 Ohm speaker will not be any different in terms of sensations. Both here and there the hair will move and it will be difficult to breathe. But let’s write down the poor quality as a big minus of the low-impedance connection, just in case. I repeat: I listened to the S15L72 at 1 Ohm with the Oris AD2000 and it seemed to me that everything was fine with the quality. I didn't listen to 4 ohms.
Now read check: TASK
Let there be 2 speakers with 2 coils of 4 ohms each (nominal 1 kW to keep things even) and there is 1 amplifier with the following characteristics:
RMS@4ohm:1000W
RMS@2ohm:1500W
RMS@1ohm:2000W
How to connect speakers to an amplifier, provided that all coils of all subs must be powered in order to:
1) provide maximum pressure (1 Ohm)
2) ensure maximum quality (4 Ohms)<-4 ом, т.к. 16 Ом - экстрим
Answer:
1) all coils in parallel, speakers in parallel, total resistance 1 ohm. (max amplifier power is reached)
2) all coils in series (2 x 8 ohms), subs in parallel. Total resistance 4 ohm
OR
all coils in parallel (2 x 2 ohms), speakers in series, total resistance 4 ohm.

Question: “Well, I heard the opinion that 8-ohm acoustics are better (meaning the same speakers, but in two types 4 and 8 ohms), they seem to create greater sound pressure and have less dependence of the unevenness of the frequency response on volume. Who has any opinions on this?”

Answer. In principle there is no difference, but in practice, given that the question probably refers to:

a) to the same amplifier with the same final output impedance;

b) to the same amplifier power supply with finite load current (short circuit);

c) to the same connecting cable with the same length;

d) to acoustic systems with different ohmic resistance (4 and 8 ohms), but structurally similar and with presumably the same percentage unevenness in the characteristics of the dependence of alternating current resistance on frequency;

...there is a difference and can vary from insignificant to significant and even critical.

1 . According to points a) and b), the power released by the same amplifier on 8 and 4 ohm speaker systems with the same input signal and the same position of the volume control can vary from equal if the amplifier is in paired with a power supply is an ideal current generator, up to halved at an 8 ohm load if it is an ideal voltage generator.

In practice, the truth, as always, is in the middle. The basis is Ohm's law for a closed circuit. The power output at an 8-myohm load is one to two times lower.

So, we sorted out the power.

2 . According to the same two points, a transformerless amplifier that allows the connection of a 4-ohm load works without problems at an 8-ohm load, with a slight decrease in the output power. On the contrary, it is not always the case - an amplifier designed for an 8-ohm load may fail when connected to a 4-ohm load. The reason is the excess of the permissible load current at maximum volume levels. This is an exit from the standard current mode with all the ensuing possible consequences.

3 . The cable contribution to the signal when connecting a 4-ohm load will be approximately twice as high. A cable, as a complex element of a path with distributed parameters, is the bearer of a number of properties that can affect the signal received at the output.

The recommended length, at which, as a rule, the contribution of a classic speaker cable is practically absent, can be 2 meters for a 4-ohm load and 4 for an 8-ohm load. The properties of the cable may vary depending on the length, material of the wire and insulation, type of winding, thickness of the cores (cores), quality and direction of pulling the conductive part of the structure through the feeder.

In most cases, this should not be given undue importance, since often, in the case of exotic cable designs, the combination of an expensive cable and expensive acoustics works as an attempt to compensate for some properties (and shortcomings) with others. That is, the need to use a specific cable is actually due to the shortcomings of specific speakers, although the combination can be quite harmonious and even interesting.

As a rule, for a well-executed technical design of a classical acoustic system, a not too expensive universal acoustic cable, manufactured with an understanding of the laws of physics, is sufficient. And what is above is more likely an adjustment after the fact, based on the shortcomings of the speaker design.

4 . The back EMF generated by the AC, as a response to the incoming signal, is applied to the terminals of the AC, causing instability of the output current-voltage characteristic. To neutralize this effect, use an amplifier with a low output impedance (the back-EMF signal is shunted at the output terminals). That is, in a closed circuit of alternating current of audio frequency, which consists of the capacitors of the power supply (pumping energy source), the transition resistances of the output transistors (pumping energy management), acoustic systems (energy consumer), according to Ohm’s law for a complete closed circuit, they are trying to achieve minimization voltage drop across the amplifier (the first two links) and maximization at the speakers. In this way, high efficiency of the sound amplification and reproduction system is achieved.

Obviously, a system with a higher resistance will be more stable here. But only except for those cases where the output stage modes are determined by the load resistance and/or are formed dynamically.

In total, we have:

According to points 2,3, and partly 4, the advantage is in favor of 8-ohm acoustics. According to point 1 - in favor of 4 ohm. So choose the acoustics for yourself, and don’t forget to read the instructions.

if the speakers say 140 W power (the word is written without a soft sign in the middle), this means that when such power is applied to it, the speaker will not fall apart at least immediately (that is, it will not “burn out”) and will most likely expire during its warranty period. that is, happiness is guaranteed to last a year. and that's all. Moreover, there may also be a hidden “ambush” here: the manufacturer may not indicate exactly what power can be safely supplied to its speaker. power can be both long-term and short-term, and in the latter case the time during which such power can be supplied must be specified (for example, no more than 1 second with an hour break). After all, what is a power of, say, 100 watts? with an efficiency much lower than that of a locomotive, all supplied power is converted into heat. turn on a 100-watt incandescent light bulb at home and hold it with your hand. This is exactly how the speaker inside heats up in exactly the same way when such power is applied to it (or at least hold a 60-watt soldering iron with your hand - the same effect). Therefore, when selecting an amplifier for a speaker, it is important not to supply more power to the speaker than it can “digest”, otherwise it will be “kiddyk” (it will not have time to dissipate heat or mechanically the diffuser will simply “jump out of orbit” and be damaged). and each speaker also has its resistance (as a characteristic). Usually they are standard 4-ohm, although there are deviations quite often.
and therefore, when selecting an amplifier for speakers, it is important to ensure that its power is not greater than the power that the speaker can safely digest. but there’s an ambush here too. because none of the manufacturers ever “honestly” reports the power of their amplifiers. everyone lies to varying degrees and hides behind various reservations and tricks. any dead amp can be capable of delivering some rated power for a long time. but he, if necessary, is capable of briefly “farting” with much greater power. but, again, this is very short-lived, just a fraction of a second. they can, with a clear conscience, measure this “fart” and pass it off as the “honest” power of their amplifier, “forgetting” (“as if”), however, indicate such a “trifle” as the duration of action of this very “fart”. it is usually so small that it is smaller than even the normal bass drum hit in music. that is, the sound of the blow lasts longer than the amplifier “runs out of power” (although during the time between blows it manages to accumulate power). Therefore, if you select an amplifier for the speakers based on these “inflated” power figures, the speaker will be underloaded and will visually play “quietly”. Of course, if, for example, a speaker suddenly turns out to have an “honest” power of 140 W (and a resistance of 4 Ohms), then this is exactly what it needs in order to create normal sound pressure for listening. and if in an amplifier with, say, also 140 watts of output power (at a resistance of 4 ohms), these watts will turn out to be “inflated”, but in fact there will be 35-40 “honest” watts (but still this is much more than in “ tape recorder"), then such a speaker with such an amplifier will play “quietly” and in order to play normally you will have to turn the volume knob to almost maximum. then distortions will “sprinkle” out of the amplifier (since it plays close to its upper limit and there will be no power reserve) and the dynamics will only get worse (in a mechanical and thermal sense), and the sound will become “dirty”. Therefore, it is always better to take an amplifier with a little power reserve, but never turn on the music “to the fullest.” then the sound will be “clearer” and “louder” at the same time. True, I know many cases when this was the case, until people in nature began to act strangely "drunk"... so many speakers were burned like this.. any amplifier, no matter how much power ("in reality") it has, is desirable so that it is not overloaded beyond its capacity. yes, briefly (again) they all suffer some slight power overload. with a long-term overload, as a rule, they begin to get very hot, for many the protection is triggered (if it has time), and some (especially with prolonged “abuse”) simply “burn” without warning. and the load on the amplifier is precisely determined by the load resistance, that is, the speaker resistance. power is always (as a rule) indicated at what load it is “produced”. when the load resistance is reduced by 2 times, the power (of the same amplifier) should theoretically also increase by 2 times. but this does not always happen, or rather it never happens at all. this is only in theory. actually “a little” less. On many amplifiers, the power for, for example, a 2 Ohm load may not be indicated at all. if so, then such an amplifier is not capable of handling such a large load at all (and there is no need to torture it). When 2 identical speakers are connected in parallel, their resistance decreases by 2 times, and accordingly the load on the amplifier increases by 2 times. and if you already have an amplifier that is not designed for such a load, then 2 speakers can always be connected (if you already have speakers and really want them) in series, then the resistance will increase by 2 times and the load on the amplifier will also decrease by 2 times. but then such speakers with this amplifier will play much quieter. so here you will have to either simply take a twice as powerful amplifier, or connect each speaker separately to its own amplification channel.
and the power figures at different loads characterize the amplifier’s ability to cope with a “complex” load. it’s just that, in fact, the resistance of the speaker is not always stably constant, but depends on the frequency of the input signal, and very often with “formally” 4-Ohm speakers it actually turns out that the resistance at some frequencies is much lower. that is, the load on the amplifier at these frequencies is much higher than the “calculated” one (although at other frequencies it’s just the opposite). such a sound will then not be “powerful”, it will not have “depth”. That’s why they often talk about “bundles” of speakers and amplifiers. about which speaker will work with which amplifier. although usually just advice is enough to take an amplifier a little more powerful than required and not overload it (that is, do not turn the volume knob to maximum).
and amplifier manufacturers still like to indicate the “maximum” power, which is 2 times greater than the long-term “honest” one. if a 4-channel amplifier says 1200 watts, this means that there are 300 maximum watts per channel and its rated power is 150 watts per channel. somewhere like that. therefore, you can connect a speaker with a “power” of 140 watts to it.

Question: I’ve heard the opinion that 8-ohm acoustics are better (meaning the same speakers, but in two types 4 and 8 ohms), it seems to create greater sound pressure and have less dependence of the unevenness of the frequency response on volume. Who has any opinions on this matter?

Answer: In principle there is no difference, but in practice, given that the question probably refers to:

to the same amplifier with the same final output impedance;

to the same amplifier power supply with finite load current (short circuit);

to the same connecting cable with the same length;

to acoustic systems with different ohmic resistance (4 and 8 ohms), but structurally similar and with presumably the same percentage unevenness in the characteristics of the dependence of alternating current resistance on frequency;

There is a difference and can vary from insignificant to significant and even critical.

1. According to points a) and b), the power released by the same amplifier on 8 and 4 ohm speaker systems with the same input signal and the same position of the volume control can vary from equal if An amplifier paired with a power supply is an ideal current generator, up to halved at an 8 ohm load if it is an ideal voltage generator.

In practice, the truth, as always, is in the middle. The basis is Ohm's law for a closed circuit. The power output at an 8-myohm load is one to two times lower.

So, we sorted out the power.

2. According to the same two points, a transformerless amplifier that allows the connection of a 4-ohm load works without problems at an 8-ohm load, with a slight decrease in the output power. On the contrary, it is not always the case - an amplifier designed for an 8-ohm load may fail when connected to a 4-ohm load. The reason is the excess of the permissible load current at maximum volume levels. This is an exit from the standard current mode with all the ensuing possible consequences.

3. The cable contribution to the signal when connecting a 4-ohm load will be approximately twice as high. A cable, as a complex element of a path with distributed parameters, is the bearer of a number of properties that can affect the signal received at the output.

The recommended length, at which, as a rule, the contribution of a classic speaker cable is practically absent, can be 2 meters for a 4-ohm load and 4 for an 8-ohm load. The properties of the cable may vary depending on the length, material of the wire and insulation, type of winding, thickness of the cores (cores), quality and direction of pulling the conductive part of the structure through the feeder.

In most cases, this should not be given undue importance, since often, in the case of exotic cable designs, the combination of an expensive cable and expensive acoustics works as an attempt to compensate for some properties (and shortcomings) with others. That is, the need to use a specific cable is actually due to the shortcomings of specific speakers, although the combination can be quite harmonious and even interesting.

As a rule, for a well-executed technical design of a classical acoustic system, a not too expensive universal acoustic cable, manufactured with an understanding of the laws of physics, is sufficient. And what is above is more likely an adjustment after the fact, based on the shortcomings of the speaker design.

4. The back EMF generated by the AC, as a response to the incoming signal, is applied to the terminals of the AC, causing instability of the output current-voltage characteristic. To neutralize this effect, use an amplifier with a low output impedance (the back-EMF signal is shunted at the output terminals). That is, in a closed circuit of alternating current of audio frequency, which consists of the capacitors of the power supply (pumping energy source), the transition resistances of the output transistors (pumping energy management), acoustic systems (energy consumer), according to Ohm’s law for a complete closed circuit, they are trying to achieve minimization voltage drop across the amplifier (the first two links) and maximization at the speakers. In this way, high efficiency of the sound amplification and reproduction system is achieved.

Obviously, a system with a higher resistance will be more stable here. But only except for those cases where the output stage modes are determined by the load resistance and/or are formed dynamically.

In total, we have:

According to points 2,3, and partly 4, the advantage is in favor of 8-ohm acoustics.

According to point 1 - in favor of 4 ohm.

So choose the acoustics for yourself, and don’t forget to read the instructions.