Zašto je loše ako je impedancija zvučnika preniska? Na vaše pitanje je odgovoreno

Može biti zbunjujuće kada govorimo o impedanciji, ohmima i svemu tome u vezi s automobilskim ili kućnim audio zvučnicima. Da, većina ljudi je upoznata sa zvučnicima, ohmskim vrijednostima i više...ali što to zapravo znači?

Točno zašto je li loše ako je impedancija zvučnika preniska? To je ono što ću odgovoriti ovdje i raščistiti jednom zauvijek.

U ovom ću članku pokriti sve što trebate znati:

Što točno je impedancija zvučnika?
Dva velika razloga zašto niska impedancija zvučnika može biti loša...i zašto je to važno
Zašto možete koristite zvučnike veće impedancije, ali ne niže (i što očekivati)

Puno je toga za pokriti pa krenimo odmah!

Što impedancija znači za zvučnike? Govornik Ohms objasnio

Ilustrirani prikaz dijelova koji čine zvučnik uključujući glasovnu zavojnicu. Glasovna zavojnica je čvrsto namotana, dugačka žica koja ima određeni otpor od korištenog električnog vodiča. Stvara magnetska polja koja pokreću membranu zvučnika naprijed i natrag, stvarajući zvuk dok pomiče zrak.

U svijetu električne energije i elektronike potrebno nam je nekoliko stvari za obavljanje korisnog posla:

Izvor napajanja s naponom za pokretanje električne struje kroz otpornik, motor itd. kako bi se učinilo nešto korisno. To omogućuje kućno ili automobilsko pojačalo ili radio.
Električni vodiči (žica zvučnika) za stvaranje puta za protok te struje
Određena razina otpora kako biste ograničili koliko struje može teći (previše struje uzrokuje izgaranje, zagrijavanje itd.)

Po istom principu, baš kao i drugi električni uređaji, zvučnici su poput malih motora koji koriste struju da bi pretvorili kretanje (stožac) u zvuk koji možemo ovdje – to su zapravo svi zvučnici!

Što znači impedancija zvučnika?

Impedancija zvučnika, mjerena u jedinicama otpora koje se nazivaju omi, je ukupna količina otpora koju zvučnik ima protoku električne energije.

Impedancija zvučnika dolazi iz dvije stvari:

Otpor dugog namotaja žice koja čini glasovnu zavojnicu
Posebno svojstvo koje se stvara kada se žica namota u zavojnicu naziva se induktivnost

Baš kao što ne možete imati kratki spoj na bateriji, pojačalo ili stereo treba malo iznos otpora zvučnika kako bi se ograničilo koliko električne struje radio ili pojačalo pokušava dati.

Glasovne zavojnice zvučnika koriste vrlo dugu duljinu žice koja je čvrsto namotana u glasovnu zavojnicu potrebnu za stvaranje magnetskih polja za stvaranje kretanja stošca. Zbog ove duljine uvijek postoji određena količina otpora koja je dio onoga što čini impedanciju zvučnika.

Otpor određenog zvučnika je gotovo uvijek nekoliko jedinica otpora, mjereno u Ohmima.

Što znači induktivitet? Zašto je to važno kod zvučnika

Induktori su vrlo korisni električni dijelovi koji iskorištavaju induktivitet. Induktivnost je svojstvo elektrona koji teku kroz žičanu petlju i magnetskih polja koja se zbog toga stvaraju. Slično tome, zvučnici imaju induktivnost zbog svojih glasovnih zavojnica, iako malu.

Zavojnice žice imaju zanimljivu nuspojavu koja se događa za razliku od ravnih dijelova žice. Namotaj žice glasovne zavojnice tvori petlju koja ima električno svojstvo koje se naziva induktivnost. Kada se izmjenična frekvencija poput glazbenog signala primijeni na zavojnicu s induktivitetom, postoji suprotnost protoku električne struje zbog prisutnih magnetskih polja.

This is called inductive reactance and it’s different from resistance as it changes as the frequency changes; resistance stays the same.

For speakers, this matters because it means that the total resistance is made up of the two things I mentioned:wire resistance and inductive reactance. The name used to describe this total is impedance.

For speakers, this means that impedance (the total resistance) changes slightly as music plays because of the changing sound frequencies. However, the good news is that we can still categorize speakers according to an Ohms rating since it’s always pretty close.

When we talk about the impedance of a speaker, most of the time people are referring to the range of the speaker assigned to categories like 2 ohms, 4 ohms, 8 ohms, and so on. This is how we match speakers to a car or home amplifier, radio, and so on.

In the electrical world, resistance units measured in Ohms can be written as the Greek symbol Omega, or “Ω.”

How does speaker impedance work?

When a musical signal (made up of alternating current) is applied to a speaker it generates magnetic fields as current flows through the tightly wound wire coil. Interestingly enough, a coil of wire develops magnetic fields that resist the flow of the current (resistance, also called reactance in this case).

Similarly, many other electrical components like motors deal with the same electrical resistance as alternating current (AC) is applied.

How the math works (yeah, it’s a little complicated!)

Because of how inductance works and the physics involved, the speaker “impedance” (total resistance) isn’t the sum of the resistance and the inductive reactance. Instead it’s the “algebraic” sum, meaning it’s the square root of the sum of the squares. You may remember this kind of math from trigonometry class.

Speaker impedance isn’t as simple as just adding the measured DC resistance of the coil wire and the inductive reactance for a given frequency.

Instead, speaker impedance is found from the algebraic sum of the coil’s wire resistance and inductive reactance. You can find this by squaring each and then taking the square root of the two numbers added together.

Inductive reactance is commonly written as “Xl”, pronounced “X sub L” and is measured in units of Ohms just like resistance. Inductance is measured using a unit called the “Henrie” and commonly noted with an “H”:“uH” for microHenries, “mH” for milliHendries, and so on.

There’s also a corresponding value for capacitors called capacitive reactance (Xc) but that doesn’t usually apply for speaker voice coils. It’s very important for speaker crossovers, however.

Why is it bad if speaker impedance is too low?

Just like any other device connected to an electrical power source, the speaker impedance will determine how much or how little current a home or car receiver, amplifier, etc will produce. The speaker impedance also affects how some speaker components such as speaker crossovers behave too.

What happens if speaker impedance is too low?

You can connect a higher speaker impedance in most cases without any problems (at least not major ones). A radio, home or car amplifier, etc will still produce sound and run at normal or low temperatures. That’s because a speaker with a higher impedance than expected will reduce how much electrical current the audio source tries to produce.

As a side effect, you’ll get sound but with much lower power output than you would with the correct speaker load. Car stereos or amps, for example, have to work with lower voltages than home stereos so they need a lower impedance 4 ohm speaker typically to produce more power.

Home stereos, on the other hand, have higher voltage available and can use a higher speaker impedance (8 ohms, typically).

Internal view of an amplifier. When connected to a speaker impedance load that’s too low, the amp will begin to get very hot and this can burn out the output transistors as they can’t handle the heat caused by trying to supply excessive current to a lower speaker load.

However, using a lower speaker impedance is bad because it causes the radio or amp to attempt to put out twice as much (or more!) current than it’s designed for. Your home or car stereo will get very hot quickly and if you’re lucky will go into a self-protect mode and shut itself off.

However, in my experience, it’s pretty common for the output stage electronics to burn out when connected to a lower speaker load than they should be. The high-power transistors in a home or car amplifier or stereo are only rated for a certain amount of heat &electrical current.

When they’re forced to try and handle an amount outside that range they become super hot and start to break down permanently. It doesn’t take long before the damage is permanent and they no longer produce sound.

Caution! Never wire speakers in a way that gives a total speaker load lower than the radio or amp is rated for. Also, don’t guess about the correct speaker impedance – check first.

I’ve seen cases where someone’s “friend who’s smart” has as a way to “get more power” but caused a stereo or amp to try to and put out more power than it was designed for. The end result was a burned-out amplifier.

Why does speaker impedance matter for crossovers?

Speaker crossovers work to separate the sound sent to certain speakers for improved sound, reducing distortion, and to give you more control over how they’re used. For example, they block bass that tweeters can’t produce and highs that a woofer can’t produce well. However, they’re designed for a specific speaker impedance. Changing the speaker impedance affects the sound.

Speaker crossovers are amazingly helpful for getting better sound with speakers. Even the cheapest, most basic capacitor connected inline with a tweeter working as a high-pass filter makes a big difference in the sound.

The result is cleaner sound and avoiding possibly damaging it when bass sounds are played.

The catch is that because of how crossover components (capacitors and inductors) behave, they’re designed for specific speaker loads and can’t be used with other Ohm loads without affecting the sound output.

Crossover shift when using different impedance speakers

When you change the speaker impedance connected to a speaker crossover it can significantly shift the crossover’s cutoff frequency. As a general rule:

Halving the speaker impedance (ex.:8ohms to 4 ohms) doubles the frequency
Doubling the speaker impedance (ex:8 ohms to 16 ohms) halves the frequency

That’s bad because it allows the speakers to be sent a sound range they’re not suited for. In the case of tweeters, bass &midrange are bad because they can’t produce it properly. Similarly, many woofers can’t produce high frequency sounds well.

The end result in either case is poor sound that’s a lot worse sounding that it should be. If you change the speaker Ohms load you’ll have to replace the speaker crossover as you’ll need different parts values for it to work the same.

Is 8 or 4 ohm better? Is higher or lower impedance better for speakers?

8, 4, and 2 ohm speakers aren’t necessarily “better” than one another. The correct answer is that it depends on the application and what stereo or amplifier is being used. The best impedance is the one that matches an amplifier or stereo’s impedance spec correctly.

By industry tradition, 8 ohms are used for home and some theater speakers. 4 ohm speakers are generally used for car and marine audio, with some 2 ohm models also (usually subwoofers).

Na primjer:

8 ohm speakers are used in home stereo systems and require 1/2 the current of a 4 ohm speaker. That means they can use smaller speaker wire as they can take advantage of home electrical systems that have a high voltage supply for driving speaker amplifiers.
4 ohm speakers are used because car stereos and amplifiers (particularly car head units) can’t make large amounts of power in speakers as they have a very low 12V power supply. Reducing the speaker impedance from 8 to 4 means we can double the power for the same output voltage.

As a matter of fact, car stereos can only put out about a small 15-18 watts RMS per channel, despite the exaggerated peak power ratings you may see in advertisements. That’s because they only have about 12 volts to work with and have to divide that in half in order to produce AC waves that drive a speaker.

Car amplifiers are able to deliver huge amounts of power to 4 and 2 ohm speakers. They use an internal “inverter” power supply that steps up the +12V supply to higher voltages. This way they’re able to supply much more power to 2 or 4 ohm speakers than would be possible otherwise.