Speaker Impedance - How do they do it?

[rockman85]

So, for speaker design, a company may make both 4ohm and 8ohm versions of the same speaker. So what is the component that is changing from 8 to 4, do they make thicker internal wires, bigger terminals, different materials???

What creates the lower impedance?

[routlaw]

There are many different way a speaker can arrive at 4 vs 8 ohms. The individual drivers themselves might be made in both 4 and 8 ohms, or if two identical 8 ohm drivers are employed in tandem such as an MTM (mid range-tweeter-midrange) confguration then the impedance by default becomes 4 ohms vs 8 ohms, well assuming they are wired in parallel not series which would almost always be the case. It has absolutely nothing to do with wiring, terminals or accessories but rather about each individual driver or groups of drivers within the overall speaker arrangement.

If you take two resistors of the same value and wire them in series, the value doubles but if they are wired in parallel the value is then halved. This is a gross oversimplification in regards to speaker design which tends to be a very complex component to properly design and implement.

Hope this helps

[geeqner]

For those among us who do not have a more in-depth education in Electrical / Electronic Theory:

IMPEDANCE VS. RESISTANCE:
They are BOTH expressed in units of Electrical Resistance, which is Ohms. However

• RESISTANCE = usually something that is FIXED. It is a Number / Value that does not change (other than maybe a bit as something warms-up / cools-down)
• IMPEDANCE = Frequency Dependent (You could plot a graph of Electrical Resistance vs. Frequency and/or Current vs frequency at a fixed AC Voltage and you would see some sort of a curve or "squiggle".) = it CHANGES with the frequency of the applied signal

SPEAKERS:
SINGLE-DRIVER SPEAKER:
Even a simple Single-Driver Speaker uses a Voice Coil that is suspended within a magnetic field.
The Voice Coil stores and releases energy, like ALL coils do, in the form of a Magnetic Field
At Lower Frequencies - the Voice Coil acts more like a "simple chunk of Wire" and PASSES most of the energy applied to it
AT Higher Frequencies - Generating and Collapsing of the Magnetic Field increasingly "bogs-down" the flow of energy through the wire

MULTI-DRIVER (2-WAY, 3-WAY etc.) SPEAKERS:

• CROSSOVERS - Passive networks of Inductors and Capacitors are used to separate the Full-Range signal from the Amplifier into several narrower bands -
  with each band feeding a different speaker (highs to tweeters, lows to woofer, mid-range to mid-range, etc.
• Crossovers incorporate Capacitors as "High-Pass Filters" = they Pass Highs / Block Lows and store Energy in the form of Electric Fields
  
• Crossovers also incorporate more Inductors (Coils) as "Low-Pass Filters" = they Pass Low Frequencies and Block High Frequencies

These Cross-Over Networks add EVEN MORE COMPLEX "bumps" and "curves" to the Current vs. Frequency Graph as mentioned above

Multiple Speakers (Drivers) = Multiple Voice Coils of several different designs in order to meet the purpose of EACH chosen speaker driver.
When fed from the various cross-over sections, these add EVEN MORE complexity to the Current / Frequency  and Resistance / Frequency Graphs

SOUND-LEVEL VS. FREQUENCY GOAL = SOMETHING AKIN TO LINEAR:
The idea is to "Blend" the fall-off of one Speaker Driver with the "Ramp-UP" of the next higher speaker being used.

Optimally, the SOUND LEVEL Output of the speaker vs. frequency should be a relatively straight line (or in-line with the sensitivity of the human ear)
(Neutral - ALL frequencies represented equally)

However, doing this usually requires a complex, NON-Linear "Current vs. Frequency" & Resistance / Frequency Graphs.
Like I stated above - this is a byproduct of the desired result from an AUDIO standpoint - due to the "Physics" of the Speakers and the crossover components.

IN THE END (BOIL ALL OF THIS "MUMBO-JUMBO" DOWN):
In the end - the Industry HAS to "Classify" the speaker - so they look at the Mean / Average Impedance across the human Audible Frequency Range
(which usually goes from 20 Hertz up to about 20,000 Hertz [20 kHz])
-If the result is closer to "8" - they call it an 8-Ohm Speaker
-If the result is closer to "4" - they call it a 4-Ohm Speaker

(Most ARE NOT actually 4 or 8 "on the head" and as I stated earlier - most also vary considerably with Frequency)

But the "Average" speakers give you an idea of how to best match your speaker to an Amplifier.

Low-Impedance Speakers usually perform better with Amplifiers that can deliver relatively high current
Higher-Impedance Speakers usually perform better with Amplifiers that can deliver higher Voltages

TWO VERSIONS OF THE SAME SPEAKER:
I think that in this case - it is a matter of a Speaker Manufacturer choosing to develop two different versions for people with different Amplifiers:
If the manufacturer wanted them to look essentially the same when viewed from the front - it would logically be a difference in the design of the Voice Coils used within the speakers and the corresponding changes to the crossovers that drive them.

• 4-OHM VERSION - Probably uses Voice Coils with shorter lengths and/or heavier-guage wire, intended for those with High-Current Amplifiers (Generates the Mechanical Power to drive the speaker cone using stronger "surges" of current from the Amplifier)
• 8-OHM VERSION - Probably uses Voice Coils with longer lengths of lighter-guage wire (Generates roughly equivalent Mechanical Power to drive the speaker cone using less current / more "Wraps" to the Electromagnet that drives the speakers)

[KeithL]

The impedance of an entire speaker system is determined by several different things which all interact with each other....

Including the impedance of the drivers chosen and the crossover design.

You would usually choose the drivers that have the characteristics you want, then calculate the values you need for crossover components to produce the crossover slope and response you want with those drivers.

So both the drivers and most of the crossover components would be different.

And don't forget that many of the characteristics of the drivers in the finished speaker will depend on the characteristics of the cabinet designed to go with them.

The bottom line is that there are a whole bunch of interrelated and interdependent details.

There is no single component you can change to change a speaker form 4 Ohms to 8 Ohms or vice versa.

As I've mentioned before, when we design speakers, we consider things like sound quality, and exactly what we want it to sound like, first.

So, for example, in a T2, we wanted to use a certain woofer, and the 8 Ohm version had the characteristics we wanted...

And, since we wanted to use two woofers, that resulted in a 4 Ohm impedance...

The impedance of the woofer sort of dominates that design, and the options were 4 Ohms (two woofers in parallel), or 16 Ohms (two woofers in series).

Since most modern amplifiers don't deliver much power into 16 Ohms, we went with the 4 Ohm option.

In general, internal wires and terminals are far heavier than necessary...

Therefore, they would probably NOT have to be changed...

Nov 20, 2019 14:23:17 GMT -5 rockman85 said:

So, for speaker design, a company may make both 4ohm and 8ohm versions of the same speaker. So what is the component that is changing from 8 to 4, do they make thicker internal wires, bigger terminals, different materials???

What creates the lower impedance?

[audiosyndrome]

Nov 20, 2019 15:39:50 GMT -5 geeqner said:

For those among us who do not have a more in-depth education in Electrical / Electronic Theory:

IMPEDANCE VS. RESISTANCE:
They are BOTH expressed in units of Electrical Resistance, which is Ohms. However

• RESISTANCE = usually something that is FIXED. It is a Number / Value that does not change (other than maybe a bit as something warms-up / cools-down)
• IMPEDANCE = Frequency Dependent (You could plot a graph of Electrical Resistance vs. Frequency and/or Current vs frequency at a fixed AC Voltage and you would see some sort of a curve or "squiggle".) = it CHANGES with the frequency of the applied signal

SPEAKERS:
SINGLE-DRIVER SPEAKER:
Even a simple Single-Driver Speaker uses a Voice Coil that is suspended within a magnetic field.
The Voice Coil stores and releases energy, like ALL coils do, in the form of a Magnetic Field
At Lower Frequencies - the Voice Coil acts more like a "simple chunk of Wire" and PASSES most of the energy applied to it
AT Higher Frequencies - Generating and Collapsing of the Magnetic Field increasingly "bogs-down" the flow of energy through the wire

MULTI-DRIVER (2-WAY, 3-WAY etc.) SPEAKERS:

• CROSSOVERS - Passive networks of Inductors and Capacitors are used to separate the Full-Range signal from the Amplifier into several narrower bands -
  with each band feeding a different speaker (highs to tweeters, lows to woofer, mid-range to mid-range, etc.
• Crossovers incorporate Capacitors as "High-Pass Filters" = they Pass Highs / Block Lows and store Energy in the form of Electric Fields
  
• Crossovers also incorporate more Inductors (Coils) as "Low-Pass Filters" = they Pass Low Frequencies and Block High Frequencies

These Cross-Over Networks add EVEN MORE COMPLEX "bumps" and "curves" to the Current vs. Frequency Graph as mentioned above

Multiple Speakers (Drivers) = Multiple Voice Coils of several different designs in order to meet the purpose of EACH chosen speaker driver.
When fed from the various cross-over sections, these add EVEN MORE complexity to the Current / Frequency  and Resistance / Frequency Graphs

SOUND-LEVEL VS. FREQUENCY GOAL = SOMETHING AKIN TO LINEAR:
The idea is to "Blend" the fall-off of one Speaker Driver with the "Ramp-UP" of the next higher speaker being used.

Optimally, the SOUND LEVEL Output of the speaker vs. frequency should be a relatively straight line (or in-line with the sensitivity of the human ear)
(Neutral - ALL frequencies represented equally)

However, doing this usually requires a complex, NON-Linear "Current vs. Frequency" & Resistance / Frequency Graphs.
Like I stated above - this is a byproduct of the desired result from an AUDIO standpoint - due to the "Physics" of the Speakers and the crossover components.

IN THE END (BOIL ALL OF THIS "MUMBO-JUMBO" DOWN):
In the end - the Industry HAS to "Classify" the speaker - so they look at the Mean / Average Impedance across the human Audible Frequency Range
(which usually goes from 20 Hertz up to about 20,000 Hertz [20 kHz])
-If the result is closer to "8" - they call it an 8-Ohm Speaker
-If the result is closer to "4" - they call it a 4-Ohm Speaker

(Most ARE NOT actually 4 or 8 "on the head" and as I stated earlier - most also vary considerably with Frequency)

But the "Average" speakers give you an idea of how to best match your speaker to an Amplifier.

Low-Impedance Speakers usually perform better with Amplifiers that can deliver relatively high current
Higher-Impedance Speakers usually perform better with Amplifiers that can deliver higher Voltages

TWO VERSIONS OF THE SAME SPEAKER:
I think that in this case - it is a matter of a Speaker Manufacturer choosing to develop two different versions for people with different Amplifiers:
If the manufacturer wanted them to look essentially the same when viewed from the front - it would logically be a difference in the design of the Voice Coils used within the speakers and the corresponding changes to the crossovers that drive them.

• 4-OHM VERSION - Probably uses Voice Coils with shorter lengths and/or heavier-guage wire, intended for those with High-Current Amplifiers (Generates the Mechanical Power to drive the speaker cone using stronger "surges" of current from the Amplifier)
• 8-OHM VERSION - Probably uses Voice Coils with longer lengths of lighter-guage wire (Generates roughly equivalent Mechanical Power to drive the speaker cone using less current / more "Wraps" to the Electromagnet that drives the speakers)

A little bit of knowledge is dangerous.

Russ

[DYohn]

The simple answer is the system designer specifies drivers at the nominal impedance they want. I can order drivers (woofers, mids, tweeters) at any impedance rating. The standards are 2, 4, 8, 16 and 32 ohms. But if I'm designing a system than needs custom 17.5 ohm woofers, I can have those made. 4 and 8 are simply the default industry standards that people look for these days.

[405x5]

I believe once you understand how loudspeaker impedance plays into the mix and unless you’re undertaking a DIY project, the important thing is to stay focused on the sound of a loudspeaker YOU prefer and then apply the proper amplification to it.
The power requirements for a particular db. output between a say, 16 ohm. vs a 4ohm system can be very significant.

Bill

[geeqner]

Yup - DYohn.

That's the "simple" answer and accounts for a large chunk of a completed Speaker Assembly's Impedance Rating.

However, even though your woofer or tweeter is stamped with "8 Ohms" or "4 Ohms" (or whatever) - That value only holds true or close to it at a particular frequency or within a particular range of frequencies.

The linked article shows an example of a speaker's Impedance vs. Frequency and as you can see, it jumps all-over the map...
www.stereophile.com/content/elac-adante-af-61-loudspeaker-measurements

[audiosyndrome]

Nov 21, 2019 11:15:04 GMT -5 geeqner said:

Yup - DYohn.

That's the "simple" answer and accounts for a large chunk of a completed Speaker Assembly's Impedance Rating.

However, even though your woofer or tweeter is stamped with "8 Ohms" or "4 Ohms" (or whatever) - That value only holds true or close to it at a particular frequency or within a particular range of frequencies.

The linked article shows an example of a speaker's Impedance vs. Frequency and as you can see, it jumps all-over the map...
www.stereophile.com/content/elac-adante-af-61-loudspeaker-measurements

Once again, a little knowledge is dangerous.

Russ

[geeqner]

You're RIGHT!

I'll admit that the information that I provided is, in some cases, an over-simplification / just the "TIP of the Iceberg".

Maybe my initial response to the post came-off as long-winded and condescending.  That was not the intent.

I do not claim to know or understand ALL of the nuances involved.
A FULL understanding of what determines the Impedance of a speaker could probably involve a Doctoral Dissertation.
(which would make most readers' eyes glaze-over around here)

If YOU'RE such an Effin' GENIUS - Then YOU explain it...

[DYohn]

Loudspeaker systems are rated at their impedance at 400Hz. A typical woofer impedance curve looks like the attached, and a good system designer will use filter circuits (like Zobel networks) to compensate for the rise due to inductance and will cross the driver over to exploit the flattest portion of both the impedance and the frequency response curves.



But again, the basic answer to the question of what determines a loudspeaker's impedance is the drivers voice coils, and a designer can get drivers that are rated at whatever nominal impedance is required by their system design goal.

Oh by the way I have designed loudspeaker drivers and systems since 1973 and I DO have a doctorate, although not in impedance.

[klinemj]

I was listening to a friend's particular B&W model and found that it sounded like the midrange was being sucked into a black hole. Didn't like them at all. The next day, I was with another friend who had a German magazine that showed various speakers full specs, including impedance as f(frequency). It showed the speakers in question dropped below 2 ohms (1.6-ish, IIRC) right in the heart of the midrange. Very telling. I'd say the amp just didn't have the oomph to push the mids given the impedance in that range.

Mark

[routlaw]

It also sounds like a very poor design to me. This far into the 21st Century I find it amazing speaker designers make such systems that are so difficult to drive when its really not necessary given all of the very high quality drivers available and that don't present such a difficult load to drive. But even with that such anomalies should be correctable with the circuits in the crossover. All this for what one would assume is very expensive speaker. Thanks

[donh50]

The crossovers may be responsible for the dips; trades made for optimal phase/time alignment and all that jazz.

Note the cabinet itself also plays into the impedance, due to port resonances or volume resonances if sealed, that can create large impedance excursions.

[klinemj]

At the end of the day, the moral of the story is this...a speaker's impedance rating is just a number. I don't typically worry about it and just try to make sure my amp can handle the load.

The only time I really paid attention was with my outdoor speakers. I had a long run from my amp to my pool speakers, so I choose 8 ohm nominal. Even then, my Sonos Connect Amp wasn't quite enough. I switched to a Sonos Connect with a more powerful Rotel amp and all is good. I can float in the pool and rock out now.

Mark

[audiobill]

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[audiosyndrome]

Nov 22, 2019 11:03:59 GMT -5 geeqner said:

You're RIGHT!

I'll admit that the information that I provided is, in some cases, an over-simplification / just the "TIP of the Iceberg".

Maybe my initial response to the post came-off as long-winded and condescending.  That was not the intent.

I do not claim to know or understand ALL of the nuances involved.
A FULL understanding of what determines the Impedance of a speaker could probably involve a Doctoral Dissertation.
(which would make most readers' eyes glaze-over around here)

If YOU'RE such an Effin' GENIUS - Then YOU explain it...

OK, not a genius, just an engineer,  but to answer the OPs question:

First, speaker manufacturers DO NOT make an 8ohm or 4ohm version of the same speaker.
Second, the correct answer simply should have been "Since a speaker is not purely resistive, its impedance varies with frequency. Some speakers may dip down as low as 2, 3 4ohms; the manufacturer (reviewer) would call that a 4ohm speaker. A speaker measuring 5,6ohms and above would typically then be called an 8ohm speaker. Those numbers are not hard and fast but typical of how John Atkinson (Stereophile) or Keith Howard (Hifi News) goes about it.

Your initial answer seemed to be a poor understanding taken from wikipedia; that's what i meant by a little knowledge is dangerous.

Russ

[audiosyndrome]

Nov 22, 2019 16:22:10 GMT -5 DYohn said:

Loudspeaker systems are rated at their impedance at 400Hz. A typical woofer impedance curve looks like the attached, and a good system designer will use filter circuits (like Zobel networks) to compensate for the rise due to inductance and will cross the driver over to exploit the flattest portion of both the impedance and the frequency response curves.



But again, the basic answer to the question of what determines a loudspeaker's impedance is the drivers voice coils, and a designer can get drivers that are rated at whatever nominal impedance is required by their system design goal.

Oh by the way I have designed loudspeaker drivers and systems since 1973 and I DO have a doctorate, although not in impedance.

DYoyn - I don't think you meant to say "loudspeaker SYSTEMS are rated at their ........."

Russ

[geeqner]

Nov 24, 2019 17:19:55 GMT -5 audiosyndrome said:

OK, not a genius, just an engineer,  but to answer the OPs question:

First, speaker manufacturers DO NOT make an 8ohm or 4ohm version of the same speaker.
Second, the correct answer simply should have been "Since a speaker is not purely resistive, its impedance varies with frequency. Some speakers may dip down as low as 2, 3 4ohms; the manufacturer (reviewer) would call that a 4ohm speaker. A speaker measuring 5,6ohms and above would typically then be called an 8ohm speaker. Those numbers are not hard and fast but typical of how John Atkinson (Stereophile) or Keith Howard (Hifi News) goes about it.

Your initial answer seemed to be a poor understanding taken from wikipedia; that's what i meant by a little knowledge is dangerous.

Russ

Yep - Also an Engineer here (but not an Audio one)
NOT taken from Wikipedia - it was "off the top of my head" attempting to provide a little fundamental background of the principles behind what is going on.
Admittedly over-simplified and I did not know the details of how the actual tested curve is turned into an "official" rating, but I stand by my explanation of the basic principles.
 
I THOUGHT that the OP was referring to two different versions of the same speaker (theoretically, they COULD).

Sorry if I took it a bit personal (and I WAS "calling YOU out" more than DYohn...)  Water under the bridge? 

Ron

[405x5]

Nov 20, 2019 14:23:17 GMT -5 rockman85 said:

So, for speaker design, a company may make both 4ohm and 8ohm versions of the same speaker. So what is the component that is changing from 8 to 4, do they make thicker internal wires, bigger terminals, different materials???

What creates the lower impedance?

Just another “impedance story”....
My earlier pair of main loudspeakers had (4), four ohm. Woofers, series wired, with a passive crossover to end up with a nominal 8ohm. Load.

A smaller version of that loudspeaker was Available with those four smaller woofers ( that were built as 16ohm drivers) however, wired in parallel to a passive network. for the same nominal load.

Engineering decision....not sure why it was done that way.

Bill