[Engine-Ear]

In this article, we look at understanding the concepts of Resistance, Impedance and the electrical dimensions that define both: OHMS. We'll also touch on a real world speaker situation I dealt with in Ramblin' Rose.

Like the last article, this one's geared toward the old-car hobbyist.

Please read it: https://redirad.com/blogs/news/why-r...e-is-important

[nytrainer]

Interesting and humorous article Matt. Signed up for your newsletter.
Thanks.

[694.1]

Never could understand why the aftermarket does not seem to offer 10 Ohm speakers....
First thing we did when we picked up the 67, 68 & 69 Pontiacs as teenagers was to install the Jensen 6X9s

[Bill Hanlon]

Good job Matt. Maybe next week you can cover Fleming's left hand rule. ;

[dataway]

Haven't read it yet ... but will momentarily. I have a firm grasp on voltage, current, resistance and how they work together ... but impedance always baffles me

In about 12 hours I will be using your info to test a 68 AM radio that hasn't made a sound in 40 years ... can't wait to see how it goes.

[Engine-Ear]

Originally Posted by 694.1

Never could understand why the aftermarket does not seem to offer 10 Ohm speakers....

...as the title of this reply says, and to your point on adding "6-by-9s", the battle of numbers got underway in the late '70s and continues to this day...something we call "specsmanship", making the numbers look better than your competitors.

[Engine-Ear]

Thanks for the compliments, gents.

[Greg Reid]

Yes, very good article...Now, I have a question- I know I can't use a resistor to manipulate the impedence of the speaker circuit...but can I connect two (or more) suitable speakers in parallel or series to manipulate the circuit impedence?
Say, two 4 ohm speakers in series?
I've been planning to do this for a while but I had not confirmed whether it would work or not.

[Bill Hanlon]

Originally Posted by Greg Reid

Yes, very good article...Now, I have a question- I know I can't use a resistor to manipulate the impedence of the speaker circuit...but can I connect two (or more) suitable speakers in parallel or series to manipulate the circuit impedence?
Say, two 4 ohm speakers in series?
I've been planning to do this for a while but I had not confirmed whether it would work or not.

Just to throw a wrench into the works, here is an impedance chart of a typical 4 ohm speaker. You'll note that the speaker's impedance changes with the frequency of the sound. So really the "4 ohm" rating is the minimum impedance.

The short answer to your question is that you could connect two 4 ohm speakers IN SERIES and end up with the electrical equivalent of an 8 ohm speaker. You need to be sure each speaker has both connections isolated from the frame of the speaker (some speakers do not).

Adding a 4 ohm resistor in series with the speaker would make the radio's amplifier happy, but half of the power would be lost across the resistor with no sound produced.

[1966Lemans]

Impedance "seems" weird because, unlike a normal resistor, it's really resistance as a function of frequency. For things like speakers and coaxial cables, I never understood why they don't quote the impedance at some specific frequency it's calculated at. For a speaker, it's because it's really a big inductor (coil of wire) without very much resistance. For coaxial cable, it's a big capacitor without much resistance.

[Greg Reid]

Good info guys. I already have the speakers mounted and wired in series, I just never remembered to investigate whether that would work. Impedence has always been a bit of a mystery to me.

[Old Goat 67]

This will either help or hurt.

https://en.wikipedia.org/wiki/Electrical_impedance

[Greg Reid]

"Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of a sinusoidal voltage between its terminals to the complex representation of the current flowing through it"

Ok, got it!
lol... Thanks Charles, that article actually is helpful to the extent that my two remaining brain cells can comprehend it.

[dataway]

A lot depends on how the McGanzer flange is mounted to the Turbo-Encabulator.

[Old Goat 67]

Yeah, but not all of them were made with particular flange.

[Engine-Ear]

Originally Posted by Greg Reid

but can I connect two (or more) suitable speakers in parallel or series to manipulate the circuit impedence?
Say, two 4 ohm speakers in series?

Although I haven't done so myself, in my opinion two 4s in series should "look" like 8 ohms to the radio's amplifier circuit.

...might be difficult to implement in your dash, however! (which is why I prefer getting the right speaker for the job in the first place)

[Engine-Ear]

Thanks for your post, Bill!

Originally Posted by Bill Hanlon

Just to throw a wrench into the works, here is an impedance chart of a typical 4 ohm speaker. You'll note that the speaker's impedance changes with the frequency of the sound. So really the "4 ohm" rating is the minimum impedance.

Since impedance is inherently an "at a frequency" value, I think the audio industry / engineers specify speaker Z (impedance) at 400 hertz (Hz).

If anyone reading this knows for sure, please chime in and educate us.

On that diagram, specifically what:
- speaker did you measure?
- equipment did you measure that with?

Also, I see the measurement stops at 2000 Hz...can you provide a measurement that goes out to 15,000 Hz (the practical upper frequency of adult human hearing)?

Originally Posted by Bill Hanlon

The short answer to your question is that you could connect two 4 ohm speakers IN SERIES and end up with the electrical equivalent of an 8 ohm speaker. You need to be sure each speaker has both connections isolated from the frame of the speaker (some speakers do not).

EXCELLENT caveat!

[Engine-Ear]

Originally Posted by 1966Lemans

Impedance "seems" weird because...

I spent many years in industry making impedance measurements over a wide range of frequencies, on both passive (unpowered) and active (powered) devices and circuits...in the '90s, companies like Hewlett-Packard (later Agilent, and now, who knows WTF they are) released some fantastic T&M (Test and Measurement) equipment that really enabled people to perform some VERY accurate measurements of extremely sensitive circuits and devices. It was (is) HEADY sh!t, but a LOT of fun.

From that perspective, I feel that because defining the actual impedance of something is accurate "at X Hz", and things like transmission lines (co-axial cable) and loudspeakers can carry a wide number of frequencies, they specify the "characteristic impedance" of a device, sometimes based on one "test" frequency.

Also keep in mind that measurements like this are often provided in Log Mag* form and as such, amplitude variations of the data on a LINEAR scale look a lot flatter on that of a logarithmic one.

*Log Mag is an abbreviation for the result of calculating the logarithm (base-10) of the magnitude (the square root of the sum of the squares [think: pythagorean's theorem]) of the real and imaginary components (that TRULY define an impedance) of a value in phasor (vector) form.

...sorry, the Reddy Kilowatt in me was awakened. Any arithmetic-induced nightmares that you have from the above are YOUR fault, people, not mine...

[Greg Reid]

Originally Posted by Engine-Ear

Although I haven't done so myself, in my opinion two 4s in series should "look" like 8 ohms to the radio's amplifier circuit.

...might be difficult to implement in your dash, however! (which is why I prefer getting the right speaker for the job in the first place)

Thanks, they are under package tray.

[Bill Hanlon]

Originally Posted by Engine-Ear

Thanks for your post, Bill!
On that diagram, specifically what:
- speaker did you measure?
- equipment did you measure that with?

The graph came from the internet, so it must be true Matt. It had no references to speaker type of measuring procedure.

Back in the late 60s/early 70s we used to do these kinds of measurements to tune bass reflex speaker cabinets. By adjusting the diameter and length of a tube used to vent the cabinet the impedance shown in the low frequency spike is reduced and turned into two spikes. Imagine pushing the point of the spike down with your finger and letting it bubble back up some on either side of your finger. It increased the volume at low frequencies as well as extended the ability of the speaker and enclosure to produce lower frequencies.

Originally Posted by Engine-Ear

Also, I see the measurement stops at 2000 Hz...can you provide a measurement that goes out to 15,000 Hz (the practical upper frequency of adult human hearing)?

Here it is Matt, although still without speaker or measuring specifics.