How to check Ohms of speaker simply?

[Willen]

I guessed this ohm is 'impedance' of Audio frequency. So may be hard to measure? I think like this way-
https://m.wikihow.com/Measure-Speaker-Impedance

But at step-7, they are talking about polarity of speaker. Speaker has a simple coil only, then how polarity been determined? What to do if there is no polarity marking? I think it not not more critical

 

[KeepItSimpleStupid]

Here https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers is a blurb explaining speaker Z.

The DC resistance gets you close. Measuring 4 or 8 ohms with "normal" meters is problematic anyway because of errors on the order of an ohm.

You asked about polarity. You can check the polarity of drivers that you can see by taking a 1.5V D cell and connecting to the speaker. When the polarity is correct, the cone will move outward.

If you have a known full range speaker that works, you can connect any of the drivers in any polarity and listen for volume differences. Speakers phased improperly will sound lower in volume.

 

[Nigel Goodwin]

As a rule of thumb a 4 ohm speaker reads 3 ohms, and an 8 ohm reads 6 ohms on a multimeter.

As already mentioned, simply apply a 1.5V battery to find out what the polarity connections are - 'generally' the cone will move forwards with the +ve of the battery connected to the +ve of the speaker.

Out of phase speakers don't sound 'quieter' as such, the bass cancels out and you have a profound lack of bass if they are reverse phased.

 

[Willen]

Oh no...! I never take cared about polarity of speaker while connecting them to amplifier!!! I did not know all speakers are polarity sensitive! Now I know that I have to connect amplifier's 'audio out' to speaker's +Ve and ground to -Ve pole.

I learnt informally that a hi impedance speaker means- it produces smaller sound and sensitive with smaller signals and needs very low currents. Low impedance speakers means- it produces very high level audio sound and needs very high currents to operate. Is it good concept?

 

[Nigel Goodwin]

Oh no...! I never take cared about polarity of speaker while connecting them to amplifier!!! I did not know all speakers are polarity sensitive! Now I know that I have to connect amplifier's 'audio out' to speaker's +Ve and ground to -Ve pole.

Only for multi drivers - most commonly for stereo.

I learnt informally that a hi impedance speaker means- it produces smaller sound and sensitive with smaller signals and needs very low currents. Low impedance speakers means- it produces very high level audio sound and needs very high currents to operate. Is it good concept?

Not really, power remains the same - so a higher impedance speaker needs more voltage and less current, but it works out the same.

 

[Willen]

***** (duplicated!)

 

[Willen]

Ok, if there is a mono driver, then should't I have to know the polarity of speaker? Why only for stereo driver? (your answers are very short )

And another thing want to ask-
What about 20K ohms speaker? Look this one www.josepino.com/diy/making-high-impedance-headphones I didn't find crystal earpiece for Crystal Radio project, so trying to do with piezoelectric method. What you think, does it play louder as crystal earphone or is it sensitive as crystal earpiece?

 

[Diver300]

You do not need to worry about speaker polarity when measuring the impedance.

The page that you quoted, http://m.wikihow.com/Measure-Speaker-Impedance, referenced this page:-**broken link removed**

The man in the video says that direction doesn't matter when measuring a speaker impedance, only when connecting them up, but that has go missed on the Wikihow page.

If you only have one speaker, like in a mono radio, direction doesn't matter. Speaker direction is important for low frequencies where there are several speakers, especially if the speakers are close together. In a speaker cabinet with two speakers, if one pushes air out while the other pulls air in, there will be far less volume than if they both work in the same direction.

 

[Nigel Goodwin]

Ok, if there is a mono driver, then should't I have to know the polarity of speaker? Why only for stereo driver? (your answers are very short )

The only reason to need to know the polarity is to ensure that all speakers are in phase, for just one it doesn't matter at all.

And another thing want to ask-
What about 20K ohms speaker? Look this one www.josepino.com/diy/making-high-impedance-headphones I didn't find crystal earpiece for Crystal Radio project, so trying to do with piezoelectric method. What you think, does it play louder as crystal earphone or is it sensitive as crystal earpiece?

It's NOT a speaker, it's a pair of headphones - they were common back in the VERY, VERY early days of radio, particularly on crystal sets.

But by the 60's high impedance headphones had all but disappeared, and crystal ear pieces were used for such purposes.

I've never even seen a pair of high impedance headphones, only photographs.

 

[WTP Pepper]

In the 70's when messing around with crystal sets as a kid, a radio ham kindly lent me a pair of Hi Z earphones. At the time I expected audio volume similar to my record player. Sadly not. The crystal earpiece was fine. The headphones just cut out ambient noise, but in minutes I learned a hand was just as effective

 

[Willen]

Exactly what about piezoelectric? Can't I use it as high Z earpiece?

 

[MikeMl]

Exactly what about piezoelectric? Can't I use it as high Z earpiece?

The issue with crystal sets is efficient conversion of electrical signal power to audio signal power in the ear canal. Hi-Z doesn't necessarily translate into high-efficiency conversion. If fact, hi-z requires high voltage to get a given (audible) sound power. A crystal set doesn't generate high audio signal voltages. You may be better off with a "magnetic" set of headphones...

 

[Willen]

But all are saying Crystal radio sets need hi impadence (20k ohm) earpiece.

I don't know about earpiece of cell phone. What impedance has on general earpiece (external) of cell phone (eg. nokia, samsung)? Will it perform on Batteryless crystal radio?

 

[dr pepper]

You can measure the impedance of a driver with a wheatstone bridge, a power amp, sig gen and ac vtvm at any frequency you wanted if you wanted to be really fussy.
You'd do this if you were designing a passive crossover and wanted to know the exact impedance of a driver at the xover freq, or if you were designing an impedance equalizer as part of the xover.
You can get devices made for the job now, and no doubt there have been articles in electronics mags for doing this.
Sometimes if you had a xover that had different orders for bass and tweeter you would deliberatly reverse the polarity of one of the drivers due to the phase differences at the xover freq, so if you see this it might not be a mistake.

Why do you want to know the impedance, if just for a quick check then Nige's idea works well, an ohm less than specified.

A check CD is good for testing phase, they often have a soundtrack of a bass freq in and out of phase, it should sound louder during the inphase track.

 

[audioguru]

The frequency response of a piezo transducer is absolutely HORRIBLE. It produces no bass sounds and its treble is full of peaks and nulls.
Here is the frequency response graph of a typical inexpensive piezo transducer:

 

[Nigel Goodwin]

But all are saying Crystal radio sets need hi impadence (20k ohm) earpiece.

I don't know about earpiece of cell phone. What impedance has on general earpiece (external) of cell phone (eg. nokia, samsung)?

All are low impedance - as I said earlier, I've never even seen high impedance headphones.

The thing to use is a crystal earpiece, which are easily available.

 

[Ramussons]

But all are saying Crystal radio sets need hi impadence (20k ohm) earpiece.

I don't know about earpiece of cell phone. What impedance has on general earpiece (external) of cell phone (eg. nokia, samsung)? Will it perform on Batteryless crystal radio?

The normal Impedance of the headsets of Mobile Phones is 16 Ω or 32 Ω. They will be unsuitable for use in a Crystal Radio.

Ramesh

 

[Willen]

How they have been made so they have such hi impedance like 20k ohms? Small wire and lots of turns?

 

[The Electrician]

I've never even seen high impedance headphones.

They aren't made anymore, but they occasionally show up on ebay:

**broken link removed**

 

[The Electrician]

How they have been made so they have such hi impedance like 20k ohms? Small wire and lots of turns?

Yes.

Headphones like that aren't made anymore, but you can find them on auction sites. Here's an example of vintage high impedance magnetic earphones:

**broken link removed**