Help Measuring Speaker Ohmage

[Omnipharious]

I am trying to build a small 2.1 amplifier for my room, and I already know the ohmage/wattage of the two mains, but the sub isn't marked. I know it is a 10watt, 6.5in that used to be a small practice bass amplifier. I have seen a few videos and posts elsewhere on the internet explaining how to measure the ohmage of a speaker, but they always use a digital, usually auto-ranging, meter, or if analog or digital, they use the x200Ω setting. The problem is that my analog meter only has a x1kΩ and x10Ω settings. If I can be frank, I am usually electronically savvy, but I am very bad with math, and I don't know the theory to determine what I am trying to about this speaker from what my meter is telling me on these settings.

Measuring the resistance between the - and + on the speaker, this is the measurement on 1kΩ

This is the measurement on 10Ω

I'm sure the conversion is painfully simple, but please appease my stupidity and help me out here.

 

[duke37]

Nice pictures.

The reading looks to be 1.5 * 10 = 15, a reasonable value, if a bit high.
The impedance of the speaker will be a combination of resistance and inductance so resistance is only a guide.

 

[Omnipharious]

Nice pictures.

The reading looks to be 1.5 * 10 = 15, a reasonable value, if a bit high.
The impedance of the speaker will be a combination of resistance and inductance so resistance is only a guide.

Okay, well how might I find the ohm rating of this specific speaker? Everyone I have heard or seen doing it said that setting your meter to 200Ω and testing between the two contacts will give you the ohm rating of a speaker. How can I use either the 10Ω or 1kΩ to do that?

 

[davenn]

NOTE!

you WONT measure the speaker Ohms with a normal multimeter the reading you get is pretty irrelevent

The rated Ohms of a speaker eg. 4, 8, 16 Ohms etc is its IMPEDANCE
to measure that correctly you need an impedance meter
Impedance is AC resistance NOT DC resistance as measured with a multimeter in Ohms range

Dave

 

[Omnipharious]

Since I don't have $50 to spend on a meter that can read AC resistance, or have time to wait two weeks for a cheap one to ship just to be used once or twice, is there some way I can find out the impedance now?

 

[CocaCola]

Why is it that important that you know right now? Most 'amps' will tolerate a range of values, and most consumer manufactured speakers are within that range... The only time you really start seeing much variance in consumer speakers is when you get into the small ones, most woofers and subs are in the 4-16Ω range... And remember it's just a number, that gives a generalization of the entire speakers performance, the actual impedance actually jumps all over the place... Taking a half azzed guess with a ohm meter isn't going to provide you with a true answer anyway, you are still left guessing...

Are you running these off a tube amp? If so your concerns about the impedance is much more valid, and caution is noted... But, with modern solid state amps much of the concern is negated, built in protections will/should prevent any damage if the miss match was that drastic and got out of hand... The only real concern with solid state amps is too low of impedance, but that is only when pushing the limits of the amp, at low to medium volumes they will generally still function without the excess heat that would shut them down... But, as I stated earlier I would argue that the speaker is likely not below the rated impedance of your average amp in most cases...

 

[Raven Luni]

You can send the speaker a wave of a fixed amplitude and frequency (usually chosen to be in the middle of the desired band) and measure the AC current going to the speaker and the RMS voltage across it, then you can use ohms law to give you the impedence (Z = V / I : divide the voltage reading by the current reading)

 

[duke37]

The impedance of the basic spaker can never be below the resistance, the reactance has to be considered. This will go up and down depending on the frequency, the resonance of the speaker, the effects of any crossover network and the way it is installed. Hi Fi magazines often give plots of impedance versus frequency these can be quite wild as Coca Cola said.

I would think that your speaker would be described as 15 ohms

Why are you concerned?