What you are reading is the DC resistance of the voice coil - likely only the woofer combination. A speaker's impedance is different from DC resistance; it has an inductive reactance and a capacitive reactance component.

The inductive reactance is from the voice coil of the speaker(s) and the coil (inductor) in the crossover; the capacitance is from the capacitors in the crossover. Since the 901's don't have tweeters and no crossover, there is no crossover, so the reactance is from the voice coils only.

A speaker's impedance is the combination of the resisitance and the reactance components. It will be somewhat different from the DC resistance and will vary with frequency. The rated impedance is a nominal figure computed over a frequency range. It may or may not be the lowest impedance that the speaker will present to the amplifier at all frequencies. Some 8 ohm speakers can be as low as 3-4 ohms at some frequencies, typically in the bass range.

Hope this helps.

 

Hello Jones. I am sorry, but this thing has gone over my head, It is just that the reading is not showing me a smaller figure it is showing me an impedance of 12.9, when I connect this to my amplifier, will the amplifier read it as 8 ohms or 16 ohms, since I use other 8 ohms speakers on the same amplifier, I am afraid, I will be doing something wrong..the spec of my system are..
2 pairs of 8 Ohms speakers +
1 pair of Bose 901 Series VI
the amplifier is a Crown XLS602D, which gives out 380W per channel at 8 ohms(stereo), or 600 watts at 4 ohms (stereo) or 1200 watts bridged..
How do you suppose I connect these speakers. Thanks,

 

Again, the multimeter is measuring only the DC resistance. I would trust the manufacturer's impedance reading.

If you parallel two 8 ohm speakers (connect both to the amplifier terminals at the same time), then the resultant load on the amplifier is 4 ohms. The formula is Z1*Z2/Z1+Z2, where the Zs are the rated speaker impedance. For this case: 8*8/8+8 = 64/16 = 4 ohms.

If you add a third pair of 8 ohm speakers, then the resultant load on the amp is 4*8/4+8 = 32/12 = 2.67 ohms. Unless the amplifier is rated for 2 ohm loads, it likely will overheat if driven to high volumes.

One thing you can do is connect one pair in series: Connect a single wire between the + on one and the - terminals on the other. Then connect your speaker wires to the remaining speaker terminals. That gives an equivalent impedance of the pair as 8 + 8 = 16 ohms. Using the paralleling forumula, the resultant load on the amp then would be 16*8/16+8 = 128/24 = 5.33 ohms, which would be fine.

 

Hi, Thanks for the Info, it is kind of confusing now to me..Is it ok, if I connect 2 8ohms speakers of a different company, like for instance, 1 rcf 8 ohms with 1 bose 8 ohms speaker in series. will it be ok..that way 2 pairs will be in series and 1 in parallel. Please let me know..

 

Connecting speakers in series can produce hard to predict frequency response and distortion anomolies. Your impedance may not be an issue for the amp but the performance is a big question. A series parallel combination with the 901s would likely not be a big problem, as they are already essentially that internally, but another brand of speaker introduces variables that are hard to account for.

 

Connecting speakers in series can produce hard to predict frequency response and distortion anomolies. Your impedance may not be an issue for the amp but the performance is a big question.

+1.

 

Hi Avalon,

I am not sure what you are experiencing, but the speaker should spec out at about 5.1-5.9 ohms.

There is NO crossover in the speakers and they are just (9) drivers wired in series at about .8 ohms each.

If you need any more info feel free to visit me at 5.1.cashkats

Hope this helps,

John

 

I've never heard of a multi-meter being used to verify published specs of a speaker. "8 ohms" means 8 ohms *nominal*. The truth is that impedance will change, sometimes greatly, depending on the frequencies it's being asked to reproduce. Do they both show the same reading? If concerned I would open one up and carefully inspect all the solder joints, both to the binding posts and to the back of each driver. If a voice coil is froze up somewhere that could throw off a multi-meter reading but it would be quite unusual to see both speakers with the identical problem.

Also call Bose?

 

You are correct about the impedance vs resistance, however if you have measured about 100 of these series speakers and come up with the specs that I have given then a multimeter will at least tell him if there is high or low resistance in the circuit and thus indicating a possible problem.

Thanks :yikes:

 

Possibly there's a high resistance connection somewhere, most likely at one of the voice coil leads on the side of the cone. Per the service manual, high power signal should reveal a bad connection with a puff of smoke in the immediate vicinity...

But I'd guess the most likely scenario is that somebody replaced one or more of the drivers with one(s) of the wrong impedance. The drivers were made in different impedances, both original and aftermarket. I would guess that careful listening might reveal which one(s) were higher impedance, as they will have substantially lower output than the rest.