I have an unmarked speaker with no indication of rating, model, or brand. How do I figure out what the ohm rating is?
I own a simple multi meter if that helps.
I own a simple multi meter if that helps.
Enjoy the benefits of a premium membership!
Upgrade Account
-
TalkBass has been independent since 1998. Add your voice.
Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
Join free Log in
Want zero display ads or expanded classifieds tools? Compare plans.
Unmarked speaker ohm rating?
- Thread starter James Simonson
- Start date
I have been ballpark successful using a high-impedance digital multimeter such as a fluke 77.
It will not tell you the actual impedance but will give you a ballpark figure assuming either 4 ohm, 8 ohm or 16 ohm. For instance my 4x10 cab is rated at 4 ohms. I read somewhere around 5.1 ohms on the meter. My 8 ohm (rated on the speaker) 1x18 reads 6.6 om the Fluke and 6.9 on a radioshack cat. no. 22-812 multimeter.
Next, of course, would be the "power" rating of the speaker. Is there anything stamped on the frame or elsewhere?
Good luck.
~
It will not tell you the actual impedance but will give you a ballpark figure assuming either 4 ohm, 8 ohm or 16 ohm. For instance my 4x10 cab is rated at 4 ohms. I read somewhere around 5.1 ohms on the meter. My 8 ohm (rated on the speaker) 1x18 reads 6.6 om the Fluke and 6.9 on a radioshack cat. no. 22-812 multimeter.
Next, of course, would be the "power" rating of the speaker. Is there anything stamped on the frame or elsewhere?
Good luck.
~
The DC resistance of the individual speaker will read slightly less than the rated AC impedance of the speaker.
I could be wrong about the 5.1 reading on the 4 ohm 4x10, I do not have that cab here to re-check. It might actually read 4.1 or something but I would be unconcerned with either reading and test every time before I plug in my SS head. I am looking to avoid powering up into a short.
^ What MglMatador said. If the speaker is rated fairly, the DC resistance of the coil should be about 20-30% less than the nominal impedance rating. This is, of course, because the actual impedance at any frequency is the vector sum of DC resistance and AC reactance of the coil, and in the usable passband of the speaker the sum should be slightly greater than the DC resistance.
First we need to understand a couple basic terms. 1. Resistance, This is the opposition to flow of a DC voltage. Its measured in ohms and it does not change with frequency which means that there is no energy stored in the system being measured. 2. Impedance. This is used to describe reactive loads. This is measured in ohms as well but, its not quite as simple.
The DC resistance is ALWAYS lower that the impedance for speakers. it is usually about 75% of the impedance. An 8 ohm speaker will read DC resistance of about 6 ohms and a 4 ohm speaker will read somewhere around 3 ohms. In reality a speaker changes its impedance with frequency quite a bit. You have both mechanical and electrical things at work. A speaker out of an enclosure will always have its impedance peak at free air resonance. If you tap the cone of a speaker you will hear the free air resonance pitch. the impedance at the frequency can be as high as 20-40 ohms. impedance quickly drops below resonance. This is why its a good idea to filter out frequencies below resonance with your subs. a 4ohm system can drop to below 2 ohms below resonance which is not nice for your amps or your speakers.
Caution: Big ugly tech follows, Brain pain is possible!
With a resistive system any energy dissipated by the system is turned in to heat. With a reactive system, some energy is stored in the system. With inductive reactance (coils, chokes,Etc.) energy is stored as magnetic flux. in series, It increases as frequency increases. With Capacitive reactance, Energy is stored as static electricity and when in series, it decreases with frequency. Impedance is the equivalent resistance at a given frequency or in the case of speaker its the average resistance over the range used. Reactance is usually described in the form of XXohms plus or minus XXj. The first part tells you the resistive part of the impedance and the second part tells you about the part that stores energy. a speakers reactance might be 6ohms-2j.
Speakers are also subject to interaction with the enclosure. The enclosure can change the resonant frequency of the speaker and can also change the Q or the sharpness of the peak. In some cases the enclosure can cause a second peak to occur. Horn loaded speaker often have higher impedances than the rated impedance of the driver because of the mechanical loading of the driver.
I hope I haven't hurt anybodies brain too much
Archie
The DC resistance is ALWAYS lower that the impedance for speakers. it is usually about 75% of the impedance. An 8 ohm speaker will read DC resistance of about 6 ohms and a 4 ohm speaker will read somewhere around 3 ohms. In reality a speaker changes its impedance with frequency quite a bit. You have both mechanical and electrical things at work. A speaker out of an enclosure will always have its impedance peak at free air resonance. If you tap the cone of a speaker you will hear the free air resonance pitch. the impedance at the frequency can be as high as 20-40 ohms. impedance quickly drops below resonance. This is why its a good idea to filter out frequencies below resonance with your subs. a 4ohm system can drop to below 2 ohms below resonance which is not nice for your amps or your speakers.
Caution: Big ugly tech follows, Brain pain is possible!
With a resistive system any energy dissipated by the system is turned in to heat. With a reactive system, some energy is stored in the system. With inductive reactance (coils, chokes,Etc.) energy is stored as magnetic flux. in series, It increases as frequency increases. With Capacitive reactance, Energy is stored as static electricity and when in series, it decreases with frequency. Impedance is the equivalent resistance at a given frequency or in the case of speaker its the average resistance over the range used. Reactance is usually described in the form of XXohms plus or minus XXj. The first part tells you the resistive part of the impedance and the second part tells you about the part that stores energy. a speakers reactance might be 6ohms-2j.
Speakers are also subject to interaction with the enclosure. The enclosure can change the resonant frequency of the speaker and can also change the Q or the sharpness of the peak. In some cases the enclosure can cause a second peak to occur. Horn loaded speaker often have higher impedances than the rated impedance of the driver because of the mechanical loading of the driver.
I hope I haven't hurt anybodies brain too much
Archie
