Question: How can speakers drop in ohms?

[admin_exported]

Hi there,

could someone explain how passive speakers, let say 8 Ohms can drop to a lower number 4 or 2 ohms?

 

[aliEnRIK]

Theres no set figure for a speaker. It changes throughout the frequency range. Most speakers tend to be between 5 and 8 ohms, but mainly between 6 and 8 ohms most of the time

The biggest changes are usually at the crossover points (My speakers have 3 cones and a tweeter for example, so ill have several frequency sections where it drops)

 

[proffski]

A coil will have specific 'impedance' which will indeed change with frequency.

If you are talking about measured "DC Resistance" with a multimeter then it could be several factors.

The worst scenario would be shorted turns on the loudspeaker coil which would also probably manifest as a loss of efficiency.

The second is a cheap multimeter, try twisting and re-inserting the leads, do the readings change?

Finally depending as to which loudspeaker you are testing and as to whether it is in circuit there is a very small chance of a crossover fault but unless you have been blasting them at a party highly unlikely...

 

[SteveR750]

The important thing is what impedance load they present top the amp, DC resistance is irrelevant. The impedance will change with frequency as it is a combination of mainly capacitance and inductance effect of resisting AC signals. Think of it as an electrical spring, a capacitor is like using a tight spring, and an inductor a loose one - the former poses less 'resistance' at higher frequencies (as ultimately no current flows across the plates, only charge) whereas an inductor increases resistance as the current frequency is increased.

A loudspeaker driver is effectively a large inductor with the mechanical spring effects of the driver, plus any capacitors in the cross overs, cable effect etc all influence the electrical resonance frequencies. The impedance drops where these 'resonances' occur