Impedance and Freq Response

[5m3g_head]

Hi Folks

Im just trying to understand the effect of Impedance on Frequency Response.

I have assumed that a peak in Impeadance makes the speaker less efficient at that freq, meaning that a rise in impedance equates to a drop in frequency response.

The fix for this in a crosover is a Zobel network ?

I assume there is only so much the zobel network can flatten things out.
a few questions about Zobel networks.

I have only seen them applied to woofers is it OK to use them on mids and tweeters ?


What sort of capacitor is best to use for a Zobel network.

Cheers

[Jeff B.]

Hi Folks

Im just trying to understand the effect of Impedance on Frequency Response.

I have assumed that a peak in Impeadance makes the speaker less efficient at that freq, meaning that a rise in impedance equates to a drop in frequency response.

The fix for this in a crosover is a Zobel network ?

I assume there is only so much the zobel network can flatten things out.
a few questions about Zobel networks.

I have only seen them applied to woofers is it OK to use them on mids and tweeters ?


What sort of capacitor is best to use for a Zobel network.

Cheers

There is no direct relationship between impedance and frequency response. What you have assumed isn't really correct. The purpose of a Zobel is to allow a crossover to function more as intended, but they are not necessary at all if you use computer models to optimize a crossover.

[Æ]

Most impedance curves look like roller coaster rides. Imagine what the frequency response would look like it it depended on the impedance.

True, there are some instances where anomalies in the frequency response have a direct correlation to the impedance, but usually minor or insignificant.

[5m3g_head]

Clearly Im wrong about the Impedance and its relation to frequency response.

so why do we measure impedance curves and what do they tell us ?

[Jeff B.]

Clearly Im wrong about the Impedance and its relation to frequency response.

so why do we measure impedance curves and what do they tell us ?

Well, you can't design a crossover without them, and you don't want to present your amp with a load it can't handle. And, from the impedance curve you are able to derive the Theile/Small parameters of a driver.

[billfitzmaurice]

what do they tell us ?Mainly whether the cab is working properly. All sorts of defects will show up in a chart, from improper tuning to leaks.
Impedance can affect response depending on which component dominates. If it's resistive, as seen in the spike at Fb with a sealed box or the two spikes above and below Fb in a VB, response isn't bothered, but if it's inductive, as seen in the rising impedance with frequency, enough inductance will choke off response, and that's one factor considered in where to cross over to a higher frequency driver.

[Dirk]

Clearly Im wrong about the Impedance and its relation to frequency response.

so why do we measure impedance curves and what do they tell us ?

Crossovers, at their most basic level, work by restricting the flow of electricity to one driver or the other. They do this by raising the impedance so high that less electricity will want to flow through one driver or the other. The driver's natural impedance tells you what components you'll need to use to get the amount of attenuation / roll-off you desire.

[brianp]

There is no direct relationship between impedance and frequency response.

Only an oblique relationship. Good drivers are designed foremost for the flattest possible FR within their intended passband, which is a function of a number of mechanical and electromagnetic variables. When the designer has achieved this goal, the impedance curve falls where it will. Some designers do incorporate such things as copper-clad pole pieces or Faraday rings in the motor to smooth out the impedance a bit.

[Jeff B.]

Only an oblique relationship. Good drivers are designed foremost for the flattest possible FR within their intended passband, which is a function of a number of mechanical and electromagnetic variables. When the designer has achieved this goal, the impedance curve falls where it will. Some designers do incorporate such things as copper-clad pole pieces or Faraday rings in the motor to smooth out the impedance a bit.

but this is not for the purpose of adjusting frequency response per se, it is intended to accomplish other objectives like lowering distortion, etc.