Impeadence/phase graphs

[mayemX 0]

So I've always noticed the impeadence/graph phases on most (good) subwoofer companies manuals, but I've never understood necessarily how they worked. Of course I know what impeadence and phase meant, but not too sure how it works on this graph (the frequency on the X axis, resistance on Y). To my understanding, it has to do with backpressure in the intended enclosure, so at the certain frequency where the resistance peaks that is where the backpressure in the enclosure its meant for peaks? And as for phase I guess thats just saying that 1 line is at 0 degrees and the other is at 180? But thats my guess whether its right or wrong the factor of backpressure? I've been getting into more advanced mechanics of audio but I've never fully understood this graph.

Thanks you guys!

MayemX <--- Not mayhem this wasn't a spelling error

[ssh 924]

The impedance - frequency graph shows exactly as title.

At given frequency the speaker has an impedance of xxx. The higher the impedance causes the amp to produce less power. So I would assume that that would cause a dip in the response. Though it may or may not be audible.

[mayemX 0]

The impedance - frequency graph shows exactly as title.

At given frequency the speaker has an impedance of xxx. The higher the impedance causes the amp to produce less power. So I would assume that that would cause a dip in the response. Though it may or may not be audible.

Ohhh ha thats soooo simple!!! thats something anyone could figure out Nah but I was just overthinking it.

Thanks bro!

[Impious 1,476]

While it's true that the impedance will rise very high in impedance on the graph, it's not necessarily true that there will be a dip in response as the point(s) where this occurs. As correctly explained, the impedance graph is simply a representation of the driver's impedance across the frequencies. A few things can be found out from an impedance graph. This is a quick but not comprehensive list of some of the things an impedance graph can tell us.

First, there will be a large peak in the impedance. This big peak defines the resonant frequency (Fs) of the driver. If impedance spikes at 25hz, then the Fs of the driver is 25hz. The impedance at Fs (25hz in our example) may spike up to 30ohm or more. This very high impedance at Fs means the amplifier's output will drop substantially. So why is there not a huge drop in output at that frequency? Pretty simple, the driver doesn't need as much power at Fs as it does elsewhere. The driver will naturally resonate at Fs, so it doesn't take much power to get it going.

The shape of this large impedance peak will be determined by the Q of the driver (Q describes the various damping characteristics of the loudspeaker at resonance). If you were so inclined, you could calculate the Qms, Qes and Qts from the impedance graph. More specifically, you can calculate the various Q parameters from the size and shape of the impedance peak at Fs.

Minimum impedance is also shown on the impedance graph and is important to know, especially in situations where amplifiers can not handle low impedance loads. For example, in home audio a lot of amplifiers (especially those in receivers) may not be able to handle loads below 4ohm or 8ohm. So if the minimum impedance of the driver drops too low during a critical range, it may be a load too difficult for the amplifier to handle.

Another thing to look for, which is less applicable to subwoofers and more towards higher frequency related drivers, are ripples in the impedance away from the big spike at Fs. If there are ripples in the impedance that indicates there are some type of resonance issues with the driver at the frequency where those ripples occur. A common issue, for example, would be cone breakup. Cone break up can create a small ripple in the impedance graph.

Also the impedance graph will indicate the inductance of the voice coil. The inductance limits the high frequency response of the driver. As frequency increases above Fs the impedance will be relatively flat for a while, and then gradually start to rise. What frequency the impedance begins to rise and how quickly it rises are determined by the inductance of the voice coil. If you pick some points off of the impedance graph, you can go back and calculate the inductance of the voice coil. This is a situation (unlike Fs) where rising impedance will cause the response of the driver to begin to fall. This is because the inductance limits the ability of the driver to react to changes in current, so the driver can't adequately respond to the signal at those higher frequencies....so the response will begin to drop off.

You can also tell some other things from an impedance graph of the loudspeaker in an enclosure. For example, you can determine the tuning frequency of a ported enclosure from the impedance graph. Resonance issues in the enclosure can show up in an impedance graph. You can apply a lot of the same analysis to describe the behavior of a loudspeaker in a sealed enclosure as you can to the driver in free air. Etc Etc.

So, overall there are a lot of information in that impedance graph. Most of it isn't extremely relevant to the weekend warrior, however.

[ssh 924]

While it's true that the impedance will rise very high in impedance on the graph, it's not necessarily true that there will be a dip in response as the point(s) where this occurs. As correctly explained, the impedance graph is simply a representation of the driver's impedance across the frequencies. A few things can be found out from an impedance graph. This is a quick but not comprehensive list of some of the things an impedance graph can tell us.

First, there will be a large peak in the impedance. This big peak defines the resonant frequency (Fs) of the driver. If impedance spikes at 25hz, then the Fs of the driver is 25hz. The impedance at Fs (25hz in our example) may spike up to 30ohm or more. This very high impedance at Fs means the amplifier's output will drop substantially. So why is there not a huge drop in output at that frequency? Pretty simple, the driver doesn't need as much power at Fs as it does elsewhere. The driver will naturally resonate at Fs, so it doesn't take much power to get it going.

The shape of this large impedance peak will be determined by the Q of the driver (Q describes the various damping characteristics of the loudspeaker at resonance). If you were so inclined, you could calculate the Qms, Qes and Qts from the impedance graph. More specifically, you can calculate the various Q parameters from the size and shape of the impedance peak at Fs.

Minimum impedance is also shown on the impedance graph and is important to know, especially in situations where amplifiers can not handle low impedance loads. For example, in home audio a lot of amplifiers (especially those in receivers) may not be able to handle loads below 4ohm or 8ohm. So if the minimum impedance of the driver drops too low during a critical range, it may be a load too difficult for the amplifier to handle.

Another thing to look for, which is less applicable to subwoofers and more towards higher frequency related drivers, are ripples in the impedance away from the big spike at Fs. If there are ripples in the impedance that indicates there are some type of resonance issues with the driver at the frequency where those ripples occur. A common issue, for example, would be cone breakup. Cone break up can create a small ripple in the impedance graph.

Also the impedance graph will indicate the inductance of the voice coil. The inductance limits the high frequency response of the driver. As frequency increases above Fs the impedance will be relatively flat for a while, and then gradually start to rise. What frequency the impedance begins to rise and how quickly it rises are determined by the inductance of the voice coil. If you pick some points off of the impedance graph, you can go back and calculate the inductance of the voice coil. This is a situation (unlike Fs) where rising impedance will cause the response of the driver to begin to fall. This is because the inductance limits the ability of the driver to react to changes in current, so the driver can't adequately respond to the signal at those higher frequencies....so the response will begin to drop off.

You can also tell some other things from an impedance graph of the loudspeaker in an enclosure. For example, you can determine the tuning frequency of a ported enclosure from the impedance graph. Resonance issues in the enclosure can show up in an impedance graph. Etc Etc.

So, overall there are a lot of information in that impedance graph. Most of it isn't extremely relevant to the weekend warrior, however.

Hoping you would find the topic and clear it up.