Driver Specs., Frequency Range

[rogoll]

1. How accurate are the typical driver specs? I've notices that PE decreases the frequency range on some (over zealous) manufacturer's specs. On a woofer, should I be able to obtain good sound quality, without cone breakup, through the frequency range listed? Or in other words, if I keep the driver within the frequency range listed, can I be pretty much assured of "good" performance from that driver.

2. Also, can someone give me an overview of "Frequency Impedance Phase". I understand that at Fs there is a peak in impedence, followed by a decline, then a more gradual rise as frequency increases, due to the reactance of the coil in the driver. But what all does this graph/information tell me? Does the plot of the impedence parallel the frequency range of the driver? Basically, I can perform all the calculations and arrive at an appropriate box design, etc., but I want to *understand why* things are the way they are.

Respectfully,
Leonard

[Wolf]

1. How accurate are the typical driver specs? I've notices that PE decreases the frequency range on some (over zealous) manufacturer's specs. On a woofer, should I be able to obtain good sound quality, without cone breakup, through the frequency range listed? Or in other words, if I keep the driver within the frequency range listed, can I be pretty much assured of "good" performance from that driver.

2. Also, can someone give me an overview of "Frequency Impedance Phase". I understand that at Fs there is a peak in impedence, followed by a decline, then a more gradual rise as frequency increases, due to the reactance of the coil in the driver. But what all does this graph/information tell me? Does the plot of the impedence parallel the frequency range of the driver? Basically, I can perform all the calculations and arrive at an appropriate box design, etc., but I want to *understand why* things are the way they are.

Respectfully,
Leonard

1- The freq range in the specs on PE's site are just a statement of a possibility, and should not be taken as the range that it is nicely acceptable. Most of the time, the top-end is higher than it will go. In tweeters rating range down to Fs is also not a good idea.

2-Okay- you have 4 plots for a given driver;
-impedance
-impedance phase
-frequency response
-acoustic phase

Impedance is the varying resistance for the driver, as you have described. If the measured impedance has any small bumps for a woofer above Fs region, this could be seen as energy storage, and a possible issue in the FR. In a tweeter, the amplitude of the Fs could be important and possibly need filtered out. Most tweeters are in the 8-15 ohm range at Fs. Much higher could create the male vocal buzz.

The IP is the capacitance or inductance of the impedance plot, where below 0 deg is capacitive and vise versa. The remain the least objectionable to the amplifier being used, try to keep the IP between the 40's in degrees, and more minimal/inductive if possible for more stability.

FR is of course the response of a particular driver, and comes with all the blemishes to filter out if required.

Acoustic Phase is the acoustic phase angle of the frequency response, and is one of the targeting methods to align the drivers around the xover point.

Hope this helps,
Wolf

[curt_c]

1. How accurate are the typical driver specs? I've notices that PE decreases the frequency range on some (over zealous) manufacturer's specs. On a woofer, should I be able to obtain good sound quality, without cone breakup, through the frequency range listed? Or in other words, if I keep the driver within the frequency range listed, can I be pretty much assured of "good" performance from that driver.

As Wolf indicates, the published frequency range of most drivers is one of those 'specifications' best ignored. Often they just indicate the frequency where the driver starts its ultimate roll off, break up modes and all. Even if the response of a 6.5" driver is flat to 5K doesn't mean it would be optimally utilized up to 5K. While it could be made to sum flat with a tweeter on axis at that frequency, the response of the system would have a significant dip off axis where the woofer rolls off sooner due to beaming. One rule of thumb is to not cross above the frequency whose wavelength is smaller than the driver diameter. For a 6.5” driver this would be somewhere around 2K but can vary significantly depending on the driver. I generally measure drivers on axis, and at 45 degrees off axis, and target an optimal crossover frequency upper limit based on the combined on and off axis performance.

The driver plot below could conceivably be described as having a frequency range of 60 Hz to 8.5 kHz, although I’m sure no one would consider using it for that passband. Ignoring the cone break up peak at 4.5 kHz, for a moment, the off axis plots suggest to me a crossover around 2K would be optimal, although it probably could be stretched to 3K. -However, doing in doing so, the power response would likely suffer an audible dip in the 2-3 kHz region.
-But of course, we cannot ignore that peak. It would have to be notched out and would suggest a higher order crossover be utilized to push those frequencies significantly down into the stopband.

Every driver has its own unique signature, and the response, impedance, and T/S's only tell part of the tale...

C